Effects of rice straw returning methods in wheat-growing season on CH_4 emissions from following rice-growing season

A field experiment was carried out to study the effect of rice straw returning methods in wheat-growing season including no straw application,rice straw mulched onto the field surface,rice straw burned in-situ and rice straw incorporated into the topsoil,on CH4 emissions during the following rice-growing season,in order to study the residual effect of straw returning on greenhouse gases emission from rice fields in rice-wheat rotation system.Rice straw was returned to soil by different methods with an equivalent amount at 4.8 t·hm-2(except for no rice straw application) at wheat seeding stage in 2007,CH4 emission during the following rice-growing season was observed by the static chamber-gas chromatographic techniques in 2008.Results indicated that rice straw returning method during wheat season had significant effects on the CH4 emission from the following rice-growing season.Compared with no rice straw application,CH4 emission was increased by 75% and 40% in rice straw mulched onto the field surface and rice straw incorporated into the topsoil,respectively,where the difference in CH4 emission between these methods was mainly embodied in the early stage of rice growing.No significant difference of CH4 emission was observed between rice straw burned in-situ and no rice straw application in CH4 emission.The contents of soil total C and total N were significantly increased by 6% and 12% in rice straw incorporated into the topsoil,compared with no rice straw application.Also,rice yield was not profoundly influenced by rice straw returning method among different treatments.In rice straw incorporated into the topsoil treatment,the contents of soil total C and total N were significantly increased by 6% and 12%,respectively,when compared with no rice straw application.Incorporation of rice straw into the topsoil could be the rational and practicable rice straw returning method prior to wheat cultivation,as this method could decrease CH4 emission from the following rice-growing season comparing with mulched onto the field surface,and avoid the big losses of beneficial elements such as C、N and P during straw burning process.