Effects of ryegrass incorporation on CH4 and N2O emission from double rice paddy soil

Ryegrass-double rice rotation is an important cropping system and commonly adopted in Southern China. However, the effects of ryegrass incorporation on CH4 and N2O emissions from paddy soils have been seldom estimated. A chamber-pot combined device was applied in the current study to measure CH4 and N2O gases emitted from different treatments of urea (CF), ryegrass incorporation at the same amount N as urea (RG), half nitrogen from urea plus half nitrogen from ryegrass (RGCF) residue and the control (CK, no fertilizer). Results indicated that total seasonal CH4 emission from RG and RGCF were 152%, 371% and 66%, 210% greater than that of CF and CK, respectively(P＜0.05). CF increased CH4 emission by 87%, when compared with CK(P＜0.05). RG emitted CH4 evenly during the three observing phases (before early rice transplanting, early rice season and late rice season) and approximately 60% of total seasonal CH4 emission happened before early rice transplanting and during the early rice season. N2O emission from CF was 18, 6.6 and 25 times as large as RG, RGCF and CK, respectively. Global warming potential (GWP) values calculated from CH4 and N2O emissions were in following order: RG＞RGCF＞CF＞CK (P＜0.05). Incorporation of ryegrass increased CH4 emission, but decreased N2O emission and restricted N2O emission from urea when urea was applied in conjunction with ryegrass.