Ammonia volatilization modeling optimization for rice watersheds under climatic differences.

The ammonia (NH) volatilization mechanism is complicated with pronounced watershed differences of climate conditions, soil properties, and tillage practices. The watershed NH emission dynamics model was developed with the combination of field measurements, Soil Water Assessment Tool and NH volatilization algorithms. The temporal NH emissions patterns and the watershed NH volatilization dynamics were simulated with the improved NH 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 NH emissions of the three watersheds ranged from 14.94 to 120.33 kg N ha, 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 NH volatilization (R = 0.758 and 0.834, p < 0.01). These analysis imply that environmental variabilities were more important than N input amounts.