Annual fluxes and seasonal patterns of NO and N2O from a maize field in Northeast China

The Northeast China is one of the most important grain production regions in China, and maize is the major grain crop. Large amount of fertilizer is often applied to agriculture soils, resulting in gaseous N loss. However, it remains unknown how much N is lost via NO and N₂O for this region. We have used a fully automated measuring system to measure soil NO and N₂O emissions from April 28, 2017 to April 20, 2018 for a typical maize filed in this region, and the measurement is ongoing. On the basis of these high temporal resolution measurements, we found that the NO and N₂O emissions at our site are 9.1 kg NO-N ha^-1 and 2.7 kg N₂O-N ha^-1, respectively, during the measurement period. Relatively high NO emission rate might have been caused by relatively low annual precipitation (400 mm) and all measured soil moisture were less than 60% WFPS. We observed an emission peak lasting approximately two months. During this time period, the emissions are 6.7 kg N ha^-1 and 1.0 kg N ha^-1 for NO and N₂O, respectively, and were responsible for 75% and 57% of the annual total NO and N₂O loss. Seasonal patterns of NO and N₂O emission were similar and there is a significant linear relationship between NO and N₂O emissions (R² = 0.7), indicating they were produced from same processes and were controlled by similar factors. Soil temperature and moisture were significantly related to the emissions of these gases.