Effects of deficit irrigation on the yield and yield components of drip irrigated cotton in a mediterranean environment

A field study on cotton (Gossypium hirsutum L., cv.) was carried out from 2005 to 2008 in the Çukurova Region, Eastern Mediterranean, Turkey. Treatments were designated as I₁₀₀ full irrigation; DI₇₀, DI₅₀ and DI₀₀ which received 70, 50, and 0% of the irrigation water amount applied in the I₁₀₀ treatment. The irrigation water amount to be applied to the plots was calculated using cumulative pan evaporation that occurred during the irrigation intervals. The effect of water deficit or water stress on crop yield and some plant growth parameters such as yield response, water use efficiencies, dry matter yield (DM), leaf area index (LAI) as well as on lint quality components was evaluated. The average seasonal evapotranspiration ranged from 287 ± 15 (DI₀₀) to 584 ± 80 mm (I₁₀₀). Deficit irrigation significantly affected crop yield and all yield components considered in this study. The average seed cotton yield varied from 1369 ± 197 (DI₀₀) to 3397 ± 508 kg ha⁻¹ (I₁₀₀). The average water use efficiency (WUE_ET) ranged from 6.0 ± 1.6 (I₁₀₀) to 4.8 ± 0.9 kg ha⁻¹ mm⁻¹ (DI₀₀), while average irrigation water use efficiency (WUE_I) was between 9.4 ± 3.0 (I₁₀₀) and 14.4 ± 4.8 kg ha⁻¹ mm⁻¹ (DI₅₀). Deficit irrigation increased the harvest index (HI) values from 0.26 ± 0.054 (I₁₀₀) to 0.32 ± 0.052 kg kg⁻¹ (DI₅₀). Yield response factor (Ky) was determined to be 0.98 based on four-year average. Leaf area index (LAI) and dry matter yields (DM) increased with increasing water use. This study demonstrated that the full irrigated treatment (I₁₀₀) should be used for semiarid conditions with no water shortage. However, DI₇₀ treatment needs to be considered as a viable alternative for the development of reduced irrigation strategies in semiarid regions where irrigation water supplies are limited.     

Effect of timing of first and last irrigation on the yield and water use efficiency in cotton

With increasing concern about declining water resources, there is increasing thrust in improving water management in farming systems to improve water use efficiency. The present investigation was undertaken to determine the optimum timing for the first and last irrigation of cotton on the basis of meteorological approach for scheduling irrigations. The experiment was conducted in a split plot design with three timings of first irrigation as main-plots and three timing of last irrigation as sub-plots. Delay of first irrigation from 28 days after sowing (DAS) to 42 DAS, irrespective of last irrigation, resulted in an increase of 8, 14 and 17% in seed cotton yield during first, second and third year, respectively. The corresponding increases due to delay in the last irrigation from 130 to 170 DAS were 14, 32 and 8%, respectively. On the basis of 3 years average, application of first and last irrigation at optimum time (after 42 and 170 days after sowing) resulted in an increase of 36% in seed cotton yield without involving any additional cost. Water expense efficiency (WEE) increased by 54%.     

Effects of drip irrigation levels and planting methods on yield and yield components of green pepper (Capsicum annuum, L.) in Bako, Ethiopia

A field experiment was conducted to investigate the effects of different levels of drip irrigation and planting methods on yield and yield components (number of fruits per plant, number of primary and secondary branches per plant, and plant height) of green pepper (Capsicum annuum, L.) in Bako, Ethiopia. Three irrigation levels (50, 75 and 100% of ET_c) and two planting methods (normal and paired-row planting) were applied. The experiment was laid out in a split plot design, with irrigation levels as main plots and planting methods as sub-plots, in three replications. It was found that the effects of both treatments on yield, number of fruits per plant and plant height of green pepper were highly significant (p < 0.01) whereas the number of primary and secondary branches per plant was affected significantly (p < 0.05). The maximum and minimum values of the yield and yield components were recorded from treatment plots I₁₀₀P (full irrigation level with paired-row planting method) and I₅₀P (50% of ET_c irrigation level with paired-row planting method), respectively, with the exception of plant height. However, the average plant height (cm) recorded from the I₁₀₀N treatment plot was not significantly different from the I₁₀₀P treatment plot. Moreover, it was found that the effect of treatment interactions on both yield and yield components of green pepper was found to be highly significant (p < 0.01). A 50% reduction in irrigation level caused a reduction in yield of about 48.3 and 74.4% under the normal and paired-row planting methods, respectively, whereas, a 25% reduction in irrigation level caused a reduction in yield of about 22.8 and 47.7% under the same planting methods. Under both deficit irrigation levels (I₅₀ and I₇₅), the normal planting method gave higher total yield and yield components of green pepper than the paired-row planting method. Yield response factor (k_y) values of 0.96 and 1.57 were determined for the normal and paired-row planting methods, respectively, suggesting utmost precautions when using the paired-row planting in areas with limited water supply. The results revealed that full irrigation water supply under paired-row planting method (I₁₀₀P) could be used for the production of green pepper in an area with no water shortage. Moreover, it was found that the average yields recorded from the I₇₅ under the paired-row planting method is fairly greater than the national average.     

Effects of water stress at different development stages on yield and water productivity of winter and summer safflower (Carthamus tinctorius L.)

A field study was carried out to determine the effects of water stress imposed at different development stages on grain yield, seasonal evapotranspiration, crop-water relationships, yield response to water and water use efficiency of safflower (Carthamus tinctorius L.) for winter and summer sowing. The field trials were conducted on a loam Entisol soil in Thrace Region in Turkey, using Dincer, the most popular safflower variety in the research area. A randomised complete block design with three replications was used. Three known growth stages of the plant were considered and a total of 8 (including rainfed) irrigation treatments were applied. The effect of irrigation or water stress at any stage of development on grain yield per hectare and 1000 kernel weight, was evaluated. Results of this study showed that safflower was significantly affected by water shortage in the soil profile due to omitted irrigation during the sensitive vegetative stage. The highest yield was observed in the fully irrigated control and was higher for winter sowing than for summer sowing. Evapotranspiration calculated for non-stressed production was 728 and 673 mm for winter and summer sowing, respectively. Safflower grain yield of the fully irrigated treatments was 4.05 and 3.74 t ha⁻¹ for winter and summer season, respectively. The seasonal yield response factor was 0.97 and 0.81 for winter and summer sowing, respectively. The highest total water use efficiency was obtained in the treatment irrigated only at vegetative stage while the lowest value was observed when the crop was irrigated only at yield stage. As conclusions: (i) winter sowing is suggested; (ii) if deficit irrigation is to apply at only one or two stages, Y stage or Y and F stages should be omitted, respectively.     

灌溉时段及水温对膜下滴灌棉花生长及产量的影响

为探究不同灌溉时段及水温对膜下滴灌棉花生理特性及产量的影响,设置4个灌溉水温梯度分别为15.00(正常灌溉水温),20.00,25.00,30.00℃,2个灌溉时段分别为日间、夜间(分别记为DW,NW)进行完全组合设计,共计8个处理.结果表明,增温灌溉提前了棉花生育进程,促进了棉花株高、茎粗、叶面积增长,有利于棉花光合作用的进行,且在夜间进行增温灌溉效果更显著.增温灌溉使棉花产量显著提高2.95%～14.13%,夜间灌溉较日间灌溉棉花产量平均提高3.34%.基于回归分析确定提高棉花产量的最佳灌溉时段为夜间,最佳灌溉水温为26.38℃,对应的产量为7 482.96 kg/hm².该研究可为北疆膜下滴灌棉花实施增温灌溉技术提供理论依据和技术参考.     

Effects of irrigation strategies and soils on field grown potatoes: Yield and water productivity

Yield and water productivity of potatoes grown in 4.32 m² lysimeters were measured in coarse sand, loamy sand, and sandy loam and imposed to full (FI), deficit (DI), and partial root-zone drying (PRD) irrigation strategies. PRD and DI as water-saving irrigation treatments received 65% of FI after tuber bulking and lasted for 6 weeks until final harvest. Analysis across the soil textures showed that fresh yields were not significant between the irrigation treatments. However, the same analysis across the irrigation treatments revealed that the effect of soil texture was significant on the fresh yield and loamy sand produced significantly higher fresh yield than the other two soils, probably because of higher leaf area index, higher photosynthesis rates, and “stay-green” effect late in the growing season. More analysis showed that there was a significant interaction between the irrigation treatments and soil textures that the highest fresh yield was obtained under FI in loamy sand. Furthermore, analysis across the soil textures showed that water productivities, WP (kg ha⁻¹ fresh tuber yield mm⁻¹ ET) were not significantly different between the irrigation treatments. However, across the irrigation treatments, the soil textures were significantly different. This showed that the interaction between irrigation treatments and soil textures was significant that the highest significant WP was obtained under DI in sandy loam. While PRD and DI treatments increased WP by, respectively, 11 and 5% in coarse sand and 28 and 36% in sandy loam relative to FI, they decreased WP in loamy sand by 15 and 13%. The reduced WP in loamy sand was due to nearly 28% fresh tuber yield loss in PRD and DI relative to FI even though ET was reduced by 9 and 11% in these irrigation treatments. This study showed that different soils will affect water-saving irrigation strategies that are worth knowing for suitable agricultural water management. So, under non-limited water resources conditions, loamy sand produces the highest yield under full irrigation but water-saving irrigations (PRD and DI) are not recommended due to considerable loss (28%) in yield. However, under restricted water resources, it is recommended to apply water-saving irrigations in sandy loam and coarse sand to achieve the highest water productivity.     

Effect of irrigation amounts applied with subsurface drip irrigation on corn evapotranspiration, yield, water use efficiency, and dry matter production in a semiarid climate

Quantifying the local crop response to irrigation is important for establishing adequate irrigation management strategies. This study evaluated the effect of irrigation applied with subsurface drip irrigation on field corn (Zea mays L.) evapotranspiration (ETc), yield, water use efficiencies (WUE = yield/ETc, and IWUE = yield/irrigation), and dry matter production in the semiarid climate of west central Nebraska. Eight treatments were imposed with irrigation amounts ranging from 53 to 356 mm in 2005 and from 22 to 226 mm in 2006. A soil water balance approach (based on FAO-56) was used to estimate daily soil water and ETc. Treatments resulted in seasonal ETc of 580–663 mm and 466–656 mm in 2005 and 2006, respectively. Yields among treatments differed by as much as 22% in 2005 and 52% in 2006. In both seasons, irrigation significantly affected yields, which increased with irrigation up to a point where irrigation became excessive. Distinct relationships were obtained each season. Yields increased linearly with seasonal ETc (R² = 0.89) and ETc/ETp (R² = 0.87) (ETp = ETc with no water stress). The yield response factor (ky), which indicates the relative reduction in yield to relative reduction in ETc, averaged 1.58 over the two seasons. WUE increased non-linearly with seasonal ETc and with yield. WUE was more sensitive to irrigation during the drier 2006 season, compared with 2005. Both seasons, IWUE decreased sharply with irrigation. Irrigation significantly affected dry matter production and partitioning into the different plant components (grain, cob, and stover). On average, the grain accounted for the majority of the above-ground plant dry mass (≈59%), followed by the stover (≈33%) and the cob (≈8%). The dry mass of the plant and that of each plant component tended to increase with seasonal ETc. The good relationships obtained in the study between crop performance indicators and seasonal ETc demonstrate that accurate estimates of ETc on a daily and seasonal basis can be valuable for making tactical in-season irrigation management decisions and for strategic irrigation planning and management.     

Comparison of drip and sprinkler irrigation strategies on sunflower seed and oil yield and quality under Mediterranean climatic conditions

This study compares the effects of different irrigation regimes on seed yield and oil yield quality and water productivity of sprinkler and drip irrigated sunflower (Helianthus annus L.) on silty-clay-loam soils in 2006 and 2007 in the Mediterranean region of Turkey. In sprinkler irrigation a line-source system was used in order to create gradually varying irrigation levels. Irrigation regimes consisted of full irrigation (I₁) and three deficit irrigation treatments (I₂, I₃ and I₄), and rain-fed treatment (I₅). In the drip system, irrigation regimes included full irrigation (FI-100), three deficit irrigation treatments (DI-25, DI-50, DI-75), partial root zone drying (PRD-50) and rain-fed treatment (RF). Irrigations were scheduled at weekly intervals both in sprinkler and drip irrigation, based on soil water depletion within a 0.90 m root zone in FI-100 and I₁ plots. Irrigation treatments influenced significantly (P < 0.01) sunflower seed and oil yields, and oil quality both with sprinkler and drip systems. Seed yields decreased with increasing water stress levels under drip and sprinkler irrigation in both experimental years. Seed yield response to irrigation varied considerably due to differences in soil water contents and spring rainfall distribution in the experimental years. Although PRD-50 received about 36% less irrigation water as compared to FI-100, sunflower yield was reduced by an average of 15%. PRD-50 produced greater seed and oil yields than DI-50 in the drip irrigation system. Yield reduction was mainly due to less number of seeds per head and lower seed mass. Soil water deficits significantly reduced crop evapotranspiration (ET), which mainly depends on irrigation amounts. Significant linear relationships (R² = 0.96) between ET and oil yield (Y) were obtained in each season. The seed yield response factors (ky_seed) were 1.24 and 0.86 for the sprinkler and 1.19 and 1.06 for the drip system in 2006 and 2007, respectively. The oil yield response factor (ky_oil) for sunflower was found to be 1.08 and 1.49 for both growing seasons for the sprinkler and 1.36 and 1.25 for the drip systems, respectively. Oil content decreased with decreasing irrigation amount. Consistently greater values of oil content were obtained from the full irrigation treatment plots. The saturated (palmitic and stearic acid) and unsaturated (oleic and linoleic acid) fatty acid contents were significantly affected by water stress. Water stress caused an increase in oleic acid with a decrease in linoleic acid contents. The palmitic and stearic acid concentrations decreased under drought conditions. Water productivity (WP) values were significantly affected by irrigation amounts and ranged from 0.40 to 0.71 kg m⁻³ in 2006, and from 0.69 to 0.91 kg m⁻³ in 2007. The PRD-50 treatment resulted in the greatest WP (1.0 kg m⁻³) and irrigation water productivity (IWP) (1.4 kg m⁻³) in both growing seasons. The results revealed that under water scarcity situation, PRD-50 in drip and I₂ in sprinkler system provide acceptable irrigation strategies to increase sunflower yield and quality.     

水氮盐调控对膜下滴灌棉花产量的影响及耦合模型

为探讨水、盐、氮三因素对棉花生长的耦合效应及最优水肥制度,分别设置了4种灌溉定额(1 575,2 100,2 625,3 150 m³/hm²)、4种施氮量(0,150,300,450 kg/hm²)和4种土壤盐分(非盐化土、轻度、中度和重度盐化土),通过盆栽试验,研究了水、氮、盐对膜下滴灌棉花产量的影响.结果表明：灌溉定额、施氮量和土壤盐分与棉花产量之间符合回归模型,模型对水氮盐的耦合效果较好;单因素对棉花产量影响按因素排序由大到小为灌水量,土壤含盐量,施氮量;耦合作用的影响按因素排序由大到小为盐氮,水氮,水盐;水氮施加量对棉花产量的影响均存在阈值,低于此阈值,棉花增产效果较为明显;中、重度土壤盐分含量明显抑制棉花生长;通过回归模型进行耦合分析,最适合研究区的水肥盐耦合方式为轻盐土壤、灌溉定额2 677 m³/hm²和施氮量202 kg/hm².本研究可为盐碱区棉田水肥高效利用提供科学依据.     

Effects of irrigation regimes on yield and water productivity of safflower (Carthamus tinctorius L.) under Mediterranean climatic conditions

A field study was carried out in order to determine the effect of deficit irrigation regimes on grain yield and seasonal evapotranspiration of safflower (Carthamus tinctorius L.) in Thrace Region of Turkey. The field trials were conducted on a loam Entisol soil, on Dincer, the most popular variety in the research area. A randomised complete block design with three replications was used. Combination of four well-known growth stages of the plant, namely vegetative (V_a), late vegetative (V_b), flowering (F) and yield formation (Y) were considered to form a total of 16 (including rain fed) irrigation treatments. The effect of irrigation and water stress at any stage of development on grain yield per hectare and 1000 kernels weight was evaluated. Results showed that safflower was significantly affected by water stress during the sensitive late vegetative stage. The highest yield was obtained in V_aV_bFY treatment. Seasonal irrigation water use and evapotranspiration were 501 and 721 mm, respectively, for the non-stressed treatment. Safflower grain yield of this treatment was 5.22 Mg ha⁻¹ and weight of 1000 kernels was 55 g. The seasonal yield-water response factor value was 0.87. The total water use efficiency was 7.2 kg ha⁻¹ mm⁻¹. Irrigation schedule of the non-stressed treatment may be as follows: the first irrigation is at the vegetative stage, when after 40-50 days from sowing/elongation and branching stage, that is the end of May; the second irrigation is at the late vegetative stage, after 70-80 days from sowing/heading stage, that is in the middle of June; the third irrigation is at the flowering stage, approximately 50% level, that is the first half of July; and the fourth irrigation is at the yield formation stage, seed filling, that is the last week of July.     

The effect of salinity on water productivity of wheat under deficit irrigation above shallow groundwater

Saline groundwater is often found at shallow depth in irrigated areas of arid and semi-arid regions and is associated with problems of soil salinisation and land degradation. The conventional solution is to maintain a deeper water-table through provision of engineered drainage disposal systems, but the sustainability of such systems is disputed. This shallow groundwater should, however, be seen as a valuable resource, which can be utilised via capillary rise (i.e. sub-irrigation). In this way, it is possible to meet part of the crop water requirement, even where the groundwater is saline, thus decreasing the need for irrigation water and simultaneously alleviating the problem of disposing of saline drainage effluent. Management of conditions within the root zone can be achieved by means of a controlled drainage system.A series of lysimeter experiments have permitted a detailed investigation of capillary upward flow from a water-table controlled at shallow depth (1.0 m) under conditions of moderately high (5 mm/day) evaporative demand and with different levels of salinity. Experiments were conducted on a wheat crop grown in a sandy loam soil. Groundwater salinity was held at values from 2 to 8 dS/m while supplementary (deficit) irrigation was applied at the surface with salinity in the range 1-4 dS/m.Our experiments show that increased salinity decreased total water uptake by the crop, but in most treatments wheat still extracted 40% of its requirement from the groundwater, similar to the proportion reported for non-saline conditions. Yield depression was limited to 30% of maximum when the irrigation water was of relatively good quality (1 and 2 dS/m) even with saline groundwater (up to 6 dS/m). Crop water productivity (grain yield basis) was around 0.35 kg/m³ over a wide range of salinity conditions when calculated conventionally on the basis of total water use, but was generally above 1.0 kg/m³ if calculated on the basis of irrigation input only.     

亏缺灌溉对南疆棉花生长和水分利用的影响

针对南疆地区水资源短缺、作物水分利用效率低等问题,以棉花为试验材料进行田间小区试验,在棉花现蕾期、开花期以及结铃期分别设置3个亏缺灌溉水平(W₁:50%ET_c,W₂:65%ET_c,W₃:80%ET_c,ET_c为作物蒸发蒸腾量),以全生育期100%ET_c灌溉处理为对照(CK),研究膜下滴灌条件下,不同生育期亏缺灌溉对棉花生长、产量、氮素吸收和水分利用效率的影响.结果表明:现蕾期亏水对棉花株高、叶面积指数、地上干物质生长、氮素吸收和产量有不同程度的抑制效应,但复水后补偿效应显著,其中轻度亏水(W₃)在籽棉产量减少3.48%的条件下,WUE高达1.57 kg/m³,显著高于CK的1.48 kg/m³;开花期亏水,棉花的各项生长指标均有显著降低,复水后补偿效应不显著,不利于棉花生长发育;结铃期亏水对棉花地上干物质累积、氮素吸收和产量均有显著的抑制效应,但在W₂和W₃水平下,WUE均达1.51 kg/m³.综合考虑在保证棉花产量的同时达到节水增产的目的,可在棉花蕾期进行80%ET_c灌水,其他生育阶段实施充分灌溉,来控制营养生长,促进生殖生长,获得更高的水分利用效率.     

Response of cotton to various levels of nitrogen and water applied to normal and paired sown cotton under drip irrigation in relation to check-basin

Field experiments were conducted for 2 years to investigate the effects of various levels of nitrogen (N) and methods of cotton planting on yield, agronomic efficiency of N (AEN) and water use efficiency (WUE) in cotton irrigated through surface drip irrigation at Bathinda situated in semi-arid region of northwest India. Three levels of N (100, 75 and 50% of recommended N, 75 kg ha⁻¹) were tested under drip irrigation in comparison to 75 kg of N ha⁻¹ in check-basin. The three methods of planting tried were; normal sowing of cotton with row to row spacing of 67.5 cm (NS), normal paired row sowing with row to row spacing of 35 and 100 cm alternately (NP) and dense paired row sowing with row to row spacing of 35 and 55 cm alternately resulting in total number rows and plants to be 1.5 times (DP) than NS and NP. In NS there was one lateral along each row, but in paired sowings there was one lateral between each pair of rows. Consequently the number of laterals and quantity of water applied was 50 and 75% in NP and DP, respectively, as compared with NS in which irrigation water applied was equivalent to check-basin.Drip irrigation under NS resulted in an increase of 258 and 453 kg ha⁻¹ seed cotton yield than check-basin during first and second year, respectively, when same quantity of water and N was applied. Drip irrigation under dense paired sowing (DP) in which the quantity of irrigation water applied was 75% as compared with NS, further increased the yield by 84 and 101 kg ha⁻¹ than NS during first and second year, respectively. Drip irrigation under NP, in which the quantity of water applied and number of laterals used were 50% as compared with drip under NS, resulted in a reduction in seed cotton yield of 257 and 112 kg ha⁻¹ than NS during first and second year, respectively. However, the yield obtained in NP under drip irrigation was equivalent to yield obtained in NS under check-basin during first year but 341 kg ha⁻¹ higher yield was obtained during second year. The decrease in N applied, irrespective of methods of planting, caused a significant decline in seed cotton yield during both the years. Water use efficiency (WUE) under drip irrigation increased from 1.648 to 1.847 and from 0.983 to 1.615 kg ha⁻¹ mm⁻¹ during first and second year, respectively, when the same quantity of N and water was applied. The WUE further increased to 2.125 and 1.788 kg ha⁻¹ mm⁻¹ under DP during first and second year, respectively. The agronomic efficiency of nitrogen was higher in drip than check-basin during both the years when equal N was applied. The WUE decreased with decrease in the rate of N applied under fertigation but reverse was true for AEN. It is evident that DP under drip irrigation resulted in higher seed cotton yield, WUE and AEN than NS and also saved 25% irrigation water as well as cost of laterals.     

Effect of soil matric potential on tomato yield and water use under drip irrigation condition

Field experiment was carried out to investigate the effect of soil matric potential (SMP) on tomato yield, evapotranspiration (ET), water use efficiency (WUE) and irrigation water use efficiency (IWUE) under drip irrigation condition in North China Plain. The experiment included five treatments, which controlled SMP at 0.2 m depth immediately under drip emitter higher than −10 (S1), −20 (S2), −30 (S3), −40 (S4) and −50 kPa (S5), respectively, after tomato plant establishment. The results showed that different SMP affected irrigation amount and tomato ET. Irrigation amount decreased from 185 mm (S1) to 83.6 mm (S5) in 2004, and from 165 mm (S1) to 109 mm (S5) in 2005, respectively. The ET decreased from 270 mm (S1) to 202 mm (S5) in both years. However, it was found that SMP did not affect the tomato yield significantly, for the range of SMP investigated. Both WUE and IWUE increased as SMP decreased. The maximum WUE (253 and 217 kg/ha mm) and IWUE (620 and 406 kg/ha mm) were for S5 in 2 years, whereas the minimum WUE (178 and 155 kg/ha mm) and IWUE 261 and 259 kg/ha mm) were for S1 in 2004 and 2005. Based on the above results, therefore, it is recommended that if the tomatoes are well irrigated (SMP is higher than −20 kPa) during establishment, controlling SMP higher than −50 kPa at 0.2 m depth immediately under drip emitter can be used as an indicator for drip irrigation scheduling during following period of tomato growth in North China Plain.     

Evapotranspiration and water use of full and deficit irrigated cotton in the Mediterranean environment in northern Syria

Cotton (Gossypium hirsutum L.) is the most important industrial and summer cash crop in Syria and many other countries in the arid areas but there are concerns about future production levels, given the high water requirements and the decline in water availability. Most farmers in Syria aim to maximize yield per unit of land regardless of the quantity of water applied. Water losses can be reduced and water productivity (yield per unit of water consumed) improved by applying deficit irrigation, but this requires a better understanding of crop response to various levels of water stress. This paper presents results from a 3-year study (2004-2006) conducted in northern Syria to quantify cotton yield response to different levels of water and fertilizer. The experiment included four irrigation levels and three levels of nitrogen (N) fertilizer under drip irrigation. The overall mean cotton (lint plus seed, or lintseed) yield was 2502 kg ha⁻¹, ranging from 1520 kg ha⁻¹ under 40% irrigation to 3460 kg ha⁻¹ under 100% irrigation. Mean water productivity (WP_ET) was 0.36 kg lintseed per m³ of crop actual evapotranspiration (ET_c), ranging from 0.32 kg m⁻³ under 40% irrigation to 0.39 kg m⁻³ under the 100% treatment. Results suggest that deficit irrigation does not improve biological water productivity of drip-irrigated cotton. Water and fertilizer levels (especially the former) have significant effects on yield, crop growth and WP_ET. Water, but not N level, has a highly significant effect on crop ET_c. The study provides production functions relating cotton yield to ET_c as well as soil water content at planting. These functions are useful for irrigation optimization and for forecasting the impact of water rationing and drought on regional water budgets and agricultural economies. The WP_ET values obtained in this study compare well with those reported from the southwestern USA, Argentina and other developed cotton producing regions. Most importantly, these WP_ET values are double the current values in Syria, suggesting that improved irrigation water and system management can improve WP_ET, and thus enhance conservation and sustainability in this water-scarce region.     

灌水模式及下限对滴灌棉花产量和品质的影响

为探索滴灌条件下棉花优质高效灌溉指标,在新疆石河子研究了地下滴灌(SSDI)和膜下滴灌(SDI)条件下不同灌水控制下限对棉花耗水量、品质以及水分利用率的影响.结果表明,相同滴灌模式,棉花蕾期耗水量随灌水控制下限的提高而增加,花铃期水分胁迫处理的棉花阶段耗水量普遍低于对照处理;蕾期适度水分胁迫(灌水控制下限为60% FC)花铃期充分供水(灌水控制下限为75% FC)处理(SDI-7和SSDI-7)有利于籽棉产量的提高,与对照处理相比,籽棉产量提高了14.48%(SDI-7)和11.60%(SSDI-7);水分处理对棉花衣分、棉纤维整齐度的影响不明显,蕾期和花铃期水分胁迫对棉纤维上半部平均长度的影响随水分胁迫程度的加重而加剧,蕾期适度水分胁迫(灌水控制下限为60% FC)有利于棉纤维断裂比强度的提高.相同水分处理,地下滴灌棉花产量和灌溉水利用率均高于膜下滴灌棉花.与对照处理相比,蕾期和花铃期灌水控制下限分别为60% FC和75% FC,灌水定额为30 mm处理在节约灌溉水的同时提高了籽棉产量并改善了棉纤维品质,可作为石河子垦区滴灌棉花适宜的灌水指标.     

Irrigation rate and plant density effects on yield and water use efficiency of drip-irrigated corn

The efficient use of water by modern irrigation systems is becoming increasingly important in arid and semi-arid regions with limited water resources. This study was conducted for 2 years (2005 and 2006) to establish optimal irrigation rates and plant population densities for corn (Zea mays L.) in sandy soils using drip irrigation system. The study aimed at achieving high yield and efficient irrigation water use (IWUE) simultaneously. A field experiment was conducted using a randomized complete block split plot design with three drip irrigation rates (I₁: 1.00, I₂: 0.80, and I₃: 0.60 of the estimated evapotranspiration), and three plant population densities (D₁: 48,000, D₂: 71,000 and D₃: 95,000 plants ha⁻¹) as the main plot and split plot, respectively. Irrigation water applied at I₁, I₂ and I₃ were 5955, 4762 and 3572 m³ ha⁻¹, respectively. A 3-day irrigation interval and three-way cross 310 hybrid corn were used. Results indicated that corn yield, yield components, and IWUE increased with increasing irrigation rates and decreasing plant population densities. Significant interaction effects between irrigation rate and plant population density were detected in both seasons for yield, selected yield components, and IWUE. The highest grain yield, yield components, and IWUE were found for I₁D₁, I₁D₂, or I₂D_1, while the lowest were found for I₃D₂ or I₃D₃. Thus, a high irrigation rate with low or medium plant population densities or a medium irrigation rate with a low plant population density are recommended for drip-irrigated corn in sandy soil. Crop production functions with respect to irrigation rates, determined for grain yield and different yield components, enable the results from this study to be extrapolated to similar agro-climatic conditions.     

Different drip irrigation regimes affect cotton yield, water use efficiency and fiber quality in western Turkey

Decreasing in water availability for cotton production has forced researchers to focus on increasing water use efficiency by improving either new drought-tolerant cotton varieties or water management. A field trial was conducted to observe the effects of different drip irrigation regimes on water use efficiencies (WUE) and fiber quality parameters produced from N-84 cotton variety in the Aegean region of Turkey during 2004 and 2005. Treatments were designated as full irrigation (T₁₀₀, which received 100% of the soil water depletion) and those that received 75, 50 and 25% of the amount received by treatment T₁₀₀ on the same day (treatments T₇₅; T₅₀ and T₂₅, respectively). The average seasonal water use values ranged from 265 to 753 mm and the average seed cotton yield varied from 2550 to 5760 kg ha⁻¹. Largest average cotton yield was obtained from the full irrigation treatment (T₁₀₀). WUE ranged from 0.77 kg m⁻³ in the T₁₀₀ to 0.98 kg m⁻³ in the T₂₅ in 2004 growing season and ranged from 0.76 kg m⁻³ in the T₁₀₀ to 0.94 kg m⁻³ in the T₂₅ in 2005 growing season. The largest irrigation water use efficiency (IWUE) was observed in the T₂₅ (1.46 kg m⁻³), and the smallest IWUE was in the T₁₀₀ treatment (0.81 kg m⁻³) in the experimental years. A yield response factor (k_y) value of 0.78 was determined based on averages of two years. Leaf area index (LAI) and dry matter yields (DM) increased with increasing water use for treatments. Fiber qualities were influenced by drip irrigation levels in both years. The results revealed that well-irrigated treatments (T₁₀₀) could be used for the semi-arid climatic conditions under no water shortage. Moreover, the results also demonstrated that irrigation of cotton with drip irrigation method at 75% level (T₇₅) had significant benefits in terms of saved irrigation water and large WUE indicating a definitive advantage of deficit irrigation under limited water supply conditions. In an economic viewpoint, 25.0% saving in irrigation water (T₇₅) resulted in 34.0% reduction in the net income. However, the net income of the T₁₀₀ treatment is found to be reasonable in areas with no water shortage.     

Response of citrus trees to deficit irrigation during different phenological periods in relation to yield, fruit quality, and water productivity

Four strategies of deficit irrigation based on a different water-stress ratio (WSR) applied in each phenological stage, and a control treatment were implemented in 11-year-old citrus trees (Citrus sinensis L. Osb. Cv. Navelina) grafted onto carrizo citrange (C. sinensis L. Osb. × Poncirus Trifoliata L. Osb.). The midday stem-water potential and stomatal conductance were measured during the periods considered, and these parameters were used to estimate the plant-water status. Integrated stem-water potential (Ψ_Int) and integrated stomatal conductance (g_Int) were calculated for all treatments and used as a water-stress indicator for the crop. Reference equations were formulated to quantify the relations between water-stress indicators (WSR, Ψ_Int, g_Int) and the crop response, expressed as yield, yield components, and fruit-quality parameters under limited seasonal water availability. Significant differences in yield were found in the second year of experiment between the stressed treatments and control, although these differences were evident during the first year. The main effects were detected in treatments with a water-sever stress applied during the flowering and fruit-growth phases. When this degree of stress was applied during the maturity phase, it was reflected mainly in fruit-quality parameters (total soluble solids, and titrable acidity). These results lead to the conclusion that, in mature orange trees, deficit irrigation affects yield and fruit quality, while enabling water savings of up to 1000 m³ ha⁻¹. Therefore, yield declined on average 10-12% but boosted water productivity 24% with respect to the fully irrigated treatment. Regarding the water-stress indicators used, Ψ_Int and g_Int showed highly significant correlations with the yield and fruit-quality parameters.     

Water stress effects on growth, development and yield of opium poppy (Papaver somniferum L.)

The effects of pre-anthesis water deficit and cycle length were examined in Papaver somniferum L., cultivated for alkaloid production, in two locations in southern Spain. The vegetative period was shortened by extending the photoperiod through supplemental lighting in the field, while water deficit in pre-anthesis was induced by avoiding irrigations and installing rain shelters. The treatments were: IN (irrigated-normal photoperiod), IL (irrigated-hastened flowering), DN (water deficit in pre-anthesis-normal photoperiod) and DL (water deficit in pre-anthesis and hastened flowering). The artificial photoperiod hastened the flowering by 15 and 21 days, for irrigated and deficit treatments respectively. Seasonal evapotranspiration (ET) ranged from 398 (DN) to 505 mm (IN). There was evidence of root water uptake deeper than 1.5 m. Stomatal conductance was reduced (16%) during water stress, and did not recover in post-anthesis after resuming irrigation. Head yields (capsule + seeds + 7 cm stem) ranged between 3.8 and 4.3 t ha⁻¹; water deficit and short vegetative period both reduced the biomass accumulated, although the effect on yields in these treatments was counterbalanced by a higher harvest index. Early flowering had a detrimental effect on alkaloid concentration in the capsule. Alkaloids yield ranged between 27 and 37 kg ha⁻¹. Water use efficiency (WUE) ranged between 0.78 and 0.96 kg m⁻³ ET for yield and between 63.4 and 73.7 g m⁻³ ET for alkaloids. Water stress increased slightly the Water Use Efficiency. A shorter vegetative phase had no effect on WUE for biomass or yield, but decreased the WUE for alkaloids production.