Nitrogen Addition Affects Nitrous Oxide Emissions of Rainfed Lucerne Grassland

Nitrous oxide (N₂O) is a potent greenhouse gas. Assessing the N₂O emission from lucerne grasslands with nitrogen addition will aid in estimating the annual N₂O emissions of such agriculture areas, particularly following summer rainfall events in light of precipitation variation associated with global change. Here, we measured soil N₂O emissions, soil temperature and water content of lucerne grasslands with four levels of nitrogen addition over 25 days, which included 10 rainfall events. Results showed that nitrogen addition was observed to increase soil NO₃^--N content, but not significantly improve dry matter yield, height or leaf area index. Nitrogen addition and rainfall significantly affected N₂O emissions, while the response of N₂O emissions to increasing nitrogen input was not linear. Relative soil gas diffusivity (D/D) and water-filled pore space (WFPS) were good indicators of N₂O diurnal dynamics, and D/D was able to explain slightly more of the variation in N₂O emissions than WFPS. Collectively, nitrogen addition did not affect lucerne dry matter yield in a short term, while it induced soil N₂O emissions when rainfall events alter soil water content, and D/D could be a better proxy for predicting N₂O emissions in rainfed lucerne grasslands.