Intergrative Effects Of Green Manure And Straw Incorporation On Greenhouse Gas Emissions And Environmental Performance Under The Typical Rice Cropping Systems In Southern China

Southern China is one of the most important farming regions in China,due to its great contribution to national food security.The plantation of green manure in rice-cropping system is an effective practices to guarantee sustainable and high yield of in this area.The utilization of green manure can serve carbon and nitrogen sources for microbes in the paddy soil,resulting in profound influences on CH4 and N2O emissions.In addition,straw incorporation management can increase rice(Oryza sativa L.)yield,as well as CH4 and N2O emissions,with increased organic compounds.However,the characteristics of CH4 and N2O emissions under green manure and straw incorporation are still unclear.In this study,by using long-term experiments in different provinces,as well as static chamber-GC technologies,we investigated the characteristics of CH4 and N2O emissions after multi-years’utilization of green manure and straw incorporation in Southern China,and calculated the total CH4 and N2O emissions and carbon footprints of rice production.The joint experiments are located in Suzhou,Jiangsu province,Nanchang,Jiangxi province,and Guangzhou,Guangdong province.Field experiment in Suzhou,has three treatments,i.e.,continuous 8 years of conventional wheat-rice cropping system without straw incorporation(CK),wheat-rice cropping system with straw incorporation(SS),and green manure-rice cropping system(GM).Field experiment in Jiangxi provinces has four treatments,i.e.,continuous 31 years of conventional chemical fertilizers(CK),the combination of chemical fertilizer and green manure(GM),the combination of chemical fertilizer and green manure with straw incorporated in late rice(GM+LS),and combination of chemical fertilizer and green manure with straw covered in winter(GM+FS).Field experiment in Guangdong provinces also has four treatments,i.e.,continuous 8 years of conventional winter fallow-double rice cropping system(CK),green manure-double rice cropping system(GM),winter fallow-double rice cropping system with straw incorporation(SS),and green manure-double rice cropping system with straw incorporation(GM+SS).The conclusions were as follows:1.Increases in soil organic carbon and total nitrogen were 107 kg ha-1 a-1 and 37 kg ha-1 a-11 on average after years of the experiment,under CK treatment.The concentrations of soil organic carbon under green manure were increased by 8.4%,6.1%and 10.7%,respectively,compared to CK.The concentrations of soil microbial carbon and dissaved organic carbon were both increased significantly by green manure and straw incorporation,compared to CK.The effects of green manure and straw incorporation on soil mineral nitrogen,soil microbial biomass nitrogen,and dissaved organic nitrogen differed between sites.2.CH4 emissions were 2.14 times higher under straw incorporation than that of CK,at Jiangsu province.CH4 emissions were increased significantly under combined green manure and straw incorporation at Jiangxi province.But there was no significant effect of green manure on CH4 emissions both at Jiangsu and Jiangxi provinces.Green manure and straw incorporation,alone and interactively,increased CH4 emissions significantly at Guangdong province.CH4 emissions in early rice were 1.14,1.37 and 1.62 times higher than that of CK,respectively,at Guangdong.CH4 emissions in late rice were 1.23,1.52 and 1.95 times higher than that of CK,respectively,at Guangdong.CH4 emissions were closely relative to soil ammonium nitrogen,microbial biomass carbon and nitrogen contents.3.Straw incorporation decreased N2O emissions significantly by about 20.4%,18.9%(early rice)and 17.3%(late rice)at Jiangsu and Guangdong,respectively,compared to CK.The effects of green manure and the combined green manure and straw incorporation on N2O emissions differed among sites.There were significant effects of green manure and the combined green manure and straw incorporation on N2O emissions in both rice seasons at Guangdong province.N2O emissions were increased by 61.0%and 28.4%,22%and 20%.under green manure independently and the combined green manure and straw incorporation,with comparison with CK,respectively,at Guangdong.N2O emissions were increased by green manure in the late rice by 26.1%,but were decreased in the early rice by 57.8%at Jiangxi province.Combined green manure and straw incorporation decreased N2O emissions in both rice seasons.There was no significant effect of green manure on N2O emissions at Jiangsu province.4.Compared to CK,soil carbon storage were increased significantly by green manure and straw incorporation in three sites.Soil carbon storage were increased significantly by 20.4%,58.4%,and 47.4%compared to that of CK,respectively,under GM,GM+LS,and GM+WS treatments.Comparing with CK,soil carbon storage were increased significantly by 136%,183%,and 308%,respectively,under GM,SS and GM+SS treatments.CH4 emissions contributed to the carbon footprint largely account for 59.9%to 80%.The application of fertilization,fossil fuel and electricity for rice production contributed equally with N2O emission to carbon footprint.Compared to the conventional treatment,carbon footprint were decreased by 12.5%and 14.4%,respectively,at Jiangsu and Jiangxi,but was increased by 9.1%at Guangdong.Straw incorporation cased increases in carbon footprint of 39.2%and 8.1%at Jiangsu and Guangdong.Carbon footprint was increased by 26.7%under the combined green manure and straw incorporation at Guangdong.Compared to that of CK,carbon footprint was decreased by 8.0%under the GM+WS treatments.But there was no significant effect of GM+LS on carbon footprint.In conclusion,application of green manure and straw incorporation practices would be an efficient way to mitigate CH4 and N2O emissions in rice-cropping systems,in considering with the differed characteristic of agricultural sources,cropping systems,soil types,and fertilization and water inputs,in Southern China.