Effect Of Returning Farmland To Grassland On Soil N₂O And NO Fluxes

Since the policy of returning farmland to grassland in 1999,China has achieved remarkable results.The ecosystem functions have been improved,soil vegetation has been restored,and the loss of carbon and nitrogen has been reduced.The purpose of this study was to evaluate the significance of the conversion of farmland to grassland for ecological restoration by measuring soil-atmospheric N₂O and NO exchange.Experiment using soil cores incubation and combining with static opaque chamber/gas chromatography method and dynamic opaque chamber/gas chemiluminescent method to observe soil N₂O flux and NO of Inner Mongolia returning farmland to grassland area?sown pasture and summer corn field?under drying-wetting process and freeze-thaw cycle.The main conclusions are as follows:?1?Drying-wetting process had a significant promoting effect on N₂O and NO emissions of grassland and farmland soil?P<0.05?.The intensity of this effect was related to soil precipitation:the N₂O flux of farmland soil increased with the increase of precipitation?P<0.05?;there was no significant difference in grassland soil N₂O between different precipitation treatments?P>0.05?;the NO fluxes of grassland and farmland soil decreased with the increase of precipitation?P<0.05?.After precipitation,N₂O and NO fluxes of farmland soil were significantly higher than that of grassland soil?P<0.05?,and this difference disappeared with the increase of soil temperature and the decrease of soil moisture.?2?Freeze-thaw cycle had a significant promoting effect on grassland soil N₂O,NO and farmland soil NO emissions?P<0.05?,and the intensity of the promoting effect decreased with the increase of freeze-thaw cycle times,and freeze-thaw cycle had no significant effect on N₂O flux of farmland soil?P>0.05?.During first thaw process grassland soil N₂O emission significantly was more than farmland soil?P<0.05?,while grassland soil NO emission was less than farmland soil?P<0.05?,and this difference disappeared with the increase of freeze-thaw cycle times.?3?In the whole experiment,mean fluxes of grassland soil N₂O and NO(2.0±0.9?g N m^-22 h^-1,8.5±1.5?g N m^-22 h^-1)were less than that of farmland soil(3.3±1.4?g N m^-22 h^-1,10.2±1.8?g N m^-22 h^-1).It shows that returning farmland to grass can reduce the emissions of soil N₂O and NO and slow down global warming,thus improving the ecological environment.