Greenhouse gas emissions, soil carbon sequestration and crop yields in a rain-fed rice field with crop rotation management

Field experiments of two consecutive years (2010-2011) were conducted to investigate the effect of crop-rice rotation systems on greenhouse gas (GHG) emissions, soil carbon sequestration, and rice yield. Rotation crops were cultivated in the dry season, while rain-fed rice was grown in the wet season. Four different treatments were investigated: fallow-rice (RF), rice-rice (RR), corn-rice (RC) and sweet sorghum-rice (RS). The closed-chamber method was used for flux measurements of methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) in the field. Parameters such as soil carbon budgets (SCBs), soil organic carbon (SOC) stocks, and crop yields were also measured. In this study, it was found that RC and RS rotations reduced CH4 emissions by 78-84%, and reduced net CO2 equivalent emissions (CH4 and N2O) by 68-78%, as compared with RR. After two consecutive years of crop cultivation, SCBs were reclaimed by positive values in the RC and RR treatments. The SOC stocks were maintained in the RR, RC and RS treatments, but decreased in the RF. Although RF also reduced the net CO2 equivalent emissions by 72-84% as compared with RR, there were losses in soil carbon sequestration and agricultural land utilization. The rice grain yields of RC and RS were stable in both years, while RF fell slightly by 11%, and RR significantly reduced by 39% from the first year.