Comparative biotic and abiotic effects on greenhouse gas emissions from agricultural ecosystems: application of straw or biochar?

Farmland has become a significant contributor to greenhouse gas (GHG) emissions, and research has shown that the addition of straw or biochar may be a viable method for mitigating these emissions. However, there is a lack of understanding regarding the comparative biotic and abiotic effects of straw and biochar amendments on GHG emissions. To address this knowledge gap, we conducted a meta-analysis of 100 published papers to quantify the impact of straw and biochar application on GHG emissions. Our findings indicate that straw application significantly increased CO 2 and CH 4 emissions from agricultural ecosystems by 46.2% and 113.5%, respectively, but did not have a significant effect on N 2 O emissions. Conversely, biochar amendment significantly reduced CO 2 , CH 4 , and N 2 O emissions by an average of 11.0%, 31.7%, and 22.8%, respectively. We also found that straw and biochar amendments increased soil pH, soil organic carbon (SOC), and C/N ratio, and there were significant differences between them. Moreover, straw application significantly increased the microbial biomass carbon (MBC) content and microbial quotient by 37.1% and 20.1%, respectively, while biochar application increased the MBC content by 25.0% without a significant effect on the microbial quotient. Furthermore, both straw and biochar applications promoted the nitrification process and increased the abundance of ammonia-oxidizing bacteria (AOB) by 50.7% with straw and by 57.5% and 75.1% with biochar for ammonia-oxidizing archaea (AOA) and AOB, respectively. The denitrification process was also stimulated by straw or biochar amendment, resulting in an increase in the abundance of nirK by 22.9% and 16.8%, respectively. Biochar amendment additionally increased the abundance of nosZ by 29.4%, indicating that the main reason for reducing N 2 O emissions through biochar application is the conversion of NO 3 − -N to N 2 . Thus, compared to straw application, biochar application is a more effective method for reducing greenhouse gas emissions.