Impact of methanogens originated from cattle manure on increasing CH4 emission in paddy soil during rice cultivation

Abstract

Animal manures are widely used as an organic matter source to improve soil quality. However, livestock manure applications supply easily available carbon (C) and facilitate methane (CH4) emission from rice paddy soil. Due to the differences in the digestion processes, swine manure and rumen-based cattle manure are expected to have different effects on CH4 emission characteristics during rice cultivation, but the mechanism of the relative differences have been little investigated. Fresh cattle and swine manures were applied with the rates of 0 (Control), 20, and 40 Mg ha-1 with recommended rates of chemical fertilizers (NPK) before rice transplanting, and the CH4 emission characteristics and the changes in soil and rice yield properties were investigated under greenhouse conditions. Both manure types significantly increased CH4 emission rates, but cattle manure increased the total CH4 flux by approximately 150% more than swine manure at the same 40 Mg ha-1 application rate. This may have been affected by higher labile C concentrations and rumen-originated methanogens in cattle manure. The rice growth and productivity did not significantly differ between two manures at the same rates of application. However, the cattle manure application more significantly increased dissolved organic carbon (DOC) concentrations and the total methanogenic activities measured as mcrA gene copy number in the soil. Furthermore, new methanogenic groups which originated as ruminant methanogens was found in the plots which received cattle manure. In conclusion, cattle manure application can significantly increase CH4 emission in paddy soil during rice cultivation, and therefore its pretreatment to suppress methanogenic activity should be considered.