Abstract
Methanogenesis in irrigated rice fields is carried out by methanogenic archaea under strictly anaerobic conditions. In the present study, the effect of rice straw on methanogenesis in surface layers of paddy soil was investigated in a pot experiment with surface application of rice straw. Rice straw application led to a significant development of reduced conditions in the surface soil, and markedly increased methane (CH_4) emissions. Potential methanogenic activity in the straw residues and the soil layer immediately under the residues (0〜1 cm depth) was considerably promoted, while that in the deeper soil layers (4〜6 cm depth) was not affected by the residues of rice straw. These results indicate that the increased CH_4 emission in the treatment with surface application of rice straw was due to the activation of methanogenesis in the vicinity of the residues. Consequently, in the present study, it was demonstrated that rice straw application enhanced methanogenesis even in the surface layers of paddy soil, which are generally considered to be oxic layers.
