Effects of Winter Cover Crops Straws Incorporation on CH(4) and N(2)O Emission from Double-Cropping Paddy Fields in Southern China

Residue management in cropping systems is believed to improve soil quality. However, the effects of residue management on methane (CH(4)) and nitrous oxide (N(2)O) emissions from paddy field in Southern China have not been well researched. The emissions of CH(4) and N(2)O were investigated in double cropping rice (Oryza sativa L.) systems with straw returning of different winter cover crops by using the static chamber-gas chromatography technique. A randomized block experiment with three replications was established in 2004 in Hunan Province, China, including rice–rice–ryegrass (Lolium multiflorum L.) (Ry-R-R), rice–rice–Chinese milk vetch (Astragalus sinicus L.) (Mv-R-R) and rice–rice with winter fallow (Fa-R-R). The results showed that straw returning of winter crops significantly increased the CH(4) emission during both rice growing seasons when compared with Fa-R-R. Ry-R-R plots had the largest CH(4) emissions during the early rice growing season with 14.235 and 15.906 g m(−2) in 2012 and 2013, respectively, when Ry-R-R plots had the largest CH(4) emission during the later rice growing season with 35.673 and 38.606 g m(−2) in 2012 and 2013, respectively. The Ry-R-R and Mv-R-R also had larger N(2)O emissions than Fa-R-R in both rice seasons. When compared to Fa-R-R, total N(2)O emissions in the early rice growing season were increased by 0.05 g m(−2) in Ry-R-R and 0.063 g m(−2) in Mv-R-R in 2012, and by 0.058 g m(−2) in Ry-R-R and 0.068 g m(−2) in Mv-R-R in 2013, respectively. Similar result were obtained in the late rice growing season, and the total N(2)O emissions were increased by 0.104 g m(−2) in Ry-R-R and 0.073 g m(−2) in Mv-R-R in 2012, and by 0.108 g m(−2) in Ry-R-R and 0.076 g m(−2) in Mv-R-R in 2013, respectively. The global warming potentials (GWPs) from paddy fields were ranked as Ry-R-R>Mv-R-R>Fa-R-R. As a result, straw returning of winter cover crops has significant effects on increase of CH(4) and N(2)O emission from paddy field in double cropping rice system.