Estimation of Water Balance Components in Paddy Fields under Non-Flooded Irrigation Regimes by using Excel Solver

Water saving technologies such as non-flooded irrigation have been introduced in many rice production during the past decade. Water balance analysis is needed to quantify water supply, loss and consumption for maximization rice production under such irrigation. However, hydrological data are often limited because acquisition of measurements in the field is costly, complicated and time consuming, hence methods that can estimate water balance components based on the combined use of available measurement data and an appropriate model are required. This study presents the estimation method using excel solver to estimate non-measurable water balance components, i.e., irrigation water, crop evapotranspiration, percolation and runoff, in a paddy field under non-flooded irrigation. The method was examined in two cultivation periods under different weather conditions. The model validation, indicated by coefficient of determination (R2) values, was greater than 0.86 (p<0.01) between observed and calculated values of soil moisture. Furthermore, when relationships among precipitation and estimated runoff was compared, the reliability of the model was shown by the significant linear correlations with correlation coefficient (R2) higher than 0.98 (p<0.01). These results indicate the reliability and applicability of the proposed method for estimating non-measurable water balance components for rice production when only limited data of measurable components are available.