Optimization of furrow irrigation schedules, designs and net return to water

A seasonal furrow irrigation model consisting of irrigation scheduling and kinematic-wave-based hydraulic submodels was modified to incorporate an economic optimization submodel. The model used a systematic simulation technique to optimize furrow irrigation schedules and designs assuming 80% irrigation adequacy at cutoff time. The irrigation schedules and designs were optimized for the homogeneous and heterogeneous infiltration under the mean and observed ET0 (grass reference crop ET) conditions. The optimal management allowable depletion (MAD) level changed with the variation in ET0 condition, and with the consideration of spatial and temporal (seasonal) variability in infiltration characteristics. Irrigation design changed with both infiltration conditions and MAD level. infiltration variability did not influence the bean yield. However, the return to water decreased when spatial variability in infiltration conditions was considered. Using mean ET0 resulted in slightly higher yield and net return to water as compared to using observed ET0. A small variation in daily mean ET0 values with respect to daily observed ET0 values caused a change in both irrigation schedules and designs. Therefore, mean ET0 cannot be used to forecast irrigation schedules and designs at the beginning of crop season. The net return to water increased (1.7 to 3.6%), and the seasonal inflow, losses, and bean yield decreased in the case of variable interval scheduling (holding MAD constant) as compared to the fixed interval scheduling (MAD varies). (C) 1998 Elsevier Science B.V.