Modeling Water Balance Parameters for Rainfed Rice

A field water balance model is developed for rainfed rice in medium land (a rice field with intermittent ponding and drying phase is characterized as medium land) in eastern India with provision of supplemental irrigation from an on-farm reservoir. The model inputs consist of soil, crop, and daily climatic data. By developing a computer program in Visual Basic 6.0, the model simulates various water-balance parameters such as actual evapotranspiration, percolation, seepage, supplemental irrigation, surface runoff, and ponding depth in the field on a daily basis. Physically based saturated and unsaturated flow processes are incorporated into the model to simulate the aforesaid model parameters that occur during wet and dry periods. The model parameters are validated with the observed data of the experimental field. The Z-test was used to look for significant differences between the observed and simulated values of the parameters. The model hypothesis is found to be acceptable at a 5% level of significance for simulating the actual evapotranspiration and ponding depth and at the 1% level of significance for simulating percolation.