Canola integration into semi-arid wheat cropping systemsof the inland Pacific Northwestern USA

W L PanAC F L YoungB T M MaazA and D R HugginsB

AWashington State University Department of Crop and Soil Sciences 202 Johnson Hall PullmanWA 99164-6420 USA

BUSDA-ARS NW Sustainable Agroecosystems 215 Johnson Hall Washington State UniversityPullman WA 99164 USA

CCorresponding author Email wlpanwsuedu

Abstract The inland Pacific Northwestern USA (iPNW) wheat-producing region has a diversity of environments andsoils yet it lacks crop diversity and is one of the few semi-arid wheat-growing regions without significant integrationof oilseeds Four major agroecological zones primarily characterised by water availability feature distinctly differentfallowed and annually cropped systems each presenting different challenges and opportunities to integrate winter andspring canola Althoughmajor interests in regional energy crops and rotational diversification spurred feasibility research oniPNW canola food feed and fuel production in the 1970s commercial canola adaptation has lagged behind other semi-aridwheat regions for various socioeconomic ecophysiological and agronomic reasonsNew federal crop insurance policieswillreduce economic risks in new crop adaptation and oilseed processing facilities are creating new local markets Althoughcanola management largely relies onwheat farm equipment agronomic approaches require strategic adjustments to accountfor physiological differences between canola and cereals including seed size seedling morphology and responses totemperature extremes Climate change predictions for the region threaten to exacerbate current hot and dry summers andresearch aims to develop and adapt flexible winter and spring canola-based systems to regional water and temperaturestressors in each zone Adaptation will require novel planting fertilisation and weed control strategies to successfullyestablish improved winter canola cultivars in hot dry summers that survive cold winters and spring canola cultivars direct-seeded in cool wet springs The adaptation of winter and spring canola will somewhat mirror the rotational placement ofwinter and spring cereals within each zone Economic analysis of oilseed break crop benefits such as weed and diseasecontrol will help to demonstrate the medium-term economic benefits of crop diversification to support the growth ofa regional canola industry in the iPNW

Received 8 July 2015 accepted 5 February 2016 published online 6 May 2016

Potential for canola adaptation in the iPNW region

Over the past 125 years eastern Washington and surroundingareas of Oregon and Idaho USA have been highly mono-cropped in a wheat-fallow system (Schillinger and Papendick2008) with limited diversification using cool-season legumesThe inland PacificNorthwest (iPNW) has distinct cropping zonesdefined by precipitation temperature and soils (Douglas et al1990) A dominant eastndashwest decreasing precipitation gradienthas dictated the evolution of four major wheat-dominatedagroecological zones (Fig 1) across northern Idaho to centralWashington and Oregon (i) annual cropping zone (gt450mmannual precipitation) (ii) annual cropndashfallow transition zone(300ndash450mm annual precipitation) (iii) grain-fallow zone(lt300 to mm annual precipitation) and (iv) irrigated zone ofcentral Washington and Oregon (Huggins et al 2014) Analysisof USDA NASS interpreted satellite survey datasets haveprovided current updates and refinements of zonal estimates ofannual land areas (Table 1) and crop identities (Huggins et al2015) There is limited crop diversification within each of these

wheat- and fallow-dominated rain-fed zones in contrast to thegreater diversity of the row-cropped areas of the irrigated centralbasin of Washington and Oregon (Fig 2) Interests in energycrops and rotational diversification spurred feasibility research oniPNW canola production and end-use 40 years ago (Divine et al1977) Agronomic and variety performance field trials were thenconducted by the regional land grant universities (Bettis andAuld1980 Porter et al 1981 Kephart 1986 Gareau et al 1990Johnson andLewis 1995) later coupledwithBrassica agronomybreeding and variety testing (Brown et al 1995) and engineeringprograms (Bettis et al 1982 Petersen 1984) at the University ofIdaho Although research has continued to demonstrate thepotential to grow improved winter and spring canola cultivarsin different iPNW subregions (Brown and Davis 2015)commercial production has lagged behind other global regionsdue to systemic agronomic economic andmarketing constraintsCanola yield instability and lack of regional canola industryinfrastructure and markets were considered major reasons forthe slow adoption

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CSIRO PUBLISHING

Crop amp Pasture Science 2016 67 253ndash265httpdxdoiorg101071CP15217

Renewed interest and government support for canolaproduction in 2007 lead to state supported investments inresearch and extension programs (Sowers and Pan 2014)Between 2011 and 2014 iPNW-harvested canola areaincreased from 14 000 to 38 000 ha (USDA 2015) Althoughthe current production is roughly equivalent to the currentoilseed crushing capacity recently established in Washingtonstate another 10-fold increase in production is required tomatch the potential regional oilseed refining capacity for food

fuel and feed production equivalent to ~10 of the total row-cropped area of the region (Lang 2014 Table 1)

Canola has been effectively integrated into semi-arid wheat-cropping systems of western Canada Western Australia andthe Great Plains of the USA The crop diversification withbreak crops has effectively improved the agronomics andeconomics of these systems (Zentner et al 2002 Conley et al2004 Kirkegaard et al 2008a Seymour et al 2012 Angus et al2015) Rotational benefits from insertion of an oilseed crop into a

Legend

Agroecological classes

Cities

SpokaneOR

WA

ID

Rivers

Annual crop

Annual crop fallow transition

Grain fallow

Irrigated

Davenport

Lind

Moro

Pullman Moscow

Lewiston

Walla Walla

N0 45 90 180 Km

KennewickProsser

Yakima

Wenatchee

Pendleton

Grangeville

Fig 1 Agroecological cropping zones in the wheat-producing inland Pacific Northwestern US

Table 1 Projected predominant canolandashwheat rotations in the four agroecological cropping zones current and projected acreages required(a) to match existing Washington processing capacity and (b) to achieve 1 1 wheat to canola production levels similar to the current western

Canadian prairie production ratioWW winter wheat SW spring wheat L legume (pea chickpea lentil) F fallow Pot potato SwC sweet corn SC spring canola or camelina WC

winter canola WCF winter canola forage WGC winter canola grain NR not reported

Agroecologicalcropping zone

Land areaA

(handash1)Current

conventionalrotation

Alternativewheatndashcanola

rotation

2013 canolaareaA (ha)

Processorsupplying canola

area (handash1)

1 1 wheat canolaproductionarea (handash1)

Annual crop 568 000 WW-SW-L WW-SC-SL or WW-SW-SC 12 500 57 000 162 000Flex cropndashfallow 665 000 WW-SW-F WW-SC-F or WW-SW-SC 6000 100 000 174 000Cropndashfallow 1 245 000 WW-F-WW-F WW-F-WC-F 8500 125 000 311 000Irrigated annual crop 504 000 Pot-WW-SwC Pot-WWWCF-WCG-SwC NR 13 000 35 000

Total 2 982 000 27 000 295 000B 682 000

AHuggins et al (2015)BLang (2014)

254 Crop amp Pasture Science W L Pan et al

wheat production system are numerous including breakingdisease weed and insect cycles (Kirkegaard et al 2008a) TheiPNW has similar needs and opportunities for diversificationthat could include oilseed integration (Cook et al 2002Young et al 2014) Primary agronomic benefits motivatingiPNW growers include prospects for improved weed controlimproved nutrient cycling and water use and improved soilquality

There are both similarities and differences between theclimate and soils of the iPNW and those of other major semi-arid canola-producing regions of the world including WesternAustralia the western Canadian prairie and the Great Plains ofcentral USA (Table 2) Maximum growing-season temperaturescan subject canola to heat stress coupled to limited wateravailability in all four global regions Western Canada is leastsubject to maximum temperatures and most subject to minimumtemperatures with regional rankings of average minimumtemperatures western Canadian prairies ltGreat Plains USAltiPNW ltWestern Australia As a result only spring cultivars aregrown in the spring and summer of the Canadian prairies thecoldest of these regions but also in the winter of WesternAustralia the warmest of these global regions Due to themore moderate temperatures of the Great Plains and iPNWboth winter and spring cultivars can be grown during therespective seasons in various subregions and harvested insummer Canola is similar to wheat in that it has both winterand spring types where the winter types have a vernalisationrequirement Winter types of wheat (Schillinger et al 2010a)

and canola (Pakish et al 2015) typically out-yield their springcounterparts in this region due to their longer growing seasonmore efficient utilisation of winter precipitation with deeperroots and earlier grain filling However winter canola islimited to rotations and zones in which there is a suitableperiod with conditions for successful establishment and wintersurvival

The iPNW also has a high proportion of annual precipitationreceived during the winter months during winter canoladormancy (Table 2) The majority of precipitation in theiPNW is a mixture of snow and rain often over frozen soilsAs a result crops are more reliant on stored water and nutrientsin the subsoils for sustaining growth and development fromstem elongation through grain development As lt40 of thetotal annual precipitation is received during the spring andsummer months climate-induced water and heat stress occursduring reproductive stages of development Fortunately theaeolian and glacial medium-textured soils are generally deepto bedrock with high water-holding capacity (Schwartz andAlexander 1995) ranging from 270 to 360mm in a 180-cmprofile (Table 2) This is in contrast with canola grown duringthe wet winter in Western Australia where climate-inducedwater stress may still be an issue during the reproductivestages during drought years The highly weathered soils of theregion many with poor physical structure root restrictingcompaction (Lisson et al 2007 Smettem and Gregory 2010)and low (34ndash134mm) water-holding capacity (Oliver andRobertson 2009) exacerbate these problems (Hamza and

Irrigated annual crop(503 800 ha)

Winter wheat8

Winterwheat45

Winterwheat42

Winterwheat37

Othernon-fruit

29

Alfalfa21

Alfalfa2 Grain legume

3

Grainlegume

18

Alfalfa4

Alfalfa5

Potato14

Corn16

Springcereal

6 Springcereal

3

Springcereal21 Spring

cereal22

Springlegume

4

Fallow2

Other4

Other10

Canola1 Other

9

Fallow47

Fallow27

Fallow3

Grain fallow(1 245 800 ha)

Annual crop fallowtransition

(665 200 ha)

Annual crop (568 100 ha)

Fig 2 2007ndash2013 average land areas and crop distributions across four agroecological cropping zones in iPNW (Hugginset al 2014)

Table 2 Climate and soil characteristics of established and emerging canola production areas in semi-arid regions (6ndash8 sites) of the world

Area Minimumtemperature

(8C)

Maximumtemperature

(8C)

Annualprecipitation

(mm)

Precipitationduring growing

season

Soil water-holding capacity

Inland PNWAndash7 oC to ndash3oC 28ndash32oC 260ndash660 20ndash40 135ndash360mm (Schwartz and Alexander 1995)

US Great PlainsA ndash22oC to ndash3oC 25ndash35oC 250ndash890 65ndash75 51ndash350mm (Ji and Peters 2003)Canadian PrairiesB ndash22oC to ndash11oC 22278C 300ndash450 60ndash67 50ndash250mm (De Jong and Shields 1988)SW AustraliaC ndash2oC to 4oC 21ndash34oC 260ndash650 65ndash75 34ndash134mm (Oliver and Robertson 2009)

A1981ndash2010 Monthly Normals National Centers for Environmental Information National Oceanic and Atmospheric Administration Min temp recordedin January Max temp recorded in July

B1971ndash2010 Climate Normals Climate Government of Canada Min temp recorded in January Max temp recorded in JulyC1961ndash1990 ClimateNormals Climate data AustralianGovernment Bureau ofMeteorologyMin temp recorded in July or AugustMax temp recorded inOct

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 255

Anderson 2003) and all contribute to potential drought stressThe Great Plains of the USA and western Canadian soilshave variable water holding capacity (50ndash350mm) and ahigher percentage of precipitation during the growing seasoncompared with the iPNW (Table 2)

The greatest agronomic challenges in fostering iPNW canolaadaptation are to define wheatndashcanola-based rotations thatimprove weed control optimise soil water and N recharge andcrop use establish good plant stands maximise plant survivalduring overwinter freezing and early spring frosts and sustaincrop water and nutrient use during hot dry summer months Thediversity of environments soils and cropping systems across thefour major iPNW production zones (Fig 1 Table 1) presentchallenges to design suitable wheatndashcanola cropping systemswithin each zone The overarching goal of the Washington StateOilseed Cropping Systems project is to integrate appropriatewinter and spring canola cultivars into cropping systemstailored for each of these zones to increase crop and marketdiversification and productivity The agronomic research aimsto identify appropriate crop sequences and modifications totraditional wheat crop establishment and fertility managementstrategies to accommodate differences in physiological andmorphological traits of canola relative to wheat

Annual crop zone

Rotational fit The annual cropping zone comprises 568 000 haof the Palouse and western foothills of the Rocky mountainrange straddling the eastern WashingtonndashNorthern Idahoborder (Table 1 Fig 1) Precipitation of gt450mm per yearsupports annual cropping with winter wheat spring wheat andspring barley grown over 60 of the cropping zone land area andcool-season legumes account for only 18 (Fig 2) Typicallythere is insufficient soil moisture and growing degree-daysfollowing crop harvest to establish and grow winter canola tosufficient size before freezingwinter conditions so the focus is onadapting spring canola (discussed below) substituting springcereals or legumes in the rotation (Table 1) Winter canola ismore feasible following fallow but fallow is not normallypracticed in this region (Fig 1) unless wet spring conditionsprevent establishment of spring crops Nevertheless survivingwinter canola in this zone can yield 3000ndash4000 kg handash1 withample available soil moisture (Brown and Davis 2015 Evanset al 2015)

Weed management The predominance of cereal crops inthis zone encourages annual grassy weed infestations such asItalian ryegrass (Lolium multiflorum Lam) downy brome(Bromus tectorum L) and jointed goatgrass (Aegilopscylindrica HOST Ball et al 1999) Increasing broadleaf cropsin rotation with wheat provides better control of these grassyweeds particularly when herbicide-resistant canola is used(Young et al 2016) Nine years of substituting glyphosate-resistant spring canola for spring legumes in rotation withwinter and spring cereals was effective in controlling Italianryegrass in farm-scale strip trials near Pullman Washington(Huggins and Painter 2011) The inclusion of glyphosate-resistant spring canola also controls troublesome broadleafweeds such as mayweed chamomile (Anthemis cotula L) andcommon lambsquarters (Chenopodium album L) that are

difficult to control in cool-season food legumes A wideselection of spring canola cultivars are available in the iPNWto deal with depending on individual circumstances includingresistance toglyphosate gluphosinate and imazamoxGenerallya grass herbicide such as quizalofop should be added to agluphosinate-resistant variety to improve grass control Hybridspring canola has become available in the region and has beendemonstrated in western Canada to have higher yield potentialwhich likely imposes greater N requirements than an open-pollinated line (Mahli et al 2007 Smith et al 2010)

If fallow is dictated by poor spring crop seeding conditionsearly seeding winter canola into fallow a regional conditioncalled lsquodelayed plantingrsquo does offer the opportunity to apply thedual-purpose canola concept (Kirkegaard et al 2008b Neely2010) by taking advantage of the biennial characteristic of wintercanola cultivars to produce forage and grain from a singleplanting In an on-farm experiment in the annual croppingzone winter canola intercropped with spring pea and plantedon 2 July produced 780 kg DM handash1 forage that was harvested 2September 70 days after seeding (Kincaid et al 2011) Theforage wasmade into high quality silage feed for dairy cows Thecut plants then re-generated a smaller lateral shoot-producingplant supported by the established root system These plantssurvived the winter subsequently producing 2000 kg grainhandash1 the following season demonstrating that growth of astrong root system with reserve energy and nutrients is morecritical than having an abundance of shoot biomass for wintersurvival Cutting canola shoot meristems theoretically removesa source of auxin inhibiting lateral shoot stem initiation anddevelopment (Lia et al 2016) which may provide a mechanismfor more vigorous post-winter regrowth

Plant establishment Winter wheat can be successfullyestablished in this zone with adequate autumn precipitationfollowing summer harvest of a winter or spring grain cropbecause only a small seedling is required to survive the winter(Young et al 2008) In contrast establishment of winter canolain similar annual crop rotations has proven difficult due toprevalent dry soil conditions that delays timing of germinationuntil there are insufficient growing degree-days for establishingplants of sufficient size to overwinter (Murray and Auld 1986Moore and Guy 1997 Holman et al 2011) Post-harvestprecipitation required to initiate seed germination and seedlinggrowth typically does not occur until temperatures are too coolto foster adequate seedling root and shoot biomass productionneeded to overwinter during sub-freezing conditions As a resultwinter oilseeds do best when planted into higher surface soilmoisture in fallow in this zone as demonstrated in winter rape(Brassica napus) planted between 31 July and 5 Septemberproducing yields ranging from 3800 to 4670 kg handash1 nearMoscow Idaho (Murray and Auld 1986) Yet the fallowperiod required to establish winter canola in the high rainfallzone would waste a growing season in which a marketable cropwould otherwise be grown

Spring canola establishment must be accomplished inheavy winter wheat residue that can range from 6900 kg handash1

(Papendick and Miller 1977) to 14 500 kg handash1 (Young et al1990) as maintaining these surface residues in direct-seedsystems is needed to prevent soil erosion These high residuesreduce seedling growth by maintaining cold soil temperatures

256 Crop amp Pasture Science W L Pan et al

(Pan et al 1991) which might deter growers from producingspring canola the following year unless the fields have beenburned A 2-year study was conducted examining the effect of25-cm and 50-cm row spacing on spring canola yield Each yearspring canola was planted at 56 kg handash1 in winter wheat residuethat had yielded ~6700 kg handash1 of grain When averaged oversite-years spring canola yield was similar (1710 kg handash1 for 50-cm rows 1775 kg handash1 for 25-cm rows) regardless of row spacing(Young2012)Withwide rowspacingmachine and fuel costs arereduced because of the reduction in openers and subsequentreduction in tractor horsepower Additionally it is likely thatdelays at seeding caused by blockages of high residue loadsunder seeding equipment (lsquodrill pluggingrsquo) will be reduced withwider row spacing

Although early spring planting of canola can be a challengelate seeding also has its penalties Stands of spring canola arealso more consistent when planted before moisture levels declineas spring rainfall is generally sporadic in the region Springcanola direct-seeded into heavy wheat residue over 9 yearsshowed an inverse relationship between seeding date and grainyield (Huggins and Painter 2011 Fig 3) As in other canola-growing regions later plantings result in flowering and graindevelopment under conditions of higher water and temperaturestress that reduce grain yield (Gan et al 2004 Kirkegaard et al2016)

Nitrogen management The N management approaches mustbe tailored to the unique environment of the iPNW Regionalyield-based N recommendations for wheat are commonlycalculated by applying a single or narrowly defined unit Nrequirement (UNR) of 45 kg N per 100 kg grain for soft wheatto 6 kg N per 100 kg grain for hard wheat (Koenig 2005 Koeniget al 2011) However contrary observations of varying UNRacross variable Palouse landscapes have been observed (Fiezet al 1995) suggesting amore tactical approach toNmanagementcould be implemented

Over 6 years higher overall UNR of 7ndash13 kg N (100 kggrain)ndash1 were observed for spring canola in the zoneacross years varying in water availability This range is similarto those found in canola fertiliser guides from semi-arid westernNorth America (Pan et al 2016) and that of 7ndash8 kg N (100 kggrain)ndash1 in Australia (Norton 2016) Canola plant nutrient uptakeper unit yield is higher than soft white and hard red wheats

(Koenig et al 2011) suggesting higher levels of availablenutrients supplied by native soil fertiliser carryover or newlyapplied fertiliser are required for regional canola productioncompared with wheat nutrient management In southwesternAustralia the amount of N fertiliser required to produceoptimum yield was 40 higher for canola than wheat(Brennan and Bolland 2009) Nevertheless canola has a deeptaproot system (Gan et al 2009) as well as extensive root hairsfor fully exploiting soil nutrients andwater (Hammac et al 2011)As a result canola seed yield responds well to applied N whenresidual soil levels are low but minimal fertiliser N responsewhen soil N supply is high and yield potential is low (Fig 4 Panet al 2016) This exponential diminishing-returns response tototal available N was also observed in southwestern Australia(Seymour et al 2016) In Montana canola responded stronglyto fertiliser N when planted into low levels of residual soil nitrate(90 cm depth) where yields were optimised at 200 kg N supplyhandash1 (Jackson 2000) However the magnitude of response isvariable in the iPNW due to interacting factors of climateavailable soil N cultivar and management practices Overallalthough spring canola N supply (soil + fertiliser N) requirementsper unit grain weight are higher than wheat its extensive andefficient roots utilise deep residual soil N to 120 cm in this zoneto reduce fertiliser N requirements (Maaz et al 2016)

Annual cropndashfallow transition zone

Rotational fit The iPNW transition zone is ~665 000 ha withannual precipitation ranging from 300 to 450mm and ischaracterised by annual cropping during wetter than normalprecipitation years interspersed with fallow during drier years(Table 1 Fig 1) Growers traditionally have grown winter andspring wheat and barley in gt50 of the zone fallow in 27and spring legumes in 10 of the zone In higher than normalprecipitation years continuous crop rotations have been grownPlant establishment of winter canola or spring canola are bothpossible in this zone with opportunities and constraints

3500

3000

2500

2000

1500

1000

500

0

322 41 411 421

Planting date

Spr

ing

cano

la y

ield

(kg

handash1

)

51 511 521

Fig 3 Direct-seeded spring canola yields following spring wheat atPullman WA over 9 years as related to planting date (Huggins andPainter 2011)

2500

EONR 150 kg fertiliser N handash1

EONR 19 kg fertiliser N handash12000

1500

1000

500

00 50 100 150 200 250 300

Can

ola

yiel

d (k

g ha

ndash1)

Total N supply (kg N handash1)

Fig 4 Canola grain yield response to nitrogen supply Ns with substantivecontribution of soil N and low economically optimum fertiliser N (EONR) atDavenport WA with limited water (open symbols) compared with higherEONR due to lower soil N and higher water availability at Pullman WA in2012 (closed symbols) (Pan et al 2016)

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 257

described in the above and below sections on the annual crop andcropndashfallow zones

Flexible decisions on planting spring canola in this zoneshould be based on over-winter soil water storage to 120 cmrooting depth and weather predictions for in-seasonprecipitation Generally spring canola yields are correlated withtotal available water with water-use efficiency (WUE) slope of325 kgyieldmmndash1 availablemoisture in the inlandPacificNorth-west (Pan et al 2016) which is lower than those reported inAustralia Robertson and Kirkegaard (2005) evaluated 42datasets of dryland spring canola for WUE and found that theWUE of canola varied from 4 to 18 kg handash1mmndash1 in which latersown crops tended to have lower efficiencies Similarly theWUEof spring canola decreased from 12 to 2 kg handash1mmndash1 whenseeded in early winter rather than in early spring within theMediterranean type environment of Iran (Faraji et al 2009)Terminal heat and drought stress during the reproductiondevelopment may cause the reduction in WUE in late seededspring canola Therefore the WUE of spring canola in the inlandPacific Northwest is more comparable to Canada wherestudies report a range of 280ndash576 kg handash1mmndash1 for rain-fedspring canola sown in the spring season (Azooz and Arshad1998 Cutforth et al 2006 Gan et al 2009)

Weed management A farm-scale rotational experiment atthe Washington State University Wilke Farm located atDavenport Washington has compared fallow systems with twoor three crops with continuous cropping in replicated stripsacross a variable field (Esser and Hulbert 2013) Herbicide-resistant spring canola cultivars were included in the 4-yearrotation which thus far has enabled the best control offeral cereal rye (Secale cereale L) resulting in the highesteconomic return over input costs among the three rotationsSpring canola planted at 56 kg seed handash1 yielded 784ndash1960 kggrain handash1 following spring wheat Rotational wheat yieldincreases due to improved weed control following canola canresult in higher rotational profits even without economicbenefits of canola in single season crop comparisons (Connollyet al 2016) In certain years of relatively high canola wheat priceratios economic benefits have been obtained even withoutincluding rotational benefits

Nitrogen management Spring canola N response trials at thesame location had maximum yields averaging 1027 kg handash1 andeconomically optimal N rates averaged 23 kg N fertiliser handash1ranging from zero fertiliser N required after fallow to 6ndash65 kgfertiliser N handash1 required following wheat (Pan et al 2016) Thehigher required economic N rate for canola following winterwheat was evident despite the lower available soil water andlower canola yield potential These findings corroboratestatements in Alberta Agriculture and Rural Development(2004) about lower N availability following continuouscropping versus fallow These modest fertiliser N requirementsseemingly contrary to spring canolarsquos relatively high unit totalN supply requirements are due to high residual soil N carryoverand N mineralisation coupled with canola roots extractingwater and N from 90 to 120-cm depths Overall the UNRobserved in the transition zone ranged from 9 to 17 kg total Nsupply100 kg grain higher than the range (39ndash8 kg total Nsupply100 kg grain) reported in fertiliser guides from semi-arid western North America (Koenig et al 2011) This was due

to lower yields and NUE of this region and our more completeaccounting of root zone residual N supply and creditingsoil N mineralisation contributions to total N supply (Panet al 2016)

Grainndashfallow zone

Rotational fit The cropndashfallow zone usually has insufficientannual precipitation (lt300mm) to economically supportannual cropping (Young et al 2015) and comprises an arearoughly equivalent to the total of the other two rain-fed zonesof ~1 245 000 ha Winter wheat has greater yield potential thanspring wheat due to deeper roots more efficient water extractionand earlier flowering and grain development during hot drysummer months Similarly spring canola is not commonlygrown in this zone because spring canola yields only 50ndash60as much as winter canola (Pakish et al 2015)

Weed management Weed control in summer is typicallyaccomplished using tillage with a rod weeder or chemicalfallow-direct seeding to reduce wind erosion (Young andThorne 2004) One of the primary reasons to grow winter canolais to offer growers an added management tool to control weedsWinter annual grass weeds including feral rye downybrome jointed goatgrass and Italian ryegrass continue toplague monoculture winter wheat growers The introductionof imidazolinone-resistant wheat in 2003 (Ball et al 1999)provided growers with an additional option to manage thesepests however an imidazolinone-resistant biotype of downybrome has been found in Oregon and feral rye is one of the mostdifficult winter annual grass weeds to control with imazamox(Pester et al 2000) Feral rye is a predominant winter annualgrass weed in the low rainfall grain fallow region of theiPNW In this region quizalofop in conventionally bred wintercanola cultivars for example Amanda Falstaff and glyphosatein glyphosate-resistant canola cultivars for example Croplan115 and 125 effectively controlled feral rye (Young et al2016) A second reason to introduce winter canola into cerealproduction systems regardless of rainfall zone is availabilityof herbicide-tolerant canola cultivars These cultivars allowproducers to plant in fields with a history of sulfonylurea forexample Croplan 115 or 125 and imidazolinone herbicides forexample Claremore and Edimax (Young et al 2016) withoutenduring 9ndash40 months of plant back restrictions Commercialhybrid cultivars have recently been introduced into this regionand their potential advantages over open pollinated lines arebeing evaluated in regional trials For example winter canolacomparisons in Oklahoma have characterised greater seed sizeand yield potential under optimal conditions but less droughttolerance than open-pollinated cultivars (Bushong 2015)

Plant establishment Winter canola establishment is asignificant challenge in this zone The smaller seed size ofcanola alters seed zone requirements for optimal germinationand emergence compared with wheat which in turn can affectdepth of planting This need for deep planting is greatest in thiszone where late summer high temperatures and little to noprecipitation drives the soil moisture line into the subsoil(Schillinger et al 2010a) The range of seed sizes in canola farexceeds that of the variation in wheat seed Wheat seed plantedin the iPNW typically ranges from 31 to 38mg seedndash1 whereas

258 Crop amp Pasture Science W L Pan et al

canola seed ranges from 2 to 6mg seedndash1 (F L Young perscomm) A 3-fold variation in canola seed size makes it moreimperative to get accurate oilseed weights when targetingspecific plant population goals Seed size is affected bycultivar and the seed production environment as well ascommercial seed sizing processes (Lamb and Johnson 2004)Smaller seed reserves of energy and nutrients of individualcanola seeds restrict deep seed placement Winter wheatcultivars grown in the fallow zone are bred to emerge from verydeep seed placement (Mohan et al 2013) In contrast canola seedgenerally emerges best when placed within 2ndash3 cm of the soilsurface when moisture conditions are adequate but can emergefrom deeper placement (3ndash6 cm) when required to reachmoisture Hypocotyl length is genetically modulated indicatingpotential for future breeding opportunities (Zhao et al 2013)Larger seeds can generally emerge from greater depths due tolonger and more robust hypocotyls In addition larger seededBrassica cultivars produce greater early season biomass whichincreases crop competition with weeds (Harker et al 2015Brill et al 2016)

Winter canola establishment requires excellent soil moisturenear the soil surface and cool (298C) ambient air temperaturesfor 5ndash7days after planting (Young et al 2014)Deep furrowdrillsthat are used in the wheatndashfallow zone for placing the seed intosoil moisture are also being used successfully to plant wintercanola as the seedlings need to emerge only to the bottom of thefurrow During August the optimal time to plant winter canola(Young et al 2014) soil moisture is usually 10ndash15 cm below thesoil surface and too deep for canola seedlings to emerge To helpalleviate this problem shovels 25ndash38 cm wide have been placedin front of the openers to reach soilmoisture andmove the hot drysoil from the furrow thus reducing the distance the emergingseedling has to travel through the soil (Young et al 2008 2014)The use of shovels did not increase winter canola yield andwinter survival but did increase plant density 22 comparedwith when shovels were not used In addition there is a moreuniform plant distribution from the use of shovels whichsuppressed weed growth and reduced weed competition(Young et al 2014) Generally a 45-kg handash1 seeding rate wasoptimal for sufficient stand establishment and yield Whenwinter canola seeding was delayed until September yield wasdecreased almost 40 compared with an August plantingWinter survival can range from 56 to 83 with a subsequentspring plant population of only 20ndash40 plantsmndash2 needed foroptimum yield

Spring canola despite the lower yield potential can begrown following failed winter canola survival and glyphosate-resistant spring canola cultivars are beneficial for controllingsummer annual broadleaf weeds in this zone such as Russianthistle (Salsola tragus) which emerges with similar timing asspring canola Spring canola seed broadcast on the soil surfaceyields between 31 and 67 of spring canola that was placed inthe soil with drills equipped with double disk chisel hoe orinverted T-slot openers (Young et al 2012) Broadcast yields ofspring canola were low because generally lt5 of the seedestablished plants When left on the soil surface seedlingswere unprotected when emerging from the seed coat and werekilled by frost Rolling broadcast seed with a heavy cast-ironroller generally improved yield ~35 compared with broadcast

alone although improved yield ranged from 0 to gt100Depending on location and precipitation optimum yieldsranged from 615 kg handash1 to 1575 kg handash1 (Young et al 2012)Precipitation during flowering and seed-fill in May and Junecorrelated with increased canola yield presumably by reducingmoisture stress during reproductive growth as observed byGan et al (2004)

Shoot meristematic origins of dicotyledonous oilseedsdiffer from monocotyledonous cereal grain crops Leaves andshoot branch initiation of oilseeds occurs at or near the soilsurface (Thomas 2003) In contrast shoot tiller and rootmeristems of wheat seedlings emanate at the belowgroundcrown and stem nodes directly above the crown (Klepper et al1984) The development of aboveground shoot meristems ofoilseeds versus belowground shoot nodes of cereals is afundamental difference in freeze avoidance (Thomas 2003)Oilseeds are exposed to sudden downturns in air temperaturesabove the soil surface during late falls and winters whereascereals are more protected by the soil layer above the cerealshoot meristem that buffers against rapid and severesubfreezing spikes

The size of winter canola plants entering the winter monthscorrelates with winter survival Small seedlings with 2ndash3 trueleaves survive iPNW winters very poorly This limits wintercanola production in the non-irrigated annual cropping zoneof the iPNW as very dry soils following harvest of theprevious yearrsquos crop generally persist into October by thetime sufficient moisture has accumulated to establish a standthe seedlings are typically too small to survive the first hardfrostsWhen planted into fallow land early plantedwinter canolatakes advantage of added growing degree-days to producemore shoot and root biomass before winter dieback Plantingfive winter rapeseed cultivars in the annual cropping zone(600mm) from 2 July to 13 September indicated that laterplanting dates resulted in less winter survival and seed yield(Porter et al 1981) presumably because late season plantingshad less energy and nutrient reserves In contrast early plantingsof winter canola in the wheatndashfallow zone take advantage ofsurface soil moisture but may result in poor winter survivalWinter cultivars remain vegetative without stem boltinghowever vegetative biomass of early planted canola extractsmost of the available soil moisture to 150 cm depth producingweakened drought-stressed plants with higher shoot meristemsthat were more susceptible to winter kill than later seededplants (Reese 2015)

Several fields of winter canola were monitored over 3 yearsacross the iPNW illustrating temperature profiles associatedwith partial and complete canola winter kill (Fig 5) In thewinter of 2013ndash2014 minimum temperatures at the soilsurface fell to ndash208C in early December and again in Februaryresulting in widespread complete winter kill across the regionIn contrast minimum surface temperatures only reached ndash15to ndash178C in January of 2011ndash2012 and 2012ndash2013 followinggradual temperature declines which resulted in partial standlosses of ndash28 to ndash49 but still yielding 1700ndash4300 kg handash1

even at sites with reduced stands Winter canola grown in semi-arid environments has the ability to compensate for standlosses with increased stem branching and pod retention(Angadi et al 2003) A late spring frost in late AprilndashMay

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 259

during flowering (data not shown) severely reduced the pod setresulting in yields lt1000 kg handash1 despite good stand survival insome locations This freeze sensitivity of canola coming out of

winter dormancy has been noted in the USA Great Plains(Holman et al 2011) In a location near DavenportWashington spring frost was not a factor and winter canoladirect seeded into winter wheat stubble averaged 4100 kg handash1

(Schillinger 2013)Moderation of extreme subfreezing conditions by soil

at depths 10ndash20 cm were consistently demonstrated (Fig 5)in comparison to surface temperatures illustrating themorphological advantage of wheatrsquos ability to developsubsurface shoot meristems that are insulated by soil (Klepperet al 1984) in comparison to above surface canola shootmeristems Canola nutritional status potentially contributes tosupercooling by increasing cell solutes such as high K and Clnutrition (Evans et al 2015) Ensuring a sufficient P status ofvegetative canola plants entering into the winter season with theaddition of starter phosphorus at planting has been shown toimprove winter survival (Wilkins et al 2002)

Nitrogen management The N placement and timing forwinter canola require additional adjustments from traditional Nfertilisation methods used in winter wheat production due tointerspecies differences in root architecture Chemical fallow-direct seeded winter wheat is typically fertilised in deep bandsbelow the seed row at planting (Veseth et al 1986) Canolaseedlings produce a single taproot main axis with lateral rootsand root hairs emanating from an ammonia sensitive tap root(Madsen et al 2014) In contrast monocotyledonous cerealcrops have multiple seminal axes and shoot tillers whichinitiate from the seed the belowground crown and stem nodesthat produce shoot tillers and affiliated root seminal axes(Klepper et al 1984) As a result of these basic rootarchitectural differences canola seedlings are more sensitivethan cereals to chemical toxicities such as expanded zones ofhigh ammonia around fertiliser bands due to oilseed relianceon the development of a single tap root whereas cereals havenumerous seminal axes to explore deep soil layers This basicmorphological difference has implications for differentialfertiliser band sensitivity when a canola taproot radicleencounters a high ammonia band meristems become necroticwith subsequent seedling injury or death (Madsen et al 2014)While a seminal root axis of cereal seedlings can suffer thesame fate other seminal axes of the same seedling will growto the side of the band and successfully develop The ability ofwheat roots to morphologically overcome ammonia toxicity ofdeep banded ammonium fertilisers has allowed the developmentand commercial use of direct seed planting equipment with deepbanding capabilities (Veseth et al 1986) However canolarsquostaproot sensitivity to deep placed ammonia bands will requirealternate N placement and timing strategies Fertiliser placementstudies on canola have demonstrated the need to place N as a sideband (Grant et al 2011 Norton 2016)

High N status of the vegetative winter oilseed plants hasreduced survival during freezing conditions (Rathke et al2006) There are biochemical and morphological responses tohigh N availability that may contribute to the decrease in winterhardiness Canola leaves subjected to low temperature stressincrease levels of cryoprotectant chemicals (Janskaacute et al 2010)such as soluble sugars that facilitate cytoplasmic freezingpoint depression (Gusta et al 2004) Identification of culturalpractices and variety selections for plant survival to rapid

10

Subsurface soil Air above soil surface

0

ndash10

ndash20

10

0

ndash10

Dai

ly m

inim

um te

mpe

ratu

re (

degdegC)

ndash20

102013ndash2014

2012ndash2013

2011ndash2012

0

ndash10

ndash20

ndash30Nov Dec Jan

MonthFeb Mar

Fig 5 Temperature profiles were continuously recorded over three wintersat Davenport WA from 2012 to 2014 in the transitional cropndashfallow zonewhere winter canola is being grown Air and soil temperature probes ineach year were positioned directly above the soil surface or below the soilsurface at a depth of 10ndash15 cm

260 Crop amp Pasture Science W L Pan et al

freeze eventsmay be important to winter canola production in theiPNW as demonstrated in December 2014 when a rapidfreeze resulted in widespread loss of winter canola and winterwheat (J Schibel pers comm)

Low N status promotes increased sugar concentrationsand increased freeze resistance in plants (Lemoine et al 2013Wisniewski et al 2014) As a result this potentially changesthe N timing strategy for managing canola relative to traditionalwheat N management in the iPNW In zones less than 600mmannual precipitation where nitrate leaching below 180 cm soildepth is typically not excessive winter wheat N applicationoccurs pre-plant during summer fallow or at planting in annualcrop rotations (Veseth et al 1986 Halvorson et al 1999) Themain reason is to ensure adequate time for fertiliser N to nitrifyand move into the lower layers of the root profile ensuringadequate N availability as the surface soil dries and plantroots become increasingly reliant on subsoil N (Pan et al2001) If low N canola has higher winter survivability it mayprovide another reason to be conservative in N fertiliserapplications at planting and allow the canola to utilise residualN during early establishment An inverse relationship between Navailability and winter survival could be due to a complex set ofbiochemical shoot morphological ie raised shoot meristemsabove the ground and growth-induced water stress (Reese2015)Winter canola exhibits deep rooting depths to 180 cm andsubsoil N and water access and recovery is critically important(Hocking et al 2002 Reese 2015) Furthermore iPNW climatechange projections of hotter drier summer months (Abatzoglouet al 2015) portend a need for enhancing deep strong-rootedwinter crops such as canola for adapting to foreseen climatechange (Hatfield et al 2001 Blum 2009 Lynch 2015)

These climate change forecast models predict 5ndash15increases in iPNW regional annual precipitation but withincreasing proportions occurring during the winter andspring months with drier hotter summers This trend willnecessitate improvements in water and N infiltration and subsoilstorage during winter months for later access during active cropdevelopment Canola also has a reputation as a strong taprootedcrop capable of creating macro biopore channels for facilitatingsaturated water flow and root pathways for subsequent crops Yetcanola roots cannot always penetrate soil horizons with highphysical and chemical impedance (Cresswell and Kirkegaard1995 Watt et al 2006) Tillage pans and genetic soil horizonsin the iPNW have been observed to impede canola roots causingcharacteristic lsquoJrsquo hooking of the taproot forcing it to turn 90degrees along the plan of the soil pan until it encounters a crackwhere it can continue vertical development (Lisson et al 2007)This may be a plausible explanation for new canola growertestimonials claiming rotational benefits are not seen untila second or third rotation

Irrigated crop zone

Rotational fit The irrigated temperate desert of centralWashington and Oregon supports perennial tree and vine fruitproduction as well as 500 000 ha of many high value agronomiccrops such as potato and sweet corn where small grain cerealsare used as a rotational crop and winter wheat is only ~8 ofthe area (Table 1 Fig 1) As many high value crops for example

potato sweet corn onion beans are grown in this zone a muchlower adoption is projected for this zone with canola mostlyrestricted as a substitution for wheat in the irrigated rotationsof central Washington and Oregon

In addition with opportunities to follow early harvested freshvegetable crops dual purpose use of canola has potential todiversify and intensify irrigated rotations similar to drylandapplications (Neely 2010 Walsh 2012 Lilley et al 2015) Inthis zone of extended growing degree-days double croppingunder irrigation where biennial canola could bridge two short-season summer crops to yield three harvests over two growingseasons such asYear 1 fresh peascanola forage ndashYear 2 canolagrain (Kincaid et al 2011) Current efforts are focussed onproduction of silage from first-season canola vegetation incentral Washington Comparable canola grain yields of2300 kg handash1 were harvested with and without forage cuttingand removal (Desta et al 2013) Yield gaps between predictedand observed yields may relate to J-hooking that has beenobserved under irrigation similar to dryland root observationsdescribed above

Plant establishment As water is not a limitation underirrigation germination and seedling establishment is not asmuch of an issue in this zone For example winter rapeseedand mustard were rapidly established in late August and earlySeptember in the south andnorthColumbiabasinunder irrigationand substantial biomass and N accumulation occurs beforethe first hard frost and under these conditions deep soil N useshould still be accounted for in oilseed rotational N fertiliserrecommendations (Weinert et al 2002) Even under irrigation Nfertiliser responses in winter canola can be minimal due to buildup of residual soil N in highly fertilised rotations (Davenport et al2010) Even with ample water and N winter kill is still a problemin this zone as demonstrated in an irrigated winter wheat springbarley winter canola rotation where green-bridged Rhizoctoniasolani on spring barley residues was suspected to infect wintercanola roots perhaps contributing to winter kill in 4 of 5 years(Paulitz et al 2010 Schillinger et al 2010b) Rhizoctonia solanianastomosis group 2ndash1 has recently been identified to infectwheat and rape roots (Sturrock et al 2015)

Summary and future projections

Canola area has historically constituted less than 1 of theiPNW Advancements in the development of both winter andspring cultivars have afforded flexible options in weed controlmanagement Competitive hybrid cultivars are nowcommercially available with and without herbicide toleranceor resistance Current efforts are to identify and integratecultivars that can be successfully established survive winterand use subsoil water and N efficiently in each of the zonesEstablishment of a local oilseed processing industry increasingglobal and regional canola markets for food fuel and feedagronomic benefits in increasing rotational diversity andcontinued vigorous research and extension efforts havestimulated a recent increase in canola integration into existingmonoculture wheat production in the iPNW Modest canolarotational integration projected for each zone would achieveproduction goals to match current and future regionaloilseed processing capacity with 300 000 canola ha per year

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 261

(Table 1) An upper agronomic limit of roughly 1 1wheat canola has been reached in the semi-arid wheat-producing region of western Canada Similar crop productionratios in the iPNW would approach 700 000 ha Winter canolaintegration into the wheatndashfallow annual cropndashtransition andirrigated cropping zones and spring canola integration intoannual cropping and transition zones will improve weedcontrol and wheat yields particularly with herbicide-resistantcultivars The most critical challenges in the adaptation ofcanola into iPNW wheat-cropping systems include improvedconsistency of winter canola establishment and winter survivalin the low and intermediate precipitation zones Seeding depthand timing are critical determinants of winter and spring canolayield potential Relevant genetic research is currently focussedon increasing seed size and hypocotyl lengths for improvedseedling emergence and on the identification of freeze-tolerantcultivars Integration of spring canola into higher precipitationannual cropping systems requires research on innovative earlyplanting strategies and new earlier maturing cultivars to avoidhigh temperature and moisture stress Taproot architecture ofcanola dictates changes in standard N placement andtiming strategies that have been practiced for iPNW wheatproduction but the deep rooting habit of canola will contributeto efficient water and N recovery of the cropping systems Farmenterprise economics that account for rotational benefits andproduction risk will help growers account for multi-yearinvestments in canolandashwheat rotations to assess the benefits ofintegrated canolandashwheat systems

References

Abatzoglou J Rupp D Mote P (2015) Asymmetrical warming projectionsfor the inland Pacific Northwest In lsquoRegional approaches to climatechange for Pacific Northwest agriculture Climate science Northwestfarmers can usersquo (Eds K Borrelli D Daily Laursen S Eigenbrode BMahler R Pepper) pp 104ndash105 Available at wwwreachchpnaorg

Alberta Agriculture and Rural Development (2004) Alberta fertilizer guideIn lsquoAgric-facts practical information for Albertarsquos agriculture industryrsquoAgdex 541ndash1 (Ministry of Alberta Agriculture Food and RuralDevelopment Edmonton Alberta Canada)

Angadi SV Cutforth HW McConkey BG Gan Y (2003) Yield adjustmentby canola grown at different plant populations under semiarid conditionsCrop Science 43 1358ndash1366 doi102135cropsci20031358

Angus JF Kirkegaard JA Hunt JR Ryan MH Ohlander L Peoples MB(2015) Break crops and rotations for wheat Crop amp Pasture Science 66523ndash552 doi101071CP14252

Azooz RH Arshad MA (1998) Effect of residue and tillage managementon barley and canola growth and water use efficiency Canadian Journalof Soil Science 78 649ndash656 doi104141S97-098

Ball DA Young FL Ogg AO Jr (1999) Selective control of jointedgoatgrass (Aegilops clylindrica) with imazamox in herbicide-resistantwheat Weed Technology 13 77ndash82

Bettis B Auld D (Eds) (1980) Development of oilseeds as alternative cropsfor the Pacific Northwest Pacific Northwest Regional CommissionYearly Reports June 1979ndash31 July 1980 June 1980ndashJune 1981Pacific Northwest Regional Commission Moscow Idaho USA

Bettis BL Peterson CL Auld DL Driscoll DJ Peterson (1982) Fuelcharacteristics of vegetable oil from oilseed crops in the PacificNorthwest Agronomy Journal 74 335ndash339

Blum A (2009) Effective use of water (EUW) and not water-use efficiency(WUE) is the target of crop yield improvement under drought stressField Crops Research 112 119ndash123 doi101016jfcr200903009

Brennan RF Bolland MDA (2009) Comparing the nitrogen and phosphorusrequirements of canola and wheat for grain yield and quality Crop ampPasture Science 60 566ndash577 doi101071CP08401

Brill RD Jenkins ML Gardner MJ Lilley JM Orchard BA (2016)Optimising canola establishment and yield in south-eastern Australiawith hybrids and large seed Crop amp Pasture Science 67 409ndash418

Brown J Davis J (2015) Brassica breeding and research University of IdahoAvailable at wwwcalsuidahoedubrassica (accessed 15 December2015)

Brown J Davis JB Erickson DA Brown AP Seip L (1995) 1995 PacificNorthwest canola variety trial (PNWCVT) results and conclusions InlsquoPacificNorthwest canola conference1995proceedingsrsquo (EdsGJohnsonM Lewis) pp 29ndash36 (Department of Entomology Montana StateUniversity Bozeman MT)

BushongJ (2015)Okanola varieties andhybrids open-pollinatedvarietiesvshybrids Available at httpcanolaokstateeducropproductionvarieties(accessed 15 December 2015)

Conley SP Bordovsky D Rife C WieboldW (2004) Winter canola survivaland yield response to nitrogen and fall phosphorus Crop Managementdoi101094CM-2004-0901-01-RS

Connolly JR McCracken VA Painter KM (2016) Enterprise budget wheatand canola rotations in Eastern Washington intermediate rainfall regions12rdquo to 16rdquo Washington State University Extension PublicationWashington State University TB10 USA

Cook RJ Schillinger WF Christensen NW (2002) Rhizoctonia rootrot andtake-all of wheat in diverse direct-seed spring cropping systemsCanadian Journal of Plant Pathology 24 349ndash358 doi10108007060660209507020

Cresswell HP Kirkegaard JA (1995) Subsoil amelioration by plant-roots ndashthe process and the evidence Australian Journal of Soil Research 33221ndash239 doi101071SR9950221

Cutforth HW Angadi SV McConkey BG (2006) Stubble managementand microclimate yield and water use efficiency of canola grown inthe semiarid Canadian prairie Canadian Journal of Plant Science 8699ndash107 doi104141P05-073

Davenport J Stevens B Hang A Peters T (2010) Irrigated canola researchIn lsquoWashingtonOilseedCroppingSystemsProject partof theWashingtonState Biofuels Initiative 2010rsquo Annual Progress Report (EdsKESowersWL Pan) Available at httpcsswsuedubiofuelsfiles2012092010_Annual_Progress_Reportpdf (accessed 27 December 2015)

De Jong R Shields JA (1988) Available water-holding capacity maps ofAlberta Saskatchewan and Manitoba Canadian Journal of Soil Science68 157ndash163 doi104141cjss88-015

Desta KG Collins H Pan B (2013) Double-cropping dual purpose irrigatedbiennial canolawithgreenpea In lsquoWashingtonOilseedCroppingSystemsProject part of the Washington State Biofuels Initiative 2013rsquo AnnualProgress Report (Eds KE Sowers WL Pan) Available at httpcsswsuedubiofuelsfiles2012092013-Biofuel-Cropping-Systems-Research-Progress-Reportpdf (accessed 27 December 2015)

Divine TE Alzheimer DP Currie JW McGinnis KA Wiggins DJ (1977)Research on the potential impact of advanced oilseeds processingtechnology on Pacific Northwest Agriculture Batelle Pacific NorthwestLaboratories 231110270610690646 Richland Washington USA

Douglas CL Wysocki DJ Zuzel JF Rickman RW Klepper BL (1990)Agronomic zones for the dryland Pacific Northwest Pacific NorthwestCooperative Extension Bulletin PNW 954

Esser A Hulbert S (2013) Eastern WA low to intermediate rainfall InlsquoWashington Oilseed Cropping Systems Project part of theWashington State Biofuels Initiative 2013 Annual Progress Reportrsquo(Eds KE Sowers WL Pan) pp 31ndash36 Available at httpcsswsuedu

262 Crop amp Pasture Science W L Pan et al

wheat production system are numerous including breakingdisease weed and insect cycles (Kirkegaard et al 2008a) TheiPNW has similar needs and opportunities for diversificationthat could include oilseed integration (Cook et al 2002Young et al 2014) Primary agronomic benefits motivatingiPNW growers include prospects for improved weed controlimproved nutrient cycling and water use and improved soilquality

There are both similarities and differences between theclimate and soils of the iPNW and those of other major semi-arid canola-producing regions of the world including WesternAustralia the western Canadian prairie and the Great Plains ofcentral USA (Table 2) Maximum growing-season temperaturescan subject canola to heat stress coupled to limited wateravailability in all four global regions Western Canada is leastsubject to maximum temperatures and most subject to minimumtemperatures with regional rankings of average minimumtemperatures western Canadian prairies ltGreat Plains USAltiPNW ltWestern Australia As a result only spring cultivars aregrown in the spring and summer of the Canadian prairies thecoldest of these regions but also in the winter of WesternAustralia the warmest of these global regions Due to themore moderate temperatures of the Great Plains and iPNWboth winter and spring cultivars can be grown during therespective seasons in various subregions and harvested insummer Canola is similar to wheat in that it has both winterand spring types where the winter types have a vernalisationrequirement Winter types of wheat (Schillinger et al 2010a)

and canola (Pakish et al 2015) typically out-yield their springcounterparts in this region due to their longer growing seasonmore efficient utilisation of winter precipitation with deeperroots and earlier grain filling However winter canola islimited to rotations and zones in which there is a suitableperiod with conditions for successful establishment and wintersurvival

The iPNW also has a high proportion of annual precipitationreceived during the winter months during winter canoladormancy (Table 2) The majority of precipitation in theiPNW is a mixture of snow and rain often over frozen soilsAs a result crops are more reliant on stored water and nutrientsin the subsoils for sustaining growth and development fromstem elongation through grain development As lt40 of thetotal annual precipitation is received during the spring andsummer months climate-induced water and heat stress occursduring reproductive stages of development Fortunately theaeolian and glacial medium-textured soils are generally deepto bedrock with high water-holding capacity (Schwartz andAlexander 1995) ranging from 270 to 360mm in a 180-cmprofile (Table 2) This is in contrast with canola grown duringthe wet winter in Western Australia where climate-inducedwater stress may still be an issue during the reproductivestages during drought years The highly weathered soils of theregion many with poor physical structure root restrictingcompaction (Lisson et al 2007 Smettem and Gregory 2010)and low (34ndash134mm) water-holding capacity (Oliver andRobertson 2009) exacerbate these problems (Hamza and

Irrigated annual crop(503 800 ha)

Winter wheat8

Winterwheat45

Winterwheat42

Winterwheat37

Othernon-fruit

29

Alfalfa21

Alfalfa2 Grain legume

3

Grainlegume

18

Alfalfa4

Alfalfa5

Potato14

Corn16

Springcereal

6 Springcereal

3

Springcereal21 Spring

cereal22

Springlegume

4

Fallow2

Other4

Other10

Canola1 Other

9

Fallow47

Fallow27

Fallow3

Grain fallow(1 245 800 ha)

Annual crop fallowtransition

(665 200 ha)

Annual crop (568 100 ha)

Fig 2 2007ndash2013 average land areas and crop distributions across four agroecological cropping zones in iPNW (Hugginset al 2014)

Table 2 Climate and soil characteristics of established and emerging canola production areas in semi-arid regions (6ndash8 sites) of the world

Area Minimumtemperature

(8C)

Maximumtemperature

(8C)

Annualprecipitation

(mm)

Precipitationduring growing

season

Soil water-holding capacity

Inland PNWAndash7 oC to ndash3oC 28ndash32oC 260ndash660 20ndash40 135ndash360mm (Schwartz and Alexander 1995)

US Great PlainsA ndash22oC to ndash3oC 25ndash35oC 250ndash890 65ndash75 51ndash350mm (Ji and Peters 2003)Canadian PrairiesB ndash22oC to ndash11oC 22278C 300ndash450 60ndash67 50ndash250mm (De Jong and Shields 1988)SW AustraliaC ndash2oC to 4oC 21ndash34oC 260ndash650 65ndash75 34ndash134mm (Oliver and Robertson 2009)

A1981ndash2010 Monthly Normals National Centers for Environmental Information National Oceanic and Atmospheric Administration Min temp recordedin January Max temp recorded in July

B1971ndash2010 Climate Normals Climate Government of Canada Min temp recorded in January Max temp recorded in JulyC1961ndash1990 ClimateNormals Climate data AustralianGovernment Bureau ofMeteorologyMin temp recorded in July or AugustMax temp recorded inOct

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 255

Anderson 2003) and all contribute to potential drought stressThe Great Plains of the USA and western Canadian soilshave variable water holding capacity (50ndash350mm) and ahigher percentage of precipitation during the growing seasoncompared with the iPNW (Table 2)

The greatest agronomic challenges in fostering iPNW canolaadaptation are to define wheatndashcanola-based rotations thatimprove weed control optimise soil water and N recharge andcrop use establish good plant stands maximise plant survivalduring overwinter freezing and early spring frosts and sustaincrop water and nutrient use during hot dry summer months Thediversity of environments soils and cropping systems across thefour major iPNW production zones (Fig 1 Table 1) presentchallenges to design suitable wheatndashcanola cropping systemswithin each zone The overarching goal of the Washington StateOilseed Cropping Systems project is to integrate appropriatewinter and spring canola cultivars into cropping systemstailored for each of these zones to increase crop and marketdiversification and productivity The agronomic research aimsto identify appropriate crop sequences and modifications totraditional wheat crop establishment and fertility managementstrategies to accommodate differences in physiological andmorphological traits of canola relative to wheat

Annual crop zone

Rotational fit The annual cropping zone comprises 568 000 haof the Palouse and western foothills of the Rocky mountainrange straddling the eastern WashingtonndashNorthern Idahoborder (Table 1 Fig 1) Precipitation of gt450mm per yearsupports annual cropping with winter wheat spring wheat andspring barley grown over 60 of the cropping zone land area andcool-season legumes account for only 18 (Fig 2) Typicallythere is insufficient soil moisture and growing degree-daysfollowing crop harvest to establish and grow winter canola tosufficient size before freezingwinter conditions so the focus is onadapting spring canola (discussed below) substituting springcereals or legumes in the rotation (Table 1) Winter canola ismore feasible following fallow but fallow is not normallypracticed in this region (Fig 1) unless wet spring conditionsprevent establishment of spring crops Nevertheless survivingwinter canola in this zone can yield 3000ndash4000 kg handash1 withample available soil moisture (Brown and Davis 2015 Evanset al 2015)

Weed management The predominance of cereal crops inthis zone encourages annual grassy weed infestations such asItalian ryegrass (Lolium multiflorum Lam) downy brome(Bromus tectorum L) and jointed goatgrass (Aegilopscylindrica HOST Ball et al 1999) Increasing broadleaf cropsin rotation with wheat provides better control of these grassyweeds particularly when herbicide-resistant canola is used(Young et al 2016) Nine years of substituting glyphosate-resistant spring canola for spring legumes in rotation withwinter and spring cereals was effective in controlling Italianryegrass in farm-scale strip trials near Pullman Washington(Huggins and Painter 2011) The inclusion of glyphosate-resistant spring canola also controls troublesome broadleafweeds such as mayweed chamomile (Anthemis cotula L) andcommon lambsquarters (Chenopodium album L) that are

difficult to control in cool-season food legumes A wideselection of spring canola cultivars are available in the iPNWto deal with depending on individual circumstances includingresistance toglyphosate gluphosinate and imazamoxGenerallya grass herbicide such as quizalofop should be added to agluphosinate-resistant variety to improve grass control Hybridspring canola has become available in the region and has beendemonstrated in western Canada to have higher yield potentialwhich likely imposes greater N requirements than an open-pollinated line (Mahli et al 2007 Smith et al 2010)

If fallow is dictated by poor spring crop seeding conditionsearly seeding winter canola into fallow a regional conditioncalled lsquodelayed plantingrsquo does offer the opportunity to apply thedual-purpose canola concept (Kirkegaard et al 2008b Neely2010) by taking advantage of the biennial characteristic of wintercanola cultivars to produce forage and grain from a singleplanting In an on-farm experiment in the annual croppingzone winter canola intercropped with spring pea and plantedon 2 July produced 780 kg DM handash1 forage that was harvested 2September 70 days after seeding (Kincaid et al 2011) Theforage wasmade into high quality silage feed for dairy cows Thecut plants then re-generated a smaller lateral shoot-producingplant supported by the established root system These plantssurvived the winter subsequently producing 2000 kg grainhandash1 the following season demonstrating that growth of astrong root system with reserve energy and nutrients is morecritical than having an abundance of shoot biomass for wintersurvival Cutting canola shoot meristems theoretically removesa source of auxin inhibiting lateral shoot stem initiation anddevelopment (Lia et al 2016) which may provide a mechanismfor more vigorous post-winter regrowth

Plant establishment Winter wheat can be successfullyestablished in this zone with adequate autumn precipitationfollowing summer harvest of a winter or spring grain cropbecause only a small seedling is required to survive the winter(Young et al 2008) In contrast establishment of winter canolain similar annual crop rotations has proven difficult due toprevalent dry soil conditions that delays timing of germinationuntil there are insufficient growing degree-days for establishingplants of sufficient size to overwinter (Murray and Auld 1986Moore and Guy 1997 Holman et al 2011) Post-harvestprecipitation required to initiate seed germination and seedlinggrowth typically does not occur until temperatures are too coolto foster adequate seedling root and shoot biomass productionneeded to overwinter during sub-freezing conditions As a resultwinter oilseeds do best when planted into higher surface soilmoisture in fallow in this zone as demonstrated in winter rape(Brassica napus) planted between 31 July and 5 Septemberproducing yields ranging from 3800 to 4670 kg handash1 nearMoscow Idaho (Murray and Auld 1986) Yet the fallowperiod required to establish winter canola in the high rainfallzone would waste a growing season in which a marketable cropwould otherwise be grown

Spring canola establishment must be accomplished inheavy winter wheat residue that can range from 6900 kg handash1

(Papendick and Miller 1977) to 14 500 kg handash1 (Young et al1990) as maintaining these surface residues in direct-seedsystems is needed to prevent soil erosion These high residuesreduce seedling growth by maintaining cold soil temperatures

256 Crop amp Pasture Science W L Pan et al

(Pan et al 1991) which might deter growers from producingspring canola the following year unless the fields have beenburned A 2-year study was conducted examining the effect of25-cm and 50-cm row spacing on spring canola yield Each yearspring canola was planted at 56 kg handash1 in winter wheat residuethat had yielded ~6700 kg handash1 of grain When averaged oversite-years spring canola yield was similar (1710 kg handash1 for 50-cm rows 1775 kg handash1 for 25-cm rows) regardless of row spacing(Young2012)Withwide rowspacingmachine and fuel costs arereduced because of the reduction in openers and subsequentreduction in tractor horsepower Additionally it is likely thatdelays at seeding caused by blockages of high residue loadsunder seeding equipment (lsquodrill pluggingrsquo) will be reduced withwider row spacing

Although early spring planting of canola can be a challengelate seeding also has its penalties Stands of spring canola arealso more consistent when planted before moisture levels declineas spring rainfall is generally sporadic in the region Springcanola direct-seeded into heavy wheat residue over 9 yearsshowed an inverse relationship between seeding date and grainyield (Huggins and Painter 2011 Fig 3) As in other canola-growing regions later plantings result in flowering and graindevelopment under conditions of higher water and temperaturestress that reduce grain yield (Gan et al 2004 Kirkegaard et al2016)

Nitrogen management The N management approaches mustbe tailored to the unique environment of the iPNW Regionalyield-based N recommendations for wheat are commonlycalculated by applying a single or narrowly defined unit Nrequirement (UNR) of 45 kg N per 100 kg grain for soft wheatto 6 kg N per 100 kg grain for hard wheat (Koenig 2005 Koeniget al 2011) However contrary observations of varying UNRacross variable Palouse landscapes have been observed (Fiezet al 1995) suggesting amore tactical approach toNmanagementcould be implemented

Over 6 years higher overall UNR of 7ndash13 kg N (100 kggrain)ndash1 were observed for spring canola in the zoneacross years varying in water availability This range is similarto those found in canola fertiliser guides from semi-arid westernNorth America (Pan et al 2016) and that of 7ndash8 kg N (100 kggrain)ndash1 in Australia (Norton 2016) Canola plant nutrient uptakeper unit yield is higher than soft white and hard red wheats

(Koenig et al 2011) suggesting higher levels of availablenutrients supplied by native soil fertiliser carryover or newlyapplied fertiliser are required for regional canola productioncompared with wheat nutrient management In southwesternAustralia the amount of N fertiliser required to produceoptimum yield was 40 higher for canola than wheat(Brennan and Bolland 2009) Nevertheless canola has a deeptaproot system (Gan et al 2009) as well as extensive root hairsfor fully exploiting soil nutrients andwater (Hammac et al 2011)As a result canola seed yield responds well to applied N whenresidual soil levels are low but minimal fertiliser N responsewhen soil N supply is high and yield potential is low (Fig 4 Panet al 2016) This exponential diminishing-returns response tototal available N was also observed in southwestern Australia(Seymour et al 2016) In Montana canola responded stronglyto fertiliser N when planted into low levels of residual soil nitrate(90 cm depth) where yields were optimised at 200 kg N supplyhandash1 (Jackson 2000) However the magnitude of response isvariable in the iPNW due to interacting factors of climateavailable soil N cultivar and management practices Overallalthough spring canola N supply (soil + fertiliser N) requirementsper unit grain weight are higher than wheat its extensive andefficient roots utilise deep residual soil N to 120 cm in this zoneto reduce fertiliser N requirements (Maaz et al 2016)

Annual cropndashfallow transition zone

Rotational fit The iPNW transition zone is ~665 000 ha withannual precipitation ranging from 300 to 450mm and ischaracterised by annual cropping during wetter than normalprecipitation years interspersed with fallow during drier years(Table 1 Fig 1) Growers traditionally have grown winter andspring wheat and barley in gt50 of the zone fallow in 27and spring legumes in 10 of the zone In higher than normalprecipitation years continuous crop rotations have been grownPlant establishment of winter canola or spring canola are bothpossible in this zone with opportunities and constraints

3500

3000

2500

2000

1500

1000

500

0

322 41 411 421

Planting date

Spr

ing

cano

la y

ield

(kg

handash1

)

51 511 521

Fig 3 Direct-seeded spring canola yields following spring wheat atPullman WA over 9 years as related to planting date (Huggins andPainter 2011)

2500

EONR 150 kg fertiliser N handash1

EONR 19 kg fertiliser N handash12000

1500

1000

500

00 50 100 150 200 250 300

Can

ola

yiel

d (k

g ha

ndash1)

Total N supply (kg N handash1)

Fig 4 Canola grain yield response to nitrogen supply Ns with substantivecontribution of soil N and low economically optimum fertiliser N (EONR) atDavenport WA with limited water (open symbols) compared with higherEONR due to lower soil N and higher water availability at Pullman WA in2012 (closed symbols) (Pan et al 2016)

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 257

described in the above and below sections on the annual crop andcropndashfallow zones

Flexible decisions on planting spring canola in this zoneshould be based on over-winter soil water storage to 120 cmrooting depth and weather predictions for in-seasonprecipitation Generally spring canola yields are correlated withtotal available water with water-use efficiency (WUE) slope of325 kgyieldmmndash1 availablemoisture in the inlandPacificNorth-west (Pan et al 2016) which is lower than those reported inAustralia Robertson and Kirkegaard (2005) evaluated 42datasets of dryland spring canola for WUE and found that theWUE of canola varied from 4 to 18 kg handash1mmndash1 in which latersown crops tended to have lower efficiencies Similarly theWUEof spring canola decreased from 12 to 2 kg handash1mmndash1 whenseeded in early winter rather than in early spring within theMediterranean type environment of Iran (Faraji et al 2009)Terminal heat and drought stress during the reproductiondevelopment may cause the reduction in WUE in late seededspring canola Therefore the WUE of spring canola in the inlandPacific Northwest is more comparable to Canada wherestudies report a range of 280ndash576 kg handash1mmndash1 for rain-fedspring canola sown in the spring season (Azooz and Arshad1998 Cutforth et al 2006 Gan et al 2009)

Weed management A farm-scale rotational experiment atthe Washington State University Wilke Farm located atDavenport Washington has compared fallow systems with twoor three crops with continuous cropping in replicated stripsacross a variable field (Esser and Hulbert 2013) Herbicide-resistant spring canola cultivars were included in the 4-yearrotation which thus far has enabled the best control offeral cereal rye (Secale cereale L) resulting in the highesteconomic return over input costs among the three rotationsSpring canola planted at 56 kg seed handash1 yielded 784ndash1960 kggrain handash1 following spring wheat Rotational wheat yieldincreases due to improved weed control following canola canresult in higher rotational profits even without economicbenefits of canola in single season crop comparisons (Connollyet al 2016) In certain years of relatively high canola wheat priceratios economic benefits have been obtained even withoutincluding rotational benefits

Nitrogen management Spring canola N response trials at thesame location had maximum yields averaging 1027 kg handash1 andeconomically optimal N rates averaged 23 kg N fertiliser handash1ranging from zero fertiliser N required after fallow to 6ndash65 kgfertiliser N handash1 required following wheat (Pan et al 2016) Thehigher required economic N rate for canola following winterwheat was evident despite the lower available soil water andlower canola yield potential These findings corroboratestatements in Alberta Agriculture and Rural Development(2004) about lower N availability following continuouscropping versus fallow These modest fertiliser N requirementsseemingly contrary to spring canolarsquos relatively high unit totalN supply requirements are due to high residual soil N carryoverand N mineralisation coupled with canola roots extractingwater and N from 90 to 120-cm depths Overall the UNRobserved in the transition zone ranged from 9 to 17 kg total Nsupply100 kg grain higher than the range (39ndash8 kg total Nsupply100 kg grain) reported in fertiliser guides from semi-arid western North America (Koenig et al 2011) This was due

to lower yields and NUE of this region and our more completeaccounting of root zone residual N supply and creditingsoil N mineralisation contributions to total N supply (Panet al 2016)

Grainndashfallow zone

Rotational fit The cropndashfallow zone usually has insufficientannual precipitation (lt300mm) to economically supportannual cropping (Young et al 2015) and comprises an arearoughly equivalent to the total of the other two rain-fed zonesof ~1 245 000 ha Winter wheat has greater yield potential thanspring wheat due to deeper roots more efficient water extractionand earlier flowering and grain development during hot drysummer months Similarly spring canola is not commonlygrown in this zone because spring canola yields only 50ndash60as much as winter canola (Pakish et al 2015)

Weed management Weed control in summer is typicallyaccomplished using tillage with a rod weeder or chemicalfallow-direct seeding to reduce wind erosion (Young andThorne 2004) One of the primary reasons to grow winter canolais to offer growers an added management tool to control weedsWinter annual grass weeds including feral rye downybrome jointed goatgrass and Italian ryegrass continue toplague monoculture winter wheat growers The introductionof imidazolinone-resistant wheat in 2003 (Ball et al 1999)provided growers with an additional option to manage thesepests however an imidazolinone-resistant biotype of downybrome has been found in Oregon and feral rye is one of the mostdifficult winter annual grass weeds to control with imazamox(Pester et al 2000) Feral rye is a predominant winter annualgrass weed in the low rainfall grain fallow region of theiPNW In this region quizalofop in conventionally bred wintercanola cultivars for example Amanda Falstaff and glyphosatein glyphosate-resistant canola cultivars for example Croplan115 and 125 effectively controlled feral rye (Young et al2016) A second reason to introduce winter canola into cerealproduction systems regardless of rainfall zone is availabilityof herbicide-tolerant canola cultivars These cultivars allowproducers to plant in fields with a history of sulfonylurea forexample Croplan 115 or 125 and imidazolinone herbicides forexample Claremore and Edimax (Young et al 2016) withoutenduring 9ndash40 months of plant back restrictions Commercialhybrid cultivars have recently been introduced into this regionand their potential advantages over open pollinated lines arebeing evaluated in regional trials For example winter canolacomparisons in Oklahoma have characterised greater seed sizeand yield potential under optimal conditions but less droughttolerance than open-pollinated cultivars (Bushong 2015)

Plant establishment Winter canola establishment is asignificant challenge in this zone The smaller seed size ofcanola alters seed zone requirements for optimal germinationand emergence compared with wheat which in turn can affectdepth of planting This need for deep planting is greatest in thiszone where late summer high temperatures and little to noprecipitation drives the soil moisture line into the subsoil(Schillinger et al 2010a) The range of seed sizes in canola farexceeds that of the variation in wheat seed Wheat seed plantedin the iPNW typically ranges from 31 to 38mg seedndash1 whereas

258 Crop amp Pasture Science W L Pan et al

canola seed ranges from 2 to 6mg seedndash1 (F L Young perscomm) A 3-fold variation in canola seed size makes it moreimperative to get accurate oilseed weights when targetingspecific plant population goals Seed size is affected bycultivar and the seed production environment as well ascommercial seed sizing processes (Lamb and Johnson 2004)Smaller seed reserves of energy and nutrients of individualcanola seeds restrict deep seed placement Winter wheatcultivars grown in the fallow zone are bred to emerge from verydeep seed placement (Mohan et al 2013) In contrast canola seedgenerally emerges best when placed within 2ndash3 cm of the soilsurface when moisture conditions are adequate but can emergefrom deeper placement (3ndash6 cm) when required to reachmoisture Hypocotyl length is genetically modulated indicatingpotential for future breeding opportunities (Zhao et al 2013)Larger seeds can generally emerge from greater depths due tolonger and more robust hypocotyls In addition larger seededBrassica cultivars produce greater early season biomass whichincreases crop competition with weeds (Harker et al 2015Brill et al 2016)

Winter canola establishment requires excellent soil moisturenear the soil surface and cool (298C) ambient air temperaturesfor 5ndash7days after planting (Young et al 2014)Deep furrowdrillsthat are used in the wheatndashfallow zone for placing the seed intosoil moisture are also being used successfully to plant wintercanola as the seedlings need to emerge only to the bottom of thefurrow During August the optimal time to plant winter canola(Young et al 2014) soil moisture is usually 10ndash15 cm below thesoil surface and too deep for canola seedlings to emerge To helpalleviate this problem shovels 25ndash38 cm wide have been placedin front of the openers to reach soilmoisture andmove the hot drysoil from the furrow thus reducing the distance the emergingseedling has to travel through the soil (Young et al 2008 2014)The use of shovels did not increase winter canola yield andwinter survival but did increase plant density 22 comparedwith when shovels were not used In addition there is a moreuniform plant distribution from the use of shovels whichsuppressed weed growth and reduced weed competition(Young et al 2014) Generally a 45-kg handash1 seeding rate wasoptimal for sufficient stand establishment and yield Whenwinter canola seeding was delayed until September yield wasdecreased almost 40 compared with an August plantingWinter survival can range from 56 to 83 with a subsequentspring plant population of only 20ndash40 plantsmndash2 needed foroptimum yield

Spring canola despite the lower yield potential can begrown following failed winter canola survival and glyphosate-resistant spring canola cultivars are beneficial for controllingsummer annual broadleaf weeds in this zone such as Russianthistle (Salsola tragus) which emerges with similar timing asspring canola Spring canola seed broadcast on the soil surfaceyields between 31 and 67 of spring canola that was placed inthe soil with drills equipped with double disk chisel hoe orinverted T-slot openers (Young et al 2012) Broadcast yields ofspring canola were low because generally lt5 of the seedestablished plants When left on the soil surface seedlingswere unprotected when emerging from the seed coat and werekilled by frost Rolling broadcast seed with a heavy cast-ironroller generally improved yield ~35 compared with broadcast

alone although improved yield ranged from 0 to gt100Depending on location and precipitation optimum yieldsranged from 615 kg handash1 to 1575 kg handash1 (Young et al 2012)Precipitation during flowering and seed-fill in May and Junecorrelated with increased canola yield presumably by reducingmoisture stress during reproductive growth as observed byGan et al (2004)

Shoot meristematic origins of dicotyledonous oilseedsdiffer from monocotyledonous cereal grain crops Leaves andshoot branch initiation of oilseeds occurs at or near the soilsurface (Thomas 2003) In contrast shoot tiller and rootmeristems of wheat seedlings emanate at the belowgroundcrown and stem nodes directly above the crown (Klepper et al1984) The development of aboveground shoot meristems ofoilseeds versus belowground shoot nodes of cereals is afundamental difference in freeze avoidance (Thomas 2003)Oilseeds are exposed to sudden downturns in air temperaturesabove the soil surface during late falls and winters whereascereals are more protected by the soil layer above the cerealshoot meristem that buffers against rapid and severesubfreezing spikes

The size of winter canola plants entering the winter monthscorrelates with winter survival Small seedlings with 2ndash3 trueleaves survive iPNW winters very poorly This limits wintercanola production in the non-irrigated annual cropping zoneof the iPNW as very dry soils following harvest of theprevious yearrsquos crop generally persist into October by thetime sufficient moisture has accumulated to establish a standthe seedlings are typically too small to survive the first hardfrostsWhen planted into fallow land early plantedwinter canolatakes advantage of added growing degree-days to producemore shoot and root biomass before winter dieback Plantingfive winter rapeseed cultivars in the annual cropping zone(600mm) from 2 July to 13 September indicated that laterplanting dates resulted in less winter survival and seed yield(Porter et al 1981) presumably because late season plantingshad less energy and nutrient reserves In contrast early plantingsof winter canola in the wheatndashfallow zone take advantage ofsurface soil moisture but may result in poor winter survivalWinter cultivars remain vegetative without stem boltinghowever vegetative biomass of early planted canola extractsmost of the available soil moisture to 150 cm depth producingweakened drought-stressed plants with higher shoot meristemsthat were more susceptible to winter kill than later seededplants (Reese 2015)

Several fields of winter canola were monitored over 3 yearsacross the iPNW illustrating temperature profiles associatedwith partial and complete canola winter kill (Fig 5) In thewinter of 2013ndash2014 minimum temperatures at the soilsurface fell to ndash208C in early December and again in Februaryresulting in widespread complete winter kill across the regionIn contrast minimum surface temperatures only reached ndash15to ndash178C in January of 2011ndash2012 and 2012ndash2013 followinggradual temperature declines which resulted in partial standlosses of ndash28 to ndash49 but still yielding 1700ndash4300 kg handash1

even at sites with reduced stands Winter canola grown in semi-arid environments has the ability to compensate for standlosses with increased stem branching and pod retention(Angadi et al 2003) A late spring frost in late AprilndashMay

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 259

during flowering (data not shown) severely reduced the pod setresulting in yields lt1000 kg handash1 despite good stand survival insome locations This freeze sensitivity of canola coming out of

winter dormancy has been noted in the USA Great Plains(Holman et al 2011) In a location near DavenportWashington spring frost was not a factor and winter canoladirect seeded into winter wheat stubble averaged 4100 kg handash1

(Schillinger 2013)Moderation of extreme subfreezing conditions by soil

at depths 10ndash20 cm were consistently demonstrated (Fig 5)in comparison to surface temperatures illustrating themorphological advantage of wheatrsquos ability to developsubsurface shoot meristems that are insulated by soil (Klepperet al 1984) in comparison to above surface canola shootmeristems Canola nutritional status potentially contributes tosupercooling by increasing cell solutes such as high K and Clnutrition (Evans et al 2015) Ensuring a sufficient P status ofvegetative canola plants entering into the winter season with theaddition of starter phosphorus at planting has been shown toimprove winter survival (Wilkins et al 2002)

Nitrogen management The N placement and timing forwinter canola require additional adjustments from traditional Nfertilisation methods used in winter wheat production due tointerspecies differences in root architecture Chemical fallow-direct seeded winter wheat is typically fertilised in deep bandsbelow the seed row at planting (Veseth et al 1986) Canolaseedlings produce a single taproot main axis with lateral rootsand root hairs emanating from an ammonia sensitive tap root(Madsen et al 2014) In contrast monocotyledonous cerealcrops have multiple seminal axes and shoot tillers whichinitiate from the seed the belowground crown and stem nodesthat produce shoot tillers and affiliated root seminal axes(Klepper et al 1984) As a result of these basic rootarchitectural differences canola seedlings are more sensitivethan cereals to chemical toxicities such as expanded zones ofhigh ammonia around fertiliser bands due to oilseed relianceon the development of a single tap root whereas cereals havenumerous seminal axes to explore deep soil layers This basicmorphological difference has implications for differentialfertiliser band sensitivity when a canola taproot radicleencounters a high ammonia band meristems become necroticwith subsequent seedling injury or death (Madsen et al 2014)While a seminal root axis of cereal seedlings can suffer thesame fate other seminal axes of the same seedling will growto the side of the band and successfully develop The ability ofwheat roots to morphologically overcome ammonia toxicity ofdeep banded ammonium fertilisers has allowed the developmentand commercial use of direct seed planting equipment with deepbanding capabilities (Veseth et al 1986) However canolarsquostaproot sensitivity to deep placed ammonia bands will requirealternate N placement and timing strategies Fertiliser placementstudies on canola have demonstrated the need to place N as a sideband (Grant et al 2011 Norton 2016)

High N status of the vegetative winter oilseed plants hasreduced survival during freezing conditions (Rathke et al2006) There are biochemical and morphological responses tohigh N availability that may contribute to the decrease in winterhardiness Canola leaves subjected to low temperature stressincrease levels of cryoprotectant chemicals (Janskaacute et al 2010)such as soluble sugars that facilitate cytoplasmic freezingpoint depression (Gusta et al 2004) Identification of culturalpractices and variety selections for plant survival to rapid

10

Subsurface soil Air above soil surface

0

ndash10

ndash20

10

0

ndash10

Dai

ly m

inim

um te

mpe

ratu

re (

degdegC)

ndash20

102013ndash2014

2012ndash2013

2011ndash2012

0

ndash10

ndash20

ndash30Nov Dec Jan

MonthFeb Mar

Fig 5 Temperature profiles were continuously recorded over three wintersat Davenport WA from 2012 to 2014 in the transitional cropndashfallow zonewhere winter canola is being grown Air and soil temperature probes ineach year were positioned directly above the soil surface or below the soilsurface at a depth of 10ndash15 cm

260 Crop amp Pasture Science W L Pan et al

freeze eventsmay be important to winter canola production in theiPNW as demonstrated in December 2014 when a rapidfreeze resulted in widespread loss of winter canola and winterwheat (J Schibel pers comm)

Low N status promotes increased sugar concentrationsand increased freeze resistance in plants (Lemoine et al 2013Wisniewski et al 2014) As a result this potentially changesthe N timing strategy for managing canola relative to traditionalwheat N management in the iPNW In zones less than 600mmannual precipitation where nitrate leaching below 180 cm soildepth is typically not excessive winter wheat N applicationoccurs pre-plant during summer fallow or at planting in annualcrop rotations (Veseth et al 1986 Halvorson et al 1999) Themain reason is to ensure adequate time for fertiliser N to nitrifyand move into the lower layers of the root profile ensuringadequate N availability as the surface soil dries and plantroots become increasingly reliant on subsoil N (Pan et al2001) If low N canola has higher winter survivability it mayprovide another reason to be conservative in N fertiliserapplications at planting and allow the canola to utilise residualN during early establishment An inverse relationship between Navailability and winter survival could be due to a complex set ofbiochemical shoot morphological ie raised shoot meristemsabove the ground and growth-induced water stress (Reese2015)Winter canola exhibits deep rooting depths to 180 cm andsubsoil N and water access and recovery is critically important(Hocking et al 2002 Reese 2015) Furthermore iPNW climatechange projections of hotter drier summer months (Abatzoglouet al 2015) portend a need for enhancing deep strong-rootedwinter crops such as canola for adapting to foreseen climatechange (Hatfield et al 2001 Blum 2009 Lynch 2015)

These climate change forecast models predict 5ndash15increases in iPNW regional annual precipitation but withincreasing proportions occurring during the winter andspring months with drier hotter summers This trend willnecessitate improvements in water and N infiltration and subsoilstorage during winter months for later access during active cropdevelopment Canola also has a reputation as a strong taprootedcrop capable of creating macro biopore channels for facilitatingsaturated water flow and root pathways for subsequent crops Yetcanola roots cannot always penetrate soil horizons with highphysical and chemical impedance (Cresswell and Kirkegaard1995 Watt et al 2006) Tillage pans and genetic soil horizonsin the iPNW have been observed to impede canola roots causingcharacteristic lsquoJrsquo hooking of the taproot forcing it to turn 90degrees along the plan of the soil pan until it encounters a crackwhere it can continue vertical development (Lisson et al 2007)This may be a plausible explanation for new canola growertestimonials claiming rotational benefits are not seen untila second or third rotation

Irrigated crop zone

Rotational fit The irrigated temperate desert of centralWashington and Oregon supports perennial tree and vine fruitproduction as well as 500 000 ha of many high value agronomiccrops such as potato and sweet corn where small grain cerealsare used as a rotational crop and winter wheat is only ~8 ofthe area (Table 1 Fig 1) As many high value crops for example

potato sweet corn onion beans are grown in this zone a muchlower adoption is projected for this zone with canola mostlyrestricted as a substitution for wheat in the irrigated rotationsof central Washington and Oregon

In addition with opportunities to follow early harvested freshvegetable crops dual purpose use of canola has potential todiversify and intensify irrigated rotations similar to drylandapplications (Neely 2010 Walsh 2012 Lilley et al 2015) Inthis zone of extended growing degree-days double croppingunder irrigation where biennial canola could bridge two short-season summer crops to yield three harvests over two growingseasons such asYear 1 fresh peascanola forage ndashYear 2 canolagrain (Kincaid et al 2011) Current efforts are focussed onproduction of silage from first-season canola vegetation incentral Washington Comparable canola grain yields of2300 kg handash1 were harvested with and without forage cuttingand removal (Desta et al 2013) Yield gaps between predictedand observed yields may relate to J-hooking that has beenobserved under irrigation similar to dryland root observationsdescribed above

Plant establishment As water is not a limitation underirrigation germination and seedling establishment is not asmuch of an issue in this zone For example winter rapeseedand mustard were rapidly established in late August and earlySeptember in the south andnorthColumbiabasinunder irrigationand substantial biomass and N accumulation occurs beforethe first hard frost and under these conditions deep soil N useshould still be accounted for in oilseed rotational N fertiliserrecommendations (Weinert et al 2002) Even under irrigation Nfertiliser responses in winter canola can be minimal due to buildup of residual soil N in highly fertilised rotations (Davenport et al2010) Even with ample water and N winter kill is still a problemin this zone as demonstrated in an irrigated winter wheat springbarley winter canola rotation where green-bridged Rhizoctoniasolani on spring barley residues was suspected to infect wintercanola roots perhaps contributing to winter kill in 4 of 5 years(Paulitz et al 2010 Schillinger et al 2010b) Rhizoctonia solanianastomosis group 2ndash1 has recently been identified to infectwheat and rape roots (Sturrock et al 2015)

Summary and future projections

Canola area has historically constituted less than 1 of theiPNW Advancements in the development of both winter andspring cultivars have afforded flexible options in weed controlmanagement Competitive hybrid cultivars are nowcommercially available with and without herbicide toleranceor resistance Current efforts are to identify and integratecultivars that can be successfully established survive winterand use subsoil water and N efficiently in each of the zonesEstablishment of a local oilseed processing industry increasingglobal and regional canola markets for food fuel and feedagronomic benefits in increasing rotational diversity andcontinued vigorous research and extension efforts havestimulated a recent increase in canola integration into existingmonoculture wheat production in the iPNW Modest canolarotational integration projected for each zone would achieveproduction goals to match current and future regionaloilseed processing capacity with 300 000 canola ha per year

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 261

(Table 1) An upper agronomic limit of roughly 1 1wheat canola has been reached in the semi-arid wheat-producing region of western Canada Similar crop productionratios in the iPNW would approach 700 000 ha Winter canolaintegration into the wheatndashfallow annual cropndashtransition andirrigated cropping zones and spring canola integration intoannual cropping and transition zones will improve weedcontrol and wheat yields particularly with herbicide-resistantcultivars The most critical challenges in the adaptation ofcanola into iPNW wheat-cropping systems include improvedconsistency of winter canola establishment and winter survivalin the low and intermediate precipitation zones Seeding depthand timing are critical determinants of winter and spring canolayield potential Relevant genetic research is currently focussedon increasing seed size and hypocotyl lengths for improvedseedling emergence and on the identification of freeze-tolerantcultivars Integration of spring canola into higher precipitationannual cropping systems requires research on innovative earlyplanting strategies and new earlier maturing cultivars to avoidhigh temperature and moisture stress Taproot architecture ofcanola dictates changes in standard N placement andtiming strategies that have been practiced for iPNW wheatproduction but the deep rooting habit of canola will contributeto efficient water and N recovery of the cropping systems Farmenterprise economics that account for rotational benefits andproduction risk will help growers account for multi-yearinvestments in canolandashwheat rotations to assess the benefits ofintegrated canolandashwheat systems

References

Abatzoglou J Rupp D Mote P (2015) Asymmetrical warming projectionsfor the inland Pacific Northwest In lsquoRegional approaches to climatechange for Pacific Northwest agriculture Climate science Northwestfarmers can usersquo (Eds K Borrelli D Daily Laursen S Eigenbrode BMahler R Pepper) pp 104ndash105 Available at wwwreachchpnaorg

Alberta Agriculture and Rural Development (2004) Alberta fertilizer guideIn lsquoAgric-facts practical information for Albertarsquos agriculture industryrsquoAgdex 541ndash1 (Ministry of Alberta Agriculture Food and RuralDevelopment Edmonton Alberta Canada)

Angadi SV Cutforth HW McConkey BG Gan Y (2003) Yield adjustmentby canola grown at different plant populations under semiarid conditionsCrop Science 43 1358ndash1366 doi102135cropsci20031358

Angus JF Kirkegaard JA Hunt JR Ryan MH Ohlander L Peoples MB(2015) Break crops and rotations for wheat Crop amp Pasture Science 66523ndash552 doi101071CP14252

Azooz RH Arshad MA (1998) Effect of residue and tillage managementon barley and canola growth and water use efficiency Canadian Journalof Soil Science 78 649ndash656 doi104141S97-098

Ball DA Young FL Ogg AO Jr (1999) Selective control of jointedgoatgrass (Aegilops clylindrica) with imazamox in herbicide-resistantwheat Weed Technology 13 77ndash82

Bettis B Auld D (Eds) (1980) Development of oilseeds as alternative cropsfor the Pacific Northwest Pacific Northwest Regional CommissionYearly Reports June 1979ndash31 July 1980 June 1980ndashJune 1981Pacific Northwest Regional Commission Moscow Idaho USA

Bettis BL Peterson CL Auld DL Driscoll DJ Peterson (1982) Fuelcharacteristics of vegetable oil from oilseed crops in the PacificNorthwest Agronomy Journal 74 335ndash339

Blum A (2009) Effective use of water (EUW) and not water-use efficiency(WUE) is the target of crop yield improvement under drought stressField Crops Research 112 119ndash123 doi101016jfcr200903009

Brennan RF Bolland MDA (2009) Comparing the nitrogen and phosphorusrequirements of canola and wheat for grain yield and quality Crop ampPasture Science 60 566ndash577 doi101071CP08401

Brill RD Jenkins ML Gardner MJ Lilley JM Orchard BA (2016)Optimising canola establishment and yield in south-eastern Australiawith hybrids and large seed Crop amp Pasture Science 67 409ndash418

Brown J Davis J (2015) Brassica breeding and research University of IdahoAvailable at wwwcalsuidahoedubrassica (accessed 15 December2015)

Brown J Davis JB Erickson DA Brown AP Seip L (1995) 1995 PacificNorthwest canola variety trial (PNWCVT) results and conclusions InlsquoPacificNorthwest canola conference1995proceedingsrsquo (EdsGJohnsonM Lewis) pp 29ndash36 (Department of Entomology Montana StateUniversity Bozeman MT)

BushongJ (2015)Okanola varieties andhybrids open-pollinatedvarietiesvshybrids Available at httpcanolaokstateeducropproductionvarieties(accessed 15 December 2015)

Conley SP Bordovsky D Rife C WieboldW (2004) Winter canola survivaland yield response to nitrogen and fall phosphorus Crop Managementdoi101094CM-2004-0901-01-RS

Connolly JR McCracken VA Painter KM (2016) Enterprise budget wheatand canola rotations in Eastern Washington intermediate rainfall regions12rdquo to 16rdquo Washington State University Extension PublicationWashington State University TB10 USA

Cook RJ Schillinger WF Christensen NW (2002) Rhizoctonia rootrot andtake-all of wheat in diverse direct-seed spring cropping systemsCanadian Journal of Plant Pathology 24 349ndash358 doi10108007060660209507020

Cresswell HP Kirkegaard JA (1995) Subsoil amelioration by plant-roots ndashthe process and the evidence Australian Journal of Soil Research 33221ndash239 doi101071SR9950221

Cutforth HW Angadi SV McConkey BG (2006) Stubble managementand microclimate yield and water use efficiency of canola grown inthe semiarid Canadian prairie Canadian Journal of Plant Science 8699ndash107 doi104141P05-073

Davenport J Stevens B Hang A Peters T (2010) Irrigated canola researchIn lsquoWashingtonOilseedCroppingSystemsProject partof theWashingtonState Biofuels Initiative 2010rsquo Annual Progress Report (EdsKESowersWL Pan) Available at httpcsswsuedubiofuelsfiles2012092010_Annual_Progress_Reportpdf (accessed 27 December 2015)

De Jong R Shields JA (1988) Available water-holding capacity maps ofAlberta Saskatchewan and Manitoba Canadian Journal of Soil Science68 157ndash163 doi104141cjss88-015

Desta KG Collins H Pan B (2013) Double-cropping dual purpose irrigatedbiennial canolawithgreenpea In lsquoWashingtonOilseedCroppingSystemsProject part of the Washington State Biofuels Initiative 2013rsquo AnnualProgress Report (Eds KE Sowers WL Pan) Available at httpcsswsuedubiofuelsfiles2012092013-Biofuel-Cropping-Systems-Research-Progress-Reportpdf (accessed 27 December 2015)

Divine TE Alzheimer DP Currie JW McGinnis KA Wiggins DJ (1977)Research on the potential impact of advanced oilseeds processingtechnology on Pacific Northwest Agriculture Batelle Pacific NorthwestLaboratories 231110270610690646 Richland Washington USA

Douglas CL Wysocki DJ Zuzel JF Rickman RW Klepper BL (1990)Agronomic zones for the dryland Pacific Northwest Pacific NorthwestCooperative Extension Bulletin PNW 954

Esser A Hulbert S (2013) Eastern WA low to intermediate rainfall InlsquoWashington Oilseed Cropping Systems Project part of theWashington State Biofuels Initiative 2013 Annual Progress Reportrsquo(Eds KE Sowers WL Pan) pp 31ndash36 Available at httpcsswsuedu

262 Crop amp Pasture Science W L Pan et al

Anderson 2003) and all contribute to potential drought stressThe Great Plains of the USA and western Canadian soilshave variable water holding capacity (50ndash350mm) and ahigher percentage of precipitation during the growing seasoncompared with the iPNW (Table 2)

The greatest agronomic challenges in fostering iPNW canolaadaptation are to define wheatndashcanola-based rotations thatimprove weed control optimise soil water and N recharge andcrop use establish good plant stands maximise plant survivalduring overwinter freezing and early spring frosts and sustaincrop water and nutrient use during hot dry summer months Thediversity of environments soils and cropping systems across thefour major iPNW production zones (Fig 1 Table 1) presentchallenges to design suitable wheatndashcanola cropping systemswithin each zone The overarching goal of the Washington StateOilseed Cropping Systems project is to integrate appropriatewinter and spring canola cultivars into cropping systemstailored for each of these zones to increase crop and marketdiversification and productivity The agronomic research aimsto identify appropriate crop sequences and modifications totraditional wheat crop establishment and fertility managementstrategies to accommodate differences in physiological andmorphological traits of canola relative to wheat

Annual crop zone

Rotational fit The annual cropping zone comprises 568 000 haof the Palouse and western foothills of the Rocky mountainrange straddling the eastern WashingtonndashNorthern Idahoborder (Table 1 Fig 1) Precipitation of gt450mm per yearsupports annual cropping with winter wheat spring wheat andspring barley grown over 60 of the cropping zone land area andcool-season legumes account for only 18 (Fig 2) Typicallythere is insufficient soil moisture and growing degree-daysfollowing crop harvest to establish and grow winter canola tosufficient size before freezingwinter conditions so the focus is onadapting spring canola (discussed below) substituting springcereals or legumes in the rotation (Table 1) Winter canola ismore feasible following fallow but fallow is not normallypracticed in this region (Fig 1) unless wet spring conditionsprevent establishment of spring crops Nevertheless survivingwinter canola in this zone can yield 3000ndash4000 kg handash1 withample available soil moisture (Brown and Davis 2015 Evanset al 2015)

Weed management The predominance of cereal crops inthis zone encourages annual grassy weed infestations such asItalian ryegrass (Lolium multiflorum Lam) downy brome(Bromus tectorum L) and jointed goatgrass (Aegilopscylindrica HOST Ball et al 1999) Increasing broadleaf cropsin rotation with wheat provides better control of these grassyweeds particularly when herbicide-resistant canola is used(Young et al 2016) Nine years of substituting glyphosate-resistant spring canola for spring legumes in rotation withwinter and spring cereals was effective in controlling Italianryegrass in farm-scale strip trials near Pullman Washington(Huggins and Painter 2011) The inclusion of glyphosate-resistant spring canola also controls troublesome broadleafweeds such as mayweed chamomile (Anthemis cotula L) andcommon lambsquarters (Chenopodium album L) that are

difficult to control in cool-season food legumes A wideselection of spring canola cultivars are available in the iPNWto deal with depending on individual circumstances includingresistance toglyphosate gluphosinate and imazamoxGenerallya grass herbicide such as quizalofop should be added to agluphosinate-resistant variety to improve grass control Hybridspring canola has become available in the region and has beendemonstrated in western Canada to have higher yield potentialwhich likely imposes greater N requirements than an open-pollinated line (Mahli et al 2007 Smith et al 2010)

If fallow is dictated by poor spring crop seeding conditionsearly seeding winter canola into fallow a regional conditioncalled lsquodelayed plantingrsquo does offer the opportunity to apply thedual-purpose canola concept (Kirkegaard et al 2008b Neely2010) by taking advantage of the biennial characteristic of wintercanola cultivars to produce forage and grain from a singleplanting In an on-farm experiment in the annual croppingzone winter canola intercropped with spring pea and plantedon 2 July produced 780 kg DM handash1 forage that was harvested 2September 70 days after seeding (Kincaid et al 2011) Theforage wasmade into high quality silage feed for dairy cows Thecut plants then re-generated a smaller lateral shoot-producingplant supported by the established root system These plantssurvived the winter subsequently producing 2000 kg grainhandash1 the following season demonstrating that growth of astrong root system with reserve energy and nutrients is morecritical than having an abundance of shoot biomass for wintersurvival Cutting canola shoot meristems theoretically removesa source of auxin inhibiting lateral shoot stem initiation anddevelopment (Lia et al 2016) which may provide a mechanismfor more vigorous post-winter regrowth

Plant establishment Winter wheat can be successfullyestablished in this zone with adequate autumn precipitationfollowing summer harvest of a winter or spring grain cropbecause only a small seedling is required to survive the winter(Young et al 2008) In contrast establishment of winter canolain similar annual crop rotations has proven difficult due toprevalent dry soil conditions that delays timing of germinationuntil there are insufficient growing degree-days for establishingplants of sufficient size to overwinter (Murray and Auld 1986Moore and Guy 1997 Holman et al 2011) Post-harvestprecipitation required to initiate seed germination and seedlinggrowth typically does not occur until temperatures are too coolto foster adequate seedling root and shoot biomass productionneeded to overwinter during sub-freezing conditions As a resultwinter oilseeds do best when planted into higher surface soilmoisture in fallow in this zone as demonstrated in winter rape(Brassica napus) planted between 31 July and 5 Septemberproducing yields ranging from 3800 to 4670 kg handash1 nearMoscow Idaho (Murray and Auld 1986) Yet the fallowperiod required to establish winter canola in the high rainfallzone would waste a growing season in which a marketable cropwould otherwise be grown

Spring canola establishment must be accomplished inheavy winter wheat residue that can range from 6900 kg handash1

(Papendick and Miller 1977) to 14 500 kg handash1 (Young et al1990) as maintaining these surface residues in direct-seedsystems is needed to prevent soil erosion These high residuesreduce seedling growth by maintaining cold soil temperatures

256 Crop amp Pasture Science W L Pan et al

(Pan et al 1991) which might deter growers from producingspring canola the following year unless the fields have beenburned A 2-year study was conducted examining the effect of25-cm and 50-cm row spacing on spring canola yield Each yearspring canola was planted at 56 kg handash1 in winter wheat residuethat had yielded ~6700 kg handash1 of grain When averaged oversite-years spring canola yield was similar (1710 kg handash1 for 50-cm rows 1775 kg handash1 for 25-cm rows) regardless of row spacing(Young2012)Withwide rowspacingmachine and fuel costs arereduced because of the reduction in openers and subsequentreduction in tractor horsepower Additionally it is likely thatdelays at seeding caused by blockages of high residue loadsunder seeding equipment (lsquodrill pluggingrsquo) will be reduced withwider row spacing

Although early spring planting of canola can be a challengelate seeding also has its penalties Stands of spring canola arealso more consistent when planted before moisture levels declineas spring rainfall is generally sporadic in the region Springcanola direct-seeded into heavy wheat residue over 9 yearsshowed an inverse relationship between seeding date and grainyield (Huggins and Painter 2011 Fig 3) As in other canola-growing regions later plantings result in flowering and graindevelopment under conditions of higher water and temperaturestress that reduce grain yield (Gan et al 2004 Kirkegaard et al2016)

Nitrogen management The N management approaches mustbe tailored to the unique environment of the iPNW Regionalyield-based N recommendations for wheat are commonlycalculated by applying a single or narrowly defined unit Nrequirement (UNR) of 45 kg N per 100 kg grain for soft wheatto 6 kg N per 100 kg grain for hard wheat (Koenig 2005 Koeniget al 2011) However contrary observations of varying UNRacross variable Palouse landscapes have been observed (Fiezet al 1995) suggesting amore tactical approach toNmanagementcould be implemented

Over 6 years higher overall UNR of 7ndash13 kg N (100 kggrain)ndash1 were observed for spring canola in the zoneacross years varying in water availability This range is similarto those found in canola fertiliser guides from semi-arid westernNorth America (Pan et al 2016) and that of 7ndash8 kg N (100 kggrain)ndash1 in Australia (Norton 2016) Canola plant nutrient uptakeper unit yield is higher than soft white and hard red wheats

(Koenig et al 2011) suggesting higher levels of availablenutrients supplied by native soil fertiliser carryover or newlyapplied fertiliser are required for regional canola productioncompared with wheat nutrient management In southwesternAustralia the amount of N fertiliser required to produceoptimum yield was 40 higher for canola than wheat(Brennan and Bolland 2009) Nevertheless canola has a deeptaproot system (Gan et al 2009) as well as extensive root hairsfor fully exploiting soil nutrients andwater (Hammac et al 2011)As a result canola seed yield responds well to applied N whenresidual soil levels are low but minimal fertiliser N responsewhen soil N supply is high and yield potential is low (Fig 4 Panet al 2016) This exponential diminishing-returns response tototal available N was also observed in southwestern Australia(Seymour et al 2016) In Montana canola responded stronglyto fertiliser N when planted into low levels of residual soil nitrate(90 cm depth) where yields were optimised at 200 kg N supplyhandash1 (Jackson 2000) However the magnitude of response isvariable in the iPNW due to interacting factors of climateavailable soil N cultivar and management practices Overallalthough spring canola N supply (soil + fertiliser N) requirementsper unit grain weight are higher than wheat its extensive andefficient roots utilise deep residual soil N to 120 cm in this zoneto reduce fertiliser N requirements (Maaz et al 2016)

Annual cropndashfallow transition zone

Rotational fit The iPNW transition zone is ~665 000 ha withannual precipitation ranging from 300 to 450mm and ischaracterised by annual cropping during wetter than normalprecipitation years interspersed with fallow during drier years(Table 1 Fig 1) Growers traditionally have grown winter andspring wheat and barley in gt50 of the zone fallow in 27and spring legumes in 10 of the zone In higher than normalprecipitation years continuous crop rotations have been grownPlant establishment of winter canola or spring canola are bothpossible in this zone with opportunities and constraints

3500

3000

2500

2000

1500

1000

500

0

322 41 411 421

Planting date

Spr

ing

cano

la y

ield

(kg

handash1

)

51 511 521

Fig 3 Direct-seeded spring canola yields following spring wheat atPullman WA over 9 years as related to planting date (Huggins andPainter 2011)

2500

EONR 150 kg fertiliser N handash1

EONR 19 kg fertiliser N handash12000

1500

1000

500

00 50 100 150 200 250 300

Can

ola

yiel

d (k

g ha

ndash1)

Total N supply (kg N handash1)

Fig 4 Canola grain yield response to nitrogen supply Ns with substantivecontribution of soil N and low economically optimum fertiliser N (EONR) atDavenport WA with limited water (open symbols) compared with higherEONR due to lower soil N and higher water availability at Pullman WA in2012 (closed symbols) (Pan et al 2016)

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 257

described in the above and below sections on the annual crop andcropndashfallow zones

Flexible decisions on planting spring canola in this zoneshould be based on over-winter soil water storage to 120 cmrooting depth and weather predictions for in-seasonprecipitation Generally spring canola yields are correlated withtotal available water with water-use efficiency (WUE) slope of325 kgyieldmmndash1 availablemoisture in the inlandPacificNorth-west (Pan et al 2016) which is lower than those reported inAustralia Robertson and Kirkegaard (2005) evaluated 42datasets of dryland spring canola for WUE and found that theWUE of canola varied from 4 to 18 kg handash1mmndash1 in which latersown crops tended to have lower efficiencies Similarly theWUEof spring canola decreased from 12 to 2 kg handash1mmndash1 whenseeded in early winter rather than in early spring within theMediterranean type environment of Iran (Faraji et al 2009)Terminal heat and drought stress during the reproductiondevelopment may cause the reduction in WUE in late seededspring canola Therefore the WUE of spring canola in the inlandPacific Northwest is more comparable to Canada wherestudies report a range of 280ndash576 kg handash1mmndash1 for rain-fedspring canola sown in the spring season (Azooz and Arshad1998 Cutforth et al 2006 Gan et al 2009)

Weed management A farm-scale rotational experiment atthe Washington State University Wilke Farm located atDavenport Washington has compared fallow systems with twoor three crops with continuous cropping in replicated stripsacross a variable field (Esser and Hulbert 2013) Herbicide-resistant spring canola cultivars were included in the 4-yearrotation which thus far has enabled the best control offeral cereal rye (Secale cereale L) resulting in the highesteconomic return over input costs among the three rotationsSpring canola planted at 56 kg seed handash1 yielded 784ndash1960 kggrain handash1 following spring wheat Rotational wheat yieldincreases due to improved weed control following canola canresult in higher rotational profits even without economicbenefits of canola in single season crop comparisons (Connollyet al 2016) In certain years of relatively high canola wheat priceratios economic benefits have been obtained even withoutincluding rotational benefits

Nitrogen management Spring canola N response trials at thesame location had maximum yields averaging 1027 kg handash1 andeconomically optimal N rates averaged 23 kg N fertiliser handash1ranging from zero fertiliser N required after fallow to 6ndash65 kgfertiliser N handash1 required following wheat (Pan et al 2016) Thehigher required economic N rate for canola following winterwheat was evident despite the lower available soil water andlower canola yield potential These findings corroboratestatements in Alberta Agriculture and Rural Development(2004) about lower N availability following continuouscropping versus fallow These modest fertiliser N requirementsseemingly contrary to spring canolarsquos relatively high unit totalN supply requirements are due to high residual soil N carryoverand N mineralisation coupled with canola roots extractingwater and N from 90 to 120-cm depths Overall the UNRobserved in the transition zone ranged from 9 to 17 kg total Nsupply100 kg grain higher than the range (39ndash8 kg total Nsupply100 kg grain) reported in fertiliser guides from semi-arid western North America (Koenig et al 2011) This was due

to lower yields and NUE of this region and our more completeaccounting of root zone residual N supply and creditingsoil N mineralisation contributions to total N supply (Panet al 2016)

Grainndashfallow zone

Rotational fit The cropndashfallow zone usually has insufficientannual precipitation (lt300mm) to economically supportannual cropping (Young et al 2015) and comprises an arearoughly equivalent to the total of the other two rain-fed zonesof ~1 245 000 ha Winter wheat has greater yield potential thanspring wheat due to deeper roots more efficient water extractionand earlier flowering and grain development during hot drysummer months Similarly spring canola is not commonlygrown in this zone because spring canola yields only 50ndash60as much as winter canola (Pakish et al 2015)

Weed management Weed control in summer is typicallyaccomplished using tillage with a rod weeder or chemicalfallow-direct seeding to reduce wind erosion (Young andThorne 2004) One of the primary reasons to grow winter canolais to offer growers an added management tool to control weedsWinter annual grass weeds including feral rye downybrome jointed goatgrass and Italian ryegrass continue toplague monoculture winter wheat growers The introductionof imidazolinone-resistant wheat in 2003 (Ball et al 1999)provided growers with an additional option to manage thesepests however an imidazolinone-resistant biotype of downybrome has been found in Oregon and feral rye is one of the mostdifficult winter annual grass weeds to control with imazamox(Pester et al 2000) Feral rye is a predominant winter annualgrass weed in the low rainfall grain fallow region of theiPNW In this region quizalofop in conventionally bred wintercanola cultivars for example Amanda Falstaff and glyphosatein glyphosate-resistant canola cultivars for example Croplan115 and 125 effectively controlled feral rye (Young et al2016) A second reason to introduce winter canola into cerealproduction systems regardless of rainfall zone is availabilityof herbicide-tolerant canola cultivars These cultivars allowproducers to plant in fields with a history of sulfonylurea forexample Croplan 115 or 125 and imidazolinone herbicides forexample Claremore and Edimax (Young et al 2016) withoutenduring 9ndash40 months of plant back restrictions Commercialhybrid cultivars have recently been introduced into this regionand their potential advantages over open pollinated lines arebeing evaluated in regional trials For example winter canolacomparisons in Oklahoma have characterised greater seed sizeand yield potential under optimal conditions but less droughttolerance than open-pollinated cultivars (Bushong 2015)

Plant establishment Winter canola establishment is asignificant challenge in this zone The smaller seed size ofcanola alters seed zone requirements for optimal germinationand emergence compared with wheat which in turn can affectdepth of planting This need for deep planting is greatest in thiszone where late summer high temperatures and little to noprecipitation drives the soil moisture line into the subsoil(Schillinger et al 2010a) The range of seed sizes in canola farexceeds that of the variation in wheat seed Wheat seed plantedin the iPNW typically ranges from 31 to 38mg seedndash1 whereas

258 Crop amp Pasture Science W L Pan et al

canola seed ranges from 2 to 6mg seedndash1 (F L Young perscomm) A 3-fold variation in canola seed size makes it moreimperative to get accurate oilseed weights when targetingspecific plant population goals Seed size is affected bycultivar and the seed production environment as well ascommercial seed sizing processes (Lamb and Johnson 2004)Smaller seed reserves of energy and nutrients of individualcanola seeds restrict deep seed placement Winter wheatcultivars grown in the fallow zone are bred to emerge from verydeep seed placement (Mohan et al 2013) In contrast canola seedgenerally emerges best when placed within 2ndash3 cm of the soilsurface when moisture conditions are adequate but can emergefrom deeper placement (3ndash6 cm) when required to reachmoisture Hypocotyl length is genetically modulated indicatingpotential for future breeding opportunities (Zhao et al 2013)Larger seeds can generally emerge from greater depths due tolonger and more robust hypocotyls In addition larger seededBrassica cultivars produce greater early season biomass whichincreases crop competition with weeds (Harker et al 2015Brill et al 2016)

Winter canola establishment requires excellent soil moisturenear the soil surface and cool (298C) ambient air temperaturesfor 5ndash7days after planting (Young et al 2014)Deep furrowdrillsthat are used in the wheatndashfallow zone for placing the seed intosoil moisture are also being used successfully to plant wintercanola as the seedlings need to emerge only to the bottom of thefurrow During August the optimal time to plant winter canola(Young et al 2014) soil moisture is usually 10ndash15 cm below thesoil surface and too deep for canola seedlings to emerge To helpalleviate this problem shovels 25ndash38 cm wide have been placedin front of the openers to reach soilmoisture andmove the hot drysoil from the furrow thus reducing the distance the emergingseedling has to travel through the soil (Young et al 2008 2014)The use of shovels did not increase winter canola yield andwinter survival but did increase plant density 22 comparedwith when shovels were not used In addition there is a moreuniform plant distribution from the use of shovels whichsuppressed weed growth and reduced weed competition(Young et al 2014) Generally a 45-kg handash1 seeding rate wasoptimal for sufficient stand establishment and yield Whenwinter canola seeding was delayed until September yield wasdecreased almost 40 compared with an August plantingWinter survival can range from 56 to 83 with a subsequentspring plant population of only 20ndash40 plantsmndash2 needed foroptimum yield

Spring canola despite the lower yield potential can begrown following failed winter canola survival and glyphosate-resistant spring canola cultivars are beneficial for controllingsummer annual broadleaf weeds in this zone such as Russianthistle (Salsola tragus) which emerges with similar timing asspring canola Spring canola seed broadcast on the soil surfaceyields between 31 and 67 of spring canola that was placed inthe soil with drills equipped with double disk chisel hoe orinverted T-slot openers (Young et al 2012) Broadcast yields ofspring canola were low because generally lt5 of the seedestablished plants When left on the soil surface seedlingswere unprotected when emerging from the seed coat and werekilled by frost Rolling broadcast seed with a heavy cast-ironroller generally improved yield ~35 compared with broadcast

alone although improved yield ranged from 0 to gt100Depending on location and precipitation optimum yieldsranged from 615 kg handash1 to 1575 kg handash1 (Young et al 2012)Precipitation during flowering and seed-fill in May and Junecorrelated with increased canola yield presumably by reducingmoisture stress during reproductive growth as observed byGan et al (2004)

Shoot meristematic origins of dicotyledonous oilseedsdiffer from monocotyledonous cereal grain crops Leaves andshoot branch initiation of oilseeds occurs at or near the soilsurface (Thomas 2003) In contrast shoot tiller and rootmeristems of wheat seedlings emanate at the belowgroundcrown and stem nodes directly above the crown (Klepper et al1984) The development of aboveground shoot meristems ofoilseeds versus belowground shoot nodes of cereals is afundamental difference in freeze avoidance (Thomas 2003)Oilseeds are exposed to sudden downturns in air temperaturesabove the soil surface during late falls and winters whereascereals are more protected by the soil layer above the cerealshoot meristem that buffers against rapid and severesubfreezing spikes

The size of winter canola plants entering the winter monthscorrelates with winter survival Small seedlings with 2ndash3 trueleaves survive iPNW winters very poorly This limits wintercanola production in the non-irrigated annual cropping zoneof the iPNW as very dry soils following harvest of theprevious yearrsquos crop generally persist into October by thetime sufficient moisture has accumulated to establish a standthe seedlings are typically too small to survive the first hardfrostsWhen planted into fallow land early plantedwinter canolatakes advantage of added growing degree-days to producemore shoot and root biomass before winter dieback Plantingfive winter rapeseed cultivars in the annual cropping zone(600mm) from 2 July to 13 September indicated that laterplanting dates resulted in less winter survival and seed yield(Porter et al 1981) presumably because late season plantingshad less energy and nutrient reserves In contrast early plantingsof winter canola in the wheatndashfallow zone take advantage ofsurface soil moisture but may result in poor winter survivalWinter cultivars remain vegetative without stem boltinghowever vegetative biomass of early planted canola extractsmost of the available soil moisture to 150 cm depth producingweakened drought-stressed plants with higher shoot meristemsthat were more susceptible to winter kill than later seededplants (Reese 2015)

Several fields of winter canola were monitored over 3 yearsacross the iPNW illustrating temperature profiles associatedwith partial and complete canola winter kill (Fig 5) In thewinter of 2013ndash2014 minimum temperatures at the soilsurface fell to ndash208C in early December and again in Februaryresulting in widespread complete winter kill across the regionIn contrast minimum surface temperatures only reached ndash15to ndash178C in January of 2011ndash2012 and 2012ndash2013 followinggradual temperature declines which resulted in partial standlosses of ndash28 to ndash49 but still yielding 1700ndash4300 kg handash1

even at sites with reduced stands Winter canola grown in semi-arid environments has the ability to compensate for standlosses with increased stem branching and pod retention(Angadi et al 2003) A late spring frost in late AprilndashMay

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 259

during flowering (data not shown) severely reduced the pod setresulting in yields lt1000 kg handash1 despite good stand survival insome locations This freeze sensitivity of canola coming out of

winter dormancy has been noted in the USA Great Plains(Holman et al 2011) In a location near DavenportWashington spring frost was not a factor and winter canoladirect seeded into winter wheat stubble averaged 4100 kg handash1

(Schillinger 2013)Moderation of extreme subfreezing conditions by soil

at depths 10ndash20 cm were consistently demonstrated (Fig 5)in comparison to surface temperatures illustrating themorphological advantage of wheatrsquos ability to developsubsurface shoot meristems that are insulated by soil (Klepperet al 1984) in comparison to above surface canola shootmeristems Canola nutritional status potentially contributes tosupercooling by increasing cell solutes such as high K and Clnutrition (Evans et al 2015) Ensuring a sufficient P status ofvegetative canola plants entering into the winter season with theaddition of starter phosphorus at planting has been shown toimprove winter survival (Wilkins et al 2002)

Nitrogen management The N placement and timing forwinter canola require additional adjustments from traditional Nfertilisation methods used in winter wheat production due tointerspecies differences in root architecture Chemical fallow-direct seeded winter wheat is typically fertilised in deep bandsbelow the seed row at planting (Veseth et al 1986) Canolaseedlings produce a single taproot main axis with lateral rootsand root hairs emanating from an ammonia sensitive tap root(Madsen et al 2014) In contrast monocotyledonous cerealcrops have multiple seminal axes and shoot tillers whichinitiate from the seed the belowground crown and stem nodesthat produce shoot tillers and affiliated root seminal axes(Klepper et al 1984) As a result of these basic rootarchitectural differences canola seedlings are more sensitivethan cereals to chemical toxicities such as expanded zones ofhigh ammonia around fertiliser bands due to oilseed relianceon the development of a single tap root whereas cereals havenumerous seminal axes to explore deep soil layers This basicmorphological difference has implications for differentialfertiliser band sensitivity when a canola taproot radicleencounters a high ammonia band meristems become necroticwith subsequent seedling injury or death (Madsen et al 2014)While a seminal root axis of cereal seedlings can suffer thesame fate other seminal axes of the same seedling will growto the side of the band and successfully develop The ability ofwheat roots to morphologically overcome ammonia toxicity ofdeep banded ammonium fertilisers has allowed the developmentand commercial use of direct seed planting equipment with deepbanding capabilities (Veseth et al 1986) However canolarsquostaproot sensitivity to deep placed ammonia bands will requirealternate N placement and timing strategies Fertiliser placementstudies on canola have demonstrated the need to place N as a sideband (Grant et al 2011 Norton 2016)

High N status of the vegetative winter oilseed plants hasreduced survival during freezing conditions (Rathke et al2006) There are biochemical and morphological responses tohigh N availability that may contribute to the decrease in winterhardiness Canola leaves subjected to low temperature stressincrease levels of cryoprotectant chemicals (Janskaacute et al 2010)such as soluble sugars that facilitate cytoplasmic freezingpoint depression (Gusta et al 2004) Identification of culturalpractices and variety selections for plant survival to rapid

10

Subsurface soil Air above soil surface

0

ndash10

ndash20

10

0

ndash10

Dai

ly m

inim

um te

mpe

ratu

re (

degdegC)

ndash20

102013ndash2014

2012ndash2013

2011ndash2012

0

ndash10

ndash20

ndash30Nov Dec Jan

MonthFeb Mar

Fig 5 Temperature profiles were continuously recorded over three wintersat Davenport WA from 2012 to 2014 in the transitional cropndashfallow zonewhere winter canola is being grown Air and soil temperature probes ineach year were positioned directly above the soil surface or below the soilsurface at a depth of 10ndash15 cm

260 Crop amp Pasture Science W L Pan et al

freeze eventsmay be important to winter canola production in theiPNW as demonstrated in December 2014 when a rapidfreeze resulted in widespread loss of winter canola and winterwheat (J Schibel pers comm)

Low N status promotes increased sugar concentrationsand increased freeze resistance in plants (Lemoine et al 2013Wisniewski et al 2014) As a result this potentially changesthe N timing strategy for managing canola relative to traditionalwheat N management in the iPNW In zones less than 600mmannual precipitation where nitrate leaching below 180 cm soildepth is typically not excessive winter wheat N applicationoccurs pre-plant during summer fallow or at planting in annualcrop rotations (Veseth et al 1986 Halvorson et al 1999) Themain reason is to ensure adequate time for fertiliser N to nitrifyand move into the lower layers of the root profile ensuringadequate N availability as the surface soil dries and plantroots become increasingly reliant on subsoil N (Pan et al2001) If low N canola has higher winter survivability it mayprovide another reason to be conservative in N fertiliserapplications at planting and allow the canola to utilise residualN during early establishment An inverse relationship between Navailability and winter survival could be due to a complex set ofbiochemical shoot morphological ie raised shoot meristemsabove the ground and growth-induced water stress (Reese2015)Winter canola exhibits deep rooting depths to 180 cm andsubsoil N and water access and recovery is critically important(Hocking et al 2002 Reese 2015) Furthermore iPNW climatechange projections of hotter drier summer months (Abatzoglouet al 2015) portend a need for enhancing deep strong-rootedwinter crops such as canola for adapting to foreseen climatechange (Hatfield et al 2001 Blum 2009 Lynch 2015)

These climate change forecast models predict 5ndash15increases in iPNW regional annual precipitation but withincreasing proportions occurring during the winter andspring months with drier hotter summers This trend willnecessitate improvements in water and N infiltration and subsoilstorage during winter months for later access during active cropdevelopment Canola also has a reputation as a strong taprootedcrop capable of creating macro biopore channels for facilitatingsaturated water flow and root pathways for subsequent crops Yetcanola roots cannot always penetrate soil horizons with highphysical and chemical impedance (Cresswell and Kirkegaard1995 Watt et al 2006) Tillage pans and genetic soil horizonsin the iPNW have been observed to impede canola roots causingcharacteristic lsquoJrsquo hooking of the taproot forcing it to turn 90degrees along the plan of the soil pan until it encounters a crackwhere it can continue vertical development (Lisson et al 2007)This may be a plausible explanation for new canola growertestimonials claiming rotational benefits are not seen untila second or third rotation

Irrigated crop zone

Rotational fit The irrigated temperate desert of centralWashington and Oregon supports perennial tree and vine fruitproduction as well as 500 000 ha of many high value agronomiccrops such as potato and sweet corn where small grain cerealsare used as a rotational crop and winter wheat is only ~8 ofthe area (Table 1 Fig 1) As many high value crops for example

potato sweet corn onion beans are grown in this zone a muchlower adoption is projected for this zone with canola mostlyrestricted as a substitution for wheat in the irrigated rotationsof central Washington and Oregon

In addition with opportunities to follow early harvested freshvegetable crops dual purpose use of canola has potential todiversify and intensify irrigated rotations similar to drylandapplications (Neely 2010 Walsh 2012 Lilley et al 2015) Inthis zone of extended growing degree-days double croppingunder irrigation where biennial canola could bridge two short-season summer crops to yield three harvests over two growingseasons such asYear 1 fresh peascanola forage ndashYear 2 canolagrain (Kincaid et al 2011) Current efforts are focussed onproduction of silage from first-season canola vegetation incentral Washington Comparable canola grain yields of2300 kg handash1 were harvested with and without forage cuttingand removal (Desta et al 2013) Yield gaps between predictedand observed yields may relate to J-hooking that has beenobserved under irrigation similar to dryland root observationsdescribed above

Plant establishment As water is not a limitation underirrigation germination and seedling establishment is not asmuch of an issue in this zone For example winter rapeseedand mustard were rapidly established in late August and earlySeptember in the south andnorthColumbiabasinunder irrigationand substantial biomass and N accumulation occurs beforethe first hard frost and under these conditions deep soil N useshould still be accounted for in oilseed rotational N fertiliserrecommendations (Weinert et al 2002) Even under irrigation Nfertiliser responses in winter canola can be minimal due to buildup of residual soil N in highly fertilised rotations (Davenport et al2010) Even with ample water and N winter kill is still a problemin this zone as demonstrated in an irrigated winter wheat springbarley winter canola rotation where green-bridged Rhizoctoniasolani on spring barley residues was suspected to infect wintercanola roots perhaps contributing to winter kill in 4 of 5 years(Paulitz et al 2010 Schillinger et al 2010b) Rhizoctonia solanianastomosis group 2ndash1 has recently been identified to infectwheat and rape roots (Sturrock et al 2015)

Summary and future projections

Canola area has historically constituted less than 1 of theiPNW Advancements in the development of both winter andspring cultivars have afforded flexible options in weed controlmanagement Competitive hybrid cultivars are nowcommercially available with and without herbicide toleranceor resistance Current efforts are to identify and integratecultivars that can be successfully established survive winterand use subsoil water and N efficiently in each of the zonesEstablishment of a local oilseed processing industry increasingglobal and regional canola markets for food fuel and feedagronomic benefits in increasing rotational diversity andcontinued vigorous research and extension efforts havestimulated a recent increase in canola integration into existingmonoculture wheat production in the iPNW Modest canolarotational integration projected for each zone would achieveproduction goals to match current and future regionaloilseed processing capacity with 300 000 canola ha per year

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 261

(Table 1) An upper agronomic limit of roughly 1 1wheat canola has been reached in the semi-arid wheat-producing region of western Canada Similar crop productionratios in the iPNW would approach 700 000 ha Winter canolaintegration into the wheatndashfallow annual cropndashtransition andirrigated cropping zones and spring canola integration intoannual cropping and transition zones will improve weedcontrol and wheat yields particularly with herbicide-resistantcultivars The most critical challenges in the adaptation ofcanola into iPNW wheat-cropping systems include improvedconsistency of winter canola establishment and winter survivalin the low and intermediate precipitation zones Seeding depthand timing are critical determinants of winter and spring canolayield potential Relevant genetic research is currently focussedon increasing seed size and hypocotyl lengths for improvedseedling emergence and on the identification of freeze-tolerantcultivars Integration of spring canola into higher precipitationannual cropping systems requires research on innovative earlyplanting strategies and new earlier maturing cultivars to avoidhigh temperature and moisture stress Taproot architecture ofcanola dictates changes in standard N placement andtiming strategies that have been practiced for iPNW wheatproduction but the deep rooting habit of canola will contributeto efficient water and N recovery of the cropping systems Farmenterprise economics that account for rotational benefits andproduction risk will help growers account for multi-yearinvestments in canolandashwheat rotations to assess the benefits ofintegrated canolandashwheat systems

References

Abatzoglou J Rupp D Mote P (2015) Asymmetrical warming projectionsfor the inland Pacific Northwest In lsquoRegional approaches to climatechange for Pacific Northwest agriculture Climate science Northwestfarmers can usersquo (Eds K Borrelli D Daily Laursen S Eigenbrode BMahler R Pepper) pp 104ndash105 Available at wwwreachchpnaorg

Alberta Agriculture and Rural Development (2004) Alberta fertilizer guideIn lsquoAgric-facts practical information for Albertarsquos agriculture industryrsquoAgdex 541ndash1 (Ministry of Alberta Agriculture Food and RuralDevelopment Edmonton Alberta Canada)

Angadi SV Cutforth HW McConkey BG Gan Y (2003) Yield adjustmentby canola grown at different plant populations under semiarid conditionsCrop Science 43 1358ndash1366 doi102135cropsci20031358

Angus JF Kirkegaard JA Hunt JR Ryan MH Ohlander L Peoples MB(2015) Break crops and rotations for wheat Crop amp Pasture Science 66523ndash552 doi101071CP14252

Azooz RH Arshad MA (1998) Effect of residue and tillage managementon barley and canola growth and water use efficiency Canadian Journalof Soil Science 78 649ndash656 doi104141S97-098

Ball DA Young FL Ogg AO Jr (1999) Selective control of jointedgoatgrass (Aegilops clylindrica) with imazamox in herbicide-resistantwheat Weed Technology 13 77ndash82

Bettis B Auld D (Eds) (1980) Development of oilseeds as alternative cropsfor the Pacific Northwest Pacific Northwest Regional CommissionYearly Reports June 1979ndash31 July 1980 June 1980ndashJune 1981Pacific Northwest Regional Commission Moscow Idaho USA

Bettis BL Peterson CL Auld DL Driscoll DJ Peterson (1982) Fuelcharacteristics of vegetable oil from oilseed crops in the PacificNorthwest Agronomy Journal 74 335ndash339

Blum A (2009) Effective use of water (EUW) and not water-use efficiency(WUE) is the target of crop yield improvement under drought stressField Crops Research 112 119ndash123 doi101016jfcr200903009

Brennan RF Bolland MDA (2009) Comparing the nitrogen and phosphorusrequirements of canola and wheat for grain yield and quality Crop ampPasture Science 60 566ndash577 doi101071CP08401

Brill RD Jenkins ML Gardner MJ Lilley JM Orchard BA (2016)Optimising canola establishment and yield in south-eastern Australiawith hybrids and large seed Crop amp Pasture Science 67 409ndash418

Brown J Davis J (2015) Brassica breeding and research University of IdahoAvailable at wwwcalsuidahoedubrassica (accessed 15 December2015)

Brown J Davis JB Erickson DA Brown AP Seip L (1995) 1995 PacificNorthwest canola variety trial (PNWCVT) results and conclusions InlsquoPacificNorthwest canola conference1995proceedingsrsquo (EdsGJohnsonM Lewis) pp 29ndash36 (Department of Entomology Montana StateUniversity Bozeman MT)

BushongJ (2015)Okanola varieties andhybrids open-pollinatedvarietiesvshybrids Available at httpcanolaokstateeducropproductionvarieties(accessed 15 December 2015)

Conley SP Bordovsky D Rife C WieboldW (2004) Winter canola survivaland yield response to nitrogen and fall phosphorus Crop Managementdoi101094CM-2004-0901-01-RS

Connolly JR McCracken VA Painter KM (2016) Enterprise budget wheatand canola rotations in Eastern Washington intermediate rainfall regions12rdquo to 16rdquo Washington State University Extension PublicationWashington State University TB10 USA

Cook RJ Schillinger WF Christensen NW (2002) Rhizoctonia rootrot andtake-all of wheat in diverse direct-seed spring cropping systemsCanadian Journal of Plant Pathology 24 349ndash358 doi10108007060660209507020

Cresswell HP Kirkegaard JA (1995) Subsoil amelioration by plant-roots ndashthe process and the evidence Australian Journal of Soil Research 33221ndash239 doi101071SR9950221

Cutforth HW Angadi SV McConkey BG (2006) Stubble managementand microclimate yield and water use efficiency of canola grown inthe semiarid Canadian prairie Canadian Journal of Plant Science 8699ndash107 doi104141P05-073

Davenport J Stevens B Hang A Peters T (2010) Irrigated canola researchIn lsquoWashingtonOilseedCroppingSystemsProject partof theWashingtonState Biofuels Initiative 2010rsquo Annual Progress Report (EdsKESowersWL Pan) Available at httpcsswsuedubiofuelsfiles2012092010_Annual_Progress_Reportpdf (accessed 27 December 2015)

De Jong R Shields JA (1988) Available water-holding capacity maps ofAlberta Saskatchewan and Manitoba Canadian Journal of Soil Science68 157ndash163 doi104141cjss88-015

Desta KG Collins H Pan B (2013) Double-cropping dual purpose irrigatedbiennial canolawithgreenpea In lsquoWashingtonOilseedCroppingSystemsProject part of the Washington State Biofuels Initiative 2013rsquo AnnualProgress Report (Eds KE Sowers WL Pan) Available at httpcsswsuedubiofuelsfiles2012092013-Biofuel-Cropping-Systems-Research-Progress-Reportpdf (accessed 27 December 2015)

Divine TE Alzheimer DP Currie JW McGinnis KA Wiggins DJ (1977)Research on the potential impact of advanced oilseeds processingtechnology on Pacific Northwest Agriculture Batelle Pacific NorthwestLaboratories 231110270610690646 Richland Washington USA

Douglas CL Wysocki DJ Zuzel JF Rickman RW Klepper BL (1990)Agronomic zones for the dryland Pacific Northwest Pacific NorthwestCooperative Extension Bulletin PNW 954

Esser A Hulbert S (2013) Eastern WA low to intermediate rainfall InlsquoWashington Oilseed Cropping Systems Project part of theWashington State Biofuels Initiative 2013 Annual Progress Reportrsquo(Eds KE Sowers WL Pan) pp 31ndash36 Available at httpcsswsuedu

262 Crop amp Pasture Science W L Pan et al

(Pan et al 1991) which might deter growers from producingspring canola the following year unless the fields have beenburned A 2-year study was conducted examining the effect of25-cm and 50-cm row spacing on spring canola yield Each yearspring canola was planted at 56 kg handash1 in winter wheat residuethat had yielded ~6700 kg handash1 of grain When averaged oversite-years spring canola yield was similar (1710 kg handash1 for 50-cm rows 1775 kg handash1 for 25-cm rows) regardless of row spacing(Young2012)Withwide rowspacingmachine and fuel costs arereduced because of the reduction in openers and subsequentreduction in tractor horsepower Additionally it is likely thatdelays at seeding caused by blockages of high residue loadsunder seeding equipment (lsquodrill pluggingrsquo) will be reduced withwider row spacing

Although early spring planting of canola can be a challengelate seeding also has its penalties Stands of spring canola arealso more consistent when planted before moisture levels declineas spring rainfall is generally sporadic in the region Springcanola direct-seeded into heavy wheat residue over 9 yearsshowed an inverse relationship between seeding date and grainyield (Huggins and Painter 2011 Fig 3) As in other canola-growing regions later plantings result in flowering and graindevelopment under conditions of higher water and temperaturestress that reduce grain yield (Gan et al 2004 Kirkegaard et al2016)

Nitrogen management The N management approaches mustbe tailored to the unique environment of the iPNW Regionalyield-based N recommendations for wheat are commonlycalculated by applying a single or narrowly defined unit Nrequirement (UNR) of 45 kg N per 100 kg grain for soft wheatto 6 kg N per 100 kg grain for hard wheat (Koenig 2005 Koeniget al 2011) However contrary observations of varying UNRacross variable Palouse landscapes have been observed (Fiezet al 1995) suggesting amore tactical approach toNmanagementcould be implemented

Over 6 years higher overall UNR of 7ndash13 kg N (100 kggrain)ndash1 were observed for spring canola in the zoneacross years varying in water availability This range is similarto those found in canola fertiliser guides from semi-arid westernNorth America (Pan et al 2016) and that of 7ndash8 kg N (100 kggrain)ndash1 in Australia (Norton 2016) Canola plant nutrient uptakeper unit yield is higher than soft white and hard red wheats

(Koenig et al 2011) suggesting higher levels of availablenutrients supplied by native soil fertiliser carryover or newlyapplied fertiliser are required for regional canola productioncompared with wheat nutrient management In southwesternAustralia the amount of N fertiliser required to produceoptimum yield was 40 higher for canola than wheat(Brennan and Bolland 2009) Nevertheless canola has a deeptaproot system (Gan et al 2009) as well as extensive root hairsfor fully exploiting soil nutrients andwater (Hammac et al 2011)As a result canola seed yield responds well to applied N whenresidual soil levels are low but minimal fertiliser N responsewhen soil N supply is high and yield potential is low (Fig 4 Panet al 2016) This exponential diminishing-returns response tototal available N was also observed in southwestern Australia(Seymour et al 2016) In Montana canola responded stronglyto fertiliser N when planted into low levels of residual soil nitrate(90 cm depth) where yields were optimised at 200 kg N supplyhandash1 (Jackson 2000) However the magnitude of response isvariable in the iPNW due to interacting factors of climateavailable soil N cultivar and management practices Overallalthough spring canola N supply (soil + fertiliser N) requirementsper unit grain weight are higher than wheat its extensive andefficient roots utilise deep residual soil N to 120 cm in this zoneto reduce fertiliser N requirements (Maaz et al 2016)

Annual cropndashfallow transition zone

Rotational fit The iPNW transition zone is ~665 000 ha withannual precipitation ranging from 300 to 450mm and ischaracterised by annual cropping during wetter than normalprecipitation years interspersed with fallow during drier years(Table 1 Fig 1) Growers traditionally have grown winter andspring wheat and barley in gt50 of the zone fallow in 27and spring legumes in 10 of the zone In higher than normalprecipitation years continuous crop rotations have been grownPlant establishment of winter canola or spring canola are bothpossible in this zone with opportunities and constraints

3500

3000

2500

2000

1500

1000

500

0

322 41 411 421

Planting date

Spr

ing

cano

la y

ield

(kg

handash1

)

51 511 521

Fig 3 Direct-seeded spring canola yields following spring wheat atPullman WA over 9 years as related to planting date (Huggins andPainter 2011)

2500

EONR 150 kg fertiliser N handash1

EONR 19 kg fertiliser N handash12000

1500

1000

500

00 50 100 150 200 250 300

Can

ola

yiel

d (k

g ha

ndash1)

Total N supply (kg N handash1)

Fig 4 Canola grain yield response to nitrogen supply Ns with substantivecontribution of soil N and low economically optimum fertiliser N (EONR) atDavenport WA with limited water (open symbols) compared with higherEONR due to lower soil N and higher water availability at Pullman WA in2012 (closed symbols) (Pan et al 2016)

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 257

described in the above and below sections on the annual crop andcropndashfallow zones

Flexible decisions on planting spring canola in this zoneshould be based on over-winter soil water storage to 120 cmrooting depth and weather predictions for in-seasonprecipitation Generally spring canola yields are correlated withtotal available water with water-use efficiency (WUE) slope of325 kgyieldmmndash1 availablemoisture in the inlandPacificNorth-west (Pan et al 2016) which is lower than those reported inAustralia Robertson and Kirkegaard (2005) evaluated 42datasets of dryland spring canola for WUE and found that theWUE of canola varied from 4 to 18 kg handash1mmndash1 in which latersown crops tended to have lower efficiencies Similarly theWUEof spring canola decreased from 12 to 2 kg handash1mmndash1 whenseeded in early winter rather than in early spring within theMediterranean type environment of Iran (Faraji et al 2009)Terminal heat and drought stress during the reproductiondevelopment may cause the reduction in WUE in late seededspring canola Therefore the WUE of spring canola in the inlandPacific Northwest is more comparable to Canada wherestudies report a range of 280ndash576 kg handash1mmndash1 for rain-fedspring canola sown in the spring season (Azooz and Arshad1998 Cutforth et al 2006 Gan et al 2009)

Weed management A farm-scale rotational experiment atthe Washington State University Wilke Farm located atDavenport Washington has compared fallow systems with twoor three crops with continuous cropping in replicated stripsacross a variable field (Esser and Hulbert 2013) Herbicide-resistant spring canola cultivars were included in the 4-yearrotation which thus far has enabled the best control offeral cereal rye (Secale cereale L) resulting in the highesteconomic return over input costs among the three rotationsSpring canola planted at 56 kg seed handash1 yielded 784ndash1960 kggrain handash1 following spring wheat Rotational wheat yieldincreases due to improved weed control following canola canresult in higher rotational profits even without economicbenefits of canola in single season crop comparisons (Connollyet al 2016) In certain years of relatively high canola wheat priceratios economic benefits have been obtained even withoutincluding rotational benefits

Nitrogen management Spring canola N response trials at thesame location had maximum yields averaging 1027 kg handash1 andeconomically optimal N rates averaged 23 kg N fertiliser handash1ranging from zero fertiliser N required after fallow to 6ndash65 kgfertiliser N handash1 required following wheat (Pan et al 2016) Thehigher required economic N rate for canola following winterwheat was evident despite the lower available soil water andlower canola yield potential These findings corroboratestatements in Alberta Agriculture and Rural Development(2004) about lower N availability following continuouscropping versus fallow These modest fertiliser N requirementsseemingly contrary to spring canolarsquos relatively high unit totalN supply requirements are due to high residual soil N carryoverand N mineralisation coupled with canola roots extractingwater and N from 90 to 120-cm depths Overall the UNRobserved in the transition zone ranged from 9 to 17 kg total Nsupply100 kg grain higher than the range (39ndash8 kg total Nsupply100 kg grain) reported in fertiliser guides from semi-arid western North America (Koenig et al 2011) This was due

to lower yields and NUE of this region and our more completeaccounting of root zone residual N supply and creditingsoil N mineralisation contributions to total N supply (Panet al 2016)

Grainndashfallow zone

Rotational fit The cropndashfallow zone usually has insufficientannual precipitation (lt300mm) to economically supportannual cropping (Young et al 2015) and comprises an arearoughly equivalent to the total of the other two rain-fed zonesof ~1 245 000 ha Winter wheat has greater yield potential thanspring wheat due to deeper roots more efficient water extractionand earlier flowering and grain development during hot drysummer months Similarly spring canola is not commonlygrown in this zone because spring canola yields only 50ndash60as much as winter canola (Pakish et al 2015)

Weed management Weed control in summer is typicallyaccomplished using tillage with a rod weeder or chemicalfallow-direct seeding to reduce wind erosion (Young andThorne 2004) One of the primary reasons to grow winter canolais to offer growers an added management tool to control weedsWinter annual grass weeds including feral rye downybrome jointed goatgrass and Italian ryegrass continue toplague monoculture winter wheat growers The introductionof imidazolinone-resistant wheat in 2003 (Ball et al 1999)provided growers with an additional option to manage thesepests however an imidazolinone-resistant biotype of downybrome has been found in Oregon and feral rye is one of the mostdifficult winter annual grass weeds to control with imazamox(Pester et al 2000) Feral rye is a predominant winter annualgrass weed in the low rainfall grain fallow region of theiPNW In this region quizalofop in conventionally bred wintercanola cultivars for example Amanda Falstaff and glyphosatein glyphosate-resistant canola cultivars for example Croplan115 and 125 effectively controlled feral rye (Young et al2016) A second reason to introduce winter canola into cerealproduction systems regardless of rainfall zone is availabilityof herbicide-tolerant canola cultivars These cultivars allowproducers to plant in fields with a history of sulfonylurea forexample Croplan 115 or 125 and imidazolinone herbicides forexample Claremore and Edimax (Young et al 2016) withoutenduring 9ndash40 months of plant back restrictions Commercialhybrid cultivars have recently been introduced into this regionand their potential advantages over open pollinated lines arebeing evaluated in regional trials For example winter canolacomparisons in Oklahoma have characterised greater seed sizeand yield potential under optimal conditions but less droughttolerance than open-pollinated cultivars (Bushong 2015)

Plant establishment Winter canola establishment is asignificant challenge in this zone The smaller seed size ofcanola alters seed zone requirements for optimal germinationand emergence compared with wheat which in turn can affectdepth of planting This need for deep planting is greatest in thiszone where late summer high temperatures and little to noprecipitation drives the soil moisture line into the subsoil(Schillinger et al 2010a) The range of seed sizes in canola farexceeds that of the variation in wheat seed Wheat seed plantedin the iPNW typically ranges from 31 to 38mg seedndash1 whereas

258 Crop amp Pasture Science W L Pan et al

canola seed ranges from 2 to 6mg seedndash1 (F L Young perscomm) A 3-fold variation in canola seed size makes it moreimperative to get accurate oilseed weights when targetingspecific plant population goals Seed size is affected bycultivar and the seed production environment as well ascommercial seed sizing processes (Lamb and Johnson 2004)Smaller seed reserves of energy and nutrients of individualcanola seeds restrict deep seed placement Winter wheatcultivars grown in the fallow zone are bred to emerge from verydeep seed placement (Mohan et al 2013) In contrast canola seedgenerally emerges best when placed within 2ndash3 cm of the soilsurface when moisture conditions are adequate but can emergefrom deeper placement (3ndash6 cm) when required to reachmoisture Hypocotyl length is genetically modulated indicatingpotential for future breeding opportunities (Zhao et al 2013)Larger seeds can generally emerge from greater depths due tolonger and more robust hypocotyls In addition larger seededBrassica cultivars produce greater early season biomass whichincreases crop competition with weeds (Harker et al 2015Brill et al 2016)

Winter canola establishment requires excellent soil moisturenear the soil surface and cool (298C) ambient air temperaturesfor 5ndash7days after planting (Young et al 2014)Deep furrowdrillsthat are used in the wheatndashfallow zone for placing the seed intosoil moisture are also being used successfully to plant wintercanola as the seedlings need to emerge only to the bottom of thefurrow During August the optimal time to plant winter canola(Young et al 2014) soil moisture is usually 10ndash15 cm below thesoil surface and too deep for canola seedlings to emerge To helpalleviate this problem shovels 25ndash38 cm wide have been placedin front of the openers to reach soilmoisture andmove the hot drysoil from the furrow thus reducing the distance the emergingseedling has to travel through the soil (Young et al 2008 2014)The use of shovels did not increase winter canola yield andwinter survival but did increase plant density 22 comparedwith when shovels were not used In addition there is a moreuniform plant distribution from the use of shovels whichsuppressed weed growth and reduced weed competition(Young et al 2014) Generally a 45-kg handash1 seeding rate wasoptimal for sufficient stand establishment and yield Whenwinter canola seeding was delayed until September yield wasdecreased almost 40 compared with an August plantingWinter survival can range from 56 to 83 with a subsequentspring plant population of only 20ndash40 plantsmndash2 needed foroptimum yield

Spring canola despite the lower yield potential can begrown following failed winter canola survival and glyphosate-resistant spring canola cultivars are beneficial for controllingsummer annual broadleaf weeds in this zone such as Russianthistle (Salsola tragus) which emerges with similar timing asspring canola Spring canola seed broadcast on the soil surfaceyields between 31 and 67 of spring canola that was placed inthe soil with drills equipped with double disk chisel hoe orinverted T-slot openers (Young et al 2012) Broadcast yields ofspring canola were low because generally lt5 of the seedestablished plants When left on the soil surface seedlingswere unprotected when emerging from the seed coat and werekilled by frost Rolling broadcast seed with a heavy cast-ironroller generally improved yield ~35 compared with broadcast

alone although improved yield ranged from 0 to gt100Depending on location and precipitation optimum yieldsranged from 615 kg handash1 to 1575 kg handash1 (Young et al 2012)Precipitation during flowering and seed-fill in May and Junecorrelated with increased canola yield presumably by reducingmoisture stress during reproductive growth as observed byGan et al (2004)

Shoot meristematic origins of dicotyledonous oilseedsdiffer from monocotyledonous cereal grain crops Leaves andshoot branch initiation of oilseeds occurs at or near the soilsurface (Thomas 2003) In contrast shoot tiller and rootmeristems of wheat seedlings emanate at the belowgroundcrown and stem nodes directly above the crown (Klepper et al1984) The development of aboveground shoot meristems ofoilseeds versus belowground shoot nodes of cereals is afundamental difference in freeze avoidance (Thomas 2003)Oilseeds are exposed to sudden downturns in air temperaturesabove the soil surface during late falls and winters whereascereals are more protected by the soil layer above the cerealshoot meristem that buffers against rapid and severesubfreezing spikes

The size of winter canola plants entering the winter monthscorrelates with winter survival Small seedlings with 2ndash3 trueleaves survive iPNW winters very poorly This limits wintercanola production in the non-irrigated annual cropping zoneof the iPNW as very dry soils following harvest of theprevious yearrsquos crop generally persist into October by thetime sufficient moisture has accumulated to establish a standthe seedlings are typically too small to survive the first hardfrostsWhen planted into fallow land early plantedwinter canolatakes advantage of added growing degree-days to producemore shoot and root biomass before winter dieback Plantingfive winter rapeseed cultivars in the annual cropping zone(600mm) from 2 July to 13 September indicated that laterplanting dates resulted in less winter survival and seed yield(Porter et al 1981) presumably because late season plantingshad less energy and nutrient reserves In contrast early plantingsof winter canola in the wheatndashfallow zone take advantage ofsurface soil moisture but may result in poor winter survivalWinter cultivars remain vegetative without stem boltinghowever vegetative biomass of early planted canola extractsmost of the available soil moisture to 150 cm depth producingweakened drought-stressed plants with higher shoot meristemsthat were more susceptible to winter kill than later seededplants (Reese 2015)

Several fields of winter canola were monitored over 3 yearsacross the iPNW illustrating temperature profiles associatedwith partial and complete canola winter kill (Fig 5) In thewinter of 2013ndash2014 minimum temperatures at the soilsurface fell to ndash208C in early December and again in Februaryresulting in widespread complete winter kill across the regionIn contrast minimum surface temperatures only reached ndash15to ndash178C in January of 2011ndash2012 and 2012ndash2013 followinggradual temperature declines which resulted in partial standlosses of ndash28 to ndash49 but still yielding 1700ndash4300 kg handash1

even at sites with reduced stands Winter canola grown in semi-arid environments has the ability to compensate for standlosses with increased stem branching and pod retention(Angadi et al 2003) A late spring frost in late AprilndashMay

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 259

during flowering (data not shown) severely reduced the pod setresulting in yields lt1000 kg handash1 despite good stand survival insome locations This freeze sensitivity of canola coming out of

winter dormancy has been noted in the USA Great Plains(Holman et al 2011) In a location near DavenportWashington spring frost was not a factor and winter canoladirect seeded into winter wheat stubble averaged 4100 kg handash1

(Schillinger 2013)Moderation of extreme subfreezing conditions by soil

at depths 10ndash20 cm were consistently demonstrated (Fig 5)in comparison to surface temperatures illustrating themorphological advantage of wheatrsquos ability to developsubsurface shoot meristems that are insulated by soil (Klepperet al 1984) in comparison to above surface canola shootmeristems Canola nutritional status potentially contributes tosupercooling by increasing cell solutes such as high K and Clnutrition (Evans et al 2015) Ensuring a sufficient P status ofvegetative canola plants entering into the winter season with theaddition of starter phosphorus at planting has been shown toimprove winter survival (Wilkins et al 2002)

Nitrogen management The N placement and timing forwinter canola require additional adjustments from traditional Nfertilisation methods used in winter wheat production due tointerspecies differences in root architecture Chemical fallow-direct seeded winter wheat is typically fertilised in deep bandsbelow the seed row at planting (Veseth et al 1986) Canolaseedlings produce a single taproot main axis with lateral rootsand root hairs emanating from an ammonia sensitive tap root(Madsen et al 2014) In contrast monocotyledonous cerealcrops have multiple seminal axes and shoot tillers whichinitiate from the seed the belowground crown and stem nodesthat produce shoot tillers and affiliated root seminal axes(Klepper et al 1984) As a result of these basic rootarchitectural differences canola seedlings are more sensitivethan cereals to chemical toxicities such as expanded zones ofhigh ammonia around fertiliser bands due to oilseed relianceon the development of a single tap root whereas cereals havenumerous seminal axes to explore deep soil layers This basicmorphological difference has implications for differentialfertiliser band sensitivity when a canola taproot radicleencounters a high ammonia band meristems become necroticwith subsequent seedling injury or death (Madsen et al 2014)While a seminal root axis of cereal seedlings can suffer thesame fate other seminal axes of the same seedling will growto the side of the band and successfully develop The ability ofwheat roots to morphologically overcome ammonia toxicity ofdeep banded ammonium fertilisers has allowed the developmentand commercial use of direct seed planting equipment with deepbanding capabilities (Veseth et al 1986) However canolarsquostaproot sensitivity to deep placed ammonia bands will requirealternate N placement and timing strategies Fertiliser placementstudies on canola have demonstrated the need to place N as a sideband (Grant et al 2011 Norton 2016)

High N status of the vegetative winter oilseed plants hasreduced survival during freezing conditions (Rathke et al2006) There are biochemical and morphological responses tohigh N availability that may contribute to the decrease in winterhardiness Canola leaves subjected to low temperature stressincrease levels of cryoprotectant chemicals (Janskaacute et al 2010)such as soluble sugars that facilitate cytoplasmic freezingpoint depression (Gusta et al 2004) Identification of culturalpractices and variety selections for plant survival to rapid

10

Subsurface soil Air above soil surface

0

ndash10

ndash20

10

0

ndash10

Dai

ly m

inim

um te

mpe

ratu

re (

degdegC)

ndash20

102013ndash2014

2012ndash2013

2011ndash2012

0

ndash10

ndash20

ndash30Nov Dec Jan

MonthFeb Mar

Fig 5 Temperature profiles were continuously recorded over three wintersat Davenport WA from 2012 to 2014 in the transitional cropndashfallow zonewhere winter canola is being grown Air and soil temperature probes ineach year were positioned directly above the soil surface or below the soilsurface at a depth of 10ndash15 cm

260 Crop amp Pasture Science W L Pan et al

freeze eventsmay be important to winter canola production in theiPNW as demonstrated in December 2014 when a rapidfreeze resulted in widespread loss of winter canola and winterwheat (J Schibel pers comm)

Low N status promotes increased sugar concentrationsand increased freeze resistance in plants (Lemoine et al 2013Wisniewski et al 2014) As a result this potentially changesthe N timing strategy for managing canola relative to traditionalwheat N management in the iPNW In zones less than 600mmannual precipitation where nitrate leaching below 180 cm soildepth is typically not excessive winter wheat N applicationoccurs pre-plant during summer fallow or at planting in annualcrop rotations (Veseth et al 1986 Halvorson et al 1999) Themain reason is to ensure adequate time for fertiliser N to nitrifyand move into the lower layers of the root profile ensuringadequate N availability as the surface soil dries and plantroots become increasingly reliant on subsoil N (Pan et al2001) If low N canola has higher winter survivability it mayprovide another reason to be conservative in N fertiliserapplications at planting and allow the canola to utilise residualN during early establishment An inverse relationship between Navailability and winter survival could be due to a complex set ofbiochemical shoot morphological ie raised shoot meristemsabove the ground and growth-induced water stress (Reese2015)Winter canola exhibits deep rooting depths to 180 cm andsubsoil N and water access and recovery is critically important(Hocking et al 2002 Reese 2015) Furthermore iPNW climatechange projections of hotter drier summer months (Abatzoglouet al 2015) portend a need for enhancing deep strong-rootedwinter crops such as canola for adapting to foreseen climatechange (Hatfield et al 2001 Blum 2009 Lynch 2015)

These climate change forecast models predict 5ndash15increases in iPNW regional annual precipitation but withincreasing proportions occurring during the winter andspring months with drier hotter summers This trend willnecessitate improvements in water and N infiltration and subsoilstorage during winter months for later access during active cropdevelopment Canola also has a reputation as a strong taprootedcrop capable of creating macro biopore channels for facilitatingsaturated water flow and root pathways for subsequent crops Yetcanola roots cannot always penetrate soil horizons with highphysical and chemical impedance (Cresswell and Kirkegaard1995 Watt et al 2006) Tillage pans and genetic soil horizonsin the iPNW have been observed to impede canola roots causingcharacteristic lsquoJrsquo hooking of the taproot forcing it to turn 90degrees along the plan of the soil pan until it encounters a crackwhere it can continue vertical development (Lisson et al 2007)This may be a plausible explanation for new canola growertestimonials claiming rotational benefits are not seen untila second or third rotation

Irrigated crop zone

Rotational fit The irrigated temperate desert of centralWashington and Oregon supports perennial tree and vine fruitproduction as well as 500 000 ha of many high value agronomiccrops such as potato and sweet corn where small grain cerealsare used as a rotational crop and winter wheat is only ~8 ofthe area (Table 1 Fig 1) As many high value crops for example

potato sweet corn onion beans are grown in this zone a muchlower adoption is projected for this zone with canola mostlyrestricted as a substitution for wheat in the irrigated rotationsof central Washington and Oregon

In addition with opportunities to follow early harvested freshvegetable crops dual purpose use of canola has potential todiversify and intensify irrigated rotations similar to drylandapplications (Neely 2010 Walsh 2012 Lilley et al 2015) Inthis zone of extended growing degree-days double croppingunder irrigation where biennial canola could bridge two short-season summer crops to yield three harvests over two growingseasons such asYear 1 fresh peascanola forage ndashYear 2 canolagrain (Kincaid et al 2011) Current efforts are focussed onproduction of silage from first-season canola vegetation incentral Washington Comparable canola grain yields of2300 kg handash1 were harvested with and without forage cuttingand removal (Desta et al 2013) Yield gaps between predictedand observed yields may relate to J-hooking that has beenobserved under irrigation similar to dryland root observationsdescribed above

Plant establishment As water is not a limitation underirrigation germination and seedling establishment is not asmuch of an issue in this zone For example winter rapeseedand mustard were rapidly established in late August and earlySeptember in the south andnorthColumbiabasinunder irrigationand substantial biomass and N accumulation occurs beforethe first hard frost and under these conditions deep soil N useshould still be accounted for in oilseed rotational N fertiliserrecommendations (Weinert et al 2002) Even under irrigation Nfertiliser responses in winter canola can be minimal due to buildup of residual soil N in highly fertilised rotations (Davenport et al2010) Even with ample water and N winter kill is still a problemin this zone as demonstrated in an irrigated winter wheat springbarley winter canola rotation where green-bridged Rhizoctoniasolani on spring barley residues was suspected to infect wintercanola roots perhaps contributing to winter kill in 4 of 5 years(Paulitz et al 2010 Schillinger et al 2010b) Rhizoctonia solanianastomosis group 2ndash1 has recently been identified to infectwheat and rape roots (Sturrock et al 2015)

Summary and future projections

Canola area has historically constituted less than 1 of theiPNW Advancements in the development of both winter andspring cultivars have afforded flexible options in weed controlmanagement Competitive hybrid cultivars are nowcommercially available with and without herbicide toleranceor resistance Current efforts are to identify and integratecultivars that can be successfully established survive winterand use subsoil water and N efficiently in each of the zonesEstablishment of a local oilseed processing industry increasingglobal and regional canola markets for food fuel and feedagronomic benefits in increasing rotational diversity andcontinued vigorous research and extension efforts havestimulated a recent increase in canola integration into existingmonoculture wheat production in the iPNW Modest canolarotational integration projected for each zone would achieveproduction goals to match current and future regionaloilseed processing capacity with 300 000 canola ha per year

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 261

(Table 1) An upper agronomic limit of roughly 1 1wheat canola has been reached in the semi-arid wheat-producing region of western Canada Similar crop productionratios in the iPNW would approach 700 000 ha Winter canolaintegration into the wheatndashfallow annual cropndashtransition andirrigated cropping zones and spring canola integration intoannual cropping and transition zones will improve weedcontrol and wheat yields particularly with herbicide-resistantcultivars The most critical challenges in the adaptation ofcanola into iPNW wheat-cropping systems include improvedconsistency of winter canola establishment and winter survivalin the low and intermediate precipitation zones Seeding depthand timing are critical determinants of winter and spring canolayield potential Relevant genetic research is currently focussedon increasing seed size and hypocotyl lengths for improvedseedling emergence and on the identification of freeze-tolerantcultivars Integration of spring canola into higher precipitationannual cropping systems requires research on innovative earlyplanting strategies and new earlier maturing cultivars to avoidhigh temperature and moisture stress Taproot architecture ofcanola dictates changes in standard N placement andtiming strategies that have been practiced for iPNW wheatproduction but the deep rooting habit of canola will contributeto efficient water and N recovery of the cropping systems Farmenterprise economics that account for rotational benefits andproduction risk will help growers account for multi-yearinvestments in canolandashwheat rotations to assess the benefits ofintegrated canolandashwheat systems

References

Abatzoglou J Rupp D Mote P (2015) Asymmetrical warming projectionsfor the inland Pacific Northwest In lsquoRegional approaches to climatechange for Pacific Northwest agriculture Climate science Northwestfarmers can usersquo (Eds K Borrelli D Daily Laursen S Eigenbrode BMahler R Pepper) pp 104ndash105 Available at wwwreachchpnaorg

Alberta Agriculture and Rural Development (2004) Alberta fertilizer guideIn lsquoAgric-facts practical information for Albertarsquos agriculture industryrsquoAgdex 541ndash1 (Ministry of Alberta Agriculture Food and RuralDevelopment Edmonton Alberta Canada)

Angadi SV Cutforth HW McConkey BG Gan Y (2003) Yield adjustmentby canola grown at different plant populations under semiarid conditionsCrop Science 43 1358ndash1366 doi102135cropsci20031358

Angus JF Kirkegaard JA Hunt JR Ryan MH Ohlander L Peoples MB(2015) Break crops and rotations for wheat Crop amp Pasture Science 66523ndash552 doi101071CP14252

Azooz RH Arshad MA (1998) Effect of residue and tillage managementon barley and canola growth and water use efficiency Canadian Journalof Soil Science 78 649ndash656 doi104141S97-098

Ball DA Young FL Ogg AO Jr (1999) Selective control of jointedgoatgrass (Aegilops clylindrica) with imazamox in herbicide-resistantwheat Weed Technology 13 77ndash82

Bettis B Auld D (Eds) (1980) Development of oilseeds as alternative cropsfor the Pacific Northwest Pacific Northwest Regional CommissionYearly Reports June 1979ndash31 July 1980 June 1980ndashJune 1981Pacific Northwest Regional Commission Moscow Idaho USA

Bettis BL Peterson CL Auld DL Driscoll DJ Peterson (1982) Fuelcharacteristics of vegetable oil from oilseed crops in the PacificNorthwest Agronomy Journal 74 335ndash339

Blum A (2009) Effective use of water (EUW) and not water-use efficiency(WUE) is the target of crop yield improvement under drought stressField Crops Research 112 119ndash123 doi101016jfcr200903009

Brennan RF Bolland MDA (2009) Comparing the nitrogen and phosphorusrequirements of canola and wheat for grain yield and quality Crop ampPasture Science 60 566ndash577 doi101071CP08401

Brill RD Jenkins ML Gardner MJ Lilley JM Orchard BA (2016)Optimising canola establishment and yield in south-eastern Australiawith hybrids and large seed Crop amp Pasture Science 67 409ndash418

Brown J Davis J (2015) Brassica breeding and research University of IdahoAvailable at wwwcalsuidahoedubrassica (accessed 15 December2015)

Brown J Davis JB Erickson DA Brown AP Seip L (1995) 1995 PacificNorthwest canola variety trial (PNWCVT) results and conclusions InlsquoPacificNorthwest canola conference1995proceedingsrsquo (EdsGJohnsonM Lewis) pp 29ndash36 (Department of Entomology Montana StateUniversity Bozeman MT)

BushongJ (2015)Okanola varieties andhybrids open-pollinatedvarietiesvshybrids Available at httpcanolaokstateeducropproductionvarieties(accessed 15 December 2015)

Conley SP Bordovsky D Rife C WieboldW (2004) Winter canola survivaland yield response to nitrogen and fall phosphorus Crop Managementdoi101094CM-2004-0901-01-RS

Connolly JR McCracken VA Painter KM (2016) Enterprise budget wheatand canola rotations in Eastern Washington intermediate rainfall regions12rdquo to 16rdquo Washington State University Extension PublicationWashington State University TB10 USA

Cook RJ Schillinger WF Christensen NW (2002) Rhizoctonia rootrot andtake-all of wheat in diverse direct-seed spring cropping systemsCanadian Journal of Plant Pathology 24 349ndash358 doi10108007060660209507020

Cresswell HP Kirkegaard JA (1995) Subsoil amelioration by plant-roots ndashthe process and the evidence Australian Journal of Soil Research 33221ndash239 doi101071SR9950221

Cutforth HW Angadi SV McConkey BG (2006) Stubble managementand microclimate yield and water use efficiency of canola grown inthe semiarid Canadian prairie Canadian Journal of Plant Science 8699ndash107 doi104141P05-073

Davenport J Stevens B Hang A Peters T (2010) Irrigated canola researchIn lsquoWashingtonOilseedCroppingSystemsProject partof theWashingtonState Biofuels Initiative 2010rsquo Annual Progress Report (EdsKESowersWL Pan) Available at httpcsswsuedubiofuelsfiles2012092010_Annual_Progress_Reportpdf (accessed 27 December 2015)

De Jong R Shields JA (1988) Available water-holding capacity maps ofAlberta Saskatchewan and Manitoba Canadian Journal of Soil Science68 157ndash163 doi104141cjss88-015

Desta KG Collins H Pan B (2013) Double-cropping dual purpose irrigatedbiennial canolawithgreenpea In lsquoWashingtonOilseedCroppingSystemsProject part of the Washington State Biofuels Initiative 2013rsquo AnnualProgress Report (Eds KE Sowers WL Pan) Available at httpcsswsuedubiofuelsfiles2012092013-Biofuel-Cropping-Systems-Research-Progress-Reportpdf (accessed 27 December 2015)

Divine TE Alzheimer DP Currie JW McGinnis KA Wiggins DJ (1977)Research on the potential impact of advanced oilseeds processingtechnology on Pacific Northwest Agriculture Batelle Pacific NorthwestLaboratories 231110270610690646 Richland Washington USA

Douglas CL Wysocki DJ Zuzel JF Rickman RW Klepper BL (1990)Agronomic zones for the dryland Pacific Northwest Pacific NorthwestCooperative Extension Bulletin PNW 954

Esser A Hulbert S (2013) Eastern WA low to intermediate rainfall InlsquoWashington Oilseed Cropping Systems Project part of theWashington State Biofuels Initiative 2013 Annual Progress Reportrsquo(Eds KE Sowers WL Pan) pp 31ndash36 Available at httpcsswsuedu

262 Crop amp Pasture Science W L Pan et al

described in the above and below sections on the annual crop andcropndashfallow zones

Flexible decisions on planting spring canola in this zoneshould be based on over-winter soil water storage to 120 cmrooting depth and weather predictions for in-seasonprecipitation Generally spring canola yields are correlated withtotal available water with water-use efficiency (WUE) slope of325 kgyieldmmndash1 availablemoisture in the inlandPacificNorth-west (Pan et al 2016) which is lower than those reported inAustralia Robertson and Kirkegaard (2005) evaluated 42datasets of dryland spring canola for WUE and found that theWUE of canola varied from 4 to 18 kg handash1mmndash1 in which latersown crops tended to have lower efficiencies Similarly theWUEof spring canola decreased from 12 to 2 kg handash1mmndash1 whenseeded in early winter rather than in early spring within theMediterranean type environment of Iran (Faraji et al 2009)Terminal heat and drought stress during the reproductiondevelopment may cause the reduction in WUE in late seededspring canola Therefore the WUE of spring canola in the inlandPacific Northwest is more comparable to Canada wherestudies report a range of 280ndash576 kg handash1mmndash1 for rain-fedspring canola sown in the spring season (Azooz and Arshad1998 Cutforth et al 2006 Gan et al 2009)

Weed management A farm-scale rotational experiment atthe Washington State University Wilke Farm located atDavenport Washington has compared fallow systems with twoor three crops with continuous cropping in replicated stripsacross a variable field (Esser and Hulbert 2013) Herbicide-resistant spring canola cultivars were included in the 4-yearrotation which thus far has enabled the best control offeral cereal rye (Secale cereale L) resulting in the highesteconomic return over input costs among the three rotationsSpring canola planted at 56 kg seed handash1 yielded 784ndash1960 kggrain handash1 following spring wheat Rotational wheat yieldincreases due to improved weed control following canola canresult in higher rotational profits even without economicbenefits of canola in single season crop comparisons (Connollyet al 2016) In certain years of relatively high canola wheat priceratios economic benefits have been obtained even withoutincluding rotational benefits

Nitrogen management Spring canola N response trials at thesame location had maximum yields averaging 1027 kg handash1 andeconomically optimal N rates averaged 23 kg N fertiliser handash1ranging from zero fertiliser N required after fallow to 6ndash65 kgfertiliser N handash1 required following wheat (Pan et al 2016) Thehigher required economic N rate for canola following winterwheat was evident despite the lower available soil water andlower canola yield potential These findings corroboratestatements in Alberta Agriculture and Rural Development(2004) about lower N availability following continuouscropping versus fallow These modest fertiliser N requirementsseemingly contrary to spring canolarsquos relatively high unit totalN supply requirements are due to high residual soil N carryoverand N mineralisation coupled with canola roots extractingwater and N from 90 to 120-cm depths Overall the UNRobserved in the transition zone ranged from 9 to 17 kg total Nsupply100 kg grain higher than the range (39ndash8 kg total Nsupply100 kg grain) reported in fertiliser guides from semi-arid western North America (Koenig et al 2011) This was due

to lower yields and NUE of this region and our more completeaccounting of root zone residual N supply and creditingsoil N mineralisation contributions to total N supply (Panet al 2016)

Grainndashfallow zone

Rotational fit The cropndashfallow zone usually has insufficientannual precipitation (lt300mm) to economically supportannual cropping (Young et al 2015) and comprises an arearoughly equivalent to the total of the other two rain-fed zonesof ~1 245 000 ha Winter wheat has greater yield potential thanspring wheat due to deeper roots more efficient water extractionand earlier flowering and grain development during hot drysummer months Similarly spring canola is not commonlygrown in this zone because spring canola yields only 50ndash60as much as winter canola (Pakish et al 2015)

Weed management Weed control in summer is typicallyaccomplished using tillage with a rod weeder or chemicalfallow-direct seeding to reduce wind erosion (Young andThorne 2004) One of the primary reasons to grow winter canolais to offer growers an added management tool to control weedsWinter annual grass weeds including feral rye downybrome jointed goatgrass and Italian ryegrass continue toplague monoculture winter wheat growers The introductionof imidazolinone-resistant wheat in 2003 (Ball et al 1999)provided growers with an additional option to manage thesepests however an imidazolinone-resistant biotype of downybrome has been found in Oregon and feral rye is one of the mostdifficult winter annual grass weeds to control with imazamox(Pester et al 2000) Feral rye is a predominant winter annualgrass weed in the low rainfall grain fallow region of theiPNW In this region quizalofop in conventionally bred wintercanola cultivars for example Amanda Falstaff and glyphosatein glyphosate-resistant canola cultivars for example Croplan115 and 125 effectively controlled feral rye (Young et al2016) A second reason to introduce winter canola into cerealproduction systems regardless of rainfall zone is availabilityof herbicide-tolerant canola cultivars These cultivars allowproducers to plant in fields with a history of sulfonylurea forexample Croplan 115 or 125 and imidazolinone herbicides forexample Claremore and Edimax (Young et al 2016) withoutenduring 9ndash40 months of plant back restrictions Commercialhybrid cultivars have recently been introduced into this regionand their potential advantages over open pollinated lines arebeing evaluated in regional trials For example winter canolacomparisons in Oklahoma have characterised greater seed sizeand yield potential under optimal conditions but less droughttolerance than open-pollinated cultivars (Bushong 2015)

Plant establishment Winter canola establishment is asignificant challenge in this zone The smaller seed size ofcanola alters seed zone requirements for optimal germinationand emergence compared with wheat which in turn can affectdepth of planting This need for deep planting is greatest in thiszone where late summer high temperatures and little to noprecipitation drives the soil moisture line into the subsoil(Schillinger et al 2010a) The range of seed sizes in canola farexceeds that of the variation in wheat seed Wheat seed plantedin the iPNW typically ranges from 31 to 38mg seedndash1 whereas

258 Crop amp Pasture Science W L Pan et al

canola seed ranges from 2 to 6mg seedndash1 (F L Young perscomm) A 3-fold variation in canola seed size makes it moreimperative to get accurate oilseed weights when targetingspecific plant population goals Seed size is affected bycultivar and the seed production environment as well ascommercial seed sizing processes (Lamb and Johnson 2004)Smaller seed reserves of energy and nutrients of individualcanola seeds restrict deep seed placement Winter wheatcultivars grown in the fallow zone are bred to emerge from verydeep seed placement (Mohan et al 2013) In contrast canola seedgenerally emerges best when placed within 2ndash3 cm of the soilsurface when moisture conditions are adequate but can emergefrom deeper placement (3ndash6 cm) when required to reachmoisture Hypocotyl length is genetically modulated indicatingpotential for future breeding opportunities (Zhao et al 2013)Larger seeds can generally emerge from greater depths due tolonger and more robust hypocotyls In addition larger seededBrassica cultivars produce greater early season biomass whichincreases crop competition with weeds (Harker et al 2015Brill et al 2016)

Winter canola establishment requires excellent soil moisturenear the soil surface and cool (298C) ambient air temperaturesfor 5ndash7days after planting (Young et al 2014)Deep furrowdrillsthat are used in the wheatndashfallow zone for placing the seed intosoil moisture are also being used successfully to plant wintercanola as the seedlings need to emerge only to the bottom of thefurrow During August the optimal time to plant winter canola(Young et al 2014) soil moisture is usually 10ndash15 cm below thesoil surface and too deep for canola seedlings to emerge To helpalleviate this problem shovels 25ndash38 cm wide have been placedin front of the openers to reach soilmoisture andmove the hot drysoil from the furrow thus reducing the distance the emergingseedling has to travel through the soil (Young et al 2008 2014)The use of shovels did not increase winter canola yield andwinter survival but did increase plant density 22 comparedwith when shovels were not used In addition there is a moreuniform plant distribution from the use of shovels whichsuppressed weed growth and reduced weed competition(Young et al 2014) Generally a 45-kg handash1 seeding rate wasoptimal for sufficient stand establishment and yield Whenwinter canola seeding was delayed until September yield wasdecreased almost 40 compared with an August plantingWinter survival can range from 56 to 83 with a subsequentspring plant population of only 20ndash40 plantsmndash2 needed foroptimum yield

Spring canola despite the lower yield potential can begrown following failed winter canola survival and glyphosate-resistant spring canola cultivars are beneficial for controllingsummer annual broadleaf weeds in this zone such as Russianthistle (Salsola tragus) which emerges with similar timing asspring canola Spring canola seed broadcast on the soil surfaceyields between 31 and 67 of spring canola that was placed inthe soil with drills equipped with double disk chisel hoe orinverted T-slot openers (Young et al 2012) Broadcast yields ofspring canola were low because generally lt5 of the seedestablished plants When left on the soil surface seedlingswere unprotected when emerging from the seed coat and werekilled by frost Rolling broadcast seed with a heavy cast-ironroller generally improved yield ~35 compared with broadcast

alone although improved yield ranged from 0 to gt100Depending on location and precipitation optimum yieldsranged from 615 kg handash1 to 1575 kg handash1 (Young et al 2012)Precipitation during flowering and seed-fill in May and Junecorrelated with increased canola yield presumably by reducingmoisture stress during reproductive growth as observed byGan et al (2004)

Shoot meristematic origins of dicotyledonous oilseedsdiffer from monocotyledonous cereal grain crops Leaves andshoot branch initiation of oilseeds occurs at or near the soilsurface (Thomas 2003) In contrast shoot tiller and rootmeristems of wheat seedlings emanate at the belowgroundcrown and stem nodes directly above the crown (Klepper et al1984) The development of aboveground shoot meristems ofoilseeds versus belowground shoot nodes of cereals is afundamental difference in freeze avoidance (Thomas 2003)Oilseeds are exposed to sudden downturns in air temperaturesabove the soil surface during late falls and winters whereascereals are more protected by the soil layer above the cerealshoot meristem that buffers against rapid and severesubfreezing spikes

The size of winter canola plants entering the winter monthscorrelates with winter survival Small seedlings with 2ndash3 trueleaves survive iPNW winters very poorly This limits wintercanola production in the non-irrigated annual cropping zoneof the iPNW as very dry soils following harvest of theprevious yearrsquos crop generally persist into October by thetime sufficient moisture has accumulated to establish a standthe seedlings are typically too small to survive the first hardfrostsWhen planted into fallow land early plantedwinter canolatakes advantage of added growing degree-days to producemore shoot and root biomass before winter dieback Plantingfive winter rapeseed cultivars in the annual cropping zone(600mm) from 2 July to 13 September indicated that laterplanting dates resulted in less winter survival and seed yield(Porter et al 1981) presumably because late season plantingshad less energy and nutrient reserves In contrast early plantingsof winter canola in the wheatndashfallow zone take advantage ofsurface soil moisture but may result in poor winter survivalWinter cultivars remain vegetative without stem boltinghowever vegetative biomass of early planted canola extractsmost of the available soil moisture to 150 cm depth producingweakened drought-stressed plants with higher shoot meristemsthat were more susceptible to winter kill than later seededplants (Reese 2015)

Several fields of winter canola were monitored over 3 yearsacross the iPNW illustrating temperature profiles associatedwith partial and complete canola winter kill (Fig 5) In thewinter of 2013ndash2014 minimum temperatures at the soilsurface fell to ndash208C in early December and again in Februaryresulting in widespread complete winter kill across the regionIn contrast minimum surface temperatures only reached ndash15to ndash178C in January of 2011ndash2012 and 2012ndash2013 followinggradual temperature declines which resulted in partial standlosses of ndash28 to ndash49 but still yielding 1700ndash4300 kg handash1

even at sites with reduced stands Winter canola grown in semi-arid environments has the ability to compensate for standlosses with increased stem branching and pod retention(Angadi et al 2003) A late spring frost in late AprilndashMay

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 259

during flowering (data not shown) severely reduced the pod setresulting in yields lt1000 kg handash1 despite good stand survival insome locations This freeze sensitivity of canola coming out of

winter dormancy has been noted in the USA Great Plains(Holman et al 2011) In a location near DavenportWashington spring frost was not a factor and winter canoladirect seeded into winter wheat stubble averaged 4100 kg handash1

(Schillinger 2013)Moderation of extreme subfreezing conditions by soil

at depths 10ndash20 cm were consistently demonstrated (Fig 5)in comparison to surface temperatures illustrating themorphological advantage of wheatrsquos ability to developsubsurface shoot meristems that are insulated by soil (Klepperet al 1984) in comparison to above surface canola shootmeristems Canola nutritional status potentially contributes tosupercooling by increasing cell solutes such as high K and Clnutrition (Evans et al 2015) Ensuring a sufficient P status ofvegetative canola plants entering into the winter season with theaddition of starter phosphorus at planting has been shown toimprove winter survival (Wilkins et al 2002)

Nitrogen management The N placement and timing forwinter canola require additional adjustments from traditional Nfertilisation methods used in winter wheat production due tointerspecies differences in root architecture Chemical fallow-direct seeded winter wheat is typically fertilised in deep bandsbelow the seed row at planting (Veseth et al 1986) Canolaseedlings produce a single taproot main axis with lateral rootsand root hairs emanating from an ammonia sensitive tap root(Madsen et al 2014) In contrast monocotyledonous cerealcrops have multiple seminal axes and shoot tillers whichinitiate from the seed the belowground crown and stem nodesthat produce shoot tillers and affiliated root seminal axes(Klepper et al 1984) As a result of these basic rootarchitectural differences canola seedlings are more sensitivethan cereals to chemical toxicities such as expanded zones ofhigh ammonia around fertiliser bands due to oilseed relianceon the development of a single tap root whereas cereals havenumerous seminal axes to explore deep soil layers This basicmorphological difference has implications for differentialfertiliser band sensitivity when a canola taproot radicleencounters a high ammonia band meristems become necroticwith subsequent seedling injury or death (Madsen et al 2014)While a seminal root axis of cereal seedlings can suffer thesame fate other seminal axes of the same seedling will growto the side of the band and successfully develop The ability ofwheat roots to morphologically overcome ammonia toxicity ofdeep banded ammonium fertilisers has allowed the developmentand commercial use of direct seed planting equipment with deepbanding capabilities (Veseth et al 1986) However canolarsquostaproot sensitivity to deep placed ammonia bands will requirealternate N placement and timing strategies Fertiliser placementstudies on canola have demonstrated the need to place N as a sideband (Grant et al 2011 Norton 2016)

High N status of the vegetative winter oilseed plants hasreduced survival during freezing conditions (Rathke et al2006) There are biochemical and morphological responses tohigh N availability that may contribute to the decrease in winterhardiness Canola leaves subjected to low temperature stressincrease levels of cryoprotectant chemicals (Janskaacute et al 2010)such as soluble sugars that facilitate cytoplasmic freezingpoint depression (Gusta et al 2004) Identification of culturalpractices and variety selections for plant survival to rapid

10

Subsurface soil Air above soil surface

0

ndash10

ndash20

10

0

ndash10

Dai

ly m

inim

um te

mpe

ratu

re (

degdegC)

ndash20

102013ndash2014

2012ndash2013

2011ndash2012

0

ndash10

ndash20

ndash30Nov Dec Jan

MonthFeb Mar

Fig 5 Temperature profiles were continuously recorded over three wintersat Davenport WA from 2012 to 2014 in the transitional cropndashfallow zonewhere winter canola is being grown Air and soil temperature probes ineach year were positioned directly above the soil surface or below the soilsurface at a depth of 10ndash15 cm

260 Crop amp Pasture Science W L Pan et al

freeze eventsmay be important to winter canola production in theiPNW as demonstrated in December 2014 when a rapidfreeze resulted in widespread loss of winter canola and winterwheat (J Schibel pers comm)

Low N status promotes increased sugar concentrationsand increased freeze resistance in plants (Lemoine et al 2013Wisniewski et al 2014) As a result this potentially changesthe N timing strategy for managing canola relative to traditionalwheat N management in the iPNW In zones less than 600mmannual precipitation where nitrate leaching below 180 cm soildepth is typically not excessive winter wheat N applicationoccurs pre-plant during summer fallow or at planting in annualcrop rotations (Veseth et al 1986 Halvorson et al 1999) Themain reason is to ensure adequate time for fertiliser N to nitrifyand move into the lower layers of the root profile ensuringadequate N availability as the surface soil dries and plantroots become increasingly reliant on subsoil N (Pan et al2001) If low N canola has higher winter survivability it mayprovide another reason to be conservative in N fertiliserapplications at planting and allow the canola to utilise residualN during early establishment An inverse relationship between Navailability and winter survival could be due to a complex set ofbiochemical shoot morphological ie raised shoot meristemsabove the ground and growth-induced water stress (Reese2015)Winter canola exhibits deep rooting depths to 180 cm andsubsoil N and water access and recovery is critically important(Hocking et al 2002 Reese 2015) Furthermore iPNW climatechange projections of hotter drier summer months (Abatzoglouet al 2015) portend a need for enhancing deep strong-rootedwinter crops such as canola for adapting to foreseen climatechange (Hatfield et al 2001 Blum 2009 Lynch 2015)

These climate change forecast models predict 5ndash15increases in iPNW regional annual precipitation but withincreasing proportions occurring during the winter andspring months with drier hotter summers This trend willnecessitate improvements in water and N infiltration and subsoilstorage during winter months for later access during active cropdevelopment Canola also has a reputation as a strong taprootedcrop capable of creating macro biopore channels for facilitatingsaturated water flow and root pathways for subsequent crops Yetcanola roots cannot always penetrate soil horizons with highphysical and chemical impedance (Cresswell and Kirkegaard1995 Watt et al 2006) Tillage pans and genetic soil horizonsin the iPNW have been observed to impede canola roots causingcharacteristic lsquoJrsquo hooking of the taproot forcing it to turn 90degrees along the plan of the soil pan until it encounters a crackwhere it can continue vertical development (Lisson et al 2007)This may be a plausible explanation for new canola growertestimonials claiming rotational benefits are not seen untila second or third rotation

Irrigated crop zone

Rotational fit The irrigated temperate desert of centralWashington and Oregon supports perennial tree and vine fruitproduction as well as 500 000 ha of many high value agronomiccrops such as potato and sweet corn where small grain cerealsare used as a rotational crop and winter wheat is only ~8 ofthe area (Table 1 Fig 1) As many high value crops for example

potato sweet corn onion beans are grown in this zone a muchlower adoption is projected for this zone with canola mostlyrestricted as a substitution for wheat in the irrigated rotationsof central Washington and Oregon

In addition with opportunities to follow early harvested freshvegetable crops dual purpose use of canola has potential todiversify and intensify irrigated rotations similar to drylandapplications (Neely 2010 Walsh 2012 Lilley et al 2015) Inthis zone of extended growing degree-days double croppingunder irrigation where biennial canola could bridge two short-season summer crops to yield three harvests over two growingseasons such asYear 1 fresh peascanola forage ndashYear 2 canolagrain (Kincaid et al 2011) Current efforts are focussed onproduction of silage from first-season canola vegetation incentral Washington Comparable canola grain yields of2300 kg handash1 were harvested with and without forage cuttingand removal (Desta et al 2013) Yield gaps between predictedand observed yields may relate to J-hooking that has beenobserved under irrigation similar to dryland root observationsdescribed above

Plant establishment As water is not a limitation underirrigation germination and seedling establishment is not asmuch of an issue in this zone For example winter rapeseedand mustard were rapidly established in late August and earlySeptember in the south andnorthColumbiabasinunder irrigationand substantial biomass and N accumulation occurs beforethe first hard frost and under these conditions deep soil N useshould still be accounted for in oilseed rotational N fertiliserrecommendations (Weinert et al 2002) Even under irrigation Nfertiliser responses in winter canola can be minimal due to buildup of residual soil N in highly fertilised rotations (Davenport et al2010) Even with ample water and N winter kill is still a problemin this zone as demonstrated in an irrigated winter wheat springbarley winter canola rotation where green-bridged Rhizoctoniasolani on spring barley residues was suspected to infect wintercanola roots perhaps contributing to winter kill in 4 of 5 years(Paulitz et al 2010 Schillinger et al 2010b) Rhizoctonia solanianastomosis group 2ndash1 has recently been identified to infectwheat and rape roots (Sturrock et al 2015)

Summary and future projections

Canola area has historically constituted less than 1 of theiPNW Advancements in the development of both winter andspring cultivars have afforded flexible options in weed controlmanagement Competitive hybrid cultivars are nowcommercially available with and without herbicide toleranceor resistance Current efforts are to identify and integratecultivars that can be successfully established survive winterand use subsoil water and N efficiently in each of the zonesEstablishment of a local oilseed processing industry increasingglobal and regional canola markets for food fuel and feedagronomic benefits in increasing rotational diversity andcontinued vigorous research and extension efforts havestimulated a recent increase in canola integration into existingmonoculture wheat production in the iPNW Modest canolarotational integration projected for each zone would achieveproduction goals to match current and future regionaloilseed processing capacity with 300 000 canola ha per year

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 261

(Table 1) An upper agronomic limit of roughly 1 1wheat canola has been reached in the semi-arid wheat-producing region of western Canada Similar crop productionratios in the iPNW would approach 700 000 ha Winter canolaintegration into the wheatndashfallow annual cropndashtransition andirrigated cropping zones and spring canola integration intoannual cropping and transition zones will improve weedcontrol and wheat yields particularly with herbicide-resistantcultivars The most critical challenges in the adaptation ofcanola into iPNW wheat-cropping systems include improvedconsistency of winter canola establishment and winter survivalin the low and intermediate precipitation zones Seeding depthand timing are critical determinants of winter and spring canolayield potential Relevant genetic research is currently focussedon increasing seed size and hypocotyl lengths for improvedseedling emergence and on the identification of freeze-tolerantcultivars Integration of spring canola into higher precipitationannual cropping systems requires research on innovative earlyplanting strategies and new earlier maturing cultivars to avoidhigh temperature and moisture stress Taproot architecture ofcanola dictates changes in standard N placement andtiming strategies that have been practiced for iPNW wheatproduction but the deep rooting habit of canola will contributeto efficient water and N recovery of the cropping systems Farmenterprise economics that account for rotational benefits andproduction risk will help growers account for multi-yearinvestments in canolandashwheat rotations to assess the benefits ofintegrated canolandashwheat systems

References

Abatzoglou J Rupp D Mote P (2015) Asymmetrical warming projectionsfor the inland Pacific Northwest In lsquoRegional approaches to climatechange for Pacific Northwest agriculture Climate science Northwestfarmers can usersquo (Eds K Borrelli D Daily Laursen S Eigenbrode BMahler R Pepper) pp 104ndash105 Available at wwwreachchpnaorg

Alberta Agriculture and Rural Development (2004) Alberta fertilizer guideIn lsquoAgric-facts practical information for Albertarsquos agriculture industryrsquoAgdex 541ndash1 (Ministry of Alberta Agriculture Food and RuralDevelopment Edmonton Alberta Canada)

Angadi SV Cutforth HW McConkey BG Gan Y (2003) Yield adjustmentby canola grown at different plant populations under semiarid conditionsCrop Science 43 1358ndash1366 doi102135cropsci20031358

Angus JF Kirkegaard JA Hunt JR Ryan MH Ohlander L Peoples MB(2015) Break crops and rotations for wheat Crop amp Pasture Science 66523ndash552 doi101071CP14252

Azooz RH Arshad MA (1998) Effect of residue and tillage managementon barley and canola growth and water use efficiency Canadian Journalof Soil Science 78 649ndash656 doi104141S97-098

Ball DA Young FL Ogg AO Jr (1999) Selective control of jointedgoatgrass (Aegilops clylindrica) with imazamox in herbicide-resistantwheat Weed Technology 13 77ndash82

Bettis B Auld D (Eds) (1980) Development of oilseeds as alternative cropsfor the Pacific Northwest Pacific Northwest Regional CommissionYearly Reports June 1979ndash31 July 1980 June 1980ndashJune 1981Pacific Northwest Regional Commission Moscow Idaho USA

Bettis BL Peterson CL Auld DL Driscoll DJ Peterson (1982) Fuelcharacteristics of vegetable oil from oilseed crops in the PacificNorthwest Agronomy Journal 74 335ndash339

Blum A (2009) Effective use of water (EUW) and not water-use efficiency(WUE) is the target of crop yield improvement under drought stressField Crops Research 112 119ndash123 doi101016jfcr200903009

Brennan RF Bolland MDA (2009) Comparing the nitrogen and phosphorusrequirements of canola and wheat for grain yield and quality Crop ampPasture Science 60 566ndash577 doi101071CP08401

Brill RD Jenkins ML Gardner MJ Lilley JM Orchard BA (2016)Optimising canola establishment and yield in south-eastern Australiawith hybrids and large seed Crop amp Pasture Science 67 409ndash418

Brown J Davis J (2015) Brassica breeding and research University of IdahoAvailable at wwwcalsuidahoedubrassica (accessed 15 December2015)

Brown J Davis JB Erickson DA Brown AP Seip L (1995) 1995 PacificNorthwest canola variety trial (PNWCVT) results and conclusions InlsquoPacificNorthwest canola conference1995proceedingsrsquo (EdsGJohnsonM Lewis) pp 29ndash36 (Department of Entomology Montana StateUniversity Bozeman MT)

BushongJ (2015)Okanola varieties andhybrids open-pollinatedvarietiesvshybrids Available at httpcanolaokstateeducropproductionvarieties(accessed 15 December 2015)

Conley SP Bordovsky D Rife C WieboldW (2004) Winter canola survivaland yield response to nitrogen and fall phosphorus Crop Managementdoi101094CM-2004-0901-01-RS

Connolly JR McCracken VA Painter KM (2016) Enterprise budget wheatand canola rotations in Eastern Washington intermediate rainfall regions12rdquo to 16rdquo Washington State University Extension PublicationWashington State University TB10 USA

Cook RJ Schillinger WF Christensen NW (2002) Rhizoctonia rootrot andtake-all of wheat in diverse direct-seed spring cropping systemsCanadian Journal of Plant Pathology 24 349ndash358 doi10108007060660209507020

Cresswell HP Kirkegaard JA (1995) Subsoil amelioration by plant-roots ndashthe process and the evidence Australian Journal of Soil Research 33221ndash239 doi101071SR9950221

Cutforth HW Angadi SV McConkey BG (2006) Stubble managementand microclimate yield and water use efficiency of canola grown inthe semiarid Canadian prairie Canadian Journal of Plant Science 8699ndash107 doi104141P05-073

Davenport J Stevens B Hang A Peters T (2010) Irrigated canola researchIn lsquoWashingtonOilseedCroppingSystemsProject partof theWashingtonState Biofuels Initiative 2010rsquo Annual Progress Report (EdsKESowersWL Pan) Available at httpcsswsuedubiofuelsfiles2012092010_Annual_Progress_Reportpdf (accessed 27 December 2015)

De Jong R Shields JA (1988) Available water-holding capacity maps ofAlberta Saskatchewan and Manitoba Canadian Journal of Soil Science68 157ndash163 doi104141cjss88-015

Desta KG Collins H Pan B (2013) Double-cropping dual purpose irrigatedbiennial canolawithgreenpea In lsquoWashingtonOilseedCroppingSystemsProject part of the Washington State Biofuels Initiative 2013rsquo AnnualProgress Report (Eds KE Sowers WL Pan) Available at httpcsswsuedubiofuelsfiles2012092013-Biofuel-Cropping-Systems-Research-Progress-Reportpdf (accessed 27 December 2015)

Divine TE Alzheimer DP Currie JW McGinnis KA Wiggins DJ (1977)Research on the potential impact of advanced oilseeds processingtechnology on Pacific Northwest Agriculture Batelle Pacific NorthwestLaboratories 231110270610690646 Richland Washington USA

Douglas CL Wysocki DJ Zuzel JF Rickman RW Klepper BL (1990)Agronomic zones for the dryland Pacific Northwest Pacific NorthwestCooperative Extension Bulletin PNW 954

Esser A Hulbert S (2013) Eastern WA low to intermediate rainfall InlsquoWashington Oilseed Cropping Systems Project part of theWashington State Biofuels Initiative 2013 Annual Progress Reportrsquo(Eds KE Sowers WL Pan) pp 31ndash36 Available at httpcsswsuedu

262 Crop amp Pasture Science W L Pan et al

canola seed ranges from 2 to 6mg seedndash1 (F L Young perscomm) A 3-fold variation in canola seed size makes it moreimperative to get accurate oilseed weights when targetingspecific plant population goals Seed size is affected bycultivar and the seed production environment as well ascommercial seed sizing processes (Lamb and Johnson 2004)Smaller seed reserves of energy and nutrients of individualcanola seeds restrict deep seed placement Winter wheatcultivars grown in the fallow zone are bred to emerge from verydeep seed placement (Mohan et al 2013) In contrast canola seedgenerally emerges best when placed within 2ndash3 cm of the soilsurface when moisture conditions are adequate but can emergefrom deeper placement (3ndash6 cm) when required to reachmoisture Hypocotyl length is genetically modulated indicatingpotential for future breeding opportunities (Zhao et al 2013)Larger seeds can generally emerge from greater depths due tolonger and more robust hypocotyls In addition larger seededBrassica cultivars produce greater early season biomass whichincreases crop competition with weeds (Harker et al 2015Brill et al 2016)

Winter canola establishment requires excellent soil moisturenear the soil surface and cool (298C) ambient air temperaturesfor 5ndash7days after planting (Young et al 2014)Deep furrowdrillsthat are used in the wheatndashfallow zone for placing the seed intosoil moisture are also being used successfully to plant wintercanola as the seedlings need to emerge only to the bottom of thefurrow During August the optimal time to plant winter canola(Young et al 2014) soil moisture is usually 10ndash15 cm below thesoil surface and too deep for canola seedlings to emerge To helpalleviate this problem shovels 25ndash38 cm wide have been placedin front of the openers to reach soilmoisture andmove the hot drysoil from the furrow thus reducing the distance the emergingseedling has to travel through the soil (Young et al 2008 2014)The use of shovels did not increase winter canola yield andwinter survival but did increase plant density 22 comparedwith when shovels were not used In addition there is a moreuniform plant distribution from the use of shovels whichsuppressed weed growth and reduced weed competition(Young et al 2014) Generally a 45-kg handash1 seeding rate wasoptimal for sufficient stand establishment and yield Whenwinter canola seeding was delayed until September yield wasdecreased almost 40 compared with an August plantingWinter survival can range from 56 to 83 with a subsequentspring plant population of only 20ndash40 plantsmndash2 needed foroptimum yield

Spring canola despite the lower yield potential can begrown following failed winter canola survival and glyphosate-resistant spring canola cultivars are beneficial for controllingsummer annual broadleaf weeds in this zone such as Russianthistle (Salsola tragus) which emerges with similar timing asspring canola Spring canola seed broadcast on the soil surfaceyields between 31 and 67 of spring canola that was placed inthe soil with drills equipped with double disk chisel hoe orinverted T-slot openers (Young et al 2012) Broadcast yields ofspring canola were low because generally lt5 of the seedestablished plants When left on the soil surface seedlingswere unprotected when emerging from the seed coat and werekilled by frost Rolling broadcast seed with a heavy cast-ironroller generally improved yield ~35 compared with broadcast

alone although improved yield ranged from 0 to gt100Depending on location and precipitation optimum yieldsranged from 615 kg handash1 to 1575 kg handash1 (Young et al 2012)Precipitation during flowering and seed-fill in May and Junecorrelated with increased canola yield presumably by reducingmoisture stress during reproductive growth as observed byGan et al (2004)

Shoot meristematic origins of dicotyledonous oilseedsdiffer from monocotyledonous cereal grain crops Leaves andshoot branch initiation of oilseeds occurs at or near the soilsurface (Thomas 2003) In contrast shoot tiller and rootmeristems of wheat seedlings emanate at the belowgroundcrown and stem nodes directly above the crown (Klepper et al1984) The development of aboveground shoot meristems ofoilseeds versus belowground shoot nodes of cereals is afundamental difference in freeze avoidance (Thomas 2003)Oilseeds are exposed to sudden downturns in air temperaturesabove the soil surface during late falls and winters whereascereals are more protected by the soil layer above the cerealshoot meristem that buffers against rapid and severesubfreezing spikes

The size of winter canola plants entering the winter monthscorrelates with winter survival Small seedlings with 2ndash3 trueleaves survive iPNW winters very poorly This limits wintercanola production in the non-irrigated annual cropping zoneof the iPNW as very dry soils following harvest of theprevious yearrsquos crop generally persist into October by thetime sufficient moisture has accumulated to establish a standthe seedlings are typically too small to survive the first hardfrostsWhen planted into fallow land early plantedwinter canolatakes advantage of added growing degree-days to producemore shoot and root biomass before winter dieback Plantingfive winter rapeseed cultivars in the annual cropping zone(600mm) from 2 July to 13 September indicated that laterplanting dates resulted in less winter survival and seed yield(Porter et al 1981) presumably because late season plantingshad less energy and nutrient reserves In contrast early plantingsof winter canola in the wheatndashfallow zone take advantage ofsurface soil moisture but may result in poor winter survivalWinter cultivars remain vegetative without stem boltinghowever vegetative biomass of early planted canola extractsmost of the available soil moisture to 150 cm depth producingweakened drought-stressed plants with higher shoot meristemsthat were more susceptible to winter kill than later seededplants (Reese 2015)

Several fields of winter canola were monitored over 3 yearsacross the iPNW illustrating temperature profiles associatedwith partial and complete canola winter kill (Fig 5) In thewinter of 2013ndash2014 minimum temperatures at the soilsurface fell to ndash208C in early December and again in Februaryresulting in widespread complete winter kill across the regionIn contrast minimum surface temperatures only reached ndash15to ndash178C in January of 2011ndash2012 and 2012ndash2013 followinggradual temperature declines which resulted in partial standlosses of ndash28 to ndash49 but still yielding 1700ndash4300 kg handash1

even at sites with reduced stands Winter canola grown in semi-arid environments has the ability to compensate for standlosses with increased stem branching and pod retention(Angadi et al 2003) A late spring frost in late AprilndashMay

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 259

during flowering (data not shown) severely reduced the pod setresulting in yields lt1000 kg handash1 despite good stand survival insome locations This freeze sensitivity of canola coming out of

winter dormancy has been noted in the USA Great Plains(Holman et al 2011) In a location near DavenportWashington spring frost was not a factor and winter canoladirect seeded into winter wheat stubble averaged 4100 kg handash1

(Schillinger 2013)Moderation of extreme subfreezing conditions by soil

at depths 10ndash20 cm were consistently demonstrated (Fig 5)in comparison to surface temperatures illustrating themorphological advantage of wheatrsquos ability to developsubsurface shoot meristems that are insulated by soil (Klepperet al 1984) in comparison to above surface canola shootmeristems Canola nutritional status potentially contributes tosupercooling by increasing cell solutes such as high K and Clnutrition (Evans et al 2015) Ensuring a sufficient P status ofvegetative canola plants entering into the winter season with theaddition of starter phosphorus at planting has been shown toimprove winter survival (Wilkins et al 2002)

Nitrogen management The N placement and timing forwinter canola require additional adjustments from traditional Nfertilisation methods used in winter wheat production due tointerspecies differences in root architecture Chemical fallow-direct seeded winter wheat is typically fertilised in deep bandsbelow the seed row at planting (Veseth et al 1986) Canolaseedlings produce a single taproot main axis with lateral rootsand root hairs emanating from an ammonia sensitive tap root(Madsen et al 2014) In contrast monocotyledonous cerealcrops have multiple seminal axes and shoot tillers whichinitiate from the seed the belowground crown and stem nodesthat produce shoot tillers and affiliated root seminal axes(Klepper et al 1984) As a result of these basic rootarchitectural differences canola seedlings are more sensitivethan cereals to chemical toxicities such as expanded zones ofhigh ammonia around fertiliser bands due to oilseed relianceon the development of a single tap root whereas cereals havenumerous seminal axes to explore deep soil layers This basicmorphological difference has implications for differentialfertiliser band sensitivity when a canola taproot radicleencounters a high ammonia band meristems become necroticwith subsequent seedling injury or death (Madsen et al 2014)While a seminal root axis of cereal seedlings can suffer thesame fate other seminal axes of the same seedling will growto the side of the band and successfully develop The ability ofwheat roots to morphologically overcome ammonia toxicity ofdeep banded ammonium fertilisers has allowed the developmentand commercial use of direct seed planting equipment with deepbanding capabilities (Veseth et al 1986) However canolarsquostaproot sensitivity to deep placed ammonia bands will requirealternate N placement and timing strategies Fertiliser placementstudies on canola have demonstrated the need to place N as a sideband (Grant et al 2011 Norton 2016)

High N status of the vegetative winter oilseed plants hasreduced survival during freezing conditions (Rathke et al2006) There are biochemical and morphological responses tohigh N availability that may contribute to the decrease in winterhardiness Canola leaves subjected to low temperature stressincrease levels of cryoprotectant chemicals (Janskaacute et al 2010)such as soluble sugars that facilitate cytoplasmic freezingpoint depression (Gusta et al 2004) Identification of culturalpractices and variety selections for plant survival to rapid

10

Subsurface soil Air above soil surface

0

ndash10

ndash20

10

0

ndash10

Dai

ly m

inim

um te

mpe

ratu

re (

degdegC)

ndash20

102013ndash2014

2012ndash2013

2011ndash2012

0

ndash10

ndash20

ndash30Nov Dec Jan

MonthFeb Mar

Fig 5 Temperature profiles were continuously recorded over three wintersat Davenport WA from 2012 to 2014 in the transitional cropndashfallow zonewhere winter canola is being grown Air and soil temperature probes ineach year were positioned directly above the soil surface or below the soilsurface at a depth of 10ndash15 cm

260 Crop amp Pasture Science W L Pan et al

freeze eventsmay be important to winter canola production in theiPNW as demonstrated in December 2014 when a rapidfreeze resulted in widespread loss of winter canola and winterwheat (J Schibel pers comm)

Low N status promotes increased sugar concentrationsand increased freeze resistance in plants (Lemoine et al 2013Wisniewski et al 2014) As a result this potentially changesthe N timing strategy for managing canola relative to traditionalwheat N management in the iPNW In zones less than 600mmannual precipitation where nitrate leaching below 180 cm soildepth is typically not excessive winter wheat N applicationoccurs pre-plant during summer fallow or at planting in annualcrop rotations (Veseth et al 1986 Halvorson et al 1999) Themain reason is to ensure adequate time for fertiliser N to nitrifyand move into the lower layers of the root profile ensuringadequate N availability as the surface soil dries and plantroots become increasingly reliant on subsoil N (Pan et al2001) If low N canola has higher winter survivability it mayprovide another reason to be conservative in N fertiliserapplications at planting and allow the canola to utilise residualN during early establishment An inverse relationship between Navailability and winter survival could be due to a complex set ofbiochemical shoot morphological ie raised shoot meristemsabove the ground and growth-induced water stress (Reese2015)Winter canola exhibits deep rooting depths to 180 cm andsubsoil N and water access and recovery is critically important(Hocking et al 2002 Reese 2015) Furthermore iPNW climatechange projections of hotter drier summer months (Abatzoglouet al 2015) portend a need for enhancing deep strong-rootedwinter crops such as canola for adapting to foreseen climatechange (Hatfield et al 2001 Blum 2009 Lynch 2015)

These climate change forecast models predict 5ndash15increases in iPNW regional annual precipitation but withincreasing proportions occurring during the winter andspring months with drier hotter summers This trend willnecessitate improvements in water and N infiltration and subsoilstorage during winter months for later access during active cropdevelopment Canola also has a reputation as a strong taprootedcrop capable of creating macro biopore channels for facilitatingsaturated water flow and root pathways for subsequent crops Yetcanola roots cannot always penetrate soil horizons with highphysical and chemical impedance (Cresswell and Kirkegaard1995 Watt et al 2006) Tillage pans and genetic soil horizonsin the iPNW have been observed to impede canola roots causingcharacteristic lsquoJrsquo hooking of the taproot forcing it to turn 90degrees along the plan of the soil pan until it encounters a crackwhere it can continue vertical development (Lisson et al 2007)This may be a plausible explanation for new canola growertestimonials claiming rotational benefits are not seen untila second or third rotation

Irrigated crop zone

Rotational fit The irrigated temperate desert of centralWashington and Oregon supports perennial tree and vine fruitproduction as well as 500 000 ha of many high value agronomiccrops such as potato and sweet corn where small grain cerealsare used as a rotational crop and winter wheat is only ~8 ofthe area (Table 1 Fig 1) As many high value crops for example

potato sweet corn onion beans are grown in this zone a muchlower adoption is projected for this zone with canola mostlyrestricted as a substitution for wheat in the irrigated rotationsof central Washington and Oregon

In addition with opportunities to follow early harvested freshvegetable crops dual purpose use of canola has potential todiversify and intensify irrigated rotations similar to drylandapplications (Neely 2010 Walsh 2012 Lilley et al 2015) Inthis zone of extended growing degree-days double croppingunder irrigation where biennial canola could bridge two short-season summer crops to yield three harvests over two growingseasons such asYear 1 fresh peascanola forage ndashYear 2 canolagrain (Kincaid et al 2011) Current efforts are focussed onproduction of silage from first-season canola vegetation incentral Washington Comparable canola grain yields of2300 kg handash1 were harvested with and without forage cuttingand removal (Desta et al 2013) Yield gaps between predictedand observed yields may relate to J-hooking that has beenobserved under irrigation similar to dryland root observationsdescribed above

Plant establishment As water is not a limitation underirrigation germination and seedling establishment is not asmuch of an issue in this zone For example winter rapeseedand mustard were rapidly established in late August and earlySeptember in the south andnorthColumbiabasinunder irrigationand substantial biomass and N accumulation occurs beforethe first hard frost and under these conditions deep soil N useshould still be accounted for in oilseed rotational N fertiliserrecommendations (Weinert et al 2002) Even under irrigation Nfertiliser responses in winter canola can be minimal due to buildup of residual soil N in highly fertilised rotations (Davenport et al2010) Even with ample water and N winter kill is still a problemin this zone as demonstrated in an irrigated winter wheat springbarley winter canola rotation where green-bridged Rhizoctoniasolani on spring barley residues was suspected to infect wintercanola roots perhaps contributing to winter kill in 4 of 5 years(Paulitz et al 2010 Schillinger et al 2010b) Rhizoctonia solanianastomosis group 2ndash1 has recently been identified to infectwheat and rape roots (Sturrock et al 2015)

Summary and future projections

Canola area has historically constituted less than 1 of theiPNW Advancements in the development of both winter andspring cultivars have afforded flexible options in weed controlmanagement Competitive hybrid cultivars are nowcommercially available with and without herbicide toleranceor resistance Current efforts are to identify and integratecultivars that can be successfully established survive winterand use subsoil water and N efficiently in each of the zonesEstablishment of a local oilseed processing industry increasingglobal and regional canola markets for food fuel and feedagronomic benefits in increasing rotational diversity andcontinued vigorous research and extension efforts havestimulated a recent increase in canola integration into existingmonoculture wheat production in the iPNW Modest canolarotational integration projected for each zone would achieveproduction goals to match current and future regionaloilseed processing capacity with 300 000 canola ha per year

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 261

(Table 1) An upper agronomic limit of roughly 1 1wheat canola has been reached in the semi-arid wheat-producing region of western Canada Similar crop productionratios in the iPNW would approach 700 000 ha Winter canolaintegration into the wheatndashfallow annual cropndashtransition andirrigated cropping zones and spring canola integration intoannual cropping and transition zones will improve weedcontrol and wheat yields particularly with herbicide-resistantcultivars The most critical challenges in the adaptation ofcanola into iPNW wheat-cropping systems include improvedconsistency of winter canola establishment and winter survivalin the low and intermediate precipitation zones Seeding depthand timing are critical determinants of winter and spring canolayield potential Relevant genetic research is currently focussedon increasing seed size and hypocotyl lengths for improvedseedling emergence and on the identification of freeze-tolerantcultivars Integration of spring canola into higher precipitationannual cropping systems requires research on innovative earlyplanting strategies and new earlier maturing cultivars to avoidhigh temperature and moisture stress Taproot architecture ofcanola dictates changes in standard N placement andtiming strategies that have been practiced for iPNW wheatproduction but the deep rooting habit of canola will contributeto efficient water and N recovery of the cropping systems Farmenterprise economics that account for rotational benefits andproduction risk will help growers account for multi-yearinvestments in canolandashwheat rotations to assess the benefits ofintegrated canolandashwheat systems

References

Abatzoglou J Rupp D Mote P (2015) Asymmetrical warming projectionsfor the inland Pacific Northwest In lsquoRegional approaches to climatechange for Pacific Northwest agriculture Climate science Northwestfarmers can usersquo (Eds K Borrelli D Daily Laursen S Eigenbrode BMahler R Pepper) pp 104ndash105 Available at wwwreachchpnaorg

Alberta Agriculture and Rural Development (2004) Alberta fertilizer guideIn lsquoAgric-facts practical information for Albertarsquos agriculture industryrsquoAgdex 541ndash1 (Ministry of Alberta Agriculture Food and RuralDevelopment Edmonton Alberta Canada)

Angadi SV Cutforth HW McConkey BG Gan Y (2003) Yield adjustmentby canola grown at different plant populations under semiarid conditionsCrop Science 43 1358ndash1366 doi102135cropsci20031358

Angus JF Kirkegaard JA Hunt JR Ryan MH Ohlander L Peoples MB(2015) Break crops and rotations for wheat Crop amp Pasture Science 66523ndash552 doi101071CP14252

Azooz RH Arshad MA (1998) Effect of residue and tillage managementon barley and canola growth and water use efficiency Canadian Journalof Soil Science 78 649ndash656 doi104141S97-098

Ball DA Young FL Ogg AO Jr (1999) Selective control of jointedgoatgrass (Aegilops clylindrica) with imazamox in herbicide-resistantwheat Weed Technology 13 77ndash82

Bettis B Auld D (Eds) (1980) Development of oilseeds as alternative cropsfor the Pacific Northwest Pacific Northwest Regional CommissionYearly Reports June 1979ndash31 July 1980 June 1980ndashJune 1981Pacific Northwest Regional Commission Moscow Idaho USA

Bettis BL Peterson CL Auld DL Driscoll DJ Peterson (1982) Fuelcharacteristics of vegetable oil from oilseed crops in the PacificNorthwest Agronomy Journal 74 335ndash339

Blum A (2009) Effective use of water (EUW) and not water-use efficiency(WUE) is the target of crop yield improvement under drought stressField Crops Research 112 119ndash123 doi101016jfcr200903009

Brennan RF Bolland MDA (2009) Comparing the nitrogen and phosphorusrequirements of canola and wheat for grain yield and quality Crop ampPasture Science 60 566ndash577 doi101071CP08401

Brill RD Jenkins ML Gardner MJ Lilley JM Orchard BA (2016)Optimising canola establishment and yield in south-eastern Australiawith hybrids and large seed Crop amp Pasture Science 67 409ndash418

Brown J Davis J (2015) Brassica breeding and research University of IdahoAvailable at wwwcalsuidahoedubrassica (accessed 15 December2015)

Brown J Davis JB Erickson DA Brown AP Seip L (1995) 1995 PacificNorthwest canola variety trial (PNWCVT) results and conclusions InlsquoPacificNorthwest canola conference1995proceedingsrsquo (EdsGJohnsonM Lewis) pp 29ndash36 (Department of Entomology Montana StateUniversity Bozeman MT)

BushongJ (2015)Okanola varieties andhybrids open-pollinatedvarietiesvshybrids Available at httpcanolaokstateeducropproductionvarieties(accessed 15 December 2015)

Conley SP Bordovsky D Rife C WieboldW (2004) Winter canola survivaland yield response to nitrogen and fall phosphorus Crop Managementdoi101094CM-2004-0901-01-RS

Connolly JR McCracken VA Painter KM (2016) Enterprise budget wheatand canola rotations in Eastern Washington intermediate rainfall regions12rdquo to 16rdquo Washington State University Extension PublicationWashington State University TB10 USA

Cook RJ Schillinger WF Christensen NW (2002) Rhizoctonia rootrot andtake-all of wheat in diverse direct-seed spring cropping systemsCanadian Journal of Plant Pathology 24 349ndash358 doi10108007060660209507020

Cresswell HP Kirkegaard JA (1995) Subsoil amelioration by plant-roots ndashthe process and the evidence Australian Journal of Soil Research 33221ndash239 doi101071SR9950221

Cutforth HW Angadi SV McConkey BG (2006) Stubble managementand microclimate yield and water use efficiency of canola grown inthe semiarid Canadian prairie Canadian Journal of Plant Science 8699ndash107 doi104141P05-073

Davenport J Stevens B Hang A Peters T (2010) Irrigated canola researchIn lsquoWashingtonOilseedCroppingSystemsProject partof theWashingtonState Biofuels Initiative 2010rsquo Annual Progress Report (EdsKESowersWL Pan) Available at httpcsswsuedubiofuelsfiles2012092010_Annual_Progress_Reportpdf (accessed 27 December 2015)

De Jong R Shields JA (1988) Available water-holding capacity maps ofAlberta Saskatchewan and Manitoba Canadian Journal of Soil Science68 157ndash163 doi104141cjss88-015

Desta KG Collins H Pan B (2013) Double-cropping dual purpose irrigatedbiennial canolawithgreenpea In lsquoWashingtonOilseedCroppingSystemsProject part of the Washington State Biofuels Initiative 2013rsquo AnnualProgress Report (Eds KE Sowers WL Pan) Available at httpcsswsuedubiofuelsfiles2012092013-Biofuel-Cropping-Systems-Research-Progress-Reportpdf (accessed 27 December 2015)

Divine TE Alzheimer DP Currie JW McGinnis KA Wiggins DJ (1977)Research on the potential impact of advanced oilseeds processingtechnology on Pacific Northwest Agriculture Batelle Pacific NorthwestLaboratories 231110270610690646 Richland Washington USA

Douglas CL Wysocki DJ Zuzel JF Rickman RW Klepper BL (1990)Agronomic zones for the dryland Pacific Northwest Pacific NorthwestCooperative Extension Bulletin PNW 954

Esser A Hulbert S (2013) Eastern WA low to intermediate rainfall InlsquoWashington Oilseed Cropping Systems Project part of theWashington State Biofuels Initiative 2013 Annual Progress Reportrsquo(Eds KE Sowers WL Pan) pp 31ndash36 Available at httpcsswsuedu

262 Crop amp Pasture Science W L Pan et al

during flowering (data not shown) severely reduced the pod setresulting in yields lt1000 kg handash1 despite good stand survival insome locations This freeze sensitivity of canola coming out of

winter dormancy has been noted in the USA Great Plains(Holman et al 2011) In a location near DavenportWashington spring frost was not a factor and winter canoladirect seeded into winter wheat stubble averaged 4100 kg handash1

(Schillinger 2013)Moderation of extreme subfreezing conditions by soil

at depths 10ndash20 cm were consistently demonstrated (Fig 5)in comparison to surface temperatures illustrating themorphological advantage of wheatrsquos ability to developsubsurface shoot meristems that are insulated by soil (Klepperet al 1984) in comparison to above surface canola shootmeristems Canola nutritional status potentially contributes tosupercooling by increasing cell solutes such as high K and Clnutrition (Evans et al 2015) Ensuring a sufficient P status ofvegetative canola plants entering into the winter season with theaddition of starter phosphorus at planting has been shown toimprove winter survival (Wilkins et al 2002)

Nitrogen management The N placement and timing forwinter canola require additional adjustments from traditional Nfertilisation methods used in winter wheat production due tointerspecies differences in root architecture Chemical fallow-direct seeded winter wheat is typically fertilised in deep bandsbelow the seed row at planting (Veseth et al 1986) Canolaseedlings produce a single taproot main axis with lateral rootsand root hairs emanating from an ammonia sensitive tap root(Madsen et al 2014) In contrast monocotyledonous cerealcrops have multiple seminal axes and shoot tillers whichinitiate from the seed the belowground crown and stem nodesthat produce shoot tillers and affiliated root seminal axes(Klepper et al 1984) As a result of these basic rootarchitectural differences canola seedlings are more sensitivethan cereals to chemical toxicities such as expanded zones ofhigh ammonia around fertiliser bands due to oilseed relianceon the development of a single tap root whereas cereals havenumerous seminal axes to explore deep soil layers This basicmorphological difference has implications for differentialfertiliser band sensitivity when a canola taproot radicleencounters a high ammonia band meristems become necroticwith subsequent seedling injury or death (Madsen et al 2014)While a seminal root axis of cereal seedlings can suffer thesame fate other seminal axes of the same seedling will growto the side of the band and successfully develop The ability ofwheat roots to morphologically overcome ammonia toxicity ofdeep banded ammonium fertilisers has allowed the developmentand commercial use of direct seed planting equipment with deepbanding capabilities (Veseth et al 1986) However canolarsquostaproot sensitivity to deep placed ammonia bands will requirealternate N placement and timing strategies Fertiliser placementstudies on canola have demonstrated the need to place N as a sideband (Grant et al 2011 Norton 2016)

High N status of the vegetative winter oilseed plants hasreduced survival during freezing conditions (Rathke et al2006) There are biochemical and morphological responses tohigh N availability that may contribute to the decrease in winterhardiness Canola leaves subjected to low temperature stressincrease levels of cryoprotectant chemicals (Janskaacute et al 2010)such as soluble sugars that facilitate cytoplasmic freezingpoint depression (Gusta et al 2004) Identification of culturalpractices and variety selections for plant survival to rapid

10

Subsurface soil Air above soil surface

0

ndash10

ndash20

10

0

ndash10

Dai

ly m

inim

um te

mpe

ratu

re (

degdegC)

ndash20

102013ndash2014

2012ndash2013

2011ndash2012

0

ndash10

ndash20

ndash30Nov Dec Jan

MonthFeb Mar

Fig 5 Temperature profiles were continuously recorded over three wintersat Davenport WA from 2012 to 2014 in the transitional cropndashfallow zonewhere winter canola is being grown Air and soil temperature probes ineach year were positioned directly above the soil surface or below the soilsurface at a depth of 10ndash15 cm

260 Crop amp Pasture Science W L Pan et al

freeze eventsmay be important to winter canola production in theiPNW as demonstrated in December 2014 when a rapidfreeze resulted in widespread loss of winter canola and winterwheat (J Schibel pers comm)

Low N status promotes increased sugar concentrationsand increased freeze resistance in plants (Lemoine et al 2013Wisniewski et al 2014) As a result this potentially changesthe N timing strategy for managing canola relative to traditionalwheat N management in the iPNW In zones less than 600mmannual precipitation where nitrate leaching below 180 cm soildepth is typically not excessive winter wheat N applicationoccurs pre-plant during summer fallow or at planting in annualcrop rotations (Veseth et al 1986 Halvorson et al 1999) Themain reason is to ensure adequate time for fertiliser N to nitrifyand move into the lower layers of the root profile ensuringadequate N availability as the surface soil dries and plantroots become increasingly reliant on subsoil N (Pan et al2001) If low N canola has higher winter survivability it mayprovide another reason to be conservative in N fertiliserapplications at planting and allow the canola to utilise residualN during early establishment An inverse relationship between Navailability and winter survival could be due to a complex set ofbiochemical shoot morphological ie raised shoot meristemsabove the ground and growth-induced water stress (Reese2015)Winter canola exhibits deep rooting depths to 180 cm andsubsoil N and water access and recovery is critically important(Hocking et al 2002 Reese 2015) Furthermore iPNW climatechange projections of hotter drier summer months (Abatzoglouet al 2015) portend a need for enhancing deep strong-rootedwinter crops such as canola for adapting to foreseen climatechange (Hatfield et al 2001 Blum 2009 Lynch 2015)

These climate change forecast models predict 5ndash15increases in iPNW regional annual precipitation but withincreasing proportions occurring during the winter andspring months with drier hotter summers This trend willnecessitate improvements in water and N infiltration and subsoilstorage during winter months for later access during active cropdevelopment Canola also has a reputation as a strong taprootedcrop capable of creating macro biopore channels for facilitatingsaturated water flow and root pathways for subsequent crops Yetcanola roots cannot always penetrate soil horizons with highphysical and chemical impedance (Cresswell and Kirkegaard1995 Watt et al 2006) Tillage pans and genetic soil horizonsin the iPNW have been observed to impede canola roots causingcharacteristic lsquoJrsquo hooking of the taproot forcing it to turn 90degrees along the plan of the soil pan until it encounters a crackwhere it can continue vertical development (Lisson et al 2007)This may be a plausible explanation for new canola growertestimonials claiming rotational benefits are not seen untila second or third rotation

Irrigated crop zone

Rotational fit The irrigated temperate desert of centralWashington and Oregon supports perennial tree and vine fruitproduction as well as 500 000 ha of many high value agronomiccrops such as potato and sweet corn where small grain cerealsare used as a rotational crop and winter wheat is only ~8 ofthe area (Table 1 Fig 1) As many high value crops for example

potato sweet corn onion beans are grown in this zone a muchlower adoption is projected for this zone with canola mostlyrestricted as a substitution for wheat in the irrigated rotationsof central Washington and Oregon

In addition with opportunities to follow early harvested freshvegetable crops dual purpose use of canola has potential todiversify and intensify irrigated rotations similar to drylandapplications (Neely 2010 Walsh 2012 Lilley et al 2015) Inthis zone of extended growing degree-days double croppingunder irrigation where biennial canola could bridge two short-season summer crops to yield three harvests over two growingseasons such asYear 1 fresh peascanola forage ndashYear 2 canolagrain (Kincaid et al 2011) Current efforts are focussed onproduction of silage from first-season canola vegetation incentral Washington Comparable canola grain yields of2300 kg handash1 were harvested with and without forage cuttingand removal (Desta et al 2013) Yield gaps between predictedand observed yields may relate to J-hooking that has beenobserved under irrigation similar to dryland root observationsdescribed above

Plant establishment As water is not a limitation underirrigation germination and seedling establishment is not asmuch of an issue in this zone For example winter rapeseedand mustard were rapidly established in late August and earlySeptember in the south andnorthColumbiabasinunder irrigationand substantial biomass and N accumulation occurs beforethe first hard frost and under these conditions deep soil N useshould still be accounted for in oilseed rotational N fertiliserrecommendations (Weinert et al 2002) Even under irrigation Nfertiliser responses in winter canola can be minimal due to buildup of residual soil N in highly fertilised rotations (Davenport et al2010) Even with ample water and N winter kill is still a problemin this zone as demonstrated in an irrigated winter wheat springbarley winter canola rotation where green-bridged Rhizoctoniasolani on spring barley residues was suspected to infect wintercanola roots perhaps contributing to winter kill in 4 of 5 years(Paulitz et al 2010 Schillinger et al 2010b) Rhizoctonia solanianastomosis group 2ndash1 has recently been identified to infectwheat and rape roots (Sturrock et al 2015)

Summary and future projections

Canola area has historically constituted less than 1 of theiPNW Advancements in the development of both winter andspring cultivars have afforded flexible options in weed controlmanagement Competitive hybrid cultivars are nowcommercially available with and without herbicide toleranceor resistance Current efforts are to identify and integratecultivars that can be successfully established survive winterand use subsoil water and N efficiently in each of the zonesEstablishment of a local oilseed processing industry increasingglobal and regional canola markets for food fuel and feedagronomic benefits in increasing rotational diversity andcontinued vigorous research and extension efforts havestimulated a recent increase in canola integration into existingmonoculture wheat production in the iPNW Modest canolarotational integration projected for each zone would achieveproduction goals to match current and future regionaloilseed processing capacity with 300 000 canola ha per year

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 261

(Table 1) An upper agronomic limit of roughly 1 1wheat canola has been reached in the semi-arid wheat-producing region of western Canada Similar crop productionratios in the iPNW would approach 700 000 ha Winter canolaintegration into the wheatndashfallow annual cropndashtransition andirrigated cropping zones and spring canola integration intoannual cropping and transition zones will improve weedcontrol and wheat yields particularly with herbicide-resistantcultivars The most critical challenges in the adaptation ofcanola into iPNW wheat-cropping systems include improvedconsistency of winter canola establishment and winter survivalin the low and intermediate precipitation zones Seeding depthand timing are critical determinants of winter and spring canolayield potential Relevant genetic research is currently focussedon increasing seed size and hypocotyl lengths for improvedseedling emergence and on the identification of freeze-tolerantcultivars Integration of spring canola into higher precipitationannual cropping systems requires research on innovative earlyplanting strategies and new earlier maturing cultivars to avoidhigh temperature and moisture stress Taproot architecture ofcanola dictates changes in standard N placement andtiming strategies that have been practiced for iPNW wheatproduction but the deep rooting habit of canola will contributeto efficient water and N recovery of the cropping systems Farmenterprise economics that account for rotational benefits andproduction risk will help growers account for multi-yearinvestments in canolandashwheat rotations to assess the benefits ofintegrated canolandashwheat systems

References

Abatzoglou J Rupp D Mote P (2015) Asymmetrical warming projectionsfor the inland Pacific Northwest In lsquoRegional approaches to climatechange for Pacific Northwest agriculture Climate science Northwestfarmers can usersquo (Eds K Borrelli D Daily Laursen S Eigenbrode BMahler R Pepper) pp 104ndash105 Available at wwwreachchpnaorg

Alberta Agriculture and Rural Development (2004) Alberta fertilizer guideIn lsquoAgric-facts practical information for Albertarsquos agriculture industryrsquoAgdex 541ndash1 (Ministry of Alberta Agriculture Food and RuralDevelopment Edmonton Alberta Canada)

Angadi SV Cutforth HW McConkey BG Gan Y (2003) Yield adjustmentby canola grown at different plant populations under semiarid conditionsCrop Science 43 1358ndash1366 doi102135cropsci20031358

Angus JF Kirkegaard JA Hunt JR Ryan MH Ohlander L Peoples MB(2015) Break crops and rotations for wheat Crop amp Pasture Science 66523ndash552 doi101071CP14252

Azooz RH Arshad MA (1998) Effect of residue and tillage managementon barley and canola growth and water use efficiency Canadian Journalof Soil Science 78 649ndash656 doi104141S97-098

Ball DA Young FL Ogg AO Jr (1999) Selective control of jointedgoatgrass (Aegilops clylindrica) with imazamox in herbicide-resistantwheat Weed Technology 13 77ndash82

Bettis B Auld D (Eds) (1980) Development of oilseeds as alternative cropsfor the Pacific Northwest Pacific Northwest Regional CommissionYearly Reports June 1979ndash31 July 1980 June 1980ndashJune 1981Pacific Northwest Regional Commission Moscow Idaho USA

Bettis BL Peterson CL Auld DL Driscoll DJ Peterson (1982) Fuelcharacteristics of vegetable oil from oilseed crops in the PacificNorthwest Agronomy Journal 74 335ndash339

Blum A (2009) Effective use of water (EUW) and not water-use efficiency(WUE) is the target of crop yield improvement under drought stressField Crops Research 112 119ndash123 doi101016jfcr200903009

Brennan RF Bolland MDA (2009) Comparing the nitrogen and phosphorusrequirements of canola and wheat for grain yield and quality Crop ampPasture Science 60 566ndash577 doi101071CP08401

Brill RD Jenkins ML Gardner MJ Lilley JM Orchard BA (2016)Optimising canola establishment and yield in south-eastern Australiawith hybrids and large seed Crop amp Pasture Science 67 409ndash418

Brown J Davis J (2015) Brassica breeding and research University of IdahoAvailable at wwwcalsuidahoedubrassica (accessed 15 December2015)

Brown J Davis JB Erickson DA Brown AP Seip L (1995) 1995 PacificNorthwest canola variety trial (PNWCVT) results and conclusions InlsquoPacificNorthwest canola conference1995proceedingsrsquo (EdsGJohnsonM Lewis) pp 29ndash36 (Department of Entomology Montana StateUniversity Bozeman MT)

BushongJ (2015)Okanola varieties andhybrids open-pollinatedvarietiesvshybrids Available at httpcanolaokstateeducropproductionvarieties(accessed 15 December 2015)

Conley SP Bordovsky D Rife C WieboldW (2004) Winter canola survivaland yield response to nitrogen and fall phosphorus Crop Managementdoi101094CM-2004-0901-01-RS

Connolly JR McCracken VA Painter KM (2016) Enterprise budget wheatand canola rotations in Eastern Washington intermediate rainfall regions12rdquo to 16rdquo Washington State University Extension PublicationWashington State University TB10 USA

Cook RJ Schillinger WF Christensen NW (2002) Rhizoctonia rootrot andtake-all of wheat in diverse direct-seed spring cropping systemsCanadian Journal of Plant Pathology 24 349ndash358 doi10108007060660209507020

Cresswell HP Kirkegaard JA (1995) Subsoil amelioration by plant-roots ndashthe process and the evidence Australian Journal of Soil Research 33221ndash239 doi101071SR9950221

Cutforth HW Angadi SV McConkey BG (2006) Stubble managementand microclimate yield and water use efficiency of canola grown inthe semiarid Canadian prairie Canadian Journal of Plant Science 8699ndash107 doi104141P05-073

Davenport J Stevens B Hang A Peters T (2010) Irrigated canola researchIn lsquoWashingtonOilseedCroppingSystemsProject partof theWashingtonState Biofuels Initiative 2010rsquo Annual Progress Report (EdsKESowersWL Pan) Available at httpcsswsuedubiofuelsfiles2012092010_Annual_Progress_Reportpdf (accessed 27 December 2015)

De Jong R Shields JA (1988) Available water-holding capacity maps ofAlberta Saskatchewan and Manitoba Canadian Journal of Soil Science68 157ndash163 doi104141cjss88-015

Desta KG Collins H Pan B (2013) Double-cropping dual purpose irrigatedbiennial canolawithgreenpea In lsquoWashingtonOilseedCroppingSystemsProject part of the Washington State Biofuels Initiative 2013rsquo AnnualProgress Report (Eds KE Sowers WL Pan) Available at httpcsswsuedubiofuelsfiles2012092013-Biofuel-Cropping-Systems-Research-Progress-Reportpdf (accessed 27 December 2015)

Divine TE Alzheimer DP Currie JW McGinnis KA Wiggins DJ (1977)Research on the potential impact of advanced oilseeds processingtechnology on Pacific Northwest Agriculture Batelle Pacific NorthwestLaboratories 231110270610690646 Richland Washington USA

Douglas CL Wysocki DJ Zuzel JF Rickman RW Klepper BL (1990)Agronomic zones for the dryland Pacific Northwest Pacific NorthwestCooperative Extension Bulletin PNW 954

Esser A Hulbert S (2013) Eastern WA low to intermediate rainfall InlsquoWashington Oilseed Cropping Systems Project part of theWashington State Biofuels Initiative 2013 Annual Progress Reportrsquo(Eds KE Sowers WL Pan) pp 31ndash36 Available at httpcsswsuedu

262 Crop amp Pasture Science W L Pan et al

freeze eventsmay be important to winter canola production in theiPNW as demonstrated in December 2014 when a rapidfreeze resulted in widespread loss of winter canola and winterwheat (J Schibel pers comm)

Low N status promotes increased sugar concentrationsand increased freeze resistance in plants (Lemoine et al 2013Wisniewski et al 2014) As a result this potentially changesthe N timing strategy for managing canola relative to traditionalwheat N management in the iPNW In zones less than 600mmannual precipitation where nitrate leaching below 180 cm soildepth is typically not excessive winter wheat N applicationoccurs pre-plant during summer fallow or at planting in annualcrop rotations (Veseth et al 1986 Halvorson et al 1999) Themain reason is to ensure adequate time for fertiliser N to nitrifyand move into the lower layers of the root profile ensuringadequate N availability as the surface soil dries and plantroots become increasingly reliant on subsoil N (Pan et al2001) If low N canola has higher winter survivability it mayprovide another reason to be conservative in N fertiliserapplications at planting and allow the canola to utilise residualN during early establishment An inverse relationship between Navailability and winter survival could be due to a complex set ofbiochemical shoot morphological ie raised shoot meristemsabove the ground and growth-induced water stress (Reese2015)Winter canola exhibits deep rooting depths to 180 cm andsubsoil N and water access and recovery is critically important(Hocking et al 2002 Reese 2015) Furthermore iPNW climatechange projections of hotter drier summer months (Abatzoglouet al 2015) portend a need for enhancing deep strong-rootedwinter crops such as canola for adapting to foreseen climatechange (Hatfield et al 2001 Blum 2009 Lynch 2015)

These climate change forecast models predict 5ndash15increases in iPNW regional annual precipitation but withincreasing proportions occurring during the winter andspring months with drier hotter summers This trend willnecessitate improvements in water and N infiltration and subsoilstorage during winter months for later access during active cropdevelopment Canola also has a reputation as a strong taprootedcrop capable of creating macro biopore channels for facilitatingsaturated water flow and root pathways for subsequent crops Yetcanola roots cannot always penetrate soil horizons with highphysical and chemical impedance (Cresswell and Kirkegaard1995 Watt et al 2006) Tillage pans and genetic soil horizonsin the iPNW have been observed to impede canola roots causingcharacteristic lsquoJrsquo hooking of the taproot forcing it to turn 90degrees along the plan of the soil pan until it encounters a crackwhere it can continue vertical development (Lisson et al 2007)This may be a plausible explanation for new canola growertestimonials claiming rotational benefits are not seen untila second or third rotation

Irrigated crop zone

Rotational fit The irrigated temperate desert of centralWashington and Oregon supports perennial tree and vine fruitproduction as well as 500 000 ha of many high value agronomiccrops such as potato and sweet corn where small grain cerealsare used as a rotational crop and winter wheat is only ~8 ofthe area (Table 1 Fig 1) As many high value crops for example

potato sweet corn onion beans are grown in this zone a muchlower adoption is projected for this zone with canola mostlyrestricted as a substitution for wheat in the irrigated rotationsof central Washington and Oregon

In addition with opportunities to follow early harvested freshvegetable crops dual purpose use of canola has potential todiversify and intensify irrigated rotations similar to drylandapplications (Neely 2010 Walsh 2012 Lilley et al 2015) Inthis zone of extended growing degree-days double croppingunder irrigation where biennial canola could bridge two short-season summer crops to yield three harvests over two growingseasons such asYear 1 fresh peascanola forage ndashYear 2 canolagrain (Kincaid et al 2011) Current efforts are focussed onproduction of silage from first-season canola vegetation incentral Washington Comparable canola grain yields of2300 kg handash1 were harvested with and without forage cuttingand removal (Desta et al 2013) Yield gaps between predictedand observed yields may relate to J-hooking that has beenobserved under irrigation similar to dryland root observationsdescribed above

Plant establishment As water is not a limitation underirrigation germination and seedling establishment is not asmuch of an issue in this zone For example winter rapeseedand mustard were rapidly established in late August and earlySeptember in the south andnorthColumbiabasinunder irrigationand substantial biomass and N accumulation occurs beforethe first hard frost and under these conditions deep soil N useshould still be accounted for in oilseed rotational N fertiliserrecommendations (Weinert et al 2002) Even under irrigation Nfertiliser responses in winter canola can be minimal due to buildup of residual soil N in highly fertilised rotations (Davenport et al2010) Even with ample water and N winter kill is still a problemin this zone as demonstrated in an irrigated winter wheat springbarley winter canola rotation where green-bridged Rhizoctoniasolani on spring barley residues was suspected to infect wintercanola roots perhaps contributing to winter kill in 4 of 5 years(Paulitz et al 2010 Schillinger et al 2010b) Rhizoctonia solanianastomosis group 2ndash1 has recently been identified to infectwheat and rape roots (Sturrock et al 2015)

Summary and future projections

Canola area has historically constituted less than 1 of theiPNW Advancements in the development of both winter andspring cultivars have afforded flexible options in weed controlmanagement Competitive hybrid cultivars are nowcommercially available with and without herbicide toleranceor resistance Current efforts are to identify and integratecultivars that can be successfully established survive winterand use subsoil water and N efficiently in each of the zonesEstablishment of a local oilseed processing industry increasingglobal and regional canola markets for food fuel and feedagronomic benefits in increasing rotational diversity andcontinued vigorous research and extension efforts havestimulated a recent increase in canola integration into existingmonoculture wheat production in the iPNW Modest canolarotational integration projected for each zone would achieveproduction goals to match current and future regionaloilseed processing capacity with 300 000 canola ha per year

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 261

(Table 1) An upper agronomic limit of roughly 1 1wheat canola has been reached in the semi-arid wheat-producing region of western Canada Similar crop productionratios in the iPNW would approach 700 000 ha Winter canolaintegration into the wheatndashfallow annual cropndashtransition andirrigated cropping zones and spring canola integration intoannual cropping and transition zones will improve weedcontrol and wheat yields particularly with herbicide-resistantcultivars The most critical challenges in the adaptation ofcanola into iPNW wheat-cropping systems include improvedconsistency of winter canola establishment and winter survivalin the low and intermediate precipitation zones Seeding depthand timing are critical determinants of winter and spring canolayield potential Relevant genetic research is currently focussedon increasing seed size and hypocotyl lengths for improvedseedling emergence and on the identification of freeze-tolerantcultivars Integration of spring canola into higher precipitationannual cropping systems requires research on innovative earlyplanting strategies and new earlier maturing cultivars to avoidhigh temperature and moisture stress Taproot architecture ofcanola dictates changes in standard N placement andtiming strategies that have been practiced for iPNW wheatproduction but the deep rooting habit of canola will contributeto efficient water and N recovery of the cropping systems Farmenterprise economics that account for rotational benefits andproduction risk will help growers account for multi-yearinvestments in canolandashwheat rotations to assess the benefits ofintegrated canolandashwheat systems

References

Abatzoglou J Rupp D Mote P (2015) Asymmetrical warming projectionsfor the inland Pacific Northwest In lsquoRegional approaches to climatechange for Pacific Northwest agriculture Climate science Northwestfarmers can usersquo (Eds K Borrelli D Daily Laursen S Eigenbrode BMahler R Pepper) pp 104ndash105 Available at wwwreachchpnaorg

Alberta Agriculture and Rural Development (2004) Alberta fertilizer guideIn lsquoAgric-facts practical information for Albertarsquos agriculture industryrsquoAgdex 541ndash1 (Ministry of Alberta Agriculture Food and RuralDevelopment Edmonton Alberta Canada)

Angadi SV Cutforth HW McConkey BG Gan Y (2003) Yield adjustmentby canola grown at different plant populations under semiarid conditionsCrop Science 43 1358ndash1366 doi102135cropsci20031358

Angus JF Kirkegaard JA Hunt JR Ryan MH Ohlander L Peoples MB(2015) Break crops and rotations for wheat Crop amp Pasture Science 66523ndash552 doi101071CP14252

Azooz RH Arshad MA (1998) Effect of residue and tillage managementon barley and canola growth and water use efficiency Canadian Journalof Soil Science 78 649ndash656 doi104141S97-098

Ball DA Young FL Ogg AO Jr (1999) Selective control of jointedgoatgrass (Aegilops clylindrica) with imazamox in herbicide-resistantwheat Weed Technology 13 77ndash82

Bettis B Auld D (Eds) (1980) Development of oilseeds as alternative cropsfor the Pacific Northwest Pacific Northwest Regional CommissionYearly Reports June 1979ndash31 July 1980 June 1980ndashJune 1981Pacific Northwest Regional Commission Moscow Idaho USA

Bettis BL Peterson CL Auld DL Driscoll DJ Peterson (1982) Fuelcharacteristics of vegetable oil from oilseed crops in the PacificNorthwest Agronomy Journal 74 335ndash339

Blum A (2009) Effective use of water (EUW) and not water-use efficiency(WUE) is the target of crop yield improvement under drought stressField Crops Research 112 119ndash123 doi101016jfcr200903009

Brennan RF Bolland MDA (2009) Comparing the nitrogen and phosphorusrequirements of canola and wheat for grain yield and quality Crop ampPasture Science 60 566ndash577 doi101071CP08401

Brill RD Jenkins ML Gardner MJ Lilley JM Orchard BA (2016)Optimising canola establishment and yield in south-eastern Australiawith hybrids and large seed Crop amp Pasture Science 67 409ndash418

Brown J Davis J (2015) Brassica breeding and research University of IdahoAvailable at wwwcalsuidahoedubrassica (accessed 15 December2015)

Brown J Davis JB Erickson DA Brown AP Seip L (1995) 1995 PacificNorthwest canola variety trial (PNWCVT) results and conclusions InlsquoPacificNorthwest canola conference1995proceedingsrsquo (EdsGJohnsonM Lewis) pp 29ndash36 (Department of Entomology Montana StateUniversity Bozeman MT)

BushongJ (2015)Okanola varieties andhybrids open-pollinatedvarietiesvshybrids Available at httpcanolaokstateeducropproductionvarieties(accessed 15 December 2015)

Conley SP Bordovsky D Rife C WieboldW (2004) Winter canola survivaland yield response to nitrogen and fall phosphorus Crop Managementdoi101094CM-2004-0901-01-RS

Connolly JR McCracken VA Painter KM (2016) Enterprise budget wheatand canola rotations in Eastern Washington intermediate rainfall regions12rdquo to 16rdquo Washington State University Extension PublicationWashington State University TB10 USA

Cook RJ Schillinger WF Christensen NW (2002) Rhizoctonia rootrot andtake-all of wheat in diverse direct-seed spring cropping systemsCanadian Journal of Plant Pathology 24 349ndash358 doi10108007060660209507020

Cresswell HP Kirkegaard JA (1995) Subsoil amelioration by plant-roots ndashthe process and the evidence Australian Journal of Soil Research 33221ndash239 doi101071SR9950221

Cutforth HW Angadi SV McConkey BG (2006) Stubble managementand microclimate yield and water use efficiency of canola grown inthe semiarid Canadian prairie Canadian Journal of Plant Science 8699ndash107 doi104141P05-073

Davenport J Stevens B Hang A Peters T (2010) Irrigated canola researchIn lsquoWashingtonOilseedCroppingSystemsProject partof theWashingtonState Biofuels Initiative 2010rsquo Annual Progress Report (EdsKESowersWL Pan) Available at httpcsswsuedubiofuelsfiles2012092010_Annual_Progress_Reportpdf (accessed 27 December 2015)

De Jong R Shields JA (1988) Available water-holding capacity maps ofAlberta Saskatchewan and Manitoba Canadian Journal of Soil Science68 157ndash163 doi104141cjss88-015

Desta KG Collins H Pan B (2013) Double-cropping dual purpose irrigatedbiennial canolawithgreenpea In lsquoWashingtonOilseedCroppingSystemsProject part of the Washington State Biofuels Initiative 2013rsquo AnnualProgress Report (Eds KE Sowers WL Pan) Available at httpcsswsuedubiofuelsfiles2012092013-Biofuel-Cropping-Systems-Research-Progress-Reportpdf (accessed 27 December 2015)

Divine TE Alzheimer DP Currie JW McGinnis KA Wiggins DJ (1977)Research on the potential impact of advanced oilseeds processingtechnology on Pacific Northwest Agriculture Batelle Pacific NorthwestLaboratories 231110270610690646 Richland Washington USA

Douglas CL Wysocki DJ Zuzel JF Rickman RW Klepper BL (1990)Agronomic zones for the dryland Pacific Northwest Pacific NorthwestCooperative Extension Bulletin PNW 954

Esser A Hulbert S (2013) Eastern WA low to intermediate rainfall InlsquoWashington Oilseed Cropping Systems Project part of theWashington State Biofuels Initiative 2013 Annual Progress Reportrsquo(Eds KE Sowers WL Pan) pp 31ndash36 Available at httpcsswsuedu

262 Crop amp Pasture Science W L Pan et al

(Table 1) An upper agronomic limit of roughly 1 1wheat canola has been reached in the semi-arid wheat-producing region of western Canada Similar crop productionratios in the iPNW would approach 700 000 ha Winter canolaintegration into the wheatndashfallow annual cropndashtransition andirrigated cropping zones and spring canola integration intoannual cropping and transition zones will improve weedcontrol and wheat yields particularly with herbicide-resistantcultivars The most critical challenges in the adaptation ofcanola into iPNW wheat-cropping systems include improvedconsistency of winter canola establishment and winter survivalin the low and intermediate precipitation zones Seeding depthand timing are critical determinants of winter and spring canolayield potential Relevant genetic research is currently focussedon increasing seed size and hypocotyl lengths for improvedseedling emergence and on the identification of freeze-tolerantcultivars Integration of spring canola into higher precipitationannual cropping systems requires research on innovative earlyplanting strategies and new earlier maturing cultivars to avoidhigh temperature and moisture stress Taproot architecture ofcanola dictates changes in standard N placement andtiming strategies that have been practiced for iPNW wheatproduction but the deep rooting habit of canola will contributeto efficient water and N recovery of the cropping systems Farmenterprise economics that account for rotational benefits andproduction risk will help growers account for multi-yearinvestments in canolandashwheat rotations to assess the benefits ofintegrated canolandashwheat systems

References

Abatzoglou J Rupp D Mote P (2015) Asymmetrical warming projectionsfor the inland Pacific Northwest In lsquoRegional approaches to climatechange for Pacific Northwest agriculture Climate science Northwestfarmers can usersquo (Eds K Borrelli D Daily Laursen S Eigenbrode BMahler R Pepper) pp 104ndash105 Available at wwwreachchpnaorg

Alberta Agriculture and Rural Development (2004) Alberta fertilizer guideIn lsquoAgric-facts practical information for Albertarsquos agriculture industryrsquoAgdex 541ndash1 (Ministry of Alberta Agriculture Food and RuralDevelopment Edmonton Alberta Canada)

Angadi SV Cutforth HW McConkey BG Gan Y (2003) Yield adjustmentby canola grown at different plant populations under semiarid conditionsCrop Science 43 1358ndash1366 doi102135cropsci20031358

Angus JF Kirkegaard JA Hunt JR Ryan MH Ohlander L Peoples MB(2015) Break crops and rotations for wheat Crop amp Pasture Science 66523ndash552 doi101071CP14252

Azooz RH Arshad MA (1998) Effect of residue and tillage managementon barley and canola growth and water use efficiency Canadian Journalof Soil Science 78 649ndash656 doi104141S97-098

Ball DA Young FL Ogg AO Jr (1999) Selective control of jointedgoatgrass (Aegilops clylindrica) with imazamox in herbicide-resistantwheat Weed Technology 13 77ndash82

Bettis B Auld D (Eds) (1980) Development of oilseeds as alternative cropsfor the Pacific Northwest Pacific Northwest Regional CommissionYearly Reports June 1979ndash31 July 1980 June 1980ndashJune 1981Pacific Northwest Regional Commission Moscow Idaho USA

Bettis BL Peterson CL Auld DL Driscoll DJ Peterson (1982) Fuelcharacteristics of vegetable oil from oilseed crops in the PacificNorthwest Agronomy Journal 74 335ndash339

Blum A (2009) Effective use of water (EUW) and not water-use efficiency(WUE) is the target of crop yield improvement under drought stressField Crops Research 112 119ndash123 doi101016jfcr200903009

Brennan RF Bolland MDA (2009) Comparing the nitrogen and phosphorusrequirements of canola and wheat for grain yield and quality Crop ampPasture Science 60 566ndash577 doi101071CP08401

Brill RD Jenkins ML Gardner MJ Lilley JM Orchard BA (2016)Optimising canola establishment and yield in south-eastern Australiawith hybrids and large seed Crop amp Pasture Science 67 409ndash418

Brown J Davis J (2015) Brassica breeding and research University of IdahoAvailable at wwwcalsuidahoedubrassica (accessed 15 December2015)

Brown J Davis JB Erickson DA Brown AP Seip L (1995) 1995 PacificNorthwest canola variety trial (PNWCVT) results and conclusions InlsquoPacificNorthwest canola conference1995proceedingsrsquo (EdsGJohnsonM Lewis) pp 29ndash36 (Department of Entomology Montana StateUniversity Bozeman MT)

BushongJ (2015)Okanola varieties andhybrids open-pollinatedvarietiesvshybrids Available at httpcanolaokstateeducropproductionvarieties(accessed 15 December 2015)

Conley SP Bordovsky D Rife C WieboldW (2004) Winter canola survivaland yield response to nitrogen and fall phosphorus Crop Managementdoi101094CM-2004-0901-01-RS

Connolly JR McCracken VA Painter KM (2016) Enterprise budget wheatand canola rotations in Eastern Washington intermediate rainfall regions12rdquo to 16rdquo Washington State University Extension PublicationWashington State University TB10 USA

Cook RJ Schillinger WF Christensen NW (2002) Rhizoctonia rootrot andtake-all of wheat in diverse direct-seed spring cropping systemsCanadian Journal of Plant Pathology 24 349ndash358 doi10108007060660209507020

Cresswell HP Kirkegaard JA (1995) Subsoil amelioration by plant-roots ndashthe process and the evidence Australian Journal of Soil Research 33221ndash239 doi101071SR9950221

Cutforth HW Angadi SV McConkey BG (2006) Stubble managementand microclimate yield and water use efficiency of canola grown inthe semiarid Canadian prairie Canadian Journal of Plant Science 8699ndash107 doi104141P05-073

Davenport J Stevens B Hang A Peters T (2010) Irrigated canola researchIn lsquoWashingtonOilseedCroppingSystemsProject partof theWashingtonState Biofuels Initiative 2010rsquo Annual Progress Report (EdsKESowersWL Pan) Available at httpcsswsuedubiofuelsfiles2012092010_Annual_Progress_Reportpdf (accessed 27 December 2015)

De Jong R Shields JA (1988) Available water-holding capacity maps ofAlberta Saskatchewan and Manitoba Canadian Journal of Soil Science68 157ndash163 doi104141cjss88-015

Desta KG Collins H Pan B (2013) Double-cropping dual purpose irrigatedbiennial canolawithgreenpea In lsquoWashingtonOilseedCroppingSystemsProject part of the Washington State Biofuels Initiative 2013rsquo AnnualProgress Report (Eds KE Sowers WL Pan) Available at httpcsswsuedubiofuelsfiles2012092013-Biofuel-Cropping-Systems-Research-Progress-Reportpdf (accessed 27 December 2015)

Divine TE Alzheimer DP Currie JW McGinnis KA Wiggins DJ (1977)Research on the potential impact of advanced oilseeds processingtechnology on Pacific Northwest Agriculture Batelle Pacific NorthwestLaboratories 231110270610690646 Richland Washington USA

Douglas CL Wysocki DJ Zuzel JF Rickman RW Klepper BL (1990)Agronomic zones for the dryland Pacific Northwest Pacific NorthwestCooperative Extension Bulletin PNW 954

Esser A Hulbert S (2013) Eastern WA low to intermediate rainfall InlsquoWashington Oilseed Cropping Systems Project part of theWashington State Biofuels Initiative 2013 Annual Progress Reportrsquo(Eds KE Sowers WL Pan) pp 31ndash36 Available at httpcsswsuedu

262 Crop amp Pasture Science W L Pan et al

biofuelsfiles2012092013-Biofuel-Cropping-Systems-Research-Progress-Reportpdf (accessed 15 December 2015)

Evans MA Skinner DZ Koenig RT Hulbert SH Pan WL (2015) Effect ofphosphorus potassium and chloride on cold tolerance of winter canola(Brassica napus L) Journal of Plant Nutrition doi101080019041672014990095

Faraji A Latifi N Soltani A Rad AHS (2009) Seed yield and water useefficiency of canola (Brassica napus L) as affected by high temperaturestress and supplemental irrigation Agricultural Water Management 96132ndash140 doi101016jagwat200807014

Fiez TE Pan WL Miller BC (1995) Nitrogen efficiency analysis of winterwheat among landscape positions Soil Science Society of AmericaJournal 59 1666ndash1671 doi102136sssaj199503615995005900060023x

Gan Y Angadi SV Cutforth H Potts D Angadi VV McDonald CL (2004)Canola and mustard response to short periods of temperature and waterstress at different developmental stages Canadian Journal of PlantScience 84 697ndash704 doi104141P03-109

Gan YT Campbell CA Janzen HH Lemke R Liu LP Basnyat P McDonaldCL (2009) Root mass for oilseed and pulse crops growth and distributionin the soil profile Canadian Journal of Plant Science 89 883ndash893doi104141CJPS08154

Gareau RM Auld DL Heikkinen MK (1990) Evaluation of seven species ofoilseeds as spring planted crops for thePacificNorthwest ProgressReportNo 277 University of Idaho Agricultural Experiment Station MoscowID USA

Grant CA Derksen DA McLaren D Irvine RB (2011) Nitrogen fertilizerand urease inhibitor effects on canola emergence and yield in a one-pass seeding and fertilizing system Field Crops Research 121 201ndash208doi101016jfcr201010012

Gusta LV Wisniewski M Nesbitt NT Gusta ML (2004) The effect of watersugars and proteins on the pattern of ice nucleation and propagationin acclimated and nonacclimated canola leaves Plant Physiology 1351642ndash1653 doi101104pp103028308

Halvorson AD Black AL Krupinsky JM Merrill SD (1999) Dryland winterwheat response to tillage and nitrogen within an annual cropping systemAgronomy Journal 91 702ndash707 doi102134agronj1999914702x

HammacA PanWL Bolton RP Koenig RT (2011) High resolution imagingto assess oilseed speciesrsquo root hair responses to soil water stressPlant andSoil 339 125ndash135 doi101007s11104-010-0335-0

Hamza MA Anderson WK (2003) Responses of soil properties and grainyields to deep ripping and gypsum application in a compacted loamysand soil contrasted with a sandy clay loam soil in Western AustraliaAustralian Journal of Agricultural Research 54 273ndash282 doi101071AR02102

Harker KN OrsquoDonovan JT Smith EG Johnson EN Peng G WillenborgCJ Gulden RH Mohr R Gill KS Grenkow LA (2015) Seed size andseeding rate effects on canola emergence development yield and seedweight Canadian Journal of Plant Science 95 1ndash8 doi104141cjps-2014-222

Hatfield JL Sauer TJ Prueger JH (2001) Managing soils to achieve greaterwater use efficiency Agronomy Journal 93 271ndash280 doi102134agronj2001932271x

Hocking PJ Kirkegaard JA Angus JF Bernardi A Mason LM (2002)Comparison of canola Indian mustard and Linola in two contrastingenvironments III Effects of nitrogen fertilizer on nitrogen uptake byplants and on soil nitrogen extraction Field Crops 79 153ndash172 doi101016S0378-4290(02)00140-5

Holman J Maxwell S Stamm M Martin K (2011) Effects of planting dateand tillage on winter canola Crop Management 10 doi101094CM-2011-0324-01-RS

Huggins DR Painter K (2011) Spring and winter canola research at CookAgronomy Farm Washington Biofuels Cropping Systems Annual

Report Available at httpcsswsuedubiofuelsfiles2012092011_Annual_Progress_Reportpdf (accessed 27 December 2015)

Huggins D Rupp R Kaur H Eigenbrode S (2014) Defining agroecologicalclasses for assessing land use dynamics In lsquoRegional approaches toclimate change for Pacific Northwest agriculture Climate scienceNorthwest farmers can usersquo (Eds K Borrelli D Daily Laursen SEigenbrode B Mahler B Stokes) (University of Idaho Moscow IDUSA) Available at wwwreachchpnaorg

HugginsD PanB SchillingerWYoungFMachadoS (2015)Crop diversityand intensity in PacificNorthwest dryland cropping systems In lsquoRegionalapproaches to climate change for Pacific Northwest agriculture Climatescience Northwest farmers can usersquo (Eds K Borrelli D Daily Laursen SEigenbrode B Mahler R Pepper) Available at wwwreachchpnaorg(accessed 1 June 2015)

Jackson GD (2000) Effects of nitrogen and sulfur on canola yield andnutrient uptake Agronomy Journal 92 644ndash649 doi102134agronj2000924644x

Janskaacute A Maršiacutek P Zelenkovaacute S Ovesnaacute J (2010) Cold stress andacclimation ndash what is important for metabolic adjustment PlantBiology 12 395ndash405 doi101111j1438-8677200900299x

Ji L Peters AJ (2003) Assessing vegetation response to drought in thenorthern Great Plains using vegetation and drought indices RemoteSensing of Environment 87 85ndash98 doi101016S0034-4257(03)00174-3

Johnson G Lewis M (1995) lsquoProceedings of the fifth Pacific Northwestcanola conferencersquo (Montana State University Bozeman MT)

Kephart K (1986) lsquoPNW winter rapeseed production conferenceproceedingsrsquo 24ndash26 February 1986 Moscow ID (Pacific NorthwestExtension Publication University of Idaho Moscow ID USA)

Kincaid R Johnson K Michal J Hulbert S Pan W Barbano J Huisman A(2011) Biennial canola for forage and ecosystem improvement indryland cropping systems Advances in Animal Biosciences 2 457

Kirkegaard J Christen O Krupinsky J Layzell D (2008a) Break cropbenefits in temperate wheat production Field Crops Research 107185ndash195 doi101016jfcr200802010

Kirkegaard JA Sprague SJ Dove H Kelman WM Marcroft SJ LieschkeA Howe GN Graham JM (2008b) Dual-purpose canola ndash a newopportunity in mixed farming systems Australian Journal ofAgricultural Research 59 291ndash302 doi101071AR07285

Kirkegaard JA Lilley JM Brill RD Sprague SJ Fettell NA Pengilley GC(2016) Re-evaluating sowing time of canola in south-eastern Australia ndashhow early is too early Crop amp Pasture Science 67 381ndash396

Klepper B Belford RK Rickman RW (1984) Root and shoot developmentin winter wheat Agronomy Journal 76 117ndash122 doi102134agronj198400021962007600010029x

Koenig RT (2005) Dryland winter wheat Eastern Washington nutrientmanagement guide Washington State University Extension EB1987EPullman WA

Koenig RT Hammac WA Pan WL (2011) Canola growth developmentand fertility Washington State University Extension Fact Sheet FS045EPullman WA

Lamb KE Johnson BL (2004) Seed size and seeding depth on canolaemergence and performance in the Northern Great Plains AgronomyJournal 96 454ndash461 doi102134agronj20040454

Lang MB (2014) Oilseed policy in Washington state Presented at the PNWdirect seed and oilseed cropping systems conference KennewickWashingtonAvailable at httpcsswsuedubiofuelsfiles201403Lang2014OSDSpdf (accessed 15 December 2015)

LemoineR LaCamera SAtanassovaRDeacutedaldeacutechampFAllario T PourtauN Bonnemain J-L Laloi M Coutos-Theacutevenot P Maurousset L FaucherM Girousse C Lemonnier P Parrilla J DurandM (2013) Source-to-sinktransport of sugar and regulation by environmental factors Frontiersin Plant Science 4 272 doi103389fpls201300272

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 263

LiaFChenBXuaKGaoGYanGQiao JLia JLiaHLiaLXiaoXZhangT Nishiob T Wua X (2016) A genome-wide association study of plantheight and primary branch number in rapeseed (Brassica napus) PlantScience 242 169ndash177

Lilley JM Lindsay AC Bell W Kirkegaard JA (2015) Optimising grainyield and grazing potential of crops across Australiarsquos high-rainfall zonea simulation analysis 2 Canola Crop amp Pasture Science 66 349ndash364doi101071CP14240

Lisson SN Kirkegaard JA Robertson MJ Zwart A (2007) What is limitingcanola yield in southern New SouthWales A diagnosis of causal factorsAustralian Journal of Experimental Agriculture 47 1435ndash1445doi101071EA07041

Lynch J (2015) Opportunities and challenges in the subsoil pathways todeeper rooted crops Journal of Experimental Botany 66 2199ndash2210doi101093jxberu508

Maaz TM Pan WL Hammac WA (2016) Components of improved canolanitrogen use efficiency with increasing water and nitrogen AgronomyJournal in press

Madsen I Bolton RP Pan WL (2014) Impacts of banding ammoniumfertilizer on canola and wheat seedling root and root hair growth anddevelopment In lsquoASA CSSA and SSSA International Annual MeetingAbstractsrsquo Nov 2ndash5 Long Beach CA Available at wwwacsmeetingsorgmeetings

Mahli SS Brandt S Ulrich D Lafond GP Johnston AM Zentner RP (2007)Comparative nitrogen response and economic evaluation for optimumyield of hybrid and open-pollinated canola Canadian Journal of PlantScience 87 449ndash460 doi104141P05-180

Mohan A Schillinger WF Gill KS (2013) Wheat seedling emergencefrom deep planting depths and its relationship with coleoptile lengthPLoS One 8 e73314 doi101371journalpone0073314

Moore MK Guy SO (1997) Agronomic response of winter rapeseed to rateand date of seeding Agronomy Journal 89 521ndash526 doi102134agronj199700021962008900030024x

Murray GA Auld DL (1986) Establishment and fertilizer practices forwinter rape in dryland areas of northern Idaho and eastern WashingtonIn lsquoPNW winter rapeseed production conferencersquo (Ed K Kephart)pp 108ndash114 (Pacific Northwest Extension Publication IdahoWashington OR)

Neely C (2010) The effect of forage harvest on forage yield forage qualityand subsequent seed yield of dual-purpose biennial winter canola(Brassica napusL)Masters Thesis University of IdahoMoscow USA

Norton MA (2016) Nitrogen management to optimise canola production inAustralia Crop amp Pasture Science 67 419ndash438

Oliver YM Robertson MJ (2009) Quantifying the benefits of accountingfor yield potential in spatially and seasonally responsive nutrientmanagement in a Mediterranean climate Soil Research 47 114ndash126doi101071SR08099

Pakish B Davis JB Wingerson D Brown J (2015) Twenty years of canolavariety performance in the Pacific Northwest Poster presentation atPacific Northwest Direct Seed Association Kennewick WashingtonAvailable at httpcsswsuedubiofuelsfiles201502Poster17Pakishpdf (accessed 21 December 2015)

Pan WL Tillman BA Ullrich SE (1991) Ammonium and nitrate uptake byspring barley genotypes in root temperatures simulating till and no-tillconditions Plant and Soil 135 1ndash8 doi101007BF00014773

Pan WL Young FL Kidwell KK (2001) Carbon and nitrogen cycling indirect-seeded spring cereal alternatives to summer fallow In lsquoProceedingsof theWesternNutrientManagementConferencersquo Vol 4 (EdBBrown)pp 202ndash209 (Potash and Phosphate Institute Brookings SD)

Pan WL Maaz TM Hammac WA McCracken VA Koenig RT (2016)Mitscherlich-modeled semi-arid canolanitrogen requirements influencedby soil N and water Agronomy Journal in press doi102134agronj20150378

Papendick RI Miller DE (1977) Conservation tillage in the PacificNorthwest Journal of Soil and Water Conservation 32 49ndash52

Paulitz TC Schroeder KL Schillinger WF (2010) Soilborne pathogens ofcereals in an irrigated cropping system Effects of tillage residuemanagement and crop rotation Plant Disease 94 61ndash68 doi101094PDIS-94-1-0061

Pester TA Westra P Anderson RL Lyon DJ Miller SD Stahlman PWNorthamFEWicksGA (2000) Secale cereale interference and economicthresholds on wheat Triticum aestivum Weed Science 48 720ndash727doi1016140043-1745(2000)048[0720SCIAET]20CO2

Petersen CL (1984) The potential of vegetable oil as an alternate source ofliquid fuel for agriculture in the Pacific Northwest ndash II Idaho AgriculturalExperiment StationUniversity of IdahoCollege ofAgricultureMoscowMisc Series No 84

Porter N Bettis B Auld D (Eds) (1981) lsquoDevelopment of oilseeds asalternative crops for the Pacific Northwestrsquo Yearly report June1980ndashJune 1981 (Pacific Northwest Regional Commission MoscowID USA)

Rathke GW Behrens T Diepenbrock W (2006) Integrated nitrogenmanagement strategies to improve seed yield oil content and nitrogenefficiency of winter oilseed rape (Brassica napus L) A reviewAgriculture Ecosystems amp Environment 117 80ndash108 doi101016jagee200604006

Reese M (2015) Dryland winter canola water and N use in easternWashington MS Thesis Washington State University Pullman WAUSA

Robertson MJ Kirkegaard JA (2005) Water use efficiency of dryland canolain an equi-seasonal rainfall environment Australian Journal ofAgricultural Research 56 1373ndash1386 doi101071AR05030

Schillinger WF (2013) Dryland and irrigated cropping systems researchwith camelina winter canola and safflower In lsquoWashington OilseedCropping Systems Project part of the Washington State BiofuelsInitiative 2013 Annual Progress Reportrsquo (Eds KE Sowers WL Pan)(Washington State University PullmanWA)Available at httpcsswsuedubiofuelsfiles2012092013-Biofuel-Cropping-Systems-Research-Progress-Reportpdf (accessed 27 December 2015)

Schillinger WF Papendick RI (2008) Then and now 125 years of drylandwheat farming in the Inland Pacific Northwest Agronomy Journal(Celebrate the Centennial - A supplement) s-166ndashs182

Schillinger WF Papendick RI McCool DM (2010a) Soil and waterchallenges for Pacific Northwest agriculture In lsquoSoil and WaterConservation Advances in the United Statesrsquo SSSA SpecialPublication 60 (Eds TM Zobeck WF Schillinger) pp 47ndash79 (SoilScience Society of America Madison WI USA)

Schillinger WF Young DL Kennedy AC Paulitz TC (2010b) Diverse no-till irrigated crop rotations instead of burning and plowing continuouswheat Field Crops Research 115 39ndash49 doi101016jfcr200910001

Schwartz GE Alexander RB (1995) Soils data for the conterminous UnitedStates derived from the NRCS State Soil Geographic (STATSGO) database US Geological Survey Report Issue_Identification 95ndash449Available at httpwaterusgsgovlookupgetspatialussoils (accessed27 December 2015)

SeymourM Kirkegaard JA PeoplesMBWhite PF French RJ (2012) Breakcrop benefits to wheat in Western Australia insights from over threedecades of research Crop amp Pasture Science 63 1ndash16 doi101071CP11320

Seymour M Sprigg S French B Bucat J Malik R Harries M (2016)Nitrogen responses of canola in low to medium rainfall environmentsof Western Australia Crop amp Pasture Science 67 450ndash466

Smettem KRJ Gregory PJ (2010) The relationship between soil waterretention and particle size distribution parameters for somepredominantly sandy soils in western Australia Australian Journal ofSoil Research 34 695ndash708 doi101071SR9960695

264 Crop amp Pasture Science W L Pan et al

Smith EG Upadhyay BH Favret ML Karamanos RE (2010) Fertilizerresponse for hybrid and open-pollinated canola and economic optimalnutrient levels Canadian Journal of Plant Science 90 305ndash310doi104141CJPS09027

Sowers KE Pan WL (Eds) (2014) Washington Oilseed CroppingSystems Project Part of the Washington State Biofuels InitiativeAvailable at httpcsswsuedubiofuelsfiles2012092013-Biofuel-Cropping-Systems-Research-Progress-Reportpdf (accessed 1 June2015)

Sturrock CJ Woodhall J Brown M Walker C Mooney SJ Ray RV (2015)Effects of damping-off caused by Rhizoctonia solani anastomosisgroup 2ndash1 on roots of wheat and oil seed rape quantified using X-rayComputed Tomography and real-time PCR Frontiers in Plant Science 61ndash11 doi103389fpls201500461

Thomas P (2003) lsquoCanola growersrsquo manualrsquo (Canola Council of CanadaWinnipeg Manitoba)

USDA (2015) USDA National Agriculture Statistics Service Available atwwwnassusdagov (accessed 15 June 2015)

Veseth R McDole R Engle C Vomocil J (1986) Fertilizer band location forcereal root access PNWConservation Tillage Handbook Series Chapter6 ndash Fertility No 4 A Pacific Northwest Extension Publication IdahoWashington Oregon PNW 283

Walsh C (2012) Potential for development of biennial winter canola(Brassica napus L) as a dual-purpose crop in the Pacific NorthwestMasters Thesis University of Idaho Moscow USA

Watt M Kirkegaard JA Passioura JB (2006) Rhizosphere biology andcrop productivity ndash a review Australian Journal of Soil Research 44299ndash317 doi101071SR05142

Weinert T Pan WL Moneymaker MR Santo GS Stevens RG (2002)Nitrogen recycling by non-leguminous winter cover crops to reduceleaching in potato rotations Agronomy Journal 94 365ndash372 doi102134agronj20020365

WilkinsDWysockiD SiemensMOtt SCorreaB JohlkeT (2002)Fertilizerplacement in annual crop direct-seeded canola Columbia BasinAgricultural Annual Report Spec Report 1040 pp 76ndash80 OregonState University in cooperation with USDA Agricultural ResearchService Pendleton OR

Wisniewski M Gusta L Neuner G (2014) Adaptive mechanisms of freezeavoidance in plants a brief update Environmental and ExperimentalBotany 99 133ndash140 doi101016jenvexpbot201311011

Young FL (2012) Winter canola production in the low to intermediaterainfall zones of the Pacific Northwest In lsquoWashington OilseedCropping Systems Project part of the Washington State BiofuelsInitiative 2012 Annual Progress Reportrsquo (Eds KE Sowers WL Pan)Available at httpcsswsuedubiofuelsfiles2013062012-Biofuel-Cropping-Systems-Research-Progress-Report-finalpdf (accessed 27December 2015)

Young FL Thorne ME (2004) Weed-species dynamics and managementin no-till and reduced-till fallow cropping systems for the semi-aridagricultural region of the Pacific Northwest USA Crop Protection 231097ndash1110 doi101016jcropro200403018

Young FL Ogg AG Jr Dotray PA (1990) Effect of postharvest fieldburning on jointed goatgrass (Aegilops cylindrical) germination WeedTechnology 4 123ndash127

Young FL Bewick LS Pan WL (2008) Systems approach to crop rotationresearch guidelines and challenges In lsquoCrop rotationrsquo (EdYUBerklian)pp 41ndash69 (Nova Science Publishers Inc New York)

Young FL Long DS Alldredge JR (2012) Effect of planting methods onspring canola (Brassica napus L) establishment and yield in the low-rainfall region of the Pacific NorthwestCropManagement 11 doi101094CM-2012-0321-01-RS

Young FL Whaley DK PanWL Roe RD Alldredge JR (2014) Introducingwinter canola to the winter wheat-fallow region of the Pacific NorthwestCrop Management doi102134CM-2013-0023-RS

YoungFLAlldredge JRPanWLHenningsC (2015)Comparisonsof annualno-till spring cereal cropping systems in the Pacific Northwest CropForage amp Turfgrass Management 1 doi102134cftm20140089

Young FL Whaley DK Lawrence NC Burke IC (2016) Feral rye (Secalecereale) control in winter canola in the Pacific Northwest WeedTechnology 30 163ndash170 doi101614WT-D-15-001091

ZentnerRPWallaDDNagyCNSmithEGYoungDLMillerPRCampbellCA McConkey BG Brandt SA Lafond GP Johnston AM Derksen DA(2002) Economics of crop diversification and soil tillage opportunities inthe Canadian prairies Agronomy Journal 94 216ndash230 doi102134agronj20020216

Zhao JD Favero HP Neff MM (2013) The Arabidopsis thaliana AHLfamily modulates hypocotyl growth redundantly by interacting witheach other via the PPCDUF296 domain Proceedings of the NationalAcademy of Sciences USA 110 E4688ndashE4697 doi101073pnas1219277110

Canola integration into semi-arid PNW USA wheat Crop amp Pasture Science 265

wwwpublishcsiroaujournalscp