Effects of short‐term tillage managements on rhizosphere soil‐labile organic carbon fractions and their hydrolytic enzyme activity under a double‐cropping rice field regime in Southern China

Abstract

AbstractThe soil‐labile organic carbon (C) fractions and their hydrolytic enzyme activity play an important role in maintaining or increasing soil quality and soil fertility, which are affected by adopting various tillage managements. But there is still limited information about how rhizosphere soil‐labile organic C fractions and their hydrolytic enzyme activity respond to different tillage managements under a double‐cropping rice (Oryza sativa L.) (early rice and late rice) in a field in Southern China. We hypothesized that rhizosphere soil‐labile organic C fractions and their hydrolytic enzyme activity in the double‐cropping rice field were modified by combined application of tillage with crop residue incorporation. Therefore, the main objectives of this study were to explore change in rhizosphere SOC content, soil‐labile organic C fractions [mineralizable C (Cmin), microbial biomass C (MBC), dissolved organic C (DOC), particulate organic C (POC), light fraction organic C (LFOC), permanganate oxidizable C (KMnO4‐C)] and their hydrolytic enzyme activity during 6‐years tillage management in a double‐cropping rice system in Southern China by using the fluorometric method. The relationship between proportion of each labile organic C fraction to SOC content were analysis using the redundancy analysis (RDA) method. The experiments included four tillage treatments: rotary tillage with all crop residues removed as a control (RTO), conventional tillage with crop residue incorporation (CT), rotary tillage with crop residue incorporation (RT), and no‐tillage with crop residue retention (NT). The results showed that combined application of tillage with crop residue incorporation managements significantly increases rhizosphere SOC content and soil‐labile organic C fractions compared without crop residue input treatment. Compared with RTO treatment, rhizosphere soil Cmin, KMnO4‐C, POC, DOC, LFOC, and MBC contents with CT treatment increased by 170.97%, 37.22%, 52.53%, 14.46%, 20.29%, and 27.35%, respectively. The proportion of labile C with CT, RT, and NT treatments was higher than that of RTO treatment. This results demonstrated that rhizosphere soil hydrolytic enzyme activity with CT, RT, and NT treatments were higher than that of RTO treatment. Compared with RTO treatment, rhizosphere soil polyphenol oxidase and peroxidase activities with NT treatment increased by 75.80% and 40.90%, respectively. They had significantly positive correlation between rhizosphere soil hydrolytic enzyme activity and SOC content and its labile organic C fractions. Rhizosphere soil polyphenol oxidase and peroxidase activities had significantly positive correlation with labile organic C fractions. The RDA results indicated that CT and RT treatments were significantly different from NT and RTO treatments, and all of them were clearly separated from each other. As a result, combined application of tillage with crop residue incorporation is a beneficial nutrient management for improving rhizosphere soil‐labile organic C fractions and their hydrolytic enzyme activity in the double‐cropping rice fields of Southern China.