ABSTRACT

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% (M₁₀₀), 75%:25% (M₇₅S₂₅), 50%:50% (M₅₀S₅₀), 25%:75% (M₂₅S₇₅), and 0%:100% (S₁₀₀), 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 S₁₀₀ at and after 37 DOI. The CO₂ emission rate of M₁₀₀ 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, S₁₀₀ resulted in the significantly higher cumulative production of CH₄ after 22 DOI. Predicted from the exponential regression models, S₁₀₀ 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.