The effects of cultural practices on methane emission from rice fields

A field experiment was conducted in a clayey soil to determine the effects of cultural practices on methane (CH(4)) emissions from rice fields. The factors evaluated were a) direct seeding on dry vs wet soil, b) age of transplanted seedlings (8 d old and 30 d old), and c) fall vs spring plowing. Methane emissions were measured weekly throughout the rice-growing season using a closed static chamber technique. Transplanted 8-d-old seedlings showed the highest emission of 42.4 g CH(4) m(-2) season(-1), followed by transplanted 30-d-seedlings (40.3 g CH(4) m(-2) season(-1)), and direct seeding on wet soil (37.1 g CH(4) m(-2) season(-1)). Direct seeding on dry soil registered the least emission of 26.9 g CH(4) m(-2) season(-1). Thus transplanting 30-d-old seedlings, direct seeding on wet soil, and direct seeding on dry soil reduced CH(4) emission by 5%, 13%, and 37%, respectively, when compared with transplanting 8-d-old seedlings. Methane emission under spring plowing was 42.0 g CH(4) m(-2) season(-1) and that under fall plowing was 31.3 g CH(4) m(-2) seasons(-1). The 26% lower emission in the field plowed in spring was caused by degradation of organic matter over the winter.