Yield and water productivity of rice as affected by time of transplanting in Punjab, India

Early planting of rice crop during the period of peak evaporative demand results in substantial mining of ground water and threats the sustainability of rice production in Punjab, northwest India. In order to increase yield and water productivity, arrest the mining of ground water, and achieve sustainability of rice production, there is need to adopt water-saving management practices. The present investigation in the Indian Punjab was aimed at investigating the effect of date of transplanting in four rice cultivars varying in growth duration (short-duration RH-257 and PR-115, and medium-duration PR-113 and PAU-201) on yield and water productivity. Delaying in transplanting from 15 June to 25 June or 5 July resulted in reduction in mean grain yield of the four cultivars by 7.2% and 15.9%, respectively. PAU-201, a photoperiod-sensitive cultivar, had higher mean grain yield (7.8 t ha⁻¹) by 14.1%, 12.8% and 11.5% over the photoperiod-insensitive cultivars, PR-113, PR-115 and RH-257, respectively. Irrespective of transplanting dates, short-duration cultivars, RH-257 and PR-115, respectively, resulted in 18.9% and 16.6% saving of water, as compared to medium-duration cultivar PR-113. With delayed transplanting after 15 June, both yield and water productivity decreased for all photoperiod insensitive cultivars, but yields remained statistically similar and water productivity greater for a photoperiod sensitive cultivar. Mean irrigation water productivity (WP_I) was highest for 15 June transplanting (0.66 kg m⁻³) and lowest for 5 July transplanting (0.57 kg m⁻³), and was highest for RH-257 (0.68 kg m⁻³) and lowest for PR-113 (0.50 kg m⁻³). Total water productivity (WP_I+R; irrigation plus rainfall) decreased by 9.1% for 5 July transplanting compared with 15 June transplanting, and was highest for RH-257 (0.49 kg m⁻³) and lowest for PR-113 (0.38 kg m⁻³). Real crop water productivity (WP_ET) of the photoperiod insensitive cultivars decreased (1.10-1.40 kg m⁻³), but that of a photoperiod sensitive cultivar increased (1.63 kg m⁻³), with delayed transplanting. We conclude that substantial amount of water can be saved and yield increased by transplanting short-duration cultivars during the period of peak evaporative demand, or water saved and yield maintained by transplanting a photoperiod-sensitive cultivar late in the season when the evaporative demand is low.     

Drip irrigation with saline water for oleic sunflower (Helianthus annuus L.)

The field experiments were carried out in 2007 and 2008 to study the effects and strategies of drip irrigation with saline water for oleic sunflower. Five treatments of irrigation water with average salinity levels of 1.6, 3.9, 6.3, 8.6, and 10.9 dS/m were designed. For each treatment, 7 mm water was applied when the soil matric potential (SMP) 0.2 m directly underneath the drip emitters was below −20 kPa, except during the seedling stage. To ensure the seedling survival, 28 mm water was applied after sowing during the seedling stage. Results indicate that amount of applied water decreases as salinity level of irrigation water increases. The emergence will be delayed when the salinity level of irrigation water is higher than 6.3 dS/m, but these differences will be alleviated if there is rainfall during emergence period. The final emergence percentage is not changed when salinity level of irrigation is less than 6.3 dS/m, and the percentage decreases by 2.0% for every 1 dS/m increase when the salinity level of irrigation water is above 6.3 dS/m, but the decreasing rate will be reduced if there is rainfall. The plant height and yield decrease with the increase of salinity of irrigation water. The height of plants decreases by 0.6-1.0% for every 1 dS/m increase in salinity level of irrigation water. The yield decreases by 1.8% for every 1 dS/m increase in salinity level of irrigation water, and irrigation water use efficiency (IWUE) increases with increase in salinity of irrigation water. The soil salinity increases as the salinity of irrigation water increasing after drip irrigation with saline water in the beginning, but the soil salinity in soil profile from 0 to 120 cm depths can be maintained in a stable level in subsequent year irrigation with saline water. From the view points of yield and soil salt balance, it can be recognized even as the salinity level of irrigation water is as high as 10.9 dS/m, saline water can be applied to irrigate oleic sunflower using drip irrigation when the soil matric potential 0.2 m directly under drip emitter is kept above −20 kPa and the beds are mulched in semi-humid area.     

Modelling the effects of climate variability and water management on crop water productivity and water balance in the North China Plain

In the North China Plain (NCP), while irrigation using groundwater has maintained a high-level crop productivity of the wheat-maize double cropping systems, it has resulted in rapid depletion of groundwater table. For more efficient and sustainable utilization of the limited water resources, improved understanding of how crop productivity and water balance components respond to climate variations and irrigation is essential. This paper investigates such responses using a modelling approach. The farming systems model APSIM (Agricultural Production Systems Simulator) was first calibrated and validated using 3 years of experimental data. The validated model was then applied to simulate crop yield and field water balance of the wheat-maize rotation in the NCP. Simulated dryland crop yield ranged from 0 to 4.5 t ha⁻¹ for wheat and 0 to 5.0 t ha⁻¹ for maize. Increasing irrigation amount led to increased crop yield, but irrigation required to obtain maximum water productivity (WP) was much less than that required to obtain maximum crop yield. To meet crop water demand, a wide range of irrigation water supply would be needed due to the inter-annual climate variations. The range was simulated to be 140-420 mm for wheat, and 0-170 mm for maize. Such levels of irrigation applications could potentially lead to about 1.5 m year⁻¹ decline in groundwater table when other sources of groundwater recharge were not considered. To achieve maximum WP, one, two and three irrigations (i.e., 70, 150 and 200 mm season⁻¹) were recommended for wheat in wet, medium and dry seasons, respectively. For maize, one irrigation and two irrigations (i.e., 60 and 110 mm season⁻¹) were recommended in medium and dry seasons, while no irrigation was needed in wet season.     

InfoCrop: A dynamic simulation model for the assessment of crop yields,losses due to pests,and environmental impact of agro-ecosystems in tropical environments. II. Performance of the model

InfoCrop, a generic crop model, simulates the effects of weather, soils, agronomic management (planting, nitrogen, residues and irrigation) and major pests on crop growth, yield, soil carbon, nitrogen and water, and greenhouse gas emissions. This paper presents results of its evaluation in terms of its validation for rice and wheat crops in contrasting agro-environments of tropics, sensitivity to the key inputs, and also illustrates two typical applications of the model. Eleven diverse field experiments, having treatments of location, seasons, varieties, nitrogen management, organic matter, irrigation, and multiple pest incidences were used for validation. Grain yields in these experiments varied from 2.8 to 7.2 ton ha⁻¹ in rice and from 3.6 to 5.5 ton ha⁻¹ in wheat. The results indicated that the model was generally able to explain the differences in biomass, grain yield, emissions of carbon dioxide, methane and nitrous oxides, and long-term trends in soil organic carbon, in diverse agro-environments. The losses in dry matter and grain yield due to different pests and their populations were also explained satisfactorily. There were some discrepancies in the simulated emission of these gases during first few days after sowing/transplanting possibly because of the absence of tillage effects in the model. The sensitivity of the model to change in ambient temperature, crop duration and pest incidence was similar to the available field knowledge. The application of the model to quantify multiple pests damage through iso-loss curves is demonstrated. Another application illustrated is the use of InfoCrop for analyzing the trade-offs between increasing crop production, agronomic management strategies, and their global warming potential.     

Rice growth, yield and water productivity responses to irrigation scheduling prior to the delayed application of continuous flooding in south-east Australia

The majority of rice grown in south-east Australia is continuously flooded for much of its growing season, but reduced irrigation water availability brought about by a combination of drought and environmental flow legislation has presented a need to maintain (or even increase) rice production with less irrigation water. Delaying the application of continuous flooding until prior to panicle initiation can increase input water productivity by reducing non-beneficial evaporation losses from free water and the soil. A field experiment was conducted over two growing seasons, 2008/9 and 2009/10, comparing a conventional dry seeded treatment (the control - continuous flooding from the 3 leaf stage) with delayed continuous flooding (10-20 days prior to panicle initiation) with several irrigation scheduling treatments prior to flooding commencement. In the first year, the delayed water treatments were irrigated at intervals of 40, 80 and 160 mm of cumulative reference evapotranspiration (ETo) prior to delayed continuous flooding, thereby imposing differing degrees of crop water stress. In year 2, the 80 and 160 mm treatments were modified by use of a crop factor (Kc) when the plants were small and the 40 mm treatment was replaced with a continuously flooded treatment throughout the crop duration.Decreases in net water input (irrigation + rain − surface drainage) and increases in input water productivity were achieved by reducing the flush irrigation frequency during the pre-flood period. Savings of 150 and 230 mm (10 and 15%) were achieved in Year 1 from the 80 and 160 mm cumulative ETo irrigation frequency treatments, respectively, in comparison to the control. In the second year, net water input savings of 230 and 330 mm (15 and 22%) were achieved with the 80/Kc and 160/Kc mm treatments, respectively. Input water productivity of the 160 mm treatment was 0.06 kg/m³ (8%) higher than the control in Year 1, while in Year 2 a 0.15 kg/m³ (17%) increase in input water productivity above the control was achieved by the 160/Kc mm treatment. Delaying the application of continuous flooding in the second year greatly extended the period of crop growth suggesting the need for earlier sowing (by 7-10 days) to ensure pollen microspore still occurs at the best time to minimise yield loss due to cold damage. Nitrogen fertiliser management is an important issue when delaying continuous flooding, and nitrogen losses appeared to increase with the frequency of irrigation prior to continuous flooding. This was likely due to increased denitrification from alternate wetting and drying of the soil. Further research is required to determine the most appropriate nitrogen management strategies, and to also better define the optimal pre-flood irrigation frequency.     

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.     

Role of irrigation and mulch on yield, evapotranspiration rate and water use pattern of tomato (Lycopersicon esculentum L.)

Irrigation management strategy invites the quantification of crop response to irrigation frequencies. Conventionally, mulches increase the yield and water use efficiency (WUE) to a great extent by augmenting the water status in the root zone profile. A field study was carried out during the winter season (November-March) of 2003-2004 and 2004-2005 at the Central Research Farm of Bidhan Chandra Krishi Viswavidyalaya (Latitude 22°58′N, Longitude 88°31′E and altitude 9.75 m amsl), Gayeshpur, India, to evaluate the effect of irrigation frequencies and mulches on evapotranspiration rate from tomato crop field as well as leaf area index (LAI), fruit yield and WUE of the crop. The experiment was laid out in a split-plot design where three irrigation treatments {rainfed (RF); CPE₅₀ and CPE₂₅ where irrigation was given at 50 and 25 mm of cumulative pan evaporation (CPE)} were kept in the main plots and the subplots contained four mulch managements {no mulch (NM), rice straw mulch (RSM), white polyethylene mulch (WPM) and black polyethylene mulch (BPM)}. Under CPE₂₅, tomato crop recorded significantly higher leaf area index (LAI) over CPE₅₀ and rainfed condition. LAI value under BPM was 9-30% more over other mulches. Maximum variation of LAI among different treatments was recorded at 60 days after transplanting (DAT). Fruit yield under CPE₂₅ was 39.4 Mg ha⁻¹; a reduction of 7 and 30% has been obtained under CPE₅₀ and RF condition. The use of mulch increased 23-57% yield in comparison to NM condition. Actual evapotranspiration rate (ET_R) was 1.82 mm day⁻¹ under CPE₂₅ and declined by 15 and 31% under CPE₅₀ and RF condition, respectively. The variation of ET_R among different mulches became more prominent under maximum water stressed (RF) condition, whereas the variation was negligible under CPE₂₅ frequency. Irrespective of mulching WUE was highest under moderately wet (CPE₅₀) soil environment. Among different mulches, BPM was responsible for attaining the highest WUE value (25.1 kg m⁻³), which declined by 22, 21 and 39% under WPM, RSM and NM, respectively.     

Drip irrigation of tea (Camellia sinensis L.): 1. Yield and crop water productivity responses to irrigation

The effects of drip irrigation on the yield and crop water productivity responses of four tea (Camellia sinensis (L.) O. Kuntze) clones were studied four consecutive years (2003/2004-2006/2007), in a large (9 ha) field experiment comprising of six drip irrigation treatments (labelled: I₁-I₆) and four clones (TRFCA PC81, AHP S15/10, BBK35 and BBT207) planted at a spacing of 1.20 m × 0.60 m at Kibena Tea Limited (KTL), Njombe in the Southern Tanzania in a situation of limited water availability. Each clone × drip irrigation treatment combination was replicated six times in a completely randomized design with 144 net plots each with an area of 72 m². Clone TRFCA PC81 gave the highest yields (range: 5920-6850 kg dried tea ha⁻¹) followed by clones BBT207 (5010-5940 kg dried tea ha⁻¹), AHP S15/10 (4230-5450 kg dried tea ha⁻¹) and BBK35 (3410-4390 kg dried tea ha⁻¹) and drip irrigation treatment I₂ gave the highest yields, ranging from 4954 to 6072 kg dried tea ha⁻¹) compared with those from other treatments (4113-5868 kg dried tea ha⁻¹). Most of these yields exceeded those (4200 kg dried tea ha⁻¹) obtained from overhead sprinkler irrigation system in Mufindi also Southern Tanzania, and Kibena Estate itself. Results showed that drip irrigation of tea not only increased yields but also gave water saving benefits of up to 50% from application of 50% less water to remove the cumulative soil water deficit (treatment I₂), and with labour saving of 85% for irrigation. The yield of dried tea per mm depth of water applied, i.e., “the crop water productivity” for drip irrigation of clones TRFCA PC81, BBT207 and BBK35, in 2003/2004 for instance, were 9.3, 8.5 and 7.1 kg dried tea [ha mm]⁻¹, respectively. The corresponding values in 2004/2005 were 2.7, 4.5 and 2.0 kg dried tea [ha mm]⁻¹ while the yield responses from clone AHP S15/10 were linear decreasing by 1 and 1.6 kg dried tea [ha mm]⁻¹ in 2003/2004 and 2004/2005, respectively. In 2005/2006 the crop water productivity from clones TRFCA PC81, AHP S15/10, BBK35 and BBT207 were 4.5, 0.4, 5.2 and 6.9 kg dried tea [ha mm]⁻¹, respectively with quadratic yield response functions to drip irrigation depth of water application. The results are presented and recommendations and implications made for technology-transfer scaling-up for increased use by large and smallholder tea growers.     

水肥耦合对温室番茄产量、水分利用效率和品质的影响

为指导日光温室番茄高产节水优质的灌溉施肥,以番茄为研究对象,设置3种施肥方式(总施肥量相同,施肥时间不同,其中F₁:不施底肥,番茄移栽后随水追施总肥量的30%,剩余70%平分6次追肥,F₂:底肥施1/2,剩余平分6次追肥,F₃:全施底肥不追肥)和3种土壤水势的灌水下限(W₁:-30 kPa,W₂:-50 kPa,W₃:-70 kPa),研究滴灌条件下水肥耦合对番茄耗水量、产量、水分利用效率和品质的影响.结果表明:施肥方式对番茄的耗水量差异不具有统计学意义,而灌水下限对耗水量有极显著性影响,且耗水量与灌水量呈极显著的正相关关系(P<0.01);与产量最大处理F₂W₁相比,F₂W₂处理产量降低6.91%,但节水14.83%,水分利用效率提高8.51%;TTS质量分数与平均单果重呈极显著负相关,而与除糖酸比外其他影响品质指标呈显著性正相关关系;综合考虑产量、WUE及TTS质量分数,利用TOPSIS综合评价方法,确定了温室滴灌条件下番茄节水调质的最优灌溉施肥模式为:移栽前施入底肥为总肥量的50%,移栽后灌水20 mm,进入开花坐果期以后,20 cm土层的土壤水势控制在-50 kPa以上,每次灌水定额为10 mm,剩余肥料每隔1次灌水追肥1次,将剩余50%的肥料分6次追肥.研究成果为制定日光温室番茄节水高产优质的灌溉模式提供了理论依据.     

Using EPIC model to manage irrigated cotton and maize

Simulation models are becoming of interest as a decision support system for management and assessment of crop water use and of crop production. The Environmental Policy Integrated Climate (EPIC) model was used to evaluate its application as a decision support tool for irrigation management of cotton and maize under South Texas conditions. Simulation of the model was performed to determine crop yield, crop water use, and the relationships between the yield and crop water use parameters such as crop evapotranspiration (ETc) and water use efficiency (WUE). We measured actual ETc using a weighing lysimeter and crop yields by field sampling, and then calibrated the model. The measured variables were compared with simulated variables using EPIC. Simulated ETc agreed with the lysimeter, in general, but some simulated ETc were biased compared with measured ETc. EPIC also simulated the variability in crop yields at different irrigation regimes. Furthermore, EPIC was used to simulate yield responses at various irrigation regimes with farm fields’ data. Maize required ∼700 mm of water input and ∼650 mm of ETc to achieve a maximum yield of 8.5 Mg ha⁻¹ while cotton required between 700 and 900 mm of water input and between 650 and 750 mm of ETc to achieve a maximum yield of 2.0-2.5 Mg ha⁻¹. The simulation results demonstrate that the EPIC model can be used as a decision support tool for the crops under full and deficit irrigation conditions in South Texas. EPIC appears to be effective in making long-term and pre-season decisions for irrigation management of crops, while reference ET and phenologically based crop coefficients can be used for in-season irrigation management.     

Salt distribution and the growth of cotton under different drip irrigation regimes in a saline area

A 3-year experiment was conducted in an extremely dry and saline wasteland to investigate the effects of the drip irrigation on salt distributions and the growth of cotton under different irrigation regimes in Xinjiang, Northwest China. The experiment included five treatments in which the soil matric potential (SMP) at 20 cm depth was controlled at −5, −10, −15, −20, and −25 kPa after cotton was established. The results indicated that a favorable low salinity zone existed in the root zone throughout the growing season when the SMP threshold was controlled below −25 kPa. When the SMP value decreased, the electrical conductivity of the saturation paste extract (EC_e) in the root zone after the growing season decreased as well. After the 3-year experiment, the seed-cotton yield had reached 84% of the average yield level for non-saline soil in the study region and the emergence rate was 78.1% when the SMP target value was controlled below −5 kPa. The average pH of the soil decreased slightly after 3 years of cultivation. The highest irrigation water use efficiency (IWUE) values were recorded when the SMP was around −20 kPa. After years of reclamation and utilization, the saline soil gradually changed to a moderately saline soil. The SMP of −5 kPa at a depth of 20 cm immediately under a drip emitter can be used as an indicator for cotton drip irrigation scheduling in saline areas in Xinjiang, Northwest China.     

Evaluation of crop water stress index for LEPA irrigated corn

This study was designed to evaluate the crop water stress index (CWSI) for low-energy precision application (LEPA) irrigated corn (Zea mays L.) grown on slowly-permeable Pullman clay loam soil (fine, mixed, Torrertic Paleustoll) during the 1992 growing season at Bushland, Tex. The effects of six different irrigation levels (100%, 80%, 60%, 40%, 20%, and 0% replenishment of soil water depleted from the 1.5-m soil profile depth) on corn yields and the resulting CWSI were investigated. Irrigations were applied in 25 mm increments to maintain the soil water in the 100% treatment within 60–80% of the “plant extractable soil water” using LEPA technology, which wets alternate furrows only. The 1992 growing season was slightly wetter than normal. Thus, irrigation water use was less than normal, but the corn dry matter and grain yield were still significantly increased by irrigation. The yield, water use, and water use efficiency of fully irrigated corn were 1.246 kg/m², 786 mm, and 1.34 kg/m³, respectively. CWSI was calculated from measurements of infrared canopy temperatures, ambient air temperatures, and vapor pressure deficit values for the six irrigation levels. A “non-water-stressed baseline” equation for corn was developed using the diurnal infrared canopy temperature measurements as T _c–T _a = 1.06–2.56 VPD, where T _c was the canopy temperature (°C), Ta was the air temperature (°C) and VPD was the vapor pressure deficit (kPa). Trends in CWSI values were consistent with the soil water contents induced by the deficit irrigations. Both the dry matter and grain yields decreased with increased soil water deficit. Minimal yield reductions were observed at a threshold CWSI value of 0.33 or less for corn. The CWSI was useful for evaluating crop water stress in corn and should be a valuable tool to assist irrigation decision making together with soil water measurements and/or evapotranspiration models. Received: 19 May 1998     

Effects of applied water and sprinkler irrigation uniformity on alfalfa growth and hay yield

This study was conducted to investigate the effects of applied water and sprinkler irrigation uniformity on alfalfa (Medicago sativa L.) growth and hay yield in a semi-arid region. Field experiments were carried out in 2006 in Varamin, Iran, on three plots of 25 m × 30 m. Each plot was subdivided into 25 subplots of 5 m × 6 m. Different irrigation depths and sprinkler water uniformities were obtained by various scenarios of sprinkler nozzle pressure. In each plot, applied water was measured at 250 points (125 points above and 125 points below canopy) and the soil water content of 40 cm deep below soil surface was monitored at 25 points, each in the center of a subplot, throughout the irrigation season. The results showed that sprinkler water and soil water content uniformity varied between 66-78 and 88-91%, respectively. The findings revealed that soil water content uniformity was around 20% higher than sprinkler water uniformity. The irrigation uniformity below the canopy was estimated to be 2.5% greater than above the canopy, and canopy-intercepted water could account for 11-15% of the total seasonal applied water. Evaluation showed that alfalfa leaf area index relies more heavily on farm water application uniformity than hay yield and crop height. The experimental results illustrated that water distribution in sprinkler irrigation systems has a direct effect on alfalfa growth, hay yield and water productivity such that the applied water reduction and the increased sprinkler water uniformity led to an increased alfalfa water productivity of 2.41 kg m⁻³.     

Farmers’ incentives to save water with new irrigation systems and water taxation—A case study of Serbian potato production

Drip irrigation systems and irrigation strategies like deficit irrigation (DI) and partial root drying (PRD) are potential water saving irrigation systems and strategies. This paper analyses the Serbian farmer's economic incentive to use these water saving systems and strategies instead of the present sprinkler irrigation. The analysis is a partial budgeting analysis, based on irrigation application efficiency from the literature, standard figures for power requirements, pumping efficiency and friction losses for various sources of water and pressure requirements, yields and water use from recent Serbian field experiments, as well as prices and cost structures for potatoes collected in the Belgrade region. The analysis shows that changing the present system and strategy can save a significant amount of water (almost 50%). At the same time, however, irrigation costs are also significantly increased (more than doubled), and the total production costs are increased by 10% (deficit drip irrigation) and 23% (PRD). Increased taxes on water, investment subsidies, increased energy prices, and an increased yield or yield quality may provide incentives for farmers to change to new systems and strategies. The analysis indicates that a 0.80 to 1.97 € m⁻³ water tax is needed to make deficit drip irrigation and PRD profitable. The socioeconomic cost of providing water for irrigation and the alternative value of saved water are probably not that high. Thus, water taxation may not be a socioeconomic efficient means to improve the irrigation water productivity of Serbian potato production. Drip irrigation and PRD may, however, also increase the yield quality, and a 10-23% quality premium (price increase) is needed to make deficit drip irrigation and PRD profitable.     

Water use and water use efficiency of sweet corn under different weather conditions and soil moisture regimes

Plant growth and development are influenced by weather conditions that also affect water use (WU) and water use efficiency (WUE) and ultimately, yield. The overall goal of this study was to determine the impact of weather and soil moisture conditions on WU and WUE of sweet corn (Zea mays L. var rugosa). An experiment consisting on three planting dates was conducted in 2006 at The University of Georgia, USA. A sweet corn genotype sh2 was planted on March 27 under irrigated and rainfed conditions and on April 10 and 25 under irrigated conditions only. Soil moisture was monitored using PR2 probes. Rainfall and irrigation were recorded with rain gauges installed in the experimental area while other weather variables were recorded with an automatic weather station located nearby. A water balance was used to obtain the crop's daily evapotranspiration (ETc). WUE was calculated as the ratio of fresh and dry matter ear yield and cumulative ETc. The potential soil moisture deficit (Dp) approach was used to determine the crop's moisture stress. Results were analyzed using a single degree freedom contrast, linear regression, and the least significant difference. WU and WUE of sweet corn were both markedly affected by the intra-seasonal weather variability and Dp. For both variables, significant (p < 0.05) differences were found between planting dates under irrigated conditions and between the irrigated and rainfed treatments. WU was as high as 268 mm for the April 10 planting date under irrigated conditions and as low as 122 mm for the March 27 planting date under rainfed conditions. The maximum soil moisture deficit was reached at the milky kernel stage and was as high as 343 mm for the March 27 planting date under rainfed conditions and as low as 260 mm for the April 10 planting date under irrigated conditions. Further work should focus on the impact of the intra-seasonal weather variability and soil moisture conditions during different crop stages to determine critical periods that affect yield.     

Validation and testing of the AquaCrop model under full and deficit irrigated wheat production in Iran

Accurate crop development models are important tools in evaluating the effects of water deficits on crop yield or productivity and predicting yields to optimize irrigation under limited available water for enhanced sustainability and profitable production. Food and Agricultural Organization (FAO) of United Nations addresses this need by providing a yield response to water simulation model (AquaCrop) with limited sophistication. The objectives of this study were to evaluate the AquaCrop model for its ability to simulate wheat (Triticum aestivum L.) performance under full and deficit water conditions in a hot dry environment in south of Iran, to study the effect of different scenarios of irrigation (crop growth stages and depth of water applied) on wheat yield. The AquaCrop model was evaluated with experimental data collected during the three field experiments conducted in Ahvaz. The AquaCrop model was able to accurately simulate soil water content of root zone, crop biomass and grain yield, with normalized root mean square error (RMSE) less than 10%. The analysis of irrigation scenarios showed that the highest grain yield could be obtained by applying four irrigations (200 mm) at sowing, tillering, stem elongation and flowering or grain filing stages for wet years, four irrigations (200 mm) at sowing, stem elongation and flowering stages for normal years and six irrigations (300 mm) at sowing, emergence, tillering, stem elongation, flowering and grain filing stages for dry years. The least amount of irrigation water to provide enough water to response to evaporative demand of environment and to obtain high WUE for wet, normal and dry years were 100, 200 and 250 mm, respectively.     

The effect of rice straw mulch on evapotranspiration, transpiration and soil evaporation of irrigated wheat in Punjab, India

Soil evaporation (Es) is considered to be a non-productive component of evapotranspiration (ET). So, measures which moderate Es may influence the amount of water available for transpiration (T), the productive component of ET. Field experiments investigating the effects of rice straw mulch on components of the water balance of irrigated wheat were conducted during 2006-2007 and 2007-2008 in Punjab, India, on a clay loam soil. Daily Es was measured using mini-lysimeters, and total seasonal ET was estimated as the missing term in the water balance equation. Mulch lowered total Es over the crop growth season by 35 and 40 mm in relatively high and low rainfall years, respectively. Much of this “saved water” was partitioned into T, which increased by 30 and 37 mm in the high and low rainfall years, respectively. As a result, total ET was not affected by mulch in either year. In both years, there was a trend for higher biomass production and grain yield with mulch, but with significant differences only in 2006-2007. Transpiration efficiency (TE) with respect to grain yield was 18.8-19.1 kg ha⁻¹ mm⁻¹ in 2006-2007, and 14.6-16.4 kg ha⁻¹ mm⁻¹ in 2007-2008. While wheat grown in the presence of mulch tended to lower TE, this was only significant in 2007-2008. The results suggest that while mulching of well-irrigated wheat reduces Es, it does not “save” water because the crop compensates by increased T and reduced TE.     

Seasonal climate change impacts on evapotranspiration, precipitation deficit and crop yield in Puerto Rico

The purpose of this study was to estimate precipitation (P), reference evapotranspiration (ET_o), precipitation deficit (PD = P − ET_o) and relative crop yield reduction (YR) for a generic crop under climate change conditions for three locations in Puerto Rico: Adjuntas, Mayagüez, and Lajas. Reference evapotranspiration was estimated by the Penman-Monteith method. Precipitation and temperature data were statistically downscaled and evaluated using the DOE/NCAR PCM global circulation model projections for the B1 (low), A2 (mid-high) and A1fi (high) emission scenarios of the Intergovernmental Panel on Climate Change Special Report on Emission Scenarios. Relative crop yield reduction was estimated from a water stress factor, which is a function of soil moisture content. Average soil moisture content for the three locations was determined by means of a simple water balance approach.Results from the analysis indicate that the rainy season will become wetter and the dry season will become drier. The 20-year average September precipitation excess (i.e., PD > 0) increased for all scenarios and locations from 121 to 321 mm between 2000 and 2090. Conversely, the 20-year average February precipitation deficit (i.e., PD < 0) changed from −27 to −77 mm between 2000 and 2090. The results suggest that additional water could be saved during the wet months to offset increased irrigation requirements during the dry months. The 20-year average relative crop yield reduction for all scenarios decreased on average from 12% to 6% between 2000 and 2090 during September, but increased on average from 51% to 64% during February. Information related to the components of the hydrologic water budget (i.e., actual evapotranspiration, surface runoff, aquifer recharge and soil moisture storage) is also presented. This study provides important information that may be useful for future water resource planning in Puerto Rico.     

Assessing yield optimization and water reduction potential for summer-sown and spring-sown maize in Pakistan

Agricultural food production in arid and semi-arid regions faces the challenge to ensure high yields with limited supply of water. This raises the question to which extent irrigation supply can be reduced without detriment to yield. Our study focuses on the yield-water uptake relationship for maize in the moderate water stress range in order to determine the onset of stress-induced dry-matter and yield losses. Compensatory plant responses under moderate stress levels are discussed in relation to seasonal climatic conditions.Summer-sown and spring-sown maize were irrigated with a decreasing amount of water in a field experiment in Pakistan. Water supply ranged from 100% water required to maintain soil at field capacity (FC) to 40% of FC. The average dry-matter and yield levels were slightly higher for summer-sown (15.0 Mg ha⁻¹) compared to spring-sown maize (13.1 Mg ha⁻¹). The onset of significant dry-matter and yield reduction started at the least irrigation treatment in both seasons. The amount of water required to avoid production losses was 272 mm in the summer-sown maize during the autumn growing season, and 407 mm for the spring-sown maize in the summer season, when the evaporative demand of the atmosphere was +27% higher. Water use efficiency (WUE_ET), normalized by vapour pressure deficit, of the summer-sown maize which was 10.0 kg kPa m⁻³, was +15% higher compared to the spring-sown crop; while the irrigation water productivity (2.9 kg m⁻³) was +11% more. WUE_ET increased over the whole range of applied water deficits for summer-sown maize, while the spring-sown crop showed a decreasing WUE_ET in the less irrigated treatment. Due to the higher efficiency in summer-sown maize, the potential in irrigation reduction without production losses (129 mm) was higher compared to the spring-sown maize (57 mm). Our results showed that in Pakistan water saving irrigation practices can be applied without yield loss mainly during the cooler growing season when the crop can efficiently compensate a lower total water uptake by increased use efficiency. For spring-sown maize the increasing evaporative demand of the atmosphere towards summer implies a higher risk of yield losses and narrows the range to exploit higher irrigation water productivity under moderate water deficit conditions.     

分蘖期水分对香稻香气及生理特性的影响

以常规香稻品种桂香占和美香占为材料,采用盆栽试验,研究了分蘖期水分对香稻香气及生理特性的影响。结果表明,分蘖期土壤水势维持在0～(-25±5)kPa时,显著增加了二香稻品种糙米的香气成分和籽粒的游离脯氨酸以及成熟期叶片、茎鞘和籽粒的脯氨酸氧化酶活性。分蘖期土壤水势维持在0～(-50±5)kPa时,降低了二品种籽粒脯氨酸氧化酶活性、糙米的香气成分和有效分蘖。因此,适当的分蘖期节水灌溉模式能有效提高香稻香气成分,且不影响水稻后期生理特性。