A Stochastic Approach to the Crop Yield‐Irrigation Relationships in Heterogeneous Soils: I. Analysis of the Field Spatial Variability

When a deterministic irrigation regime is applied to a heterogeneous field, soil‐water content, soil salinity, and crop yield will vary in space because of the inherent spatial variability in the soil properties. It is important, therefore, to analyze their spatial distributions in the field in order to suggest improved irrigation management schemes for spatially‐variable fields. A stochastic approach was used to analyze the spatial variability of four parameters of the soil‐water retention curve as well as that of the initial soil‐water content and soil salinity, using actual measured field data. These properties were used as inputs for a simplified crop yield‐soil‐water model which, in turn, was coupled with the conditional simulation method to analyze the spatial distribution of the calculated soil‐water content (θ), soil salinity (C), and relative crop yield (Y) in an irrigated field, for various combinations of irrigation water quantity and quality (salinity). Analysis of the results showed that both irrigation water quantity and quality affected the spatial variability in θ, C, and Ybut essentially did not affect the spatial dependence of these properties. Although the average (spatial) response of the field was similar to that of a fictitious equivalent homogeneous field, the response of different sites in the field was quite different. For some combinations of irrigation water amount and salinity, the relative difference between relative crop yield obtained at different sites in the field exceeded 100%.