Emissions of CH4 and CO2 from double rice cropping systems under varying tillage and seeding methods

A two-year field experiment was conducted to investigate the effects of different tillage (no-tillage [NT] and conventional tillage [CT]) and seeding methods (transplanting seedlings [TPS] and throwing of seedlings [ST]) on methane (CH4) and carbon dioxide (CO2) emissions from double rice cropping systems in central China. The CH4 and CO2 fluxes for early rice ranged from −2.52 mg m−2 h−1 to 125.0 mg m−2 h−1 and from 99.3 mg m−2 h−1 to 1463.6 mg m−2 h−1, respectively, whereas the fluxes for late rice varied from −7.22 mg m−2 h−1 to 242.3 mg m−2 h−1 and from 180.6 mg m−2 h−1 to 2219.0 mg m−2 h−1, respectively. Compared with NT, CT significantly increased (P < 0.05) the CH4 and CO2 emissions, where the seasonal total CH4 emissions from the CT treatment were 1.75-2.10 times of those from the NT treatment for early rice and 1.64-1.79 times for late rice. Moreover, compared with the CT treatment, the NT treatment significantly reduced seasonal total CO2 emissions by 19%-33% for early rice (P < 0.05) and by 27%-31% for late rice (P < 0.05). The seeding methods significantly affected CH4 and CO2 emissions. Compared with TPS, ST significantly decreased seasonal total CH4 and CO2 emissions by 15%-40% (P < 0.05) and 19%-33% (P < 0.05) for early rice, and by 38%-47% (P < 0.05) and 19%-22% (P < 0.05) for late rice, respectively. These results may be attributed to reduced root growth and aboveground biomass. Therefore, simplified cultivation technologies are effective for reducing carbon emissions from double rice cropping systems in central China, and the combination of NT with ST can more effectively decrease carbon emissions.