Influence of fertilizer management and water regime on methane emission from rice fields

Experiments were conducted to determine methane emission from a rainfed lowland rice field (water depth about 3-30 cm) and an irrigated shallow rice field (4-6 cm), both planted to the same cultivar, cv. 'Gayatri,' as influenced by fertilizer management practices. Methane emission peaked from 100 to 125 days after transplanting followed by a decline in rainfed lowland field plots. Application of prilled urea did not enhance methane emission significantly over that of the untreated control. Subsurface application of urea supergranules was, however, effective in reducing the methane flux over that of the control. Methane emission was lowest in plots treated with the mixture of prilled urea and Nimin (a nitrification inhibitor). Under irrigated shallow conditions, the application of prilled urea and green manure (Sesbania rostrata), singly and in combination, significantly increased methane emission over that of the control. Cumulative methane efflux from control and prilled urea treated lowland rice field was about 4-10 times higher than that in irrigated shallow fields. These results suggest that by virtue of their readily mineralizable carbon and ninhydrin reactive nitrogen, these substrates can serve as positive indicators of methane emission potential of rice fields.