MODELING THE EFFECTS OF SPRINKLER IRRIGATION UNIFORMITY ON CROP YIELD

This study reports the development and testing of a model which relate s yield to irrigation amount and uniformity. Required input data are t he Christiansen uniformity coefficient (CUC) and a parameter describin g the sensitivity of crop yield to water deficits obtained from empiri cal relationships between evapotranspiration and crop yield. The model was used to determine optimum irrigation amounts for corn at Cordoba (Spain) under sprinkler irrigation. The economic impact of the accurac y in the ET estimates was assessed. The results were compared to those obtained with a crop growth model (Ceres-Maize) which was adapted to simulate the effect of irrigation uniformity on yield. The assumptions behind the use of CUC were experimentally evaluated. The results show that the optimum irrigation amount depends on irrigation uniformity, and on agronomic and economic factors. For maize production at Cordoba , the optimal ratio between gross and required irrigation requirements increased from 0.77 for CUC of 55% to 1 for CUC of 95% under high wat er prices. Crop simulation models and the simple model presented here are alternative tools for determining site-specific optimum irrigation amounts, with relatively low input data requirements.