Effects of an integrated rice-crayfish farming system on soil organic carbon, enzyme activity, and microbial diversity in waterlogged paddy soil

A 10-year (2005-2015) field experiment was conducted to study the effects of an integrated rice-crayfish (CR) model on soil organic carbon, enzyme activity, and microbial diversity at soil depths of 0-10 cm, 10-20 cm, 20-30 cm, and 30-40 cm. Compared with a mid-season rice monoculture (MR) model, total organic carbon (TOC), particle organic carbon (POC), and water-soluble organic carbon (WSOC) were significantly higher in the 0-40 cm soil layers, and the content of microbial biomass carbon (MBC) was significantly higher in the 30-40 cm soil layer in the CR model. The ratios of WSOC to TOC and POC to TOC in the 0-40 cm soil layers in CR model exhibited an increasing trend, whereas the ratio of MBC to TOC in the 0-30 cm layers exhibited a decreasing trend with respect to that of the MR model, however, these differences were not statistically significant. The activity of soil invertase, acid phosphatase, and urease in the 0-40 cm soil layers in the CR model exhibited a decreasing trend with respect to that of the MR model, and the activity of urease in the 10-20 cm soil layer in the CR model was significantly lower than that in the MR model. Compared with the MR model, the CR model significantly enhanced the carbon utilization capacity of soil microbes, and the richness index, dominance index, and diversity index of the soil microbial community in the 20-30 cm layer, whereas it significantly decreased the number of dominant soil microorganism species and the carbon utilization capacity of soil microbes in the 0-10 cm layer. Soil organic carbon and its active components had a significant direct correlation with the microbial diversity index, and significantly positive correlations with invertase, urease, and acid phosphatase. With respect to the soil microbial diversity index, soil organic carbon and its active components had a closer relationship with soil enzyme activity.