effects of temporary water stress after anthesis on grain yield and yield components in different...

J. Agronomy & Crop Science 173, 3 2 ^ 0 (1994)© 1994 Blackwell Wissenschafts - Verlag. BerlinISSN 0931-2250

Institute of Crop Science and Plant Breeding, Christian-Alhrechts-University Kiel, Kiel, GermanyF.R.

Effects of Temporary Water Stress After Anthesis on Grain Yield andYield Components in Different Tiller Categories of Two Spring WheatVarieties

K. SiELiNG, O. CHRISTEN, H . RICHTER-HARDER and H. HANUS

Authors' address: Dr. K. SlELING, Dr. O. CHRISTEN', Dipl.-Ing. Agr. H. RICHTER-HARDER, Prof. Dr. H.HANUS, Institute of Crop Science and Plant Breeding, Christian-Albrechts-University Kiel, Olshausenstr.40, 24118 Kiel, Germany.

With one figure and 6 tables

Received September 6, 1993; accepted March 28, 1994

Abstract

Water stress might limit grain yields of cereals under humid conditions. The objective of this study was toinvestigate the effect of a temporary water shortage at three different stages after anthesis on the grain yieldand yield components of different tiller categories in two spring wheat varieties. A pot experiment withcontrolled water supply and rain shelters was conducted in 1984 and 1985 in Kiel, N. W. Germany. Thewater stress (pF 2.9 to 3.4) was imposed either between anthesis to early milk development of the caryopsis(WSl) (EC 65 to EC 72 according to ZADOKS scale), early milk development to late milk development ofthe caryopsis (WS2) (EC 72 to EC 77) and late milk development to maturity (WS3) (EC 77 to EC 92). THfcontrol had a constant water supply throughout the growing season of between pF 2.2 to 2.5.

The water stress treatment WSl significantly reduced the single plant yield by 10 % (1984) and 15 % (1985)in one variety (Selpek), whereas the other variety was unaffected. The response of both varieties to the twolater treatments was smaller and insignificant.

In the first year the yield decrease in the variety Selpek after the WSl treatment was mainly caused by alower number of ears per plant compared with the untreated control (WSO). In the second vear (1985)additionally a lower grain weight of the second category shoots caused by a reduction of the number ofkernels per ear contributed to the decrease of the single plant yield. The yield component thousand grainweight could not compensate for the reduction in the number of kernels per ear.

Key words: Spring wheat, water stress, grain yield, yield components, second category tillers, genotype.

Introduction

Cereal production in various environments ofthe world is frequently affected by a shortageof available soil water. Especially under semi-arid, mediterranean and continental conditionswater deficits often limit grain yields. But alsoin humid and maritime climates occasional dryperiods might cause substantial yield losses.Based on meteorological data BEINHAUER and

' To whom correspondence should be addressed.

GUNTHER (1990) estimate that for spring sowncereals on light soils in northern Germany inthree out of six years an irrigation treatment inMay with a minimum of 30 mm would con-siderably increase grain yield.

Numerous glasshouse and field experimentshave demonstrated principally that each yieldcomponent might be affected by temporarywater deficits depending on the developmental

U.S, Copyright Clearance Center Code Statement: 0931-2250/94/7301-0032$t0.50/O

Effects of Temporary Water Stress on Spring Wheat 33

stage at which water stress occurs. Dry growingconditions prevaiUng over the entire devel-opment or severe water stress at the bootingstage can reduce the final number of ears perm^ compared with a control (CAMPBELL et al.1977, INNES et al. 1981, JOHNSON and KANE-MASU 1982, BLUM and PNUEL 1990). A waterstress imposed later in the plant developmentmight additionally cause a reduction in thenumber of kernels per ear and the thousandgrain weight (DAY and INTALAP 1970, INNESand BLACKWELL 1981, MOGENSENetal. 1985).

STOCK et al. (1976) investigated the effect ofa temporary water shortage on different cerealcrops in greenhouse and field experiments.Under controlled conditions a water stressbetween anthesis (EC 65) and dough devel-opment (EC 85) reduced the grain yield ofspring wheat 24 % and caused a reduction ofall yield components, whereas under field con-ditions the effect on the grain yield was neg-ligible.

In all of these studies the yield componentswere either averaged over the different shootcategories or tillers were completely removedin order to standardize the plants (e.g. LANGERand AMPONG 1970, FiSCHER 1973). Only ASPI-NALL et al. (1964) and KOBATA et al. (1992)provide details on the yield response of thevarious tiller categories. In both experimentsthe number of kernels per ear on the main stemand the two primary tillers was significantlyreduced by a water stress at or right afteranthesis.

Extensive research has been conducted ongenotypic variation in drought tolerance, sinceirrigation is often not an economically feasibleoption in cereal production. Various mor-phological and physiological traits were ident-ified as possible explanations for genotypicdifferences. A cultivar specific reduction in thenumber of kernels per ear as the main reasonfor differential response to dry conditions wasidentified by several authors (LANGER andAMPONG 1970, DUBETZ and BOLE 1973, INNESand BLACKWELL 1981, ENTZ and FOWLER1990). Based on experiments comparing lineswith a high and a low number of ears per plant,INNES et al. (1981) argue that in environmentswith reliable water supply before anthesis,genotypes with a high ear bearing capacity givehigher yields, whereas lines with a limited till-ering capacity might be better adapted toregions where droughts before anthesis are

Table 1. Characteristics of the soil

Soil typeBulk densityTexture

PHP2O5K2OMg

sandy clay1.42 g/cm^

27.9% clay29.5% silt

42.0% sand7.3

11 mglOOg/soil13mglOOg/soil20 mg lOOg/soil

common. These studies demonstrate that theyield components of different genotypes arespecifically affected by a temporary watershortage and that cultivar variation in droughttolerance for these traits can occur.

Our objectives, therefore, were to quantifythe impact of water stress on grain yield andyield components of two spring wheat cultivarswith special emphasis on the reaction of thedifferent tiller categories.

Materials and methods

Experimental details

The effect of temporary water stress on spring wheatwas studied in 1984 and 1985 using Mitscherlich-pots, each one filled with 5 1 soil. The soil was sampledfrom a subsoil of a gravel pit and showed greathomogeneity, a relatively high proportion of clay andan extremely low content of organic material. Theseproperties ensured a sufficient water holding capacityand no interference with mineralized nitrogen fromorganic material with the different nitrogen treat-ments. Some characteristics of the soil are shown inTable 1. After sampling the soil was dried for 24 h at110 °C followed by a milling process in order tofurther homogenise the soil to an aggregate size of<5 mm using a soil mill.

The physical properties of the soil were analyzedwith a pressure membrane technique according toRICHARD (1947). The obtained moisture-tensioncurve showed a typical shape for a clay soil with amaximum water content (pF = 0) of 41.8 %, 20.7 %atpF 2.8 and 15.1 % water content at pF 3.4. Crust-ing of the top soil layer in the pots and evaporationwas minimized by topping up each pot with anapproximately 2 cm layer of gravel.

The pots were kept outside and in the case of rainthe whole experiment was sheltered with plastic foil.After rain events the foil was removed immediatelyin order to minimize negative effects on radiation.During the treatment periods the pots were regularly

34 SiELiNG, CHRISTEN, RICHTER-HARDER and HANUS

Temperature (°C)

March April May June July Aug

long term average + 1984 -^ 1985

Fig. 1. Temperature for long-term average and 1984 and 1985 growing season at Kiel

weighed and additional water was supplied whennecessary.

The weather conditions

Both years were characterized by lower average tem-peratures during most of the growing season. In thefirst year (1984) these conditions prevailed during themonths May, June and July and were accompaniedby below average number of sunshine hours. In 1985only the months June and July were cooler than anaverage year, again with less sunshine compared withthe long term mean (Fig. 1).

Treatments

The experiment is based on a polyfactorial trial in ablock design with three replicates. Within the blocksthe treatments were arranged randomly (Table 2).Since the duration of the water stress treatments werebased on the morphological stages of the wheat crop,the time periods differed between the years accordingto the weather conditions in 1984 and 1985. Thegrowth stages are defined according to ZADOKS et al.(1974).

In both years 26 germinated seeds were planted inthe last week of March in each pot. After estab-lishment, the number of plants per pot was stan-dardized to 15 (PDl) or 20 (PD2) plants dependingon the required plant density. The pots receivedfertihzation with all necessary nutrients in a sufficientamount in two applications at EC 13 and EC 25.Nitrogen was applied as ammoniumnitrate m fourapplications with 0.4 g N per pot to a total of 1.6 gN per pot. The additional nitrogen (0.4 g N per pot)

was apphed 10 days before anthesis. Therefore thesepots received a total of 2.0g N per pot. The twolast factors caused only small, mostly insignificantdifferences and therefore in this paper we will con-centrate on the effect of the interaction between thetwo varieties and the four water stress treatments.

Data collection

At maturity all plants were harvested individually anddried at 70 °C for 48 hours. The ears of the differenttiller categories were subject of a detailed yield for-mation analysis. The number of grains per ear wascounted and the individual tiller grain weight wasdetermined. The thousand grain weight was cal-culated based on the grain weight and the number ofgrains per ear. In the first year (1984) a total of 993plants and in the second year (1985) 1339 plants wereanalyzed. The minimum number of plants analysedper rephcate was 55 in 1984 and 56 m 1985.

Statistical analysis

Data were subjected to a statistical analysis usinggeneralized linear models (GLM), option LSMEANSof the SAS package (SAS 1985, SEARLE 1987). Thegeneralized linear models (GLM) were applied toallow for the unequal numbers of observations.

Results

In the two experimental years the water stress(pF 2.9 to 3.4) instead of pF 2.2 to 2.5 in thecontrol developed always within two days. The


Table 2. Factor levels

1. Water stress

2. Variety

3. Nitrogen

4. Plant density

control (pF 2.2—2.5) WSOEC 65 to 72 (pF 2.9—3.4) WSlEC 72 to 77 (pF 2.9—3.4) WS2EC 17 to 92 (pF 2.9—3.4) WS3SelpekTurbocontrol, 1.6 g N pot0.4 g N pot additional nitrogen10 days before anthesis15 plants per pot20 plants per pot

Water

1984

171315

stress period(days)

1985

161519

NO

NlPDlPD2

Table 3. Effect of temporary water stress on the single plant yield [g] andthe number of ears per plant of two spring wheat varieties in 1984 and 1985

Year

1984

1985

Year

1984

1985

Variety

SelpekTurbo

SelpekTurbo

0

Variety

SelpekTurbo

SelpekTurbo

WSO

L57b1.65ab1.61ab2.24a2.27a2.25a

WSO

2.11a1.82bc1.97a2.02 n.s.2.102.06 n.s.

Single

WSl

1.42c1.63ab1.53b1.93b2.23a2.08a

Ears

WSl

1.69c1.58c1.63b1.862.111.99

plant yield

WS2

1.53bc1.71aL62a2.14a2.24a2.19ab

per plant

WS2

2.01ab1.84bc1.93a1.902.142.02

WS3

1.56b1.74a1.65a2.23a2.28a2.26a

WS3

2.03ab1.88b1.96a1.992.U2.06

Means followed by the same letter are not statistically different at P < 0.05.Means without statistically significant interactions are labeled n.s. (notsignificant).

water stress treatment right after anthesis (WSl) Selpek 10 % in 1984 and 15 % in 1985 comparedreduced the single plant yield in the variety with the untreated control (WSO) (Table 3). The


Table 4. Effect of temporary water stress on the single ear yield [g] of themain stem shoots and second category shoots of two spring wheat varietiesin 1984 and 1985

Year

1984

1985

Year

1984

1985

Variety

SelpekTurbo

<PSelpekTurbo

Variety

SelpekTurbo

SelpekTurbo

4>

wso

1.21 n.s.1.361.29 n.s.1.52b1.59a1.55a

WSO

0.37a0.37a0.37ab0.79a0.67b0.73a

Main stem shoots

WSl

1.181.471.321.46b1.59a1.52ab

WS2

1.171.411.291.49b1.50b1.50b

Second category shoots

WSl

0.38a0.29b0.34b0.62b0.63b0.63b

WS2

0.40a0.40a0.40a0.79a0.67b0.73a

WS3

1.191.411.301.51b1.56ab1.54ab

WS3

0.38a0.39a0.39a0.77ab0.70b0.73a


single plant yield in the variety Turbo wasunaffected. A water shortage later in the devel-opment either between EC 72 to 77 (WS2) orbetween EC 77 to 92 (WS3) only reduced thesingle plant yields in the variety Selpek. Thedifference, however, was not statisticallysignificant.

In both years and all treatment levels, thevariety Turbo outyielded the variety Selpekwith the largest relative differences after a waterstress between EC 65 to 72 (WSl). Despitethese rather small effects on single plant yield,the water stress treatments compared in thisexperiment caused some substantial changes inthe yield formation of the two varieties.

According to the described effects of a tem-porary water shortage on the single plant yield,the number of ears per plant was in both yearsreduced after a temporary water shortage rightafter anthesis (WSl). This effect was most pro-nounced in the first year (1984) in the varietySelpek.

The response in single ear yield in the dif-

ferent shoot categories after a temporary watershortage reveals some compensatory effects(Table 4). In both years the grain yield of themain stem tillers of the variety Selpek was unaf-fected by the different treatments, whereas inthe first year (1984) in the variety Turbo a waterstress between EC 65 and 72 (WSl) increasedthe grain yield of the main stem tillers comparedwith the untreated control (WSO). In contrast,the yield of the second category shoots was in1984 reduced in the variety Turbo after waterstress treatment WSl, whereas in 1985 the var-iety Selpek suffered a 23 % reduction comparedwith the untreated control (WSO). The two laterwater stress treatments either between EC 72to 77 (WS2) or EC 77 to 92 (WS3) did in bothyears and both varieties increase the single earyield of the second category shoots.

The described effects were the consequenceof variety specific responses in the number ofkernels per ear and the thousand grain weightwhich are shown in Tables 5 and 6.

The reduction in the single ear yield of the


Table 5. Effect of temporary water stress on the number of kernels per earof the main stem shoots and second category shoots of two spring wheatvarieties in 1984 and 1985

Year

1984

1985

Year

1984

1985

Variety

SelpekTurbo

<pSelpekTurbo

<t>

Variety

SelpekTurbo

<pSelpekTurbo

WSO

27.8 n.s.34.731.2 n.s.34.8 n.s.37.336.1 n.s.

WSO

15.6 n.s.14.515.1bc22.6a17.4bc20.0a

Mam stem shoots

WSl

27.335.931.633.937.835.9

WS2

27.635.231.435.038.636.8


WSl

17.110.713.9c17.1bc16.3c16.7b

WS2

17.416.516.9a22.6a18.7b20.7a

WS3

27.335.231.234.437.536.0

WS3

16.415.415.9ab22.4a18.3bc20.4a


second category tillers was solely caused bydifferences in the number of kernels per ear. In1984 the water stress between EC 65 and 72(WSl) caused a reduction in the number ofkernels per ear in the second category shootsof from 14.5 to 10.5 (28%) in the varietyTurbo. In the second year (1985) the same waterstress treatment reduced the number of kernelsper ear in the variety Selpek from 22.6 to 16.9(26 %). In both varieties this reduction waspartly compensated by an increase in the thou-sand grain weight, however this increase couldnot completely eliminate the lower number ofkernels per ear.

Discussion

The yield response of spring wheat to a limitedwater availability reported herein was con-siderably smaller compared with most reportsfrom the literature based on either greenhouseor field experiments. For example, DAY andINTALAP (1970), working in Arizona, USA,

observed a yield reduction of 3 7 % if wheat wasstressed at the dough stage of developmentcompared with a fully irrigated control. A yielddecrease of more than 50 % is reported byCAMPBELL et al. (1977) from Saskatchewan,Canada. And in a study conducted inCambridge, UK, INNES and BLACKWELL(1981) compared the effect of a 10 week droughtfrom anthesis to maturity with an irrigatedcontrol and found a yield decrease of up to44 %. The reason for this discrepancy is thesmaller severity and shorter duration of thewater stress treatments applied in our exper-iment. Additionally, the high relative humidityin our experiment compared with conditionsin Canada or the US presumably reduced theimpact of the temporary water shortage (KOB-ATA et al. 1992). However, a yield response toa temporary water shortage comparable to ourresults is reported by STOCK et al. (1976) fromGermany and MOGENSEN et al. (1985) fromDenmark and might therefore be regarded astypical for a humid climate.


Table 6. Effect of temporary water stress on the thousand grain weight ofthe main stem shoots and second category shoots of two spring wheatvarieties in 1984 and 1985

Year

1984

1985

Year

1984

1985

Variety

SelpekTurbo

0SelpekTurbo

Variety

SelpekTurbo

SelpekTurbo

<t>

WSO

43.9 n.s.39.741.8ab43.7 n.s.42.843.3a

WSO

22.8 n.s.25.924.3 n.s.35.0cd39.8a37.4ab

Main stem shoots

WSl

43.441.242.3ab43.142.142.6ab

WS2

42.840.541.7b42.739.240.9b


WSl

21.727.624.636.4bc40.2a38.3a

WS2

23.224.423.835.led37.1b36.1c

WS3

43.940.942.4a44.241.843.0ab

WS3

23.426.124.733.7d39.3a36.5bc


Most results about the stage specific sen-sitivity of cereals to water stress are based onexperiments with standardized plants, i.e. alladditional tillers were removed immediatelyafter their appearance (LANGER and AMPONG

1970, FiSGHER 1973). In these experiments thecomponent responsible for the observed yieldreduction after a water stress from anthesis (EC65) to early milk development (EC 72) wasthe number of kernels per ear. Our results,however, indicate that a large contribution tothe observed yield reduction caused by a waterstress after anthesis (WS2) is due to a lowernumber of ears per plant which concurs withthe findings of STOGK et al. (1976) and MOG-ENSEN et al. (1985). Similar results reportedfrom other experiments were either restrictedto only one genotype (INNES and BLAGKWELL

1981) or one sowing date (MUSIGK and DUSEK1980). We therefore hypothesize that the var-iety Selpek and to a smaller extent the varietyTurbo had a tendency to senescence late devel-

oped tillers during a water stress from anthesis(EC 65) to the early milk stage (EC 72). Thesingle plant yields did only respond marginallyto the two later water stress treatments eitherbetween EC 72 to 77 (WS2) or between EC 77to 92 (WS3), which can be explained by thedecreasing susceptibility of the plants to sen-escence late tillers. Unlike reports by ASPINALLet al. (1964) the response of the second categoryshoots to the yield decrease after a water stressafter anthesis (WSl) was only observed in oneout of two experimental years. This effect,however, was presumably caused by thedecrease in the number of ears per plant in thefirst year (1984) which consequently lead toa compensatory effect. Conclusions about avariety specific response to a temporary waterstress based on our results have to be drawnvery carefully, because only two varieties weretested and the variety Turbo did only respondwith a small and insignificant reduction in thesingle plant yield. Thus, only changes in the


yield components occurred in one of the exper-imental years.

Zusammenfassung

Einfluf̂ zeitweisen Wasserstresses nachAnthesis auf Kornertrag und Ertragskom-ponenten unterschiedlicher Bestockungstri-ebkategorien von zwei Sommerweizensorten

Die Zielsetzung der vorliegenden Arbeit lag inder Untersuchung der Wirkung eines tem-poraren Wasserstresses zu drei unterschied-lichen Entwicklungsstadien auf den Kornertragund die Ertragskomponenten in den ver-schiedenen Ahrenkategorien von zwei Som-merweizensorten. Ein Gewachshausversuchmit kontrollierter Wasserversorgung wurde inden Jahren 1984 und 1985 in Kiel im Nordwes-ten der Bundesrepublik Deutschland durch-gefiihrt. Der Wasserstreft (pF 2.9 his 3.4) wurdeentweder zwischen Bliite und friiher Milchreife(WSl) (EC 65 his 71 nach der ZADOKSSkala), friiher Milchreife und his spater Milch-reife (WS2) (EC 71 his EC 77) oder spaterMilchreife his zur Druschreife (WS3) (EC 77his EC 92) induziert. Die Kontrollvariante hattewahrend der gesamten Vegetationsperiode eineWasserspannung zwischen 2.2 und 2.5.

Ein temporaren WasserstreE von EC 65 his72 verminderte hei der Sorte Selpek die Ein-zelahrenertrage signifikant um 10 % (1984)hzw. 15 % (1985) im Vergleich zu der unbe-handelten KontroUe. Der Einflull der beidenspateren Wasserstrefiphasen auf die Einzel-pflanzenertrage war nicht statistisch gesichert.Der Ertragsriickgang der Sorte Selpek im erstenVersuchsjahr, verursacht durch den Wasser-strefi WSl, war im wesentlichen in einer ver-minderte Ahrenzahl je Pflanze begriindet. Imzweiten Versuchsjahr (1985) trugen dariiberhinaus auch ein verminderter Einzelahrenertragder ersten Nehentriebe hervorgerufen durcheine geringere Anzahl Korner je Ahre zu demErtragsruckgang hei. Eine Kompensationdurch die Tausendkornmasse wurde nichtheobachtet.

Acknowledgements

This project was funded by the 'Deutsche For-schungsgemeinschaft*.

References

AsPiNALL, D., P. B. NiCHOLLS, and L. H. MAY,

1964: The effect of soil moisture stress on the growthof barley. I. Vegetative development and grain yield.Australian Journal of Agriculture Research 15,729—745.

BEINHAUER, R. and J. GUNTHER, 1990: Agrar-meteorologische Arbeitsunterlagen und Planungs-hilfen fur Norddeutschland. WissenschaftsverlagVauk Kiel KG.

BLUM, A., and Y. PNUEL, 1990: Physiological attri-butes associated with drought resistance of wheatcultivars in a mediterranean environment. Aus-trahan Journal of Agriculture Research 41, 799—810.

, J. W. JOHNSON, E . L. RAMSEUR, and E. W.

TOLLNER, 1991: The effect of a drying top soil andpossible non-hydraulic root signal on wheat growthand yielcl. Journal of Experimental Botany 42,1225—1231.

CAMPBELL, C . A., H. R. DAVIDSON, and F. G.

WARDER, 1977: Effects of fertilizer N and soil moist-ure on yield, yield components, protein content andN accumulation in the aboveground parts of springwheat. Canadian Journal of Soil Science 57, 311—327.

DAY, A . D . , and S. INTALAP, 1970: Some effects ofsoil moisture stress on the growth of wheat {Triticumaestivumh. emThell.). Agronomyjournal 62, 27—29.

DUBETZ, S., andj . B. BOLE, 1973: Effects of moisturestress at early heading and of nitrogen fertilizer onthree spring wheat cultivars. Canadian Journal ofPlant Science 53, 1—5.

ENTZ, M . H . , and D. B. FOWLER, 1988: Criticalstress periods affecting productivity of no-till wmterwheat in western Canada. Agronomy Journal 80,987—992.

, D. B. FOWLER, 1990: Differential agronomicresponse of winter wheat cultivars to preanthesisenvironmental stress. Crop Science 30, 1119—1123.

FISCHER, R . A., 1973: The effect of water stress atvarious stages of development on yield processes mwheat, pp. 233—241. In:SLAYTER, R. O. (ed.) Plantresponse to climatic factors. UNESCO, Paris.

INNES, P., and R. D. BLACKWELL, 1981: The effectof drought on the water use and yield of two spnngwheat genotypes. Journal of Agricultural Science,Cambridge 96, 603—610.

, R. D. BLACKWELL, R . B . AUSTIN, and M. A.

FORD, 1981: The effects of selection for number ofears on the yield and water economy of winterwheat. Journal of Agricultural Science, Cambridge97, 523—532.

JOHNSON, R . C , and E. T. KANEMASU, 1982: The

influence of water availability on winter wheatyields. Canadian Journal of Plant Science 62, 831—838.

KoBATA, T., J. A. PALTA, and N. C. TURNER, 1992:Rate of development of postanthesis water deficits


and grain filling of spring wheat. Crop Science 32,1238—1242.

LANGER, R. H . M. , and A. AMPONG, 1970: A studyof New Zealand wheats III. Effects of soil moisturestress at different stages of development. New Zea-land Journal of Agriculture Research 13, 869—877.

LAWLER, D . W . , W . DAY, A. E. JOHNSTON, B. J.

LEGG, and K. J. PARKINSON, 1981: Growth ofspring barley under drought. Crop development,photosynthesis, dry-matter accumulation and nutri-ent content. Journal of Agricultural Science, Cam-bridge 96, 167—186.

MOGENSEN, V. O., H. E. JENSEN, and MD ABDURRAB, 1985: Grain yield, yield component, droughtsensitivity and water use efficiency of spring wheatsubjected to water stress at various growth stages.Irrigation Science 6, 131—140.

MusiCK, J. T., and D. A. DUSECK, 1980: Plantingdate and water deficit effects on development andyield of irrigated winter wheat. Agronomy Journal72, 45—52.

PENMAN, H . L. , 1970: Woburn irrigation, 1960—68.

VI. Results for rotation crops. Journal of Agri-cultural Science, Cambridge, 75, 89—102.

RICHARDS, L. A., 1947. Pressure membrane appa-ratures construction and use. Agriculture Engin-eering 28, 451-^54.

SAS INSTITUTE, 1985: SAS user's guide. Statistics.SAS Institute, Cary NC (5th. Edition).

SGHONFELD, M. A. , R. C . JOHNSON, B. F . CARVER,and D. W. MORNHINWEG, 1988: Water relations inwinter wheat as drought resistance indicators. CropScience 28, 526^531.

SEARLE, S. R. , 1987. Linear models for unbalanceddata. John Wiley & Sons, New York.

SOMMER, C , M. DAMBROTH, and M. SCHWARZ,1990: Untersuchungen zum sortenspezifischenWasserbedarf von Sommerweizen. Landbaufor-schung Volkenrode 40, 126—132.

STOCK, H . G. , H . J. WICKE, and C. MULLER, 1976:Bodenfeuchteanspruche von Getreide in versch-iedenen Entwicklungsstadien. Archiv Acker-,Pflanzenbau und Bodenkunde 22, 791—803.

ZADOKS, J . C , T. T. CHANG, and C. F. KONZAK,1974: A decimal code for the growth stages ofcereals. Weed Research 14, 415—421.

effects of temporary water stress after anthesis on grain yield and yield components in different...

Documents