Ammonia volatilization modeling optimization for rice watersheds under climatic differences

The ammonia (NH3) volatilization mechanism is complicated with pronounced watershed differences of climate conditions, soil properties, and tillage practices. The watershed NH3 emission dynamics model was developed with the combination of field measurements, Soil Water Assessment Tool and NH3 volatilization algorithms. The temporal NH3 emissions patterns and the watershed NH3 volatilization dynamics were simulated with the improved NH3 volatilization modeling. Five monitoring sites and three case watersheds across China were selected to highlight the impacts of climatic conditions and validated the modeling. The average NH3 emissions of the three watersheds ranged from 14.94 to 120.33 kg N ha-1, which were mainly positively correlated with temperatures (r = 0.56, p < 0.01) and negatively correlated with soil organic carbon content (r = -0.33, p < 0.01). Analysis of similarities indicated that significant differences existed between the watersheds in terms of NH3 volatilization (RANOSIM = 0.758 and 0.834, p < 0.01). These analysis imply that environmental variabilities were more important than N input amounts.