ORIGINAL PAPER

Ali Osman Demir Æ Abdurrahim Tanju Goksoy

Hakan Buyukcangaz Æ Zeki Metin Turan

Eyup Selim Koksal

Deficit irrigation of sunflower (Helianthus annuus L.) in a sub-humidclimate

Received: 6 February 2004 / Accepted: 9 January 2006 / Published online: 26 January 2006� Springer-Verlag 2006

Abstract The response of sunflower (Helianthus annuusL.) to 14 irrigation treatments in a sub-humid environ-ment (Bursa, Turkey) was studied in the field for twoseasons. A rainfed (non-irrigated) treatment as the con-trol and 13 irrigation treatments with full and 12 differentdeficit irrigations were applied to the hybrid Sanbro(Novartis Seed Company) planted on clay soil, at threecritical development stages: heading (H), flowering (F)and milk ripening (M). The yield increased with irriga-tion water amount, and the highest seed yield(3.95 t ha�1) and oil yield (1.78 t ha�1) were obtainedfrom the HFM treatment (full irrigation at three stages);82.9 and 85.4% increases, respectively, compared tothe control. Evapotranspiration (ET) increased withincreased amounts of irrigation water supplied. Thehighest seasonal ET (average of 652 mm) was estimatedat the HFM treatment. Additionally, yield responsefactor (ky) was separately calculated for each, two andtotal growth stages, and ky was found to be 0.8382,0.9159 (the highest value) and 0.7708 (the lowest value)for the total growing season, heading, and flowering-milkripening combination stages, respectively. It is concludedthat HFM irrigation is the best choice for maximum yieldunder the local conditions, but these irrigation schemesmust be re-considered in areas where water resources aremore limited. In the case of more restricted irrigation, the

limitation of irrigation water at the flowering periodshould be avoided; as the highest water use efficiency(WUE) (7.80 kg ha�1 mm�1) and irrigation water useefficiency (IWUE) (10.19 kg ha�1 mm�1) were obtainedfrom the F treatment.

Keywords Sunflower Æ Deficitirrigation Æ Evapotranspiration Æ Water use efficiency ÆIrrigation water use efficiency Æ Crop water productionfunction Æ Yield response factor (ky)

Introduction

The objective of well-regulated deficit irrigation is tosave water by subjecting crops to periods of moisturestress with minimal effects on yields. The water stressresults in less evapotranspiration (ET) by closure of thestomata, reduced assimilation of carbon, and decreasedbiomass production. The reduced biomass productionhas little effect on ultimate yields where the crop is ableto compensate in terms of reproductive capacity. Insome cases, periods of reduced growth may triggerphysiological processes that actually increase yield and/or income (Smith et al. 2002). In sunflower, cropsstressed before anthesis regulate transpiration byreduction of interception of radiation (IR) mediated byreduced leaf expansion. In contrast, it is difficult toidentify a dominant factor in the regulation of transpi-ration of crops subjected to water deficit after anthesis.In that case there seems to be an interplay betweenreduced IR, by faster leaf senescence and wilting, andreduced canopy conductance. More work at the croplevel is necessary for an accurate determination of therelative effect of each of these factors on crop transpi-ration under various timings and intensities of waterdeficits (Connor and Sadras 1992).

Sunflower (Helianthus annuus L.) is one of the fourmost important oil crops in the world. Because of itsmoderate cultivation requirements and high oil quality,its acreage has increased in both developed and

Communicated by E. Christen

A. O. Demir (&) Æ H. BuyukcangazDepartment of Agricultural Structures and Irrigation,Agricultural Faculty, University of Uludag,16059 Bursa, TurkeyE-mail: aodemir@uludag.edu.trTel.: +90-224-4428970Fax: +90-224-4428775

A. T. Goksoy Æ Z. M. TuranDepartment of Field Crops, Agricultural Faculty,University of Uludag, 16059 Bursa, Turkey

E. S. KoksalLodumlu, Rural Affairs Research Institute,06583 Ankara, Turkey

Irrig Sci (2006) 24: 279–289DOI 10.1007/s00271-006-0028-x

undeveloped countries (Skoric 1992). Sunflower oil ishighly demanded not only for human consumption, butalso for chemical and cosmetic industries. The total areaof sunflower production is 510,000 ha in Turkey. OfTurkey’s sunflower production of 610,000 t, 13% of thisis produced in southern Marmara region (DIE 2001).

In respect of total yield produced, water requirementsof sunflower are relatively high compared to most crops.Despite its high water use, the crop has an ability towithstand short periods of severe soil water deficit of upto 15 atmosphere tensions. Long periods of severe soilwater deficit at any growth period cause leaf-drying withsubsequent reduction in seed yield. Severe water deficitsduring the early vegetative period result in reduced plantheight but may increase root depth. Adequate waterduring the late vegetative period is required for properbud development. The flowering period is the mostsensitive to water deficits which cause considerable yielddecrease since fewer flower come to full development.Yield formation is the next most sensitive period towater deficit, causing severe reduction in both yield andoil content (Doorenbos and Kassam 1979).

Although sunflower is known as a drought tolerantcrop or grown under dryland conditions, substantialyield increases are achieved by irrigation. There is noresearch on sunflower irrigation in the region (southernMarmara) where the study was carried out. Despite theregion situated in a sub-humid climatic zone, rainfallamounts are extremely low in the summer period whichis the main growing season of sunflower. Therefore,irrigation is vital for some periods during growing sea-son. Major decreases in sunflower yields have beenexperienced in some water shortage years in southernMarmara. Yield may increase with deficit irrigation fordry years in that region.

The objective of this study was to determine theeffects of rainfed (non-irrigated) treatment as the controland 13 irrigation treatments with a full and 12 differentdeficit irrigations applied at heading, flowering, and milkripening stages on the growth, yield response, water use

efficiency (WUE), and irrigation water use efficiency(IWUE) of sunflower grown on an alluvial soil in a sub-humid environment.

Materials and methods

The experiment was carried out during the growingseason of 2000 and 2001, between the months of Apriland September, on the experimental field of Researchand Application Centre of Agricultural Faculty ofUludag University, situated in Bursa (Turkey), latitude40�15¢ 29¢¢N, longitude 28�53¢39¢¢E, and altitude 72 mabove sea level.

The local climate is temperate, summers are hot anddry, and winters are mild and rainy. According to long-term meteorological data (1929–1991), annual meanrainfall, temperature, and relative humidity are 697 mm,14.6�C, and 69%, respectively (Anonymous 1992). Asub-humid climate prevails in the region according tomean rainfall amount (from 600 to 700 mm of annualprecipitation) (Jensen 1980). The climate of the region issub-humid, but rainfall amounts are extremely low inthe summer period. Seasonal rainfall amount is 73 mm,which coincides with 10% of total annual rainfall, forthe summer period (June, July, and August). Addition-ally, total annual evaporation is nearly twofold ofannual rainfall, and seasonal evaporation in the summermonths is much higher than seasonal rainfall amount(Table 1). Climatologic data of trial years (in 2000–2001) were measured at the meteorological stationnearby the experimental area.

The soils of the trial field are Typic Xerofluventaccording to American Taxonomic Classification, andCalcaric Fluvisol according to FAO/UNESCO Classi-fication System in which soils are alluvial and unregu-lated calcareous with profile. The soil is very fine(average 45.6% clay content), and having 0.1% totalnitrogen content (Kjeldhal method), 0.40 kg ha�1

phosphorus (Olsen method, P2O5), 5.70 kg ha�1

Table 1 Mean air temperature, relative humidity and total monthly rainfall in 2000–2001 and between 1929 and 1991 at Bursa

Years Jan Feb March April May June July Aug Sep Oct Nov Dec AverageTemperature (�C)

2000 3.3 5.2 7.6 15.0 17.7 21.8 25.5 24.8 21.2 14.8 12.5 6.2 14.62001 7.4 6.3 14.0 13.7 18.2 23.6 27.7 26.4 22.6 16.8 10.9 – 17.0Long-term average 5.3 6.2 8.3 13.0 17.6 22.1 24.5 24.1 20.1 15.6 11.2 7.6 14.6

Relative humidity (%)2000 79 68 66 72 65 61 51 56 60 78 74 84 682001 71 79 61 72 65 48 51 53 59 60 64 – 62Long-term average 74 73 70 70 69 62 58 60 66 72 75 74 69

Rainfall (mm) Total2000 29 105 96 109 49 16 9 11 82 129 22 50 7072001 9 66 49 86 65 17 2 13 42 – 93 128 570Long-term average 92 75 68 59 52 31 25 17 39 58 78 103 697

Evaporation (mm) (class A pan)Long-term averagea 40.8 47.2 64.7 102.3 104.3 213.5 256.1 232.7 161.2 89.8 54.5 50.6 1417.7

a29-year average of evaporation values

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exchangeable potassium (ammonium acetate method,K2O), 1.9% organic matter (Walckey–Black method),0.08% total salt, and a bulk density of 1.45, 1.53, and1.50 g cm�3 in 0–0.30, 0.30–0.60, and 0.60–0.90 m pro-file, respectively. The soil pH was 7.2. The water holdingcapacity (WC) of the experimental site was observed as122 mm in a 0.90 m soil profile. WC was determined bythe difference between the water content at field capacity(FC) and at permanent wilting point (PWP). There is nowaterlogging problem in the area.

The hybrid cultivar Sanbro variety (Novartis SeedCompany) was planted. It is a variety of an earlier singlehybrid, medium tall, large table, and high oil percentage.It has high resistance to Orobanche, Verticilum, andSclerotinia Sclerotiorum. In the experiments, plot sizewas 20.8 m2 (8.0·2.6 m2) at harvest; row spacing was0.65 m; plant–plant spacing was 0.30 m. The crops weresown on 4 April 2000 and 6 April 2001, and harvestedon 11 September 2000 and 5 September 2001. After plotswere harvested, seed and stem yield, oil percentage, andoil yield were recorded. Crude oil percentage wasdetermined by the Soxhlet extraction technique (Pom-eranz and Clifton 1994). Oil yield was calculated as afunction of seed yield and crude oil percentage.

Irrigation water was supplied from the deep wellsdrilled in the same area. Pressurized water was deliveredto the plots with polyethylene pipes, 60 mm in diameter,and was applied to the trial plots as controlled by awater meter. Required irrigation water was applied tothe plots by short blocked-end furrows. Perforated PVCpipe was used to ensure uniform water distribution toeach furrow in a plot. There are no recorded problemswith water quality.

The crop phenological cycle was divided into thethree critical growth stages which were considered to bethe most relevant from the point of view of theirresponse to irrigation, i.e., heading (H), flowering (F),and milk ripening (M), to determine the irrigationscheduling (Doorenbos and Kassam 1979). Irrigationwas applied at each of these stages as full and deficitaccording to the treatments listed in Table 2. The indi-vidual irrigation application depths were determined onthe basis of soil water storage depletion. Under fullirrigation condition, irrigation water was applied to0.9 m of the soil profile to achieve FC. There is noirrigation applied under non-irrigated or control condi-tion, and irrigation was applied in as much as 40 and60% of soil moisture deficit at three growth stages.Additionally, full irrigation was only applied at one andtwo growth stages. The total irrigation water appliedover the season for each treatment to achieve FC wasrecorded. The layout of the experiments was a com-pletely randomized block design with four replications.

Soil water contents were monitored gravimetrically in300 mm depth increments to 0.9 m prior to and afterirrigation at three growth stages (heading, flowering,and milk ripening), and weekly from the plots of thesecond replication (block) throughout the growingseason.

Crop evapotraspiration was estimated using thefollowing form of the water balance equation:

ET ¼ I þ P � DS � R� D

where ET is evapotranspiration (mm), I is the irrigationwater (mm), P is the precipitation (mm), DS is thechange in soil water storage (mm), R is the runoff, and Dis the drainage below the root zone. In the equation, Iwas measured by a water meter, P observed at theMeteorological Station of Agriculture Faculty, DS ob-tained from gravimetric moisture observations in the soilprofile to a depth of 0.9 m. Runoff was eliminated byearthen embankments and blocked-end furrows. Sincethe clayey soil characteristics are fully dominant in thefield, deep percolation (drainage) was assumed to benegligible so that only estimated water (field capacityminus available soil moisture content) was applied to0.9 m soil profile to reach field capacity.

Relationships between yield and ET, irrigation wateror transpiration are called production functions. A largenumber of models were developed to define thoserelationships in recent decades. Stewart’s equation isthe most frequently used model (Stewart et al. 1976;Doorenbos and Kassam 1979). In this study, the Stewartmodel has contributed to define the relationshipsbetween yield and ET.

ð1� Ya � Y �1m Þ ¼ ky ð1� ETa � ET�1m Þ

where Ya is the yield under water deficit conditions, Ym

is the maximum yield under full irrigation regime, ETa isthe ET under water deficit conditions and ETm is themaximum ET related to the full irrigation treatment.

Table 2 A list of irrigation treatments and description

Treatments Description

Control Rainfed (non-irrigated) treatmentH Irrigation applied only at heading stageF Irrigation applied only at flowering stageM Irrigation applied only at milk ripening stageHF Irrigation applied at heading and

flowering stagesHM Irrigation applied at heading and milk

ripening stagesFM Irrigation applied at flowering and milk

ripening stagesHFM Irrigation applied at all the stages (full-irrigated).

No water stressH60FM The same as HFM, but a 40% of water deficit

was applied at heading stageH40FM The same as HFM, but a 60% of water deficit

was applied at heading stageHF60M The same as HFM, but a 40% of water

deficit was applied at flowering stageHF40M The same as HFM, but a 60% of water deficit

was applied at flowering stageHFM60 The same as HFM, but a 40% of water deficit was

applied at milk ripening stageHFM40 The same as HFM, but a 60% of water deficit

was applied at milk ripening stage

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Values of ky indicate the sensitivity of sunflower todeficit irrigation.

The WUE was determined to evaluate the produc-tivity of irrigation in the treatments. WUE and IWUEare two terms used to promote the efficient use of irri-gation water at the crop production level (Bos 1980).

WUE was calculated as the ratio of seed yield (YLD) toETa, given as WUE = YLD/ETa (kg ha�1 mm�1).IWUE was estimated by following equation:

IWUE ðkg ha�1 mm�1Þ ¼ YLD�YLDrainfed

IRGA

Where YLDrainfed is the seed yield obtained from therainfed treatment or dryland yield and IRGA is theseasonal irrigation amount used in millimeter.

All data were subjected to analysis of variance foreach character using MSTAT-C (version 2.1-MichiganState University 1991) and MINITAB (University ofTexas at Austin) software. The significance of irrigationtreatments and treatment · year interactions weredetermined at the 0.05 and 0.01 probability levels, by theF test. The F-protected least significant difference (LSD)was calculated at the 0.05 probability level according toSteel and Torrie (1980).

Results and discussion

Irrigation water applied and ET

The amounts of applied irrigation water for each treat-ment in 2000 and 2001 are given in Table 3, andmonthly and seasonal ET values are given in Table 4.

Table 3 Applied irrigation water amounts (mm) and irrigationdates for irrigation treatments

Treatments 2000 2001

Dates Total Dates Total

16.06 28.06 19.07 13.06 27.06 11.07

Control – – – – – – – –H 129 – – 129 123 – – 123F – 118 – 118 – 91 – 91M – – 129 129 – – 129 129HF 129 118 – 247 123 91 – 214HM 129 – 129 258 123 – 121 244FM – 118 129 247 – 91 121 212HFM 129 118 129 376 123 91 121 335H60FM 77 118 129 324 74 91 121 286H40FM 52 118 129 299 49 91 121 261HF60M 129 71 129 329 123 54 121 298HF40M 129 47 129 305 123 36 121 280HFM60 129 118 77 324 123 91 73 287HFM40 129 118 52 299 123 91 48 262

Table 4 Monthly and seasonal calculated evapotranspiration (mm)

Treatments Months Total

Years Aprila May June July August Septembera

Control 2000 97 127 88 34 0 10 3562001 44 167 57 11 22 0 301

H 2000 90 133 189 63 0 11 4862001 33 182 145 26 42 0 428

F 2000 94 118 128 100 9 0 4492001 43 146 79 74 29 6 377

M 2000 101 114 97 90 45 6 4532001 43 148 68 117 24 0 400

HF 2000 103 105 239 111 25 2 5852001 45 154 177 95 28 1 500

HM 2000 103 118 196 104 50 20 5912001 74 212 69 145 23 0 523

FM 2000 125 93 107 182 55 15 5772001 52 149 34 222 17 21 495

HFM 2000 111 122 236 175 44 0 6882001 48 161 196 174 37 0 616

H60FM 2000 101 142 186 141 79 8 6572001 27 175 128 216 14 0 560

H40FM 2000 119 87 179 141 77 29 6322001 79 140 74 226 14 6 539

HF60M 2000 98 121 201 195 16 24 6552001 43 162 189 173 23 0 590

HF40M 2000 110 126 185 139 49 19 6282001 59 155 138 189 21 0 562

HFM60 2000 109 133 232 129 63 0 6662001 39 159 185 170 14 8 575

HFM40 2000 100 124 240 141 23 7 6352001 53 156 164 157 12 0 542

aEvapotranspiration was estimated for 24 and 26 days in April 2000 and 2001; for 11 and 5 days in September2000 and 2001, respectively. Total vegetation periods are 160 and 152 days in 2000 and 2001, respectively

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Irrigation dates are similar for each year. As Table 3shows that the crop was irrigated in the middle of Junein the heading period, toward the end of June in theflowering period, and in the second half of July for 2000and in the first half of July for 2001 in the milk ripeningperiod. The largest amount of irrigation water wasapplied to the HFM treatment in both years (376 mmfor 2000 and 335 mm for 2001).

Monthly and seasonal ET of sunflower was differentfor each treatment and between years (Table 4). Highestseasonal ET values were recorded for the HFM treat-ment with no water stress. Seasonal ET values of thistreatment were estimated as 688 and 616 mm for 2000and 2001, respectively. Highest monthly ET values variedwith treatments and years. Highest monthly ET valuesfor the HFM treatment were estimated as 236 mm inJune of 2000 and 196 mm in June of 2001 (Fig. 1).Heading and flowering growth stages correspond to thisperiod. Doorenbos and Kassam (1979) stated that thepercentage of total crop water use over the differentgrowth periods is about 20% during vegetative period,55% during the flowering period and the remaining 25%during the yield formation and ripening periods. Whenconsidering all treatments, the highest monthly ET val-ues were found as 240 mm in June of 2000 for the HFM40

treatment, and 226 mm in July of 2001 for the H40FMtreatment. The main reason for differences was that thetotal rainfall amount was 310 and 201 mm in April andin the previous months (February and March) for 2000and 2001, respectively. The largest amount of irrigationwater was applied in the irrigation season of 2000 (May,June, July, and August) which was drier than 2001. Totalrainfall amount was 85 and 97 mm in this period of 2000and 2001, respectively.

Estimated ET values for sunflower (688 mm for thefull irrigation treatment in 2000 and 616 mm for thesame treatment in 2001) are compatible with ET valuespointed out by Doorenboos and Kassam (1979). Theauthors stated that the water requirements of sunflowervary from 600 to 1,000 mm, depending on climate andlength of total growing period. There are many different

results given by many authors. In similar experimentselsewhere, ETc of sunflower was found between 500 and950 mm (Paltineanu and Sipos 1973; Browne 1977;Demiroren 1978; Ayla 1984; Yakan and Kanburoglu1989; Karaata 1991; Karaata and Aran 1998; Kadayıfcıand Yıldırım 2000).

It was observed that the mean monthly ET values(2-year average) of all irrigation treatments, full or def-icit, at three phenological stages (H, F, and M) weredifferent from each other. The differences on ET valuesof the irrigation treatments depend mainly on the dif-ferent irrigation water amounts applied. The peak ET ofalmost all treatments with irrigation at three growthstages occurred at June, whereas ET values of only twotreatments (H60FM and H40FM) reached to the peakvalue at July more likely due to deficit irrigation at thefirst phenological stage (H).

Mean monthly ET (2-year average) changes of theHFM treatment are shown in Fig. 2. In Fig. 2, ETchange is relatively slow at the beginning of the growthperiod and then tends to increase after mid-May.According to the graph, the peak value of 216 mm inmean monthly ET were obtained for the second half ofJune, and ET of sunflower gradually decreased untilharvest time. When considering the average of 2 years,the highest daily on average ET was 7.2 mm in June(corresponding to heading and flowering period). Doo-renboos and Kassam (1979) reported that ET increasesfrom establishment to flowering, and can be as high as12–15 mm day�1, and high ET rates are maintainedduring seed setting and early ripening period. ETincreased till flowering stage, then slightly decreased tillmilk ripening stage, and considerably decreased aftermilk ripening stage in both years of our study. Ourfindings for ET correspond to those of previous works.

Stem and seed yield

In this study, stem and seed yield were examined.According to variance analysis results, the differences

Months

2000 2001

100

Eva

potr

ansp

irat

ion

(mm

) 200

50

150

250

0April May June July August September

Fig. 1 Monthly ET values of the HFM treatment for individualyears

250

0April May June July August September

Months

Eva

potr

ansp

irat

ion

(mm

)

50

100

150

200

Fig. 2 Mean monthly ET values of the HFM treatment

283

between irrigation treatments were statistically signifi-cant at 1% level of probability for stem and seed yield inindividual years (2000 and 2001) and in the analysis ofcombined data. Also, the years significantly affectedstem and seed yield. On the other hand, ‘‘year · treat-ment’’ interactions were significant at the 5% level ofprobability for stem and seed yield.

Mean stem and seed yield results for experimentalyears and 2-year combined data were summarized inTable 5. The results indicate that the highest stem yieldwas obtained from the HFM treatment (7.04 t ha�1), inwhich crop water requirement was fully applied for thetotal growing period and the lowest stem yield wasobtained from control (5.29 t ha�1), where no irrigationwater was applied for the total growing period. Thetreatments H60FM, HF60M, HF40M, HFM60, andHFM40 were placed in the same statistical group ofHFM and their stem yields were also higher than theother limited irrigation treatments. It was concludedthat stem yield considerably decreased as the irrigationfrequency and the amount of irrigation water decreased.Similar results were obtained in individual experimentalyears as well.

In other studies elsewhere, it was also reported thatstem yield increased with frequent irrigation (Turner andRawson 1982) and irrigation applied at heading (Har-man et al. 1982) and flowering (Unger 1982) periods.Karaata (1991) found that full irrigations applied atheading, flowering and milk ripening stages and limitedirrigation at milk ripening stage (treatment HFM60,HFM40) gave the highest stem yield, whereas non-irri-gated treatments and irrigation at milk ripening stageproduced the lowest stem yield. Our results were com-patible with those experiments given above.

Unger (1990) reported that water stress at criticalstages has a marked influence on sunflower growth,achene yield, and achene quality factors. Early stress(before budding) reduced the leaf area per plant and leaf

numbers (Muriel and Downes 1974; Marc and Palmer1976). Besides affecting leaf numbers and areas, earlystress reduced plant height (Karami 1977; Selvaraj et al.1977; Patel and Singh 1979; Unger 1982, 1983).

The full and deficit irrigation at three growth periods(heading, flowering, and milk ripening) gave the highestseed yield. The mean of 2-year data indicated that seedyield of the HFM, H60FM, H40FM, HF60M, HF40M,HFM60, and HFM40 treatments were 3.95, 3.83, 3.80,3.73, 3.86, 3.83, and 3.74 t ha�1, respectively. The lowestseed yield was obtained from the non-irrigated treatment(2.16 t ha�1). These results indicate that deficit irriga-tions applied at three growth stages can maintain seedyield in sunflower. Our findings are in agreement withthose of Doorenboos and Kassam (1979) who reportedthat seed yield ranges from 2.50 to 3.50 t ha�1 underirrigation. In addition, when considering a single irri-gation at each critical growth stage, seed yield wasespecially increased with irrigation at flowering stage.Full irrigation (HFM) produced 82.9% higher seedyield, compared to the non-irrigated treatment. The seedyield increases for deficit-irrigation treatments were:31.0% for H; 49.1% for F; 29.2% for M; 50.5% for HF;56.5% for HM; 51.9% for FM; 77.3% for H60FM;75.9% for H40FM; 72.7% for HF60M; 78.7% forHF40M; 77.3% for HFM60; 73.1% for HFM40.

In previous studies, Muriel (1974) reported that thehighest seed yield was obtained from a treatment havingno water stress (full irrigation), whereas the lowest yieldwas produced from a non-irrigated application. Osmanand Talha (1975) reported that seed yield increased asthe amount of water and irrigation number increased ina study in Egypt. Unger (1982) reported that the seedyield was the highest with an irrigation treatment inwhich no water stress was applied. The author statedthat a higher seed yield was obtained for irrigationtreatments applied at flowering or at the end of theflowering stages, whereas increase in stem yield and

Table 5 The effects of irrigation treatments on stem and seed yield in 2000–2001 and combined years

Treatments Stem yield (t ha�1) Seed yield (t ha�1)

2000 2001 Average of years 2000 2001 Average of years

Control 5.94 e 4.63 d 5.29 f 2.21 f 2.11 g 2.16 dH 6.44 de 4.62 d 5.53 ef 2.96 e 2.69 ef 2.83 cF 6.57 de 5.44 ab 6.01 de 3.20 cde 3.23 cd 3.22 bM 6.79 de 4.87 d 5.83 f 2.99 de 2.59 f 2.79 cHF 7.12 cd 5.48 ab 6.30 cd 3.23 cd 3.27 cd 3.25 bHM 7.24 bcd 4.91 cd 6.08 d 3.26 c 3.50 bc 3.38 bFM 7.28 bcd 5.38 ab 6.33 bcd 3.53 b 3.03 de 3.28 bHFM 8.44 a 5.64 ab 7.04 a 3.98 a 3.92 a 3.95 aH60FM 8.37 a 5.65 ab 7.01 a 3.93 a 3.72 ab 3.83 aH40FM 7.33 bcd 5.29 bc 6.31 bcd 3.73 ab 3.86 ab 3.80 aHF60M 8.10 ab 5.37 ab 6.74 abc 3.91 a 3.54 bc 3.73 aHF40M 8.08 ab 5.49 ab 6.79 ab 3.77 ab 3.95 a 3.86 aHFM60 7.79 abc 5.71 a 6.75 abc 3.79 a 3.87 ab 3.83 aHFM40 7.78 abc 5.49 ab 6.64 abc 3.81 a 3.67 ab 3.74 aMean 7.38 a 5.29 b – 3.45 a 3.35 b –LSD (0.05) 890.2 391.5 478.6 253.8 375.1 222.9

The values with the same letter are statistically homogeneous in LSD test

284

plant height was observed under irrigations at germi-nation and heading stages. Yakan and Kanburoglu(1989) suggested that one irrigation at flowering stageproduced the highest net income and irrigation appliedat 30% level of available moisture produced highest seedyield in the Thrace region of Turkey. Karaata (1991)found that seed yield was the lowest in a non-irrigatedtreatment, whereas higher yields were obtained with fulland deficit irrigation treatments at heading, flowering,and milk ripening stages of sunflower in the same region.On the other hand, the same researcher reported that inthe case of limited irrigation, water stress should bescheduled on two growth stages (heading and milk rip-ening of grain) instead of one growth stage (flowering).

Quality components

Oil percentage and oil yield were investigated as qualitycomponents in this study. According to the results of theanalysis of variance for quality components, differencesbetween irrigation treatments were not statistically sig-nificant for oil percentage in individual year and 2-yearcombined data. However, years for oil percentage weresignificant at a confidence level of 1%. Differencesbetween irrigation treatments were statistically signifi-cant at 1% level of probability for oil yield in a singleyear and in the analysis of combined data. On the otherhand, years and ‘‘year · treatment’’ interactions for oilyield were significant at 5% level of probability.

Mean oil percentage (%) and oil yield (t ha�1) resultsfor experimental years and 2-year combined data weresummarized in Table 6. Oil percentage was not affectedby irrigation treatments applied at different growthstages. Mean oil percentages varied from 43.9 to 45.9%in all irrigation treatments.

Our findings for oil percentage do not correspond tothose of Muriel (1974), Jana et al. (1982), Decau and All(1973), Flagella et al. (2002), who reported that oilpercentage increased with irrigation. Muriel (1974)reported that oil percentage was found as 47.8, 47.3, and42.3% for treatments in which applied water was 199%of ET, 50% of ET, and non-irrigated, respectively, in astudy carried out in Romania. Unger (1982) found thatirrigation at flowering and at the end of flowering stagegave the highest oil percentage (48.8%), whereas irri-gation at germination and heading stages produced thelowest (43.4%). Ferri and Losavio (1982) reported thatoil percentage was decreased by limited irrigationbetween seed formation and milk ripening stages.Karaata (1991) reported that oil percentage did notsignificantly increase as the amount of irrigation waterincreased, but increased with irrigation applied at flow-ering and milk ripening stages. Since oil percentage isdetermined by several environmental factors (especiallytemperature) as well as genotypic structure (Fick andZimmerman 1973; Harris et al. 1978), it is likely that thedifferences between the various studies are mainly due toenvironmental conditions.

In this study, the highest mean oil yield (1.78 t ha�1)was obtained in the HFM treatment and the lowestmean oil yield (0.96 t ha�1) was obtained from the non-irrigated (or control) treatment. As similar to results ofseed yield, oil yield increased as the amount and fre-quency of irrigation water increased. When compared asa percentage, full irrigation at three growth stages(HFM) produced 85.4% more oil yield compared to thenon-irrigated treatment. The oil yield increases for def-icit-irrigation treatments were: 30.2% for H; 47.9% forF; 29.2% for M; 50.0% for HF; 59.4% for HM; 57.3%for FM; 79.2% for H60FM; 78.1% for H40FM; 77.1%for HF60M; 80.2% for HF40M; 78.1% for HFM60;

Table 6 The effects of irrigation treatments on oil percentage and oil yield in 2000–2001and combined years

Treatments Oil percentage (%) Oil yield (t ha�1)

2000 2001 Average of years 2000 2001 Average of years

Control 42.9 46.0 44.4 0.95 e 0.97 f 0.96dH 42.7 45.3 43.9 1.27 d 1.22 e 1.25 cF 42.3 45.7 44.0 1.36 cd 1.48 cd 1.42 bM 43.5 45.7 44.6 1.30 cd 1.18 e 1.24 cHF 42.9 45.5 44.2 1.38 cd 1.49 cd 1.44 bHM 43.1 47.0 45.0 1.40 c 1.65 abc 1.53 bFM 44.4 47.5 45.9 1.57 b 1.44 d 1.51 bHFM 43.5 47.3 45.3 1.71 a 1.85 a 1.78 aH60FM 43.2 47.0 45.0 1.69 ab 1.75 ab 1.72 aH40FM 44.0 46.3 45.1 1.64 ab 1.78 ab 1.71 aHF60M 44.7 46.3 45.5 1.75 a 1.64 bcd 1.70 aHF40M 43.3 46.5 44.9 1.63 ab 1.83 ab 1.73 aHFM60 43.1 46.0 44.5 1.63 ab 1.78 ab 1.71 aHFM40 43.9 46.3 45.0 1.67 ab 1.70 ab 1.69 aMean 43.4 b 46.3 a – 1.50 b 1.56 a –LSD (0.05) – – – 132.5 206.4 120.7

The values with the same letter are statistically homogeneous in LSD test

285

76.0% for HFM40. Our results are in agreement withthose of Osman and Talha (1975), Browne (1977), Janaet al. (1982), and Kadayıfcı and Yıldırım (2000) whoreported that oil yield increased as the amount of irri-gation water increased.

Crop water production functions

Water production functions for sunflower were obtainedby plotting observed yield on the Y-axis and the ET onthe X-axis in 2000 and 2001 (Fig. 3). A linear relation-ship was found between seasonal ET and seed yield at99% level of confidence. Seed yield responded linearly toapplied water.

To determine the yield response factor (ky), rela-tionships between proportional ET decreases and pro-portional yield decreases were calculated. Adjustedmaximum yield values (Ym) were calculated versusmaximum evapotranpiration (ETm) by using linearequations (from Fig. 3) for each single experimentalyear. Crop water production function and yield responsefactor (ky) were given below for total growth stage.

½1� ðYaY �1m Þ� ¼ 0:8382 ½1� ðETa ET�1m Þ�; r ¼ 0:9169

The slope of line (ky) that was given in the functionwas found as 0.8382 for the total growing period and isillustrated in Fig. 4. Additionally, crop water production

functions were calculated for each individual growthstage (heading, flowering, and milk ripening).

Crop water production functions obtained for eachgrowth stage were given below:

Heading (H)

½1� ðYaY �1m Þ� ¼ 0:9159 ½1� ðETa ET�1m Þ�; r ¼ 0:9826

Flowering (F)

½1� ðYaY �1m Þ� ¼ 0:7859 ½1� ðETa ET�1m Þ�; r ¼ 0:9160

Milk Ripening (M)

½1� ðYaY �1m Þ� ¼ 0:8971 ½1� ðETa ET�1m Þ�; r ¼ 0:9734

The graphs of these equations are shown in Fig. 5.To present wider options to irrigation planners,

obtained results from treatments in which deficit irri-gation was spread over two growth stages.

Crop water production functions obtained for twogrowth stages are given below and graphs of thosefunctions are shown in Fig. 6.

5

200

2000 4

Yie

ld (

t ha-1

)

3

y = 0.4649x + 76.529 r = 0.9405

2

1

0 300

Evapotranspiration (mm)400 500 600 700 800

5

2001 4

Yie

ld (

tha-1

)

3

2 y = 0.5589x + 55.808 r = 0.8966

1

200 0

300Evapotranspiration (mm)

500400 600 700

Fig. 3 Relationship between seed yield and evapotranspiration forsunflower during two seasons (2000–2001)

0.00

1 – ETa . ETm-1

1 –

Ya .

Ym

-1

0.20.3 0.10.40.50.6

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.0

ky = 0.8382

Fig. 4 Relationship between relative seed yield decrease andrelative ET deficit for sunflower throughout the total growingseason during 2 years (2000–2001)

1 – ETa . ETm-1

0.00.00

0.6 0.5 0.4 0.3 0.2 0.1

0.05

0.10

0.15

0.20

1 –

Ya .

Ym

-1

0.25

ky = 0.7859 (F) H 0.30

0.35F ky = 0.9159 (H) 0.40

M ky = 0.8971 (M) 0.45

0.50

Fig. 5 Relationship between relative seed yield decrease andrelative ET deficit of sunflower for the individual growth stagesduring two seasons (2000–2001)

286

Heading–flowering (HF)

½1� ðYaY �1m Þ� ¼ 0:9022 ½1� ðETa ET�1m Þ�; r ¼ 0:9631

Heading–milk ripening (HM)

½1� ðYaY �1m Þ� ¼ 0:8945 ½1� ðETa ET�1m Þ�; r ¼ 0:9774

Flowering–milk ripening (FM)

½1� ðYaY �1m Þ� ¼ 0:7708 ½1� ðETa ET�1m Þ�; r ¼ 0:9319

Doorenboos and Kassam (1979) reported ky value forsunflower as 0.95 for the total growing season. They alsoreported values for individual growth stages in which kyis 0.25, 0.50, 1.00, and 0.80 at early vegetative growth(nearly heading), late vegetative growth, flowering, andyield formation stage, respectively. In our study, ky va-lue was found as 0.8382 for the total season, and there isonly minor deviation with 0.11 from the values reported

by Doorenboos and Kassam (1979). The deviation maybe attributed to differences in phenological stages and inirrigation water amounts depending upon the differentsoil and climatic conditions. Yield response factor (k

y) at

some calculations for individual growth stage was foundto be higher than those calculated for the total growingseason (0.8382). For example; ky is 0.9159 for heading,0.8971 for milk ripening, 0.8945 for heading–milk rip-ening, and 0.9022 for heading–flowering stages.

When comparing the results for individual growthstages, it was concluded that ky for milk ripening stage(0.8971) is close to ky for yield formation stage (0.8), kyfor flowering is smaller than one (0.7859<1.000), ky forheading stage does not correspond to early or late veg-etative period. Those deviations may be attributed to theabove-mentioned reasons. In this study, the resultssupport the previous values by Doorenboos and Kassam(1979) who reported that ky value is less than one.

Water use efficiencies

The WUE and IWUE were different depending upon thetreatments and did not significantly change when irri-gation amount increased (Table 7). However, WUEvalues ranged from 6.00 (HF and HF60M) to7.80 kg ha�1 mm�1 (F). Previous studies indicated thatthe WUE ranged from 5.39 to 10.5 kg ha�1 mm�1

(Connor et al. 1985; Stone et al. 1996; Rinaldi 2001).Our results are in agreement with Stone et al. (1996) whoreported that seed yield increased with irrigationfrequency and seasonal irrigation amount, and the WUEbetween treatments was not significantly different.

The highest IWUE value (10.19 kg ha�1 mm�1) wasobtained from the F treatment and the lowest value(4.74 kg ha�1 mm�1) from the HF treatment (Table 7).Results indicate that flowering is the most importantstage for sunflower irrigation, as sunflower is more

1 – ETa . ETm

-1

0.1 0.00.5 0.4 0.3 0.20.60.00

0.05

0.10

0.15

1 –

Ya .

Ym

-1

0.20

0.25ky = 0.7708 (FM)

0.30

HMky = 0.9022 (HF) 0.35

HF 0.40

ky = 0.8945 (HM)FM

0.45

0.50

Fig. 6 Relationship between relative seed yield decrease andrelative ET deficit of sunflower for two growth stages during twoseasons (2000–2001)

Table 7 Sunflower response to irrigation treatments (2-year average, 2000–2001)

Treatments Seasonalapplied water(mm)

SeasonalETa (mm)

Seed yield(t ha�1)

WUE(kg ha�1 mm�1)

IWUE(kg ha�1 mm�1)

Control(rainfed)

– 329 2.16 6.57 0.00

H 126 457 2.83 6.19 5.32F 104 413 3.22 7.80 10.19M 129 427 2.79 6.53 4.88HF 230 542 3.25 6.00 4.74HM 251 556 3.38 6.08 4.86FM 229 536 3.28 6.12 4.89HFM 356 652 3.95 6.06 5.03H60FM 305 608 3.85 6.33 5.54H40FM 280 585 3.79 6.48 5.82HF60M 313 622 3.73 6.00 5.02HF40M 292 594 3.86 6.50 5.82HFM60 305 620 3.83 6.18 5.48HFM40 280 589 3.74 6.35 5.64

287

sensitive to water stress at flowering than other growthstages. Therefore, when seasonal irrigation water islimited, one irrigation at flowering should be applied.Our results support the previous work of Rinaldi (2001)who reported that when seasonal irrigation water waslimited, one or two irrigations in the central phase(heading and flowering stages) is profitable for IWUEand net income. Also, Rinaldi (2001) reported that in awater-limited environment, even a single irrigationwould double net income as compared to a rainfedtreatment.

Conclusions

This study was carried out to investigate the yieldresponse of sunflower to full and deficit irrigation and todetermine the irrigation scheduling which gives thegreatest production per unit irrigation water in thesouthern Marmara region of Turkey. Stem and seedyields were significantly affected by treatments of fulland deficit irrigation at different growth stages of sun-flower. When considering the yield, it was concludedthat the yield increased with irrigation frequency, andthe highest yield was obtained from a treatment of fulland deficit irrigation at three phenological stages,whereas the lowest yield was produced from the non-irrigated (control) application. In general, there is nosignificant difference between full and deficit irrigationtreatments at three growth stages. Full irrigation (theHFM treatment) and 40 and 60% of its deficits pro-duced the highest seed yield. Full and deficit irrigation atthree stages produced 82.9 and 75.8% (as an average)higher seed yield than the control, respectively. How-ever, irrigations in two growth stages produced 53.0%more seed yield than the non-irrigated (control) treat-ment, whereas irrigations at one growth stage produced36.4% more seed yield than the control treatment onaverage.

Oil percentage was not significantly affected by fulland deficit irrigation treatments. However, oil yield wassignificantly affected by treatments as occurred in seedyield. In this study, the highest oil yield was obtained bythe HFM treatment and its deficits, and the lowest meanoil yield was obtained from the non-irrigated treatment.

Monthly and seasonal ET values of sunflower weredifferentiated for each treatment and years. The greatestamount of irrigation water was applied to the HFMtreatment for both years (376 mm in 2000 and 335 mmin 2001). Seasonal ET values of the same treatment werefound as 688 and 616 mm for 2000 and 2001, respec-tively. Highest monthly ET values for treatment HFMwere estimated as 236 and 196 mm in June of 2000 and2001.

Yield response factor (ky) was separately calculatedfor each, two growth stages, and total growth period.Yield response factor (ky) is 0.8382 for the totalgrowing season. Doorenboos and Kassam (1979)reported ky value for sunflower as 0.95 for the total

growing season. In this study, heading stage gave thehighest ky (0.9159), whereas the combination of initialflowering–milk ripening stages produced the lowest ky(0.7708). The calculated ky values correspond to thoseof previous works.

Results indicate that the highest stem and seed yieldwere obtained from full and deficit irrigation at threecritical phenological stages (heading, flowering, and milkripening) under the sub-humid conditions of southernMarmara region of Turkey. Yield is not significantlyaffected by deficit irrigation at three stages in statisticalmanner. It is concluded that each of the HFM treat-ments (including its deficits) is the best choice for max-imum yield under the local conditions, but theseirrigation schemes must be re-considered in areas wherewater resources are more limited. When water is limited,water should be applied at flowering stage because ourresults showed that this maintained yield and had thehighest WUE (7.80 kg ha�1 mm�1) and IWUE(10.19 kg ha�1 mm�1).

Acknowledgement The authors are grateful to The Scientific andTechnical Research Council of Turkey (TUBITAK) for financialsupport, as the results reported in this paper are part of ‘‘Deter-mination of Relationships between Water and Yield in Sunflower(H. annuus L.) under Bursa Conditions’’ scheme (fully financed bythe TUBITAK).

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