**3.7 Application of biochar**

Biochar is a carbon-rich material produced by pyrolyzing waste biomass under anoxic conditions and high temperatures [37]. The highly porous structure and the increased surface area of carbon-rich fine-grained biochar makes it an ideal soil amendment for carbon sequestration [38, 39]. Galloway et al. [40] pointed out that compared with the plots without biochar, biochar produced by pyrolysis of crop straw can increase carbon sequestration by 22% and reduce N2O emissions by 35%. Higher levels of biochar are more effective in reducing N2O emissions from rice fields [41, 42]. Huang et al. [43] observed that the application of biochar at 10 and 40 ha−1 reduced N2O emissions by 58% and 74%, respectively. Jin et al. and Lehmann [44, 45] also recorded that the use of biochar can significantly reduce N2O emissions. The application of biochar may have a positive impact on soil organic carbon and significantly reduce N2O emissions, which may be a way to reduce greenhouse gas emissions. However, the long-term effects of biochar on the physical and chemical properties of soil and the rate of soil organic carbon sequestration require further studies to draw reliable conclusions.
