A thesis submitted in partial fulfillment of the requirement for the degree of Master of Engineering, School of Environment, Resources and Development

Thesis (M.Eng.) - Asian Institute of Technology, 1988

A simulation model has been developed on the basis of experimental observations in the field r elating crop water us e a nd yield . Using a water balance approach the model predicts the soil moisture contents of five layers in the soil profile of 120 cm depth, on a daily basis by taking into consideration crop parameters, soil physical properties and climatic conditions. The model also predicts grain yield at the end of crop growing season. The water uptake by plants has been considered by using a sink function. The model was calibrated for the prediction of grain yield by relating ratio of the actual to the potential transpiration at five crop growth stages to the ratio of actual to potential grain yield by a multiplicative type of crop production function. The Model was evaluated under prevailing irrigation practices. Th e mean absolute variation between predicted and observed soil moisture was about 8.2 %. The model was used to predict the irrigation schedules for obtaining maximum yield. It predicted six irrigations for obtaining maximum yield as a function of water provided the nutrient level is optimum. The results obtained using the simulation model were compared with the results obtained using a mathematical model based finite difference solution to the governing flow equations in soil profiles. Predictions from both the models were in close agreement with the observed data in the field.