Changes in methane production and oxidation in rice paddy soils induced by biochar addition

Biochar application to agricultural crop fields could mitigates the emission of greenhouse gases, especially methane (CH4). However, the mitigation mechanisms are not fully understood. This study aimed to investigate the mechanistic effects of biochar on CH4 production and oxidation in incubated rice paddy soils collected from multiple sites in Thailand (Ratcha Buri at Chom Bueng [CB] and Damnoen Saduak [DS] and Prachin Buri at Ban Sang [BS]). Prior to incubation, CB and BS soils were mixed with and without 2 % (w/w) biochar, while DS soil was mixed with and without 2 % and 4 % (w/w) biochar. Soils were incubated for 40 days with no oxygen to examine anaerobic CH4 production and with oxygen to examine aerobic CH4 oxidation. Addition of 2 % biochar to CB, DS, and BS soils decreased total CH4 production by 21 %, 15 %, and 9 % respectively, compared to soils without biochar. This reduction was resulted from the changes in soils including enhanced abundances of electron acceptors (nitrate [NO3−], ferric iron [Fe3+], and sulfate [SO42−]) and electron donors (organic acids). With active reduction of these oxidants, methanogenesis was reduced. Under oxic condition, biochar stimulated CH4 oxidation, particularly during the early period of incubation. CH4 oxidation activity during the first 11–day of incubation was enhanced by an average of 15 % relative to soil with no biochar. Therefore, we conclude that the mechanism by which biochar in paddy soils mitigates CH4 emissions is by reducing CH4 production and increasing CH4 oxidation.