Abstract:Crop simulation models have a pivotal role to play in evaluating irrigation management strategies for improving agricultural water use. The objective of this study was to test and validate the AquaCrop model for maize under deficit irrigation management. Field observations from three experiments consisting of four treatments were used to evaluate model performance in simulating canopy cover (CC), biomass (B), yield (Y), crop evapotranspiration (ET c ), and water use efficiency (WUE). Statistics for root mean square error, model efficiency (E), and index of agreement for B and CC suggest that the model prediction is good under non-stressed and moderate stress environments. Prediction of final B and Y under these conditions was acceptable, as indicated by the high coefficient of determination and deviations <10%. In severely stressed conditions, low E and deviations >11% for B and 9% for Y indicate a reduction in the model reliability. Simulated ET c and WUE deviation from observed values were within the range of 9.5% to 22.2% and 6.0% to 32.2%, respectively, suggesting that AquaCrop prediction of these variables is fair, becoming unsatisfactory as plant water stress intensifies. AquaCrop can be reliably used for evaluating the effectiveness of proposed irrigation management strategies for maize; however, the limitations should be kept in mind when interpreting the results in severely stressed conditions.

Abstract:Identifying irrigation strategies that improve agricultural water use efficiency (WUE) have a pivotal role to play in sustainable water development. In this study, the AquaCrop model was used to examine the impact of different irrigation scheduling options on yields to identify viable strategies to enhance WUE for irrigated maize. Two scheduling scenarios at water application depths ranging from 20 to 50 mm were investigated: schedules based on allowable depletion of total available water (TAW) in the root zone and interval schedules based on irrigating at predefined daily intervals. For both scenarios, simulated yields, seasonal water applied and percent percolation loss were within the range of 9.16 to 10.22 ton/ha, 180 to 950 mm and 0-61%, respectively. The WUE in terms of water applied (WUE Irr ) and crop evapotranspiration (WUE ET ) ranged from 1.07 to 5.48 kg/m 3 and 2.42 to 4.42 kg/m 3 , respectively. The results revealed that depletion levels of 40-50% TAW at water depths of 20-40 mm could be used to obtain high WUE without significant yield penalty. Moreover, a good balance between yield, improved WUE ET and percolation reduction was observed at water depths of 30-40 mm for daily intervals with water applied during the vegetative-reproductive stage of 7-5, 10-5 and 10-7. The identified strategies can contribute to the development of best management practices for water conservation.

As the challenges toward increasing water for irrigation become more prevalent, knowledge of crop yield response to water can facilitate the development of irrigation strategies for improving agricultural productivity. Experiments were conducted to quantify maize yield response to soil moisture deficits, and assess the effects of deficit irrigation (DI) on water productivity (water and irrigation water use efficiency, WUE and IWUE). Five irrigation treatments were investigated: a full irrigation (I 1 ) with a water application of 60 mm and four deficit treatments with application depths of 50 (I 2 ), 40 (I 3 ), 30 (I 4 ), and 20 mm (I 5 ). On average, the highest grain yield observed was 1008.41 g m −2in I 1 , and water deficits resulted in significant (p < .05) reduction within range of 6 and 33%. This reduction was significantly correlated with a decline in grain number per ear, 1000-grain weight, ear number per plant, and number of grain per row. The highest correlation was found between grain yield and grain number per ear. The WUE and IWUE were within range of 1.52-2.25 kg m , respectively. High water productivity without significant reduction in yield (<13%) for I 2 and I 3 compared to the yield in I 1 indicates that these water depths are viable practices to promote sustainable water development. Also, for assessing the benefits of irrigation practices in the region crop water production functions were established. Maize yield response to water stress was estimated as .92, suggesting the environmental conditions are conducive for implementing DI strategies.

No abstract

This study was conducted to investigate the effect of deficit irrigation on radiation capture, radiation use efficiency (RUE) and water use efficiency (WUE) in maize production, and to assess how these factors impact biomass production in water stress environments. Five irrigation levels were investigated: a full irrigation treatment with a water depth of 60 mm (I1), and four deficit irrigation treatments with depths of 50 (I2), 40 (I3), 30 (I4) and 20 mm (I5). Crop water stress index values indicated treatments I2 and I3 caused mild water stress while I4 and I5 caused severe stress. Water deficits significantly (p<0.05) reduced leaf area index compared to full irrigation. The reduction in biomass for I2 to I5 ranged between 7 and 43% relative to I1. In I1, the RUE was 3.46 g MJ-1 , while mild and severe water stress significantly reduced it to 3.11 and 2.69 g MJ −1 , respectively. A reduction in both intercepted photosynthetically active radiation and RUE contributed significantly to biomass reduction. Mild and severe water stress improved the WUE within range of 2 and 25% and 10 and 34%, respectively. The results suggest that in mild water stress environments, high RUE aids in minimizing production losses, and in cases of severe water stress, the reduced ability to capture and utilize radiation is compensated by improving the WUE.