Options for mitigating methane emission from a permanently flooded rice field.

Abstract Permanently flooded rice fields, widely distributed in south and south-west China, emit more CH₄ than those drained in the winter crop season. For understanding CH₄ emissions from permanently flooded rice fields and developing mitigation options, CH₄ emission was measured year-round for 6 years from 1995 to 2000, in a permanently flooded rice field in Chongqing, China, where two cultivations with four treatments were prepared as follows: plain-cultivation, summer rice crop and winter fallow with floodwater layer annually (convention, Ch-FF), and winter upland crop under drained conditions (Ch-Wheat); ridge-cultivation without tillage, summer rice and winter fallow with floodwater layer annually (Ch-FFR), and winter upland crop under drained conditions (Ch-RW), respectively. On a 6-year average, compared to the treatments with floodwater in the winter crop season, the CH₄ flux during rice-growing period from the treatments draining floodwater and planting winter crop was reduced by 42% in plain-cultivation and by 13% in ridge-cultivation (P < 0.05), respectively. The reduction of annual CH₄ emission reached 68 and 48%, respectively. Compared to plain-cultivation (Ch-FF), ridge-cultivation (Ch-FFR) reduced annual CH₄ emission by 33%, and which was mainly occurred in the winter crop season. These results indicate that draining floodwater layer for winter upland crop growth was not only able to prevent CH₄ emission from permanently flooded paddy soils directly in the winter crop season, but also to reduce CH₄ emission substantially during the following rice-growing period. As an alternative to the completely drainage of floodwater layer in the winter crop season, ridge-cultivation could also significantly mitigate CH₄ emissions from permanently flooded rice fields. [ABSTRACT FROM AUTHOR]