Methane emissions from five paddy fields with different amounts of rice straw application in central Hokkaido, Japan

Rice paddy fields are a major source of methane (CH4) emissions, a potent greenhouse gas. We assessed CH4 emissions from five existing paddy fields farmed in a snowy temperate region in central Hokkaido, Japan. All fields had continuous flooding and a paddy-fallow-paddy (rice) crop rotation system, but with different amounts of rice straw application. The rice straw application rate in the fields ranged from 0 to 219 g dry matter m(-2). CH4 emission increased with increasing amounts of rice straw. A peak in CH4 emission at the end of the reproductive stage was observed in all fields receiving rice straw. When continuous flooding was interrupted by drainage for harvesting, emissions from all fields also dropped quickly. Total CH4 emissions ranged from 4.04 to 40.8 g CH4-C m(-2) per growing season. We found that CH4 emissions (g CH4-C m(-2) per g dry matter) as per unit (dry matter) of rice straw applied in this study were significantly (P < 0.05) higher than those of calculated reported values, presumably because of the retardation of straw decomposition rates during the winter fallow. There was a significant correlation between rice straw carbon application (SCA) rate and total CH4 emission in continuously flooded fields (CH4 emission [g C m(-2) per growing period] = 0.486 x SCA [g C m(-2)] - 1.644, r(2) = 0.884, P < 0.05), and emissions were 2-10-fold greater than from fields with no rice straw. The results indicate that the presence of rice straw has a significant influence on CH4 emissions from paddy fields.