WATBR USE AND WATBR USE BFFICIENCYOF WEEDS AND WHBAT IN SBMI - ARID

MOROCCO

A. TANJI AND M. KARROU*

INTRODUCTION

In Morocco, wheat constitutes the basic diet of the population. More thanhalf of the r.r4reat in the country is planted in semi-arid areas under rainfedconditions wiiere anuual precipitation is between 250 and 450 mm. Rainfall inthese artas is unpredictable, and its distribution is variable within each year andamong years. Most precipitation occurs in winter monlhs while summer monthsare hot and dly. Wheat is usually planted in November-December, and harvestedin May-June. Wheat growth is often harnpered by periodic drought, Hessian l1y(N'Iayetiola destructor SAY) and wecd infestations (Regehr et al., 1988;.

water availability is a factor lirniting crop productivity. weeds compete withcrops and reduce tlte arnount of water available to cfops. weed competition forwatel is considered to be severe under conditions of drvland asriculture

* Institut National de Ia Recherche Agronomique - Settat

- 2 9 -

(Radosevich and Holt, 1984).

Water use efficiency (WUE) is commonly defined as the mtio of dry matter

produced by plants to the water volume absorbed during their growth. Water use

efficiency is frequently used to evaluate tlte impact of crop ma,nagement in

rainfed fanning systems (Cooper et al., 1987).

Water use efficiency is affected by management practices (llsiao and

Acevedo, 1974 : Gregory, 1984). In a previous study in semi-arid Morocco,

Tanji et al. (1987) lbund that wecd conuol did not alTect water use in wheat but

increased WIIE by incleasing production of grain and straw.

Fallowing for approximately 16 months is widely practiced in serni-arid

Morocco. 'lhe purpose of this fallow period is to accumulate lterbage for

grazing. Chemical fallow has improved weed control and water conservation(Mazhar, 1987 ; Bouzz-a, 1990). Thus, lhere is a need {br impr6ved water storage

in soil during the lallorv period. In harsh and variable environments where

moisture supply is limited, at underslanding of soil water dynamics and patems

for crop water use is essential in identifying management strategies for

consistent and stable yiclds.

This study '*as undertaken to dctermine the effects of weeds on water use(WU) and water use efficiency of wheat ; the effects o1 nitrogen tèrtilization on

herbagc ploductiou, water use, and WUE in weedy fallows ; and tle effecLs of

chemical fallow on soil moisture conservation.

MATERIAL AND METHODS

Field experirnents wefe conducted in 1986/87 and 1987/88 on a deep vertisol

(Chromoxerert) at thc Sidi lll Aidi experirnent stâtion located in semi-alid

Morocco. They wcre conductetl on adjacent sites each year. Procedures were the

same for both years.

Wheat (Triticurn aestivum L. cv. "Nesrna 149") was sown with a drill in 30

cm row spacing at a rate of 80 kg ha-l . The seedbed was prepared by an offset

tandem disk. Amnonium nitrate at 10 kg N ha-l and P at 14 kg ha-l were

applied in bands the first yezu't'rlt previously fallow land. The seconil year, P was

applied at the rate of 20 kg ha-r at planting ou a site previously cropped with

Uarfey. Sixty kg N ha-l {iom urea were added at wheat tillering stage in t}re

secon<l year. l,lanting dates were 16 November 1986 and 9 Novernber 1987.

Broarlleaf weeds were controlled at eally wheat tillering with a mixture of

- 3 0

ioxynil (4-hydroxy- 3.5-ri i iodobcnzonirdle) ar.160 g ha -l and mccoprop [(-)-2-(4-clrloro-2-rneûrylphenoxy) pr-opanoic acidl at 10g0 g lra -1. No grassy rveedswele present on the experirnent sitcs, cxcept voluntecr- bar-ley plants whicli wereremoved by hand pulling shortly afrer crop elncr,qence. c_'ar-bot'uran(2,3-dihydro-2,2-dirnediyl-7-bcnzoturanyl

- metliylcarbamate) was applied infunorv at planting at a rarc of l l20,q ha-l to l lnit I lessian 11y ctamage. -fhe

-itrcatments werc:

l) Wecd-frce wheat. Weeds were sprayed at early wheat tillering.

2) weedy weat. wheat rvas plante<r antl managed in ûre same way as intreatmenl 1 except that weeds wcre uot conuolled.

3) Fertilized weedy falkrw. wheat was not plantecl and weeds were allowedto grow ; fertilizers were applicd at similar rates and dmes as in ueatments7 and2.

4) Non fertilized weedy fallow. wheat wâs not planted and weeds wereallowed to grow.

5) chemical fallow. Plors rvere kept weed-free by rwo applications of amixrure of glyphosate [N (phospho'omerfiyl) glycine] ar 540 s/1ô0 I warer and2,4-D l(2,4-dichlorophenoxy) accric acidl at 720 gll001 *ater..

Treatments, in7.2 x r0 m ptot.s, were arranged in a randomized completeblock design and replicated lour times. Neutron probe access tubes wer-e placedin the center of each plot soon alter wheat emergence. Neutron probe readingswere tâken ar deprhs of 1-5, 30, 60, 90, and 120 cm in each plot at early wheattillering, wheat anthesis, and maturity. water use was calculared usingcalibration curve (Watls and Troeh, 1984) and water balarce procetiure. It wascalculated based on ùe average moisture from all r-eadings uf diff"..nt depths.water use was underestimated since soil moisture measurements were notsta'ted until early wheat ûllering. weed density. weetl clry weight, andabove-ground biomass of wheat were measured from lm2 areas within each plotat wheat anùesis. weight of above-ground biomass was determined after dr.yingplant samples or subsamples ar 60 c for 72 hours. At wheat physiologicalmaturity, an area of 3 m2 from the middle rows was cut at ground level todetermine grain and straw yields. Threshing was done with a statLnary thresherand grain was cleaned with a commerciar seed cleaner. water use efficiency ofwheat was determined for fteatrnents having ùis crop. Rainfa.ll and temDeratures

ô , t

were recortled daily at (he Sidi l1l Aidi experirnent station and monthly means

are slrorvn in'fable l. The 1986187 growing season had a shortage of

prccipitittion combincd rvith unusually warm conditions that resultcd itt tltouglit

irrcsi on att crops (Watts, 1988). Rain in rnid-Mru'ch and c:uly ApLil 1987

prevcnted crops frclln being a totitl loss, although yields rvere low. 'I'ltc

crttpping

yeat' 1987/88 was wcttcr thiul the avcrage yeal'.

RESULTS AND DISCUSSION

Weed biomass

'l'he preclominant rvcctl spcies during the (wo-yeaï study were : blue

pimperlel (Anagallis ftremina Millcr), centaury (Centaurea diluta Aiton)'

corntnon poppy (l 'apaver rhoeas I-.), l leld bindweed (Convolvulus arvensis

1,.). f ielcl mzuigoftl (Calendula arvensis L.), and wild musttu'd (Sinapis arvensis

L.). These species zue carly wintcr getminating dicotyledonous rveeds. Weed

densities in flte weedy wheat treagnent at anthesis were 38 plants rn-2 in

1986/87 and 34.5 plants m-2 in 1987/88 (Table 2).

Weed populations in fertiz-etl weedy wheat wcre 26.6 and 46.3% lower (han

fertilizcd ancl non-l-ertilized wecdy fallow plots, respectively, in 1986/87, and

61.0 and 66.3% respcctively, in 1987/88. Weed dry matter reductions due to

competition l}om wheat compared with fertilized and non-fertilized weedy

fallow averagerj abour 93% in 1986181 and 807 in 1987/88. lanii ana -Tlibene

(1989) lbund that 'Nesma 149' wheat planted at 120 kg ha-r recluced weed

density an<l dry matter by 49 and 847c' respectively.

Ilerbicide treatment resulted in reduction of 86.8 an<l96.41o in weed density

and dry marrer, respecrively, compared to weedy wheat in 1986/87 (Table 2).

Complete weetl control was achieved ùe second year. Ioxynil with Mecoprop

applied at early wheat tillcring gave consistent control of a large spectrum of

diiotyledonous weerjs, confirming previous results from Morocco (Tanji and

Regehr, 1988b) and Tunisia (CYMMIT, 1973).

The addition of fertilizer did not aff-ect density and bioma-ss of weeds in

weedy fallow. Soil fertility probably was not limiting weed grov/th at the Sidi El

Aidi experimental sites.

Absence of wheat in weedy tallows allowed more weeds to emerge and

grow.

32

f 'ablc I : N'I.nthlv rainfall ancl nrean maxinrum (l\,Iax) antl nrinimum(l\,I in) air tenrperatures at Sidi l i l Aidi experiment stationduring the grorving seasons l9g(ig7 and 1987ltJu.

t986/81 r 98 7/88'I'empclature

fcmperature

Max . M inItain

InlN

0.0

0.0

RainMax. N4in

Sep. 29.8 13.8

Oct. 26.9 12.0

. . . . . . . . . . C . . . . . . . . r n m

3-5 .6 11 .1 13 .4

25.6 12.7 t9.3

2 t .5 9 .0 62 .2

20.9 8.9 139.8

r7.4 5.6 113.6

18.-l .s.8 73.-s

22.9 5.6 14.8

23.5 1.5 -5.9

24.7 10.5 t6.l

469.2

Nov. 23.5

Dec. 19.5

1 .9

4 .8

1 .0

1 .3

38.-5

.5.0

4.s.0

57 .1

38 .1

ian. 20.4

Ircb. 20.0

Mar'. 23.7 7.3

Apr. 26.9 10.2 12.8

May. 27.5

Total

l l . 6 7 . 0

203.s

ô.)

Table II: Density and dry matter of rveeds at $'heat anthesis in 1986/87

and 1987/88.

1986/87 1987/88

Treatments

Weed-free rvheat

Weedl' rvheat

Weedy fallol

fertilized

non-fertilized

LSD (0.0s)

Density

-)flrns m -

5.0

38.0

Biomass

1

kg lu-'

5.8

160.0

De nsity

Plilnts m -

0.0

Biomass

I

kg ha-'

0.0

1686.0

5 1.8

70.8

20,1

1 1 , 1 1 1

î ' lô< Q

708.0

88.5

102.5

31.9

861 1.0

8756.5

2594.6

Table III : \!'heat grain and strarv "r:ield in 1986/87 and 1 987/88'

1986/87 1987/88

TreatmentsSûawGrain Straw Grain

kg ha-1

Weed-free wheat

Wædy wheat

LSD (0.05)

r085

994

NS

2221

2029

NS

3021

931

763

7980

6066

NS

34

II igh tnd well distributetl rainlall in 1987/88 resulted in increased weedbiomass in wecdy whcat iurd rvccdl, lhllows compiuerl to the first year. Avera.ucproductivity o1'rvccds in lallorvs u,as 2269 kg ha-l in 19g6/g7 an<j g6g-t kg ha:lin 1987/88. circatcr wcccl dcnsirics and dry marrcr production in 19g7lggcornpared ivith 1986/87 wcre rnost l ikcly rlue to rnore availalrle water.

Wheat f ields

i{etluctions of total rvhcat biolnass (grain plus str.aw) due lo wecdinterlelcncc rvere 8.7 trnd36la in l9u6/87 and 19g7/gg, rcspecrively (.fable 3).

Grain yield losses due to *'cctis rvere 8.4 u.d 69.27c, zurd suaw wasdecrcascd b;' 8.9 and 24.091 . rcspcctively. 'l'hese

ilatzi inclicare rhat interlerencebetween wheat and rveeds ivas iniluenced by rainlall and rie dcgree o1 wecdinfcst r t ion.

cornpetition ber.wcen weeds antJ wheat plants was probably very high duringthe rcproductive and grain filling periods, since available soil water was low atthat tiine. The lirnitcd alnount of watcr available lbr the whcat l}om anthesis tr-lmaturity rnight ail-ecr grain set ancl 1lll. Tanji imcl Regehr (l9gga) reported thatweeds caused rvheat glain i,ield losses as high as 63% in serni-ar.id areas ofMorocco. Allowing weeds ro grow be 1'ontl the lull - tiller stage of wheat causedintcnse cornpctition fi)r water, iurtr rvheat grain yierri was reducecr (Zimdahl.1980 : Wiesc. l98 l ) .

Water use

since 1986/87 rvas drier than l9g7/gg, the quantiry c,1 warer used during thefilst grorving season was lou,er than that used in the second season (.lable 4).For both years, wectly wheat and weerJy fallows had greater evapotlanspiration(ET) than weed-liee whcat, but the dilference in ET between weed-free andweedy wheat was nor signiticurt in 19g6/g7. The highest diflèrences betweenweed-tiee and weedy wheat were found during the period from anthesis toharvest of wheat.

weed control in wheat resulted in soil moistul€ conservation. The difÏèrencefound in water use between weed-tiee and weedy wheat in this experiment is inagreement with results from Noltheastem vicr.oria, (Ausralia), where Reeves(1976) lbund that the soil moisture level was lorver in ryegrass (Lolium rigidumGaud.) Infestation wheat than in weed-free wheat under rainfed conclitions.

35

Wced spccies and infestation levels affect water use undcr dryland fanning

conditions (Brengle. 1982).

Fertilizer applied to rvcedy lallow plots did not signilicantly affect the

alnouut of wâtcf usctl during both scasons. l-he lowest evapottanspiratiolr valucs

rvere gbscrvcd in the chcrnical lhllow Ieal.nent i l l both ye'ar-s. ( ' l 'ahlc' l).

In this study, soil watcr Incasurcments were made during approximately six

months (l)cccmber to l\{ai '). In a 3-year crop rotation study in semi-aid

Ir4orocco, Mazha1 (1987) lbuncl t|at available soil moisture rncasurcd belbre

planting (November) lor rainl-ctl whcat averaged 6.7 crn lbr tltc rot'zrtiott

wheat/tillccl làllow and 2,0 crn lbr wheat/weedy lallorv.

Water use efficiency'

water use efliciency lbf total.weetl,-free wheat biomass was 207.9 t<g ha-1

.rn-l in 1986/87 and.148.3 kg-I ctn-r in 1987/88 cornpared witlt 176'6 and

196.0 in weedy wheat (Table 5). Difl-erences tretween wUE lbr total above

ground biomass (grain plus straw) in wced-frce wheat and weedy wheat were

iot rignitt.arlt the first yeat' but rvere signitlcantl)'difJerent the second yeal'

coopei et al. (1983) fbund tlrat wtlE of f'ertihzed weed-free 'MexipaL' wlteat in

scmi-afit l Syria avcragcd 291 kg lta-l ctn- 1. while thal ol ' nonlclt i l izcd wecd-flce

whcat was iO-s tg hatI crn-l. l 'analiaet al. (1990) found n<l sigrtit ' icltnt efl 'ect ol '

fertilizer rate a-nd placement on Wtill of spring wheat in Mcxrtana' LISA. They

reported tttat wuE of total liomass of wheat at harvest (straw + g_rain) valied

rrom 1e-5 to 210 kg h" i';;-i^;;;;;;il Ë unJ ioi 1o rra rrg nà-r ""-r in udrv vear. WUL ol grain 'atic6 ll'orn 96 ro 10.5 kg ha-r cm-r in a Itormal year'

;"âit to 42 kg ha"-l crn-l in a dry year. In both years, herbicirle use reduced

water use and signihcantly increased wLIE in wheat, a-s compared wiù weedy

wheat. cooper et a1. (1987) reported that any management factor which reduces

.uapou-un.plr-ation and increases the crop's ability to extract moisture will result

in greater WLIE and increased crop production' In conffast' there were no

diffirences in rtre WUE between fertilized and nonfertilized weedy fallow'

36

' fablclV:\\ 'ateruse(evaportranspiration) inditferenttreatmentsinlgg6/g7andl9g7/gg.

r 986/87 1987/88frcaûncnts

F-ll2 Total T-Ft I;-u2 Toral

Wced-l]'ec whcal

Wccdy rvlieat

Weedy lallow

l-ertilized

non- t'ertilizcd

Chemic;rl lallorv

LSD (0.0-5)

I 1.6 4.-s

I l . ( r 6.6

16.1

1 8 . 2

22.8 8 .8 31 .6

23.8 12 .8 36 .6

l 1 . 8 8 . 6

12.3 8 .4

9.3 0.9

1 .6 2 .9

20.4

20.7

10.2

--) . --)

?? .) I ( ()

19.6 17.3

19.4 1 .0

3.7 4.4

39.r

-1c).y

26.4

4.-5

'T-F: Period l l 'om rvhcat ri lrcri '-c (20.ranuary r9g7 anct r1 Dccember r9g7,respecti'ely) to arllrcsis (-5 April 1gg7 antl 15 Mar.ch lggg, rrspectivery).water use is precipitation rec.rdcd f.om tilleri'g to anthesis of wheat plussoil water at tillcr.ing rninus soil water at antlresis of wheat.

2 f'-u , period frorn wheat1988, rcspectively). Warermaturity of wheat plus soilwheat.

anthesis ro har-vesy (19 May l9g7 and 2g Mayuse is precipitation recorilecl from anthesis to

water at anthesis minus soil water at maturity of

D N1 , I

Table v : water use efl'ecienc1, (wtlE) of rrheat and $eeds at lrarYest in 1986/87 and

1987/88.

Wheat Weedy lallow

WIJE LSD (0.05)

1986/87

WUE gran

WUE total

1987/88

WUE grain

WUE total

3.8

56.2

25.9

81 .4

CONCLUSION. Ihepresenceofr r ,heatandchemicalweet lcontro l reduccdbuhdensi t l 'ant l

biomass of rveetls. 'r.he hcrbicide, ceruor I-r, gave good conuol of broadlcar

weecls that rverc domrnant at the experirnental sites. wectly fallow permittcd

high dLy rnatter prclduction clf weeds ùat can be uscd as forage' llowever' wecds

reduced the amount of water stored in weedy lallow ; tltus' the yield of the

fo l l ow ingc ropmaybereduced .Gra inands t ra rvy ie ldswere lno rea f fec tedbyweeds rlunrlg a wet croping season ùan a drier one' Weed conuol in wheat is

more justifierj dur-tng ,uuct .ti'on' because the ellect of weeds is more signilicant

during wet scasons.

The prescnce ol wccds in wheat and weedy fallow caused highcr

evapotranspiration than in weed-free wheat' Conscquently' it is necessary to

con t ro lweeds inbo ths i t ua t i ons ino rde r to teduce t l r ecompe t i t i on fo rwa te rdur ingthewlreatgrowingSea.son,andtoconservemoistureunderfa l lowfor t l refollowing crop.

.l.he eftiiiency of water use fol wheat ptorluction is decreased

when weeds are not controlled'

38

Tltis studl' clemonstrated the bcnellt of helbicidal wecd control in rlrylan6wheat. Ilcononric srrrdics shoultl bc rnaile comparing biomass and quality ofItcrbage produccd in wcccly lzrllow, and tlie impact ol soil moisrure conservationon ilre yield of ilre follnwing crop alter chemical fallow.

SUMMARY

Fluctuations and lorv :urnual iunount ol-rainlall during the gr.ou,ing season ofrvhcat i, semi-arid Mo.occo are the most lirniting factors foigrain froducrion.[]ndcf thcsc conclit ions, soil rnoistule clcf icit is usually accentuatcd i i 'weecls ru.eplcscnt ând not controllcd. Li this stutly, \\,ater use (WU)and water.usc ell iciency(v/uE) of rainlèd bread whcat ('l'riticum ae.stiyum L.) cv. Nesma 149' andwecds rvere mcasurecl in a tu,o-)'ear field trial in a semi-a_rid envirorunent at trresidi l l l Aidi expcrirne nt statio.. Expcrirnents ,çverc co'ducted during consecuti 'esL'ason.q *' irh rai,rall oI203 rnln in 19g6/97 antl469 rn irr r9g7/gg. . lrearmenrsrvcre: 1) wccd- f ree rvhcat :2) wect ly q, l icat ;3) fer . t i l ized weedy fa l low:4)non-l-ertilized rveedv lalktrv : and -5) chernical lirllow. Soil rnoisture wasrneasurcd three tirncs cach grorving scason with a ncutron probe li.om ezulyrvlieat tillering to matulit)'. Iior boh years, weed control retlucctl t}tc total wuand increased roral wIIE (grain plus straw yield/total wu ard grain/yield/totalw[J) compaed to unweecicci wheat. The highest wu va.rues ocù'-ed in weedylallows and weedy wheat : ilrus, weeds ext'acted rnore soil moisture than wheat.Fertilizer application ditl not al'l'ect r.r,eed density, wecd biomass, water use. andwtrll in rvcedy lallow. Fallow proclucti'iry avera_{ed 2.3 antJ g.7 tons ha-l ofabove-ground dry marter in r986/g7 and l9g7/gg, respecriver),. weed control indryland rvheat is rhen nccessary to procluce high yields.

39

RESUME

I-es flucruations ct lcs laiblcs quantités de précipitations pendant le cyclc du

blé sont les lactcurs les plus l imitants cle la producti<ln en milieu serni-alide

Marocain. I)ans ces contlit iotts. le déllcit l iydrique cst généraleme nt accelltué ell

présence tlcs adVcnticcs. l):urs cctte étudc, l'ér'apouanspiration (ET) et

I'clficicnce <J'utilisatiorl de I'eau 01LrE) pal le blé tcntlrc ('friticurn aestivum L')

cv. 'Nesrna 149' ct lcs aclvcntices ont été mesurécs. Ces essais ont été conduits cn

sec au dornaine expérimcntal de Sidi El Aidi pendant dcux campagnes agricole s

consécutives clont lcs pluvirnétlies étaient dc 203 Inrn en 1986181 et 469 mm cn

1987/88. Les t rarrcrncnrs l 'c tcnus sont : l ) b lé désherbé,2) b lé non c lésherbé,3)

jac|ère ngn t-r'avlilléc fertilisée, 4) jachère non tfiryaillée et n1ll) terfilisée, ct 5)

lachère chirnique. Au cçurs tle chaque campagne agricole, I'hurnidité du sol a été

mesurée à I 'aidc rlc la sotrde à ncutron, clu sratJe début tallage jusqu'àmaturité du

blé. Le désherbage tlu blé a réduit I'llT et augmcnté l'EtIE (rendcrnent grain +

paitleÆT et rcndcmcnt gfain/llT) en comparaison avec lc blé non désherbe ' Les

uut.ur* (J'ET lcs plus élcvécs ont été obtenucs <Jans les deux jachères suivies du

blé non désherbé, ce qui démonue que les adventices ont absorbé plus d'eau que

le blé. La fcrtilisittion azotéc de laiachère n'a pas allccté la densité. la biomasse'

I'llT e t I'ELIE tlc la r,égération. La productivité rnoyenrrc des deux jachèles a été

2,3 et 8.7 lonncs/ha de rnatière sèche respectivement cn 1986187 et 1987/88' l-e

désherbagc du blé est néccssaire pour améliorer les rendements en Inilieu

semi-aride non inigué..

I\,[ots clés : Idcntillcation-Blé tlur-Protéines- Gliadines-E'léctrophorégraflrme'

40

é1, -,L:.rYl é-b ;,r " [1 Jt ,.-l LJl,-i

.-'. -;l! Àrl,+l ^4 *ttl _j

c,-.,.,Jt{ iiL+l/.ÉJ lJ.tul ê *iltf i l ôG rG,yl/lir iLlloÇi,- r.:-;LrÇ fr / li1 ;.r- L-j�l Lrb di :1ry ,i:-bl,- é .-,. _r+f l CLi! "à rçÎ eÎ\spl tA q*Jti . Ul Jt - - | iJt--i-,;+ll !rÇ p ,c^nJl liô .Jj .-,t-:.J,!l

ê cui 4:!;J etj.YL '1 4çr : . '" (TRITICUM AESTIVUM L, )

é r r ?0i tLL"'Yl i-J,- il.i .-l,+l , , 'rl àLJl .rli s.r,-ul g4-.. u]/l iJe*

i , . - ; L-J-#JI, ' . - ' i .1 q8t - 8f rs r | 469 r ' l

987 -86 . , .>t_;t tn-Jt

:.r.o r:YrLu

) Cb.'- Ji- (i .9t ' .il:*it<- i.r-r{ gj (2 ,ur ' .î iu* gj ( 1

-,l-:.rYl Lrl* e CVr F (-t 1 ,l* ê Ct. ,P (4 ,.t- (JACHERE

(SONDE A NEU- 4ttt -rJi ;u ly.-,,-Jl LJ).,.+- Ê .r-r,e .ol.r._-Jta

.e.!leâ Jl.et::l ql* cr ùlr, i TRONS)

* :o ) . ul J( -- .l Çt^i c.,slr, ;11 ;f .-Jl; _,t -il Lr(_ ;Î glc-Jl ofi,l

c.;t5#,iç'Jl;rG.,rbî .-,[:rll i-jl.(, ù_r* g-r f t:Lilts (r^n /,-. ri;a i,io

u .i;+Jl éçs LWrl ,l c...oL sr|:rll OÎq*- tr \-.l,.i4ll eJ,tJ CtJlûi,Lti;,*Jl Jt&r iiÇl tçrL ùrr qJL!:Yl te *;i-d CUJI.teft .r**";,îgt:tt.:+

;l)l u t/,* 8.7 r 2 3 ;tJ CtrJJ JiJl i-ar;;tJ.r-- ..Ul J{ - -- | ÇL-j-rL rÇ, ; Îé*J t l j l v eêJ t t . 1 q8g - B f , I gB7 - 86 . ,_ r , ôB; t+ t

.et Cp ;t JF;S L-ss-è:it+l l+,1 .j!tll j .,|-L"yl

^ 1a l

REFERENCES tsItsLIOGRAPHIQ UES

BOLIZZA, A. 1990. Watcr conscrt'ation in wheat rotations under sevelal

tnallaScmCnl and ti l l lrgc s)'stctns in scmi-arit l rcas. Plt. D. l) issertatit ln.

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