Modeling the fate of fertilizer N in paddy rice systems receiving manure and urea

• Both manure and urea N fates can be predicted by theory of first-order kinetics.
• Peaks of N loss rates appeared within 2 ~ 3 days after each manure or urea application.
• Addition of manure N had no effect on uptake of crop at supra optimal rate.
• Manure had an apparent contribution on N losses when applied at optimum level.

Manure is one of the most important N sources in paddy rice systems, while it poses a great challenge in meeting rice N requirement and simultaneously reduces adverse environmental impacts. The main objective of this study was to design a simple model for assessing N fate in swine manure amended paddy rice systems. A field experiment was conducted for three cropping seasons to determine the effectiveness of different swine manure amended levels (15%, 30%, and 45% of total N applied) on N transformations and seasonal N fate. Based on field observation data, simulation results clearly showed peaks of various N transformation rates appeared within 2 ~ 3 days after each fertilization. There was an apparent contribution of manure N on N uptake and loss when amount of manure applied was at optimum. However, at supra optimal rate, addition of manure N showed no effect on N uptake of crop and the corresponding N transformations. Across three levels, seasonal ammonia volatilization accounted for 35.6% ~ 38.0% of total N applied, N uptake was 36.7% ~ 41.1%, while N losses via vertical leaching, lateral seepage were 3.9% ~ 4.5% and 4.4% ~ 4.8%, respectively. These results were well predicted by our specific designed model, indicating the model performed effectively at assessing individual transformation process and its associated N fate and help develop efficient management strategies for swine manure amended paddy rice systems.