不同耕作方式下农田油菜季土壤温室气体的排放研究

CO_2,CH_4 and N_2O Emissions from Soils under Different Tillage Systems During the Rape Growing Season

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于1990年设立的长期免耕试验田为研究对象,利用静态暗箱/气相色谱法,研究传统的冬水田(DP)耕作方式改变为水旱轮作(SH)、厢作免耕(XM)和垄作免耕(LM)后,油菜生长季土壤CO2,CH4和N2O的排放特征.结果表明,4种处理下CH4排放通量在整个油菜季上下波动,除DP外均有吸收和排放现象;N2O的排放通量除施肥后有较大的上升外,其他时段都表现的较为稳定;CO2的排放季节变化明显.从排放总量上来看,4个处理油菜季排放的CO2总量大小顺序为:LM(5099.87)>XM(4617.33)>SH(4528.42)>DP(3715.23kg/hm2);CH4排放总量大小为:DP(20.49)>LM(1.69kg/hm2),SH和XM表现为少量的CH4的汇,大小为SH(0.55)>XM(0.13kg/hm2).N2O总排放量的大小为:SH(4.57)>XM(2.87)>LM(2.71)>DP(0.89kg/hm2).4个处理油菜季排放的CO2,CH4和N2O所产生的综合全球增温潜势(GWP)大小顺序为:20a时间尺度LM,SH,DP和XM,100a和500a时间尺度大小顺序为LM,SH,XM和DP.因此,将冬水田改成垄作免耕、厢作免耕及水旱轮作制度后,虽然CH4排放通量会显著降低,但却会显著增加土壤CO2和N2O的排放.如果3种气体同时考虑,从长远来看,耕作方式的改良会增加紫色水稻土油菜生长季土壤中CO2,CH4和N2O的总温室效应,从这一点考虑,对环境是不利的.

A tillage experiment was established in the Key Field Station for Monitoring Eco-environment of Purple Soil of the Ministry of Agriculture of China, located in the farm of Southwest University, Chongqing. Static o-paque chamber-gas chromatography was used to study the characteristics of CO2, CH4 and N2O emissions from farmland soil during the rape growing season after the transformation of the conventional tillage with single crop-ping rice system in winter water-logged paddy field （DP） to conventional tillage with rice-rape rotation system （SH）, no-till and plain culture with rice-rape rotation system （XM） and no-till and ridge culture with rice-rape ro- tation system （LM）. CH4 emission flux fluctuated with no definite regularity throughout the rape growing season, and both CH4 absorption and emission were observed in all treatments except DP. N20 emission flux appeared quite stable except that it rose considerably after fertilization. A seasonal variation was no- ticed in CO2 emission flux. In the rape growing season total CO2 emission was in the order of LM （5 099.87）〉XM （4 617.33）〉SH （4 528.42）〉DP （3 715.23 kg/hm^2）, total CH4 emission was in the order of DP （20.49）〉LM （1.69）〉SH （-0.13）〉XM （-0.55 kg/hm^2） , and total N2O emission was in the order ofSH （4.57）〉XM （2.87）〉LM （2.71）〉DP （0.89 kg/hm^2）. The integrated global warming potential （GWP） of CH〉, N20 and CO2 emissions in the rape growing season were in the following se-quence： 20-year span LM〉SH〉DP〉XM, and 100-or 500-year span LM〉SH〉XM〉DP. It is concluded that after improving the conventional tillage, CH4 emission tends to decrease, but the emission of CO2 and N20 tends to increase, and the integrated GWPs of CH4, N20 and CO2 emissions from the soil of the im-proved cropland will, unfortunately, all increase, which is not beneficial to the environment.