Decomposition characteristics of mixed maize and soybean root residues

Maize/soybean intercropping system could potentially improve crop yield and nutrient-use efficiency. It is pivotal to elucidate nutrient efficiency of crop root residue decomposition, nutrient release and the related effects on soil biological characteristics in intercropping processes. In this laboratory incubation study, we set different combined ratios of maize and soybean root residues, including sole soybean (S), sole maize (M) root residues, S:M=3:1(SM 3:1), S:M=1:1 (SM 1:1), S:M=1:3 (SM 1:3), with soil without residues (CK) as the control. The ratio of total weight of residues to soil in each treatment was 2:98, in unit of gram (g). We dynamically measured the mineralization rate of residues, contents of total carbon and nitrogen of remained root residues and SMBC (soil microbial biomass carbon) content. The results showed that the mineralization rate of root residues was fastest during 0-9 days after incubation, which then gradually decreased after 9 days. After 60 days of incubation, the mineralization rate of root residues in all the treatments stabilized. During the whole incubation period, the cumulative release of CO₂ from maize roots was higher than that from soybean roots, but the cumulative release of CO₂ under SM 1:3 treatment was always higher than the other treatments. The cumulative release of CO₂ under SM 1:3 treatment was significantly higher than that under other treatments at the end of incubation. The content of total carbon in root residues had no significant change in the first 10 days, but decreased significantly during 10-60 days of incubation, after which it stabilized. At the end of incubation, total carbon content under SM 1:3 treatment decreased by a maximum of 24.8% from the initial value, followed by maize root residue treatment (which decreased by 21.4%), and the decrease in carbon content of the soybean root residue treatment was minimum, which was 9.7%. Total nitrogen content decreased significantly in the first 10 days of incubation, and then increased significantly until the end of incubation. Total nitrogen content of soybean root residues was highest at the end of incubation, and SM 1:3 treatment had the lowest. SMBC content first increased and then decreased during the incubation, followed by a steady change. At the end of incubation, SMBC content of SM 1:3, SM 1:1, M, S and SM 3:1 were 89.4%, 58.8%, 47.1%, 41.2% and 37.5% higher than CK, respectively. Hence, the mixtures of maize and soybean root residues had higher mineralization and nutrient release than sole maize and soybean root residues. This was beneficial to the reproduction of soil microorganisms. Among the three ratios selected in this experiment, the SM 1:3 had the best effects.