crop monitoring for wheat

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Crop Monitoring and Zadoks Growth Stages for Wheat

Dr Maarten Stapper, CSIRO Plant Industry, GPO Box 1600, Canberra ACT 2601

Contents

Introduction 2

Growth stages 2

Figure 1. Wheat Growth Stages and Phases 3

Table 1. Crop Growth Stages for Cereals - Zadoks 5Figure 2. Crop Growth Chart Z05 to Z30 6Figure 2. Crop Growth Chart (cont.) Z31 to Z71 7Figure 3. Crop growth stages for wheat time curves 8

Growth stage observation target 9

Emergence 9

Sowing depth 9

Leaves 9

Tillers 10

Spike initiation 11

Start of Stem elongation 12

Nodes and Stem elongation 12

Flag leaf to Booting 13

Heading and Flowering 13

Frost damage 13

Plant height and peduncle 14

Kernel and Milk development 14

Dough development 14

Ripening 14

Plant count & sowing depth 15

Shoot count 15

Ground cover 15

Lodging score 16

Green leaves per shoot 16

Leaf wilting score 16Irrigators 17


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IntroductionCrop monitoring is the skill to link strategic and tactical management decisions to plantdevelopment and crop growth. Strategic management relates to decisions before sowingand lessons to be learned within season for future seasons, such as variety choice, cropgrowth and soil fertility, sowing conditions/sowing rate/seed quality and plant

establishment. After sowing, tactical management relates adjustments in timing andquantity of management decisions to crop observations of actual crop condition. Forexample, in relation to application timing (and need) of herbicides, fungicides, N fertiliser(and water), grazing and harvesting. Also crop monitoring to determine the timing of theoccurrence of such yield reducing factors as lodging, waterlogging and frost will, incombination with their severity, determine their effect on grain yield. Such crop relatedmanagement has been described elsewhere for high-yielding wheat1.

It requires knowledge about a developing and growing crop to know relevance of stages ofplant development, numbers of plants and plant organs such as tillers, and descriptions ofthe crop such as ground cover, green area, lodging and wilting. Experiencing usefulness ofmonitoring is the key to this learning process. Knowing whatto look for and settingstandards is the first step as was introduced in the mid-eighties2 and followed in

subsequent NSW DPI Checkprograms for wheat3 and rice by John Lacy. Targetedobservations and comparison with standards may lead to faster learning and moreknowledge.

Learn this language of management. Learning is enhanced by making observations indifferent paddocks within and between seasons as changes in place and time affect cropgrowth and development. Keeping records is important as memory fails and changes overtime. Observations should be representative for a whole paddock to allow comparison withstandards, analysis of outcomes and sharing with local group and or agronomist. It istherefore important to examine on each visit the same spots at representative sites of apaddock. Avoid headlands, crop edges and areas near trees and gates.

Crop monitoring involves quantification of crop growth and development which allowcomparison between crops and seasons, and with the standard in crop managementguides. Plant establishment, shoot number, ground cover, lodging and green leaves pershoot can be quantified as described below. Plant development can be observed withgrowth stages during the season to obtain the timing of critical stages such as start stemelongation and flowering. Figure 1 gives an overview of important development eventsduring the growing season of wheat from sowing till start of grain-filling with the Zadoks4Decimal Code (Z) for each stage shown (NB. timing not to scale). The Decimal Code Z canbe used for the timing of management tasks, helping in the diagnosis of a problem andprediction of future growth stages as shown below and for high-yielding wheat in footnote1.

Growth stagesThe Zadoks Decimal Code (Z, also DC or GS) is used internationally to describe growthstages of cereals. Developmental stages are described in the following, with an adaptedZadoks Decimal Code listed in the Table 1 Crop Growth Stages for Cereals and shown inFigure 2 with pictures of plants to help identify Z-stages. The crop may also achieve mostZ-stages not listed in Table 1, either scored as such on an individual plant or as theaverage across plants.

Figure 3 shows examples of average observed Z stage throughout the season for crops ofthree maturity groups from various sowing dates; triticale and barley following a similar

1 M.Stapper, 2007, High-Yielding Irrigated Wheat Crop Management, Irrigated Cropping Forum2

SIRAGCROP- Field Observations and Crop Standards for Wheat by M.Stapper and D.Murray, 19863 Wheatcheck Recommendations, 2003, NSW DPI, Vic DPI, GRZ, ICF.4 J.C.Zadoks et al., 1974, Weed Research 14:415-421


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pattern. They are based on observations at Griffith N.S.W., but seem valid on the plains ofsoutheastern Australia and provide a good indication of development for many other areas,where development will be mostly slower. Curves in Figure 3 are for average conditionswith average temperature. During periods in the season phasic development could gofaster or slower (eg. when warmer vscooler). Crop management (healthy vsstressed) andlocation (topography, soil type and fertility) may also affect rate of development. Changesin soil type may cause bigger variations to the curves in the Figure than regionaldifferences. For example, at Benerembah on a grey-cracking clay flowering was reached 5to 8 days later when sown on a similar date as on a red loam at Griffith 20 km away, withdevelopment at Deniliquin (black soil) more akin to Griffith which lies 170 km northeast.The wet, dark clay remains cooler during winter and hence slows development. Very lowsowing rates (< 40 kg/ha vs100 kg/ha) may cause flowering to be two (eg. 2004) to six(eg. 2003) days later than shown, while visible nitrogen stress at Z30 may cause it to betwo to five days earlier.

Z-stage during leaf emergence is independent of maturity as shown for three maturities inFigure 3. The three maturity groups shown in Figure 3 are from early to late sowing: late(group 5: Rosella, Wedgetail, Currawong), medium (group 3: Chara, Diamondbird, Giles),

and very-early (group 1: H45, H46, Hybrid Mercury), listing varieties used in recent trials(see footnote 1) with more in Table 2. Curves for groups 2 (Drysdale, Hunter, Tamaroi-d,Credit-t, Kosciuszko-t) and 4 (Snipe, Borlaug) can be projected between those for 1 and 3,and 3 and 5, respectively, or 3 to 5 days away from the drawn curves of maturity groupsnearest to them. The use of the Figure in crop monitoring is explained further below.

Table 2. Maturity groups derived from three years of core trials with 54 genotypes at Griffith, Benerembah andDeniliquin in southern New South Wales. Sowing dates were between 15 May and 9 June with resultingflowering dates mostly in the optimum flowering period. Varieties of group 6 were used in an early April sowingat Griffith.

Maturity group Variety

1 very early H46, H45, Hybrid Mercury

2 early Hunter, Babbler, Drysdale, Wentworth, Ruby, Ventura3 medium Giles, Sunvale Annuello, Janz, Chara, Arrivato, Bellaroi

4 medium late Snipe, Pardalote

5 late Rosella, Whistler, Wylah, Wedgetail, Currawong

6 very late Mackellar, Rudd

Figure 3 shows maturity groups 1, 3 and 5 as sown together on 20 May when each resultsin subsequent mid-flowering dates in the optimum flowering period on the southern plains(see Fig.4 in footnote 1). Final leaf number on the main shoot for these groups on thissowing date would have been 9.5, 11 (ie. Fig.1) and 12.5, respectively. The next twosowing date examples in the Figure provide comparisons between medium and very earlygroups. However, on that last sowing date, early July, both fall outside the optimumflowering period.

An experienced user can score growth stage of a crop with an accuracy of three days. Thecurves in Figure 3 can be used to predict next events from an observed stage on a givendate for a variety with a particular maturity. Go from that date at the bottom in a straight lineup and put a dot at the height of your Z-stage. Find the nearest curve for the maturity youhave and follow that line parallel from your dot into the future. Also keep following animaginary line parallel to one of the drawn lines if observations start to deviate fromexpected as non-average weather may be experienced. The impact of temperature can beseen in the increase from 25 to 50 days it takes to reach the fourth leaf stage from 20March to 10 June sowing dates, respectively, and decrease back to 32 days for the Augustsowing. A range of growth stages should be recorded if the crop is very variable, for

example, following uneven emergence or fertility.


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Table 1. Crop Growth Stages for CerealsAdapted Zadoks Decimal Code Zxx (also DCxx, Dxx or GSxx)

0 Emergence

00 Dry seed sown01 Seed absorbs water03 Germination, seed swollen05 Radicle emerged from seed07 Coleoptile emerged from seed09 Leaf at coleoptile tip10 First leaf through coleoptile and tip visible

1 Seedling growth11 1

stleaf more then half visible

12 2nd leaf more then half visible13 3

rdleaf more then half visible

14 4th leaf more then half visible

19 6

th

leaf more then half visible17 7th

leaf more then half visible18 8

thleaf more then half visible

19 9or more leaves visible and stem not

elongating.

2 Tillering20 Main shoot only21 Main shoot and 1 tiller22 Main shoot and 2 tillers23 Main shoot and 3 tillers24 Main shoot and 4 tillers25 Main shoot and 5 tillers

26 Main shoot and 6 tillers27 Main shoot and 7 tillers28 Main shoot and 8 tillers29 Main shoot and 9 or more tillers

3 Stem elongation30 stem starts to elongate, spike at 1cm31 swelling 1

stnode detectable

32 swelling 2nd

node detectable33 swelling 3

rdnode detectable

34 swelling 4th

node detectable35 swelling 5

thnode detectable

36 swelling 6th

node detectable

4 Flag leaf to Booting37 Flag leaf tip visible38 Flag leaf half visible39 Flag leaf ligule just visible41 Early boot, flag sheath extending43 Mid-boot, boot opposite ligule of 2

ndlast leaf

45 Full-boot, boot above ligule of 2nd

last leaf47 Flag leaf sheath opening49 First awns visible

5 Heading

51 10% of spikes visible (ear peep)5253 30% of spikes visible5455 50% of spikes visible5657 70% of spikes visible5859 90% of spikes visible60 Whole spike visible, no yellow anthers

6 Flowering (anthesis)61 Early 20% of spikes with anthers

6263 30% of spikes with yellow anthers6465 Mid half of spikes with anthers6667 70% of spikes with anthers6869 Late 90% of spikes with anthers

7 Kernel and Milk development70.2 Kernels middle spike extended 20%70.5 Kernels middle spike half formed70.8 Kernels middle spike extended 80%

71 Watery ripe, clear liquid73 Early milk, liquid off-white75 Medium milk, contents milky liquid77 Late milk, more solids in milk79 Very-late milk, half solids in milk

8 Dough development81-85 spikes turn colour from light-green to

yellow-green to yellow81 Very early dough, more solids and slides

when crushed83 Early dough, soft, elastic and almost dry,

shiny

85 Soft dough, firm, crumbles but fingernailimpression not held87 Hard dough, fingernail impression held,

spike yellow-brown89 Late hard-dough, difficult to dent

9 Ripening91 Kernels hard, difficult to divide by thumb-nail92 Harvest ripe, kernels can no longer be

divided by thumb-nail and straw still firm93 Kernels loosening in daytime94 Over-ripe, straw brittle


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Growth stage observation target The stages Z10 till Z39 are based on observations onthe main shoot of a plant, which is usually the tallest and thickest shoot as tillers lag behind indevelopment. Pull at random four plants at each sampling site in a paddock to determine thegrowth stage from the leaves and tillers before stem elongation. Have a good look first, dontstart pulling off leaves or tillers until you are sure about what you are doing. Determine themain shoot leaves and tillers per plant together as they have then more meaning (see Fig.5).

From Z39 to Z94 observations are done on average shoots or spikes as the tillers that dosurvive, elongate and form nodes, have caught up with the main stem.

Emergence Z10, takes place when the tip of the first leaf becomes visible. That first leafgrows inside the coleoptile which provides a path through the soil. The coleoptile is white atfirst and is later detectable as a transparent, withered leaf when pulling a plant out of the soil.For some varieties seeds can be sown too deep to enable the coleoptile delivering the firstleaf to the surface. Cloddy conditions and hard setting surfaces may also prevent thecoleoptile from reaching the surface. That first leaf of a plant is always easy to recognise as itis the only one with a round tip and is the shortest. All others are pointy and normally each is

longer than its predecessor (up until at least L6).Sowing depth Depth of sowing can be determined when doing the plant establishmentcounts (see below). Pull up the seedlings after loosening the soil and see the remnant seedwith (withered) coleoptile still attached. Especially measure sowing depth when experiencingvariable emergence as that may be associated with achieved depths of sowing. Figure 4gives an example of the impact sowing depth can have on seedling growth and relateddevelopment of tillers.

Deep sowing usually results in a sub-crown internode (thin stem-like) raising the crown of theplant nearer to the soil surface away from the seed. Some varieties do this consistently.Others, such as Chara, have crowns raised to various depths and may then have a first leafand tiller emerging from a crown near the seed and the second and subsequent leaves from a

raised crown or even having a third step up. The deepest sowing in Figure 4 shows a raisedcrown some two cm above the seed. As nodal roots will in time commence growing from thecrowns, such a structure could become part of strong anchorage.

Figure 4. The impact of sowing depths of 1, 3 and 6 cm on development and growth of wheat seedlings areshown. Roots had broken off the deep sown seedling as seedlings had been pulled rather than dug out.

Leaves Leaves do appear at regular intervals at the tip of the main shoot. Successiveleaves appear on alternate sides. The rate of appearance is controlled by temperature, that


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is, the higher the temperature the faster a new leaf appears. Leaves on tillers develop insynchrony with those on the main shoot. Only one leaf at a time is growing on main shoot andon each of the tillers. A leaf is fully emerged when its ligule or collar becomes visible betweenthe emerged leaf blade and its leaf sheath, the hollow stem.

Determine the first leaf (round tip), count main stem leaves and round the last emerging leaf

to the nearest whole leaf (more than half up, less than half down) with that leaf stage addedto Z10. As leaves may emerge over 4 (April sowing) to 14 (August sowing) days dependingon temperature, a more accurate Z-stage may include the visible fraction of the emergingleaf. It will certainly enhance accuracy of plotting in Figure 3. As during this phase each nextnew leaf is longer, the fraction is 0.1 when next tip is visible, 0.4 when new leaf reaches tohalf the length of the previous leaf, and 0.8 when it reaches the length of the previous leaf,with estimates of the other fractions in increments of 0.1, as described in detail elsewhere5.For example, in Figure 2 Z11.3 for Z11 and Z12.7 for Z13,21, thus narrowing the leaf gapfrom 2 to 1.4.

With more tillers appearing it becomes a little harder to determine the number of leaves onthe main stem. Whether or not a leaf is one belonging to the main stem can be determined as

follows. First find the first leaf with round tip and keep it at your right hand side (Fig. 1). All theodd leaves are now on the right and the even numbered ones on the left. Peel back the firstleaf and notice how it is firmly attached to the main stem. If we find a tiller (possibly having itsown tillers) in the axil, notice how easily it breaks off at the base unlike a true main stem leaf.By repeating this process for each alternate next leaf we can determine the number of mainstem leaves, and the primary (on main stem) and secondary (on tillers) tillers. Notice thatinitially for every leaf added to the main stem, the number of leaves on each tiller increasesby one as well; for example compare in Figure 2 going from Z14,22 to Z15,23 to Z17,24. Thatprocess will cease towards Z30 when no new tillers appear (eg. from Z15,23 to Z17,24, notZ17,26) and redundant tillers will stop growing.

Tillers Count the tillers visible on each plant and for tiller stage add the average total perplant to Z20, with a score of Z29 for more than 9 tillers; for accuracythe first decimal of theaverage may also be included, as with leaf stage above. The Z20s tiller score is alwaysgiven concurrentwith Z10s for leaves or Z30s for nodes as the latter two processes aredriven by thermal time while tillering is source (growth) dependent (Fig. 5).

A tiller emerges in the axil of a leaf and can be easily removed. The first tiller, Z21, in the axilof the first leaf can be expected when leaf three is half-way out at Z13 (Z12.5). Althoughbefore this one a coleoptile tiller may emerge on some plants under favourable conditions asnoted in Figure 1, that is, a tiller in the axil of the coleoptile at the seed (Fig.2 Z13,22).Tillering occurs very systematically and a new tiller appears on a shoot every time a new leafappears. Tillers also will start tillering and the first tiller, T11, of main stem tiller one, T1, candevelop before main stem tiller four (Fig.2 Z17,24).

The next tiller may already be growing invisibly under the leaf sheath of the leaf above thelast tiller. Tillering has ceased if more than two leaf ligules are visible above the uppermostmain stem tiller. Usually that happens when either effective ground cover has been reachedor stem elongation starts. The tillering period will lengthen or shorten with decreasing orincreasing plant density, respectively. Figure 5 shows the slowed emergence and lowernumber of tillers for stressed plants and those sown deep as presented in Figure 4.

5 M.Stapper and R.A.Fischer (1990) Australian Journal of Agricultural Research, 41(6): 997-1056


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Figure 5. Tillering as a function of leaves per plant and being dependent on management and variety. The normalcrop and low density lines show tillering for a 150 and 70 plants/m

2stand, respectively. The low density trajectory

may also be followed for early sown very late (winter) wheat, leading to 14 tillers at Z17 and 30 tillers at Z19.

Tillering stops under adverse conditions of water or nitrogen stress and water logging as newtillers only emerge when daily growth is over a threshold (see footnote 1). It may then restartwhen conditions become favourable again, depending on the stage of initiated spike andrelated start of stem elongation (see below). The next tiller may then skip one or more mainstem leaf-axils as each tiller-window remains only open for a limited time. A tiller may also bemissing in the axil of leaf one under marginal conditions during emergence. Missing tillers in

the expected tillering pattern can be used to diagnose a problem that occurred earlier in thecrops history.

The presence of coleoptile tillers will indicate achievement of a very good seedbed incombination with relatively shallow sowing. The seedling on the left and centre in Figure 4has a coleoptile tiller on its left and then the first leaf with a tiller on the right.

Figure 5 shows normal tillering for a typical 150 plants/m2 density sown in May under non-limiting conditions and typically achieving stage Z16,26 on the southern plains. Sowing beforeearly April with increasing vernalisation requirement of varieties creates a longer tillering-window. For example, very late (eg. Mackellar, Rudd; group 6), late (eg. Rosella, Currawong;group 4) and medium (eg. Janz, Chara; group 3) maturities sown in early April typically have,without stresses, about 30, 15 and 8 tillers per plant, respectively, from 110 plants/m2. These

result in shoot densities around 3400, 1800 and 1000 shoots/m2, respectively. The latter, aChara-type, had the most preferred shoot density (see below) but flowered in mid-August andwas frosted.

The number of tillers that survives depends on the achieved shoot density and availability ofsolar energy, nitrogen and water (see footnote 1). Usually tillers that do elongate and formnodes will be spike bearing. From flowering onwards their development becomes similar, withsome tillers even becoming earlier then main stems.

Spike initiation Floral initiation and terminal spikelet stages are the start and finish of thespike initiation phase (Fig. 1, box Fig. 2). Final leaf number (ie. the flag) is being set withinitiation of the floral (spike) on the main shoot. Maturity is delayed with an increasing numberof leaves that form and subsequently emerge on a plant, resulting in delayed flag leaf stageand hence flowering. Floral initiation occurs relatively later, for example from Z14 (box Fig.2)to Z15, for later maturing varieties on a given sowing date.


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For varieties with a vernalisation requirement floral initiation occurs relatively later with earlierand later sowing on either side of late-June, thereby resulting in higher final leaf numbers.This is more pronounced for the increasing vernalisation requirement from maturity group 3 to6. Vernalisation is delayed when pre-floral-initiation temperatures become higher. Forexample, likely final leaf numbers are given in brackets for early April, Mid-May and late-Julysowings, respectively, for H45 (8.5, 9, 8), Chara (13.5, 11.3, 12), Rosella (15.8, 11.8, 12.8)and Mackellar (17,12.4, no initiation); representative of very-early, medium, late and very latematurities, respectively. A late-July sowing at Griffith is too warm for Mackellar to vernaliseand remains therefore vegetative. Similar for group 5 varieties from an early Septembersowing. To achieve final leaf numbers of 17, 14, 11 and 8, spike initiation has roughly to takeplace before leaf stage 12, 10, 7 (Z17) and 5 (Z15).

Terminal spikelet initiation, the one at the tip of a spike, marks the end of spike initiation andsets the number of spikelets on the spike-to-be (see Fig. 2 spike initiation box and Z65). Thespikelets on the young spike are generally initiated between leaf stages 6.5 and 10 (Z 17 to30) for an early sown late maturity, and between 4 and 7 (Z14 to 17) for a May sown mediummaturity. This process can be monitored by looking through a magnifying glass at the growingpoint of a seedling, just above the crown (box Fig. 2). Terminal spikelet stage is associated

with spike at 1cm, Z30, and 10 mm is about the length the true stem has reached then. Uptill this point the stem of seedlings has been not a true stem, but made up of stacked leafsheaths.

Timing of terminal spikelet stage, the end of spike initiation, thus becomes visible with delaysin start of stem elongation for increased maturity as shown for the three maturities in 20 Maysowing of Figure 3; groups 5 (late), 3 (medium) and 1 (very early) having final leaf numbers of12.5, 11 (ie. Fig.1) and 9.5, respectively, causing delayed achievement of Z30. Soon afterterminal spikelet stage rapid elongation of the true stem will begin (Fig. 1). The young spike isthen still well below the soil surface. The spike remains smaller then 10mm up till flag leafstage, Z39.

Without magnifying glass the completion of spikelet initiation can therefore be determined bylooking at the length of the true stem on the developing plant. Compare stem in Figure 2spike initiation box and process in Z13,21 to Z15,23 and Z17,24 where the length of the stemincreases from a couple of mm to 10 mm during initiation of the spikelet primordia from floralinitiation to terminal spikelet stage (Fig. 1), and being already 20 mm for Z17,24.

Start of Stem elongation Figure 1 shows the height increase of the base of the spikeduring the process of stem elongation from floral initiation till after flowering. The initiatedspike is at the tip of the elongating stem, hence the term spike at 1cm as the indicator forstem elongation commencement, Z30, which will then accelerate soon. Check plants foroccurrence by pulling away main stem tiller bunches and peel away remaining main stemleaves, or using a knife. For early sown very late (and late) maturities there is sometimes afalse elongation of the first internode before the spike has been fully initiated. Such

internode stem remains short and thin before a next one starts to elongate, however, withoutforming a node in between and still remaining below the soil surface. Z17,24 in Figure 2 alsoshows another indicator for likely occurrence of Z30. That is, when the height, H, of the lastformed main stem leaf ligule reaches 10 to 12 cm above the soil.

Nodes and Stem elongationFigure 1 shows the appearance of successive nodes duringstem elongation and the increase in height above the soil surface for successive nodes,always remaining just under the spike. Stem elongation is taking place in the zone where thenode is forming just below the young spike. In the field feel the developing node on fourplants per observation site. The first node stage, Z31, is reached when a thickening, a knobcan be felt at the bottom of the main stem as low as just at the soil surface. Z32 is reachedwhen the next bump can be felt above the first node, which usually occurs when that

internode has reached 60% of its final length (ie. Z31.6 with fraction). Only one internodeelongates at the time and ceases growth with formation of a node, and continuing with


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elongation of the next internode ever pushing the spike up, which thus remains just above thedeveloping node. Hence the position of the spike remains some 10-12 cm below the ligule ofthe last fully emerged leaf (see Fig.2 Z32).

Flag leaf to Booting The final leaf or flag leaf will appear at the tip (Z37 to 39) during theformation of the second last node (Fig. 1), which is at Z32-33 for most sowings of varieties in

groups 1-3 and at Z33-34 for groups 4-6 sown before mid-April. Plants are then some 40 cmtall. Check if it really is the flag by removing the top leaves. Z39 is reached when the flag leafhas fully emerged, that is, its ligule becomes visible between blade and sheath (Fig. 1 and 2).On the plains it will on average be some 25 days from Z39 to a Z65 (mid-flowering) occurringin the optimum period around 1 October, with Z50 (start heading, ear peep) occurring halfway(Fig. 3), with this duration between 20 and 30 days for hot and cool periods, respectively.

As tillers are catching up with main stems, growth stages are now determined by looking atthe whole crop area at each observation site. Estimate the growth stage of the average shootfor booting (Z40 to 49) and heading (Z50 to 60) stages. The position of the spike or bootrelative to the ligule of the second last leaf determines the boot stages: Z41 (below ligule, noswelling), Z43 (swelling opposite ligule) or Z45 (full boot, above ligule), with examples given in

Figure 2.From flag leaf till full-boot (Z39 to Z45) the spike grows and develops roughly from 10 mm to100 mm (Fig. 1). This is an important first part of sinksize determination where before thecrop had been developing primarily the source with roots to feed it. Where source is thegreen matter of leaves and stems for the capture of carbon dioxide with solar energy(=photosynthesis) and sink the final depository of carbohydrates and nutrients in grain,determined by spike and kernel numbers and sizes (see footnote 1).

The spike has reached its full length when it emerges from the tip of the flag-leaf sheath, forexample, awns first in Figure 2 Z49. That picture shows the structure of the shoot with the leafsheath of each leaf blade, connected at ligule, wrapped around the stem and connected tothe stem at a node, for example, the flag leaf to node 5. Figure 1 shows how such a structure

develops over a season. The spike, sink size, is further developed during heading, floweringand kernel growth phases (Fig. 1; footnote 1).

Heading and Flowering Z51 is when the terminal spikelet of the spike becomes visible,ear peep. Heading continues till the complete spike has emerged, still without yellow anthersextruding from its florets, Z60 (Fig. 2 Z60). Flowering starts, Z61, when the first yellow anthersare visible on up to 10 percent of shoots. Check inside green basal florets in middle of spikewhen there are no yellow anthers visible. Under stress conditions fertilization may take placewith yellow anthers remaining inside, as barley normally may do (even sometimes in boot),otherwise the anthers are green with flowering still to commence. Mid-flowering or anthesis,Z65, is reached when half of the shoots have yellow anthers visible; on a single plant it isreached when the middle half of the spikes spikelets has anthers visible (Fig. 2 Z65). That

last one also shows a picture of a spikelet with five florets of which three would have hadanthers that fertilized. When the carpel is fertilized, the once feathery stigma shrivelsimmediately.

Flowering in the optimum period around 1 October takes place in 5 to 7 days, but somevarieties may flower outside this range as some are more synchronous than others. Visiblenitrogen stress at Z30 (senesced bottom leaves, few light-green leaves, poor tillering) mayresult in 2 to 5 days earlier flowering compared with non-stressed. Very low sowing rates (

crop monitoring for wheat

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