MODELING WATER-BALANCE COMPONENTS IN RELATION TO FIELD LAYOUT IN LOWLAND PADDY FIELDS .1. MODEL DEVELOPMENT

In this study, a water balance model applicable to lowland paddy field s was developed. The model inputs consist of irrigation supply, climat ic data, soil parameters and layout dimensions. The model is formulate d to simulate various processes such as evapotranspiration, seepage an d percolation, and surface runoff as they occur in the field water bal ance system. The model is able to predict the changes in water balance components under different land management and hydrological condition s. The model can be applied either for plot-to-plot or independent plo t layouts. It was validated using data collected from controlled plot experiments. The details of model development and validation are outli ned in this paper.