[Effects of Plastic Film Mulching and Nitrogen Fertilizer Application on N₂O Emissions from a Vegetable Field]

To investigate the effects of plastic film mulching and nitrogen fertilizer application on N₂O emissions from a chili-radish rotation system, field observations were conducted in situ from May 2014 to April 2016 in the Key Field Station for Monitoring of Eco-Environment of Purple Soil of the Ministry of Agriculture of China in the farm of Southwest University in Chongqing. Static opaque and gas chromatography was used to determine emissions. Eight treatments were set up in the field experiment:control routine (no N application and no plastic film mulching; NN0), control mulching (FN0), low N routine (NN1), low N mulching (FN1), conventional N routine (NN2), conventional N mulching (FN2), high N routine (NN3), and high N mulching (FN3). The characteristics and influencing factors of N₂O emissions and the changes of soil carbon and nitrogen composition across all treatments were examined. The results demonstrated significant differences in N₂O emissions from the vegetable fields between mulching and no mulching treatments. The mean N₂O flux under no mulching was significantly greater than that of mulching during the chili growing season (P<0.05), but the opposite was true during the radish growing season (P<0.05). During the experimental period, the average annual cumulative N₂O emissions from nitrogen-free, low-nitrogen, medium-nitrogen, and high-nitrogen vegetable plots under mulching treatment were 244.91, 730.49, 903.32, and 1865.45 mg·m^-2, respectively; the average annual cumulative N₂O emissions under no mulching treatment were 221.48, 840.33, 1256.50, and 1469.67 mg·m^-2, respectively. The N₂O emissions from vegetable plots with different N application gradients showed an increase in N₂O emissions from vegetable plots as N application increased. By calculating the N₂O emissions coefficient, it was determined that the N₂O emissions coefficient was reduced to a certain extent under mulching treatment during the chili season, while there was no obvious trend in the radish season. From May 2014 to April 2015, the N₂O emissions coefficients of low-nitrogen application under two mulching treatments were both the highest under the same mulching levels during the chili growing season, but they were both the highest in the high-nitrogen application under two mulching levels during the radish growing season. From May 2015 to April 2016, the highest N₂O emissions coefficient was observed in the high-nitrogen application under two mulching treatments during the chili season; however, the lowest values were observed in the low-nitrogen application under two mulching treatments during the radish growing season. Such results may be related to the duration of plastic film mulching and the type of plant. The N₂O fluxes were both significantly positively correlated to the content of soil N and soil temperature. Plastic film mulching can increase the soil N to a certain extent and can therefore can affect N₂O emissions.