Irrigation Scheduling Model with Groundwater and Limited Rooting

Abstract

An irrigation‐scheduling model was developed based on soil‐water budgeting, which incorporates the contribution of shallow‐groundwater tables (GWT) to crop‐water use and the effects of soil restrictions on crop rooting. Capillary flux of water from the groundwater table was estimated with a form of Darcy's equation, assuming mean soil water potential gradients between irrigations. Crop‐water use was estimated with a grass‐reference evapotranspiration (ET0) and crop coefficients (Kc). Water uptake was partitioned into the contributions of various soil zones based on root distribution. The model inputs are: soil variables (available water, allowable depletion, GWT depth, moisture‐characteristic curve, and unsaturated hydraulic conductivity); crop variables (root distribution, Kc curve); and climate (ET0). The model estimates irrigation interval, amount of water to apply per irrigation, and water contributed by the GWT. Scheduling the irrigation of wheat based on the model reduced seasonal irrigations by 28% and water application by 24%, compared with the conventional weekly irrigation.