Prediction of root zone water and nitrogen balance in an irrigated rice field using a simulation model

Abstract

In irrigated semi-arid regions, knowledge of groundwater recharge and nitrate leaching is essential for sustainable management of water resources. In this study, the potential recharge and nitrate leaching below the root zone of rice crop were estimated using a root zone modelling approach through simulation with HYDRUS-1D model. The field data collected for a single season were used for calibrating the model and validated for the next season. The simulated results, when compared with the measured soil water and nitrate contents at different soil depths showed good agreement between the HYDRUS-1D simulation and field data. The validated results indicated that 55.5 % of the applied water percolated below the root zone. Nitrogen balance within 120 cm deep soil profile indicated that volatilization, denitrification, plant uptake and leaching losses were 24.0, 18.9, 109.0 and 28.5 kg N ha-1, respectively. The magnitude of nitrate leaching was 23.7 % of added fertilizer. Different nitrate leaching scenarios were generated using different fertilizer application rates exceeding the optimal dose. These scenarios showed an increasing trend with increase of fertilizer rates, fitted with a second-order polynomial equation (R2 = 0.99). The equation can be used for estimation of nitrate leaching below root zone under different fertilizer input scenarios of rice grown in similar hydroagro- climatic regions.