Effects of Biochar, N Fertilizer, and Crop Residues on Greenhouse Gas Emissions from Acidic Soils

An incubation experiment is conducted at 20 degrees C for 30 days to explore the influence of biochar, nitrogen, and their interactions on CH4, CO2, and N2O emissions, as well as C and N variations in soils with milk vetch and rape residue amendment or in soils without plant residue. Both the biochar and nitrogen additions had negative effects on the cumulative CH4 and CO2 emissions in the presence of milk vetch and rape residues. Regardless of the biochar and nitrogen addition, the CH4 and CO2 emissions from soils amended with milk vetch residue are the highest, followed by those from soils amended with rape residue and those from soils with no plant residue. With the N application, N2O emissions from soils amended with rape residue are significantly higher than those from soils without plant residue, whereas the N2O emissions from soils amended with milk vetch residue are significantly lower than those from soil without plant residue. DOC is positively related with CO2 emissions. NH4+-N, NO3--N, and TIN are also positively correlated with N2O emissions. In soils with the N fertilizer application, milk vetch residue, and biochar decreases the global warming potential, whereas rape residue increases the global warming potential. The results indicate that milk vetch residue in combination with biochar could benefit greenhouse gas mitigation and should be recommended for agricultural practices at high nitrogen level. In contrast, rape residue incorporated with biochar should be applied cautiously, especially in N abundant soils.