Improvement and testing of ORYZA model water balance modules for alternate wetting and drying irrigation

Abstract

While the ORYZA crop model has been widely used in the simulation of rice growth, its computation ability is limited in terms of simulating the water balance components (WBCs) of paddy fields under water-saving irrigation conditions, such as alternate wetting and drying (AWD) regimes. In this study, a new water balance simulation framework (WBSF) reflecting the characteristics of AWD is integrated into the original ORYZA2000 (v2.13) model to simulate the WBC of paddy fields. In addition, algorithms for dynamically simulating the root length growing rate are added to the original ORYZA. Algorithms quantifying water stress are also modified. The improved model is further applied to paddy fields in Yongkang and Tuanlin, which are two typical rice growing areas in China. The results show that the improved model performs well at simulating WBCs. The Nash-Sutcliffe efficiency (NSE) of daily ponded water depth ranged from 0.82 to 0.94 across experiments under continuous flooding and AWD at the two sites, showing an increase in NSE of at least 0.23 compared to ORYZA (v3) levels. The absolute value of relative errors (A RE) between simulated and measured values for total irrigation and drainage amount was mostly no more than 10% and showed a reduction of at least 11%. The improved model also showed better performance in terms of evapotranspiration, percolation and root length simulation compared to ORYZA (v3). The yield predictive accuracy of the improved model is slightly better than that of ORYZA2000 (v2.13) but worse than that of ORYZA (v3), which might be due to the poor performance of nitrogen balance modules in the improved model. In general, given the results achieved, it is possible to state that the WBSF of the improved ORYZA2000 showed an enhanced capability to simulate WBCs, which are recommended for use in water balance simulations of paddy fields.