Dynamics of soil fertility and microbial community response to stocking density in rice-turtle co-culture

Co-culture modes of rice and aquatic animals as rice-crayfish, rice-fish and rice-turtle have expanded rapidly in paddy rice cultivation regions, due to its ecological efficiency, contributions to food security, food productivity and economic benefits. However, different co-culture strategies have great influences on rice or aquatic animal growth and related ecological benefits. In this study, we investigated the effect of turtle stocking density on the dynamics of paddy soil fertility and microbial community characteristics in a rice-turtle co-culture ecosystem. The Chinese soft-shell turtles (Pelodiscus sinensis) were allocated to experimental paddy fields at four gradient stocking densities ranging from 360 to 540 kg· ha−1. In comparison with conventional rice cultivation with a higher input rate of chemical fertilizer, rice yields were higher in the rice-turtle paddies. In addition, soil pH and organic matter were relatively stable in the rice-turtle mode, whereas both parameters decreased over time in conventional paddies. Stocking density significantly benefited soil fertility, with soil organic matter increasing in response to higher stocking density. Total soil nitrogen concentration was lower in the conventional rice cultivation and low stocking density co-culture groups, compared with the high stocking density groups. Furthermore, the soil microbial communities were also affected by turtle stocking density. Redundancy analysis showed that soil pH, organic matter and available potassium concentration were the major factors influencing the abundance of the dominant microbes. The findings revealed the responses of paddy soil fertility and microbial community characteristics in rice-turtle co-culture modes, which could help optimize the co-culture mode and provide a basis for soil nutrient management in such ecosystems.