Modelling water consumption and nitrogen loss in paddy fields with an improved ORYZA model

While the ORYZA model has been widely used in the simulation of rice growth, its current water-and-nitrogen balance module is unable to simulate some complex water and nitrogen management practices used in the actual paddy fields. By integrating an improved water-and-nitrogen balance module, the improved ORYZA model was developed to better simulate water consumption and nitrogen loss in paddy fields. The performance of the improved model was first evaluated with observations collected from three rice planting areas (Dali, Zhanghe and Nanchang) in China. Results showed that the observed and simulated values of daily ponded water depth, ammonia volatilization, total nitrogen concentration of ponded water, soil water at 20 cm and 40 cm depth agreed well, with average Nash-Sutcliffe efficiency values of 0.82, 0.58, 0.74, 0.66 and 0.62, respectively. The observed and simulated values of evapotranspiration, percolation, irrigation water, surface drainage water, amount of nitrogen in crop and rice yield also agreed well, with average normalized root mean squared error values of 0.08, 0.13, 0.09, 0.21, 0.16 and 0.06, respectively. Then, the calibrated model was used to simulate the water consumption, nitrogen loss and rice yield under 8 different water and nitrogen management modes (WNMMs) from 1953 to 2019 in Dali, China. Compared with the local WNMM of Dali that using continuous flooding with nitrogen application rate of 193 kg N ha(-1) and two fertilization splits, the recommended WNMM that using alternate wetting and drying with nitrogen application rate of 135 kg N ha(-1) and three fertilization splits, could reduce the irrigation water, numbers of irrigation and drainage events, and total nitrogen loss by 55%, 34% and 28% and increase the rainfall utilization efficiency, yield and irrigation water productivity by 23%, 6% and 136%, respectively. Given the results achieved, it is possible to state that the improved ORYZA model can be reliable used for the simulation of water consumption, nitrogen loss and rice growth of paddy fields.

Automated summary

The improved ORYZA model, which integrates an improved water-and-nitrogen balance module, performs well in simulating water consumption and nitrogen loss in paddy fields. The model was evaluated using observations from three rice planting areas in China, and the results showed good agreement between observed and simulated values in multiple indicators. The recommended water and nitrogen management mode based on the calibrated model significantly improves rainfall utilization efficiency, yield, and irrigation water productivity, while reducing irrigation frequency and nitrogen loss.