Use of Nitrogen Isotope To Determine Fertilizer- and Soil-Derived Ammonia Volatilization in a Rice/Wheat Rotation System

The nitrogen (N) isotope method reveals that application of fertilizer N can increase crop uptake or denitrification and leaching losses of native soil N via the added N interaction. However, there is currently little evidence of the impact of added N on soil N losses through NH3 volatilization using N-15 methodologies. In the present study, a three-year rice/wheat rotated experiment with 30% N-15-labeled urea applied in the first rice season and unlabeled urea added in the following five crop seasons was performed to investigate volatilization of NH3 from fertilizer and soil N. We found 9.28% of NH3 loss from N-15 urea and 2.88-7.70% declines in N-15-NH3 abundance occurred during the first rice season, whereas 0.11% of NH3 loss from N-15 urea and 0.02-0.21% enrichments in N-15-NH3 abundance happened in the subsequent seasons. The contributions of fertilizer- and soil-derived N to NH3 volatilization from a rice/wheat rotation were 75.8-88.4 and 11.6-24.2%, respectively. These distinct variations in N-15-NH3 and substantial soil-derived NH3 suggest that added N clearly interacts with the soil source contributing to NH3 volatilization.