Dynamic simulation of soil water and root distribution of a corn (Zea mays L.) crop [Philippines].

Microcomputer-based simulation models (i.e. SWASMOD and WATER BALANCE) using commonly measured soil, crop, weather, and management parameters as inputs were utilized to predict soil moisture contents, leaf area index (LAI), evapotranspiration (ET), and root distribution. The models were tested and evaluated on three different soil types under corn. The goodness of fit of an exponential model in predicting root distribution with soil depth and time was also evaluated. The effects of the different irrigation timing on the yield of two corn varieties were assessed. The SWASMOD satisfactorily predicted the soil moisture contents in the 15-30, 30-45, 45-60, 60-75, and 75-90 cm soil depths. However, the model significantly overestimated the moisture content in the 0-15 cm soil depth. In the case of the different soil types, the model gave better predictions in the medium- and fine-textured soils than in the coarse-textured soil. For the WATER BALANCE model, close agreements between the predicted and the measured values were obtained in the 0-15, 15-30, and 30-45 cm soil depths. Extending the simulation depths to 60 and 75 cm produced significant overestimates. Generally, the model gave higher degree of accuracy of predictions in the coarse-textured soil than in the medium- and fine-textured soils. Root distribution predicted by the model generally is in good agreement with the measured values. Consequently, the ET predictions of the two models were satisfactory, although the SWASMOD gave lower estimates. Reasonable agreement between predicted and measured LAI was obtained, although the models gave a slight overestimation. Satisfactory fit of root distribution with soil depth were obtained using the exponential model. However, as the crop matured, the accuracy of the model tended to decrease, especially in the 0-15 cm soil depth. The grain yield of corn was significantly influenced by the different irrigation timing. Corn plants irrigated at 50% depletion of the available moisture or at tasseling, silking, and grain filling stages gave higher yield as compared to those irrigated at tasseling and grain filling stages only.