Combined Effects of Rice Husk Biochar and Organic Manures on Soil Chemical Properties and Greenhouse Gas Emissions from Two Different Paddy Soils

The application of biochar is considered an alternative amendment strategy for improving soil fertility. In this study, we performed pot experiments using soils of low and medium fertility to assess the effects of different combinations of biochar and organic manure on the chemical properties of paddy rice soils and determined the best combination to improve the grain yield without increasing N2O and CH4 emissions. The applied treatments were without biochar (control), the application of rice husk biochar alone (5 and 10 t ha-1), and biochar combined with chicken or cow manure. The results indicated that for both soils, the application of 5 t ha-1 biochar combined with 5 t ha-1 chicken manure increased grain yield by improving soil total nitrogen and soil NH4+-N without increasing cumulative N2O and CH4 emissions. Multiple regression analysis showed that when combined with biochar, chicken manure significantly contributed to a higher grain yield and was negatively associated with cumulative CH4, N2O emissions, and total GWP. Furthermore, regardless of soil type, combined applications of biochar and cow manure promoted significant increases in soil available P. Our findings indicate that the C/N ratio of organic manure influences CH4 fluxes, and soil type was identified as a factor driving greenhouse gas emissions.