Change in net global warming potential of a rice-wheat cropping system with biochar soil amendment in a rice paddy from China

Soil amendment of biochar produced via pyrolysis of waste biomass had been proposed as a potential countermeasure to mitigate climate change in agriculture. An overall accounting of net greenhouse gas balance (NGHGB) and greenhouse gas intensity (GHGI) was conducted of a whole rice-winter wheat rotation year of 2010-2011 in a paddy soil under biochar soil amendment at different rates from Southeast China. Fluxes of soil carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) were measured using a static chamber method, and the net ecosystem exchange of CO2 (NEE) was estimated by the difference between net primary production (NPP) and soil CO2 emissions (RH) for both rice and winter wheat growing seasons. While no change observed in RH, NPP of both rice and winter wheat was similar between the treatments except for an increase under BSA at 10 t ha−1 over the control. However, seasonal total N2O emission was significantly and greatly decreased by 45.1% and 39.5% of rice growing season, and by 37.6% and 41.2% of winter wheat growing season under BSA treatment of 20 t ha−1 and 40 t ha−1 respectively over the control. Whereas, a 30.6% increase in seasonal total CH4 emission was observed only under BSA of 20 t ha−1 of the rice growing season. However, BSA both at 20 t ha−1 and 40 t ha−1 exerted a great reduction in both NGHGB and GHGI of wheat cropping season but of the rice season. As an overall effect, a net reduction in GHGI by 10-20% with BSA was significant across all the biochar treatments. And this reduction could be accounted mainly by the consistent decrease in N2O emission across rice and wheat growing cycles with insignificant changes in soil respiration and CH4 flux during rice season. Whereas there could be variable changes in crop yield and net ecosystem GHGs balance with biochar rates and with crop cycles, biochar soil amendment (BSA) could have a great potential to reach a low carbon intensity production with sustaining crop productivity of a whole rice and wheat rotation system in rice-based agriculture of China.