Net Greenhouse Gas Emissions From Paddy Fields As Affected By Rice Straw Incorporation Under Two Water Regimes.

The lack of studies which quantify the net greenhouse gas emissions from paddy fields makes it difficult to give a sound evaluation of the contribution of rice paddy to global warming. In this study, a field study was conducted in two consecutive rice seasons in the double rice cropping system in Southern China to quantify the net greenhouse gas emissions from paddy fields with different rice straw incorporation rates and water regimes. The results showed that straw incorporation increased methane emissions but decreased N₂O emissions significantly as compared with no straw incorporation, especially when the rice paddies were continuously flooded. The soil organic carbon change showed positive values and increased significantly with the increase of straw incorporation rate. The net greenhouse gas emissions (NGHGEs) varied from 0.44 to 3.45 t CO₂-eq ha^-1 and from 1.14 to 4.89 t CO₂-eq ha^-1 in the late and early rice seasons respectively among the treatments, and showed the lowest value in the treatment of straw incorporation at low rate plus intermittent flooding in the late rice season, but increased with the increase of straw incorporation rate in the early rice season. The intermittent flooding reduced the NGHGE by 27 to 50% as compared with continuous flooding in both rice seasons. Therefore, from a viewpoint of reducing greenhouse gas emissions, the intermittent flooding should be encouraged and straw incorporation at a rate of 3 t ha^-1 in the late rice season is recommended in the double rice cropping system.