A Stochastic Approach to the Crop Yield‐Irrigation Relationships in Heterogeneous Soils: II. Application to Irrigation Management

Abstract

AbstractIn a heterogeneous field in which the soil properties vary, under a deterministic irrigation regime, the crop yield might also differ from place to place in the field. These differences may, in turn, reduce the average (over the field) yield relative to that which would be obtained if the soil properties were uniform throughout the field. The simplified crop yield‐soil response model coupled with the conditional simulation method, presented in part I of this study, was used here to evaluate the spatial distribution of the amount of irrigation water required to maintain a prespecified relative crop yield, uniform throughout the field, for a given irrigation water salinity. By considering the water irrigation amounts at different sites in the field, rather than that of the entire field, it was shown that the amount of irrigation water required to obtain a given relative crop yield (for a given irrigation water salinity) can be reduced by 7 to 34%. The amount of water that could be saved increased as the level of the required crop yield increased and as the salinity of the irrigation water decreased. The spatial distributions of the amount of irrigation water required to maintain a given relative crop yield were combined with economic considerations in order to evaluate the spatial distribution of the optimal amounts of irrigation water for a given irrigation water salinity. It was shown that the optimal amounts of irrigation water can be reduced by 6 to 29%, when the responses of different sites in the field is considered rather than the average response of the entire field. Irrigation schemes based on imposition of engineering requirements on the spatial distributions of the optimal irrigation water amounts, increased the net benefit (price of the crop yield minus cost of the irrigation water) by 5.5 to 42% relative to that obtained under deterministic conventional water application schemes. The differences between the two schemes decreased as the irrigation water salinity increased.