Effects of Straw Recycling of Winter Covering Crop on Methane and Nitrous Oxide Emissions in Paddy Field

The emissions of methane (CH₄) and nitrous oxide (N₂O) were determined in double rice (Oryza sativa L.) cropping systems with different winter covering crops using the static chamber-gas chromatography technique to assess the effects of different covering crops on the emissions of greenhouse gases. Four cropping systems with different covering corps after double rice seasons, i.e., ryegrass with no-tillage (T1), Chinese milk vetch with no-tillage (T2), rape seed with tillage (T3), and potato with straw mulching and tillage (T4), were compared with the winter fallow after double rice seasons (CK). The results showed that straw recycling of winter crops significantly increased the emission of CH₄ during both rice growing seasons compared to CK. Treatments T4 and T1 had the largest CH₄ emissions during the early rice growing season with 20.713 and 16.068 g m⁻², respectively, and the T4 and T3 had the largest CH₄ emission during the later rice growing season with 60.421 and 48.666 g m⁻², respectively. The 4 treatments with winter covering crops also had larger N₂O emissions than CK in both rice seasons. Compared to the N₂O emission in CK, the emissions of the gas increased by 265% in T1, 320% in T2, 275% in T3, and 65% in T4 during the growth of early rice, and by 158% in T1, 113% in T2, 134% in T3, and 42% in T4 during the growth of late rice. The global warming potentials from paddy fields were ranked as T4 > T3 > T1 > T2 > CK. As a result, straw recycling of winter covering crops has significant effects on increase of CH₄ and N₂O emission from paddy field in double rice cropping system.