Evaluating the effects of nitrogen deposition on rice ecosystems across China

The influence of enhanced nitrogen (N) deposition on rice ecosystems was evaluated across China using the DNDC (DeNitrification-DeComposition) model. The simulated grain, leaf, stem, root and total biomass had good consistency with the ground measurements in controlled experiments, with absolute relative errors of 4.5, 7.3, 7.7, 7.3 and 4.7%, respectively. On a national scale, the absolute relative errors of the measured and simulated early, late and single cropping rice was 2.2, 6.6 and 5.9%, respectively. The N deposition increased rice yield accounted for 0.6% of the national rice production. Under the current fertilization conditions, The N deposition was barely absorbed and utilized for rice growth (only accounted for 1.8% of the N deposition). About 57.7% of the N deposition remained in the soil as inorganic and organic forms, and the other 40.5% of the N deposition was emitted to the environment, as nitrogen oxide emissions (24.8%), ammonia volatilization (5.6%), leaching and runoff (10.1%). These results will provide scientific bases for recommending fertilizer rates and enacting policies to protect the eco-environment.