Biochar amendment reduced greenhouse gas intensities in the rice-wheat rotation system: six-year field observation and meta-analysis

Biochar amendment to cropland has been recommended as a potential strategy to mitigate climate change. However, estimations of the long-term greenhouse gas (GHG) emissions, namely, the methane (CH4) and nitrous oxide (N2O) mitigation potential, from agricultural systems are limited. Here, a six-year field experiment was conducted to simultaneously monitor the CH4 and N2O emissions and the yield from a rice-wheat rotation system with nitrogen application (0 and 250 kg ha-1) and biochar incorporation (0, 20 and 40 t ha-1) in southeastern China. The results showed that nitrogen application significantly increased CH4 and N2O emissions and the yield compared to the control, while no significant differences were detected among the treatments with no nitrogen. In contrast, biochar amendment resulted in significant decreases in CH4 and N2O emissions by 11.2–17.5% and 19.5–26.3%, respectively, with increases in yield by 7.9-9.2%, on average. In addition, considering the GHG emissions, the soil organic carbon sequestration rate and the yield, biochar significantly decreased the net global warming potential and greenhouse gas intensity over the six-year observation period. Our results were further supported by a meta-analysis, which showed that biochar amendment in the field strongly decreased CH4 and N2O emissions by 9.3% and 18.7%, respectively, and increased the yield by 9.0% under various complex soil environments. Based on our results, biochar application would increase carbon stock by 10.3% and decrease GHG emissions by 10.4% for Chinese rice and wheat production. Our findings suggest that the application of biochar to cropland is a viable option to combat climate change over the long term by soil carbon sequestration and GHG mitigation.