地膜覆盖和施氮对菜地N2O排放的影响

为了探讨地膜覆盖和不同施氮处理对菜地N_2O排放的影响,以位于西南大学农业部重庆紫色土生态环境重点野外科学观测试验站内辣椒-萝卜轮作菜地为研究对象,采用静态暗箱/气相色谱法,进行为期2 a的田间原位观测.试验设置8个处理,分别为对照常规(NN0)、对照覆膜(FN0),低N常规(NN1)、低N覆膜(FN1),中N常规(NN2)、中N覆膜(FN2),高N常规(NN3)、高N覆膜(FN3),研究地膜覆盖和施氮对菜地N_2O的排放特征和影响因素.结果表明,覆膜与常规两种种植方式对于菜地N_2O的排放体现出明显差异,表现为辣椒季常规显著大于覆膜(P 0. 05),萝卜季为覆膜显著大于常规(P 0. 05). 2014年5月至2016年4月观测期间,覆膜种植下无氮、低氮、中氮和高氮菜地N_2O年均累积排放量分别为244. 91、730. 49、903. 32和1 867. 45 mg·m-2,常规种植下N_2O年均累积排放量为221. 48、840. 33、1 256. 50和1 469. 67 mg·m-2.不同施氮梯度对于菜地N_2O的排放呈现为随施氮量增加N_2O的排放随之增加.通过计算N_2O排放系数可知,覆膜可以一定程度上降低辣椒季N_2O的排放系数,而萝卜季则没有明显规律. 2014年5月至2015年4月,辣椒季常规和覆膜种植下均为低氮菜地的N_2O排放系数最高,在萝卜季则显示为高氮排放系数最高; 2015年5月至2016年4月,则显示辣椒季为高氮菜地N_2O排放系数最高,而萝卜季低氮菜地最高. N_2O的排放通量和土壤氮素含量以及土壤温度呈显著相关关系,而地膜覆盖可一定程度地增加土壤中氮素的含量,进而影响菜地N_2O的排放通量.

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.