Abstract
The present study evaluated the applicability of the CropSyst model under variable climatic, irrigation, and fertilizer-nitrogen regimes. The objective was to analyze wheat productivity responses to water and N-application for optimizing water productivity in an arid irrigated environment. Evaluation analysis showed that the model provided very satisfactory estimates for the emergence, flowering and physiological maturity dates. The performance of the model was reasonable as demonstrated by the close correspondence between simulated grain yield, biomass accumulation, seasonal ET, and irrigation water productivity (WPI) with measured data. The normalized root mean square error ranged between 5 and 10% for most of the parameters. Overall, the Willmott index of agreement between simulated and observed values of grain yield, biomass and seasonal ET were 0.99, 0.98 and 0.97, respectively. The validated model was employed to assess interactive effects of irrigation and fertilizer N on grain yield and water productivity indices. Scenario analyses indicated that WPI and WPET (ET water productivity) ranged from 0.16 to 2.07 kg m -3 , and from 0.07 to 1.49 kg m -3 , respectively. For predicting the best N and water application practices for maximization of water productivity, the best option found by the model was application of water and nitrogenous fertilizer in 70% and 90% of the required values, respectively, for WPI, and equal to the required values (100%) for WPET. The simulations demonstrated that the current wheat productivity of 5.0 Mg ha -1 obtained by the local farmers can be achieved at 140 kg ha -1 fertilizer N and 30% deficit irrigation regime with a WPI of 1.73 kg m -3 . The CropSyst model can be applied to derive best management options in terms of N and irrigation application of wheat under arid conditions.
Highlights
Wheat (Triticum aestivum L.) is one of the most important cereals both in Iran and globally
The results indicated that grain yield, biomass and maximum leaf area index (LAI) prediction was satisfactory
Water productivity decreases with increase in irrigation as grain yield is less than proportional increase in ET
Summary
Wheat (Triticum aestivum L.) is one of the most important cereals both in Iran and globally. There is a synergy between fertilizer-nitrogen and water for their effects on wheat productivity more so in arid and semi-arid regions that generally experience N deficiency. Both water and nitrogen are subjected to losses by many pathways if not managed properly. One can develop appropriate crop production strategies to increase yields, and to understand the links between climate variability, water availability and use, and agricultural management such as the amount and timing of N application, optimal sowing date, early and late flowering cultivar types, effect of pre-sown stored soil water and the interactive effects of all these factors on yield would require long and expensive field experiments
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