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 (WP_I) 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 WP_I and WP_ET (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 WP_I, and equal to the required values (100%) for WP_ET. 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 WP_I 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.

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