Equivalent incorporation of Chinese milk vetch and rice straw enhanced nutrient mineralization and reduced greenhouse gas emissions

Incorporation of crop residues into the soil provides essential nutrients and increases carbon stocks, which also increases greenhouse gas emissions from the soil. The present study was conducted to determine the effect of co-incorporation of Chinese milk vetch (CMV) and rice straw (RS) at different mixing rations on the dynamics of nutrient mineralization and the emissions of CO2 and CH4. The Fluvo-aquic paddy soil was collected and mixed with crop residues at 20 g kg(-1) soil and incubated for 187 days. The CMV and RS were incorporated with the ratios of 100%:0% (M-100), 75%:25% (M75S25), 50%:50% (M50S50), 25%:75% (M25S75), and 0%:100% (S-100), respectively. Results showed soil total nitrogen (N) concentrations were higher with the higher proportion of CMV in the mixing residues. At 8 days of incubation (DOI), both soil available phosphorus (P) and potassium (K) concentrations were greater in treatments with the higher ratio of RS, but there were no significant differences among M75S25, M50S50, M25S75, and S-100 at and after 37 DOI. The CO2 emission rate of M-100 was significantly higher than that of other treatments at 8 and 12 DOI. Even though the CH4 emission rate of M50S50 was significantly higher than that of other treatments at 8 DOI, S-100 resulted in the significantly higher cumulative production of CH4 after 22 DOI. Predicted from the exponential regression models, S-100 had the highest CO2-C and CH4-C mineralization potentials. Additionally, the M50S50 treatment resulted in 3.7%-54.7% higher microbial biomass carbon (MBC) concentration than other treatments at the end of the incubation. In summary, the mixing ratio of 1:1 was recommended for the co-incorporation of CMV and RS by considering both the nutrients availability and the greenhouse gas emissions.