Effects of paddy field cropping patterns on soil organic carbon and carbon pool management index in the middle reaches of the Yangtze River

To explore the effects of paddy field planting patterns on soil organic carbon pools and to optimize cropping systems, in this study, we examined five typical paddy field cropping patterns in the middle reaches of the Yangtze River, including Chinese milk vetch-early rice-late rice (CRR, control), rape-early rice-late rice (RRR), potato-early rice-late rice (PRR), Chinese milk vetch-early rice-sweet potato||late soybean (CRI), and rape-early rice-sweet potato||late soybean (RRI). Soil organic carbon, active organic carbon and its components, carbon pool management index, and economic benefits were analyzed by measuring the content of soil organic carbon, the active organic carbon components in the paddy fields, and the crops yields. The results showed that after late rice harvest, compared to CRR, the CRI, RRI, and RRR treatments increased the soil organic carbon content by 12.06%-21.01% (P < 0.05); the CRI, RRI, and PRR treatments increased the active organic carbon content and microbial biomass carbon content by 16.80%-20.45% and 38.24%-50.00% (P < 0.05), respectively; while CRR, RRI, RRR and PRR increased the dissolved organic carbon content by 3.13%-15.64% (P>0.05). The CRI and RRI treatments significantly promoted the accumulation of soil total organic carbon and microbial biomass carbon, while the PRR treatment promoted the accumulation of soil active organic carbon. Compared to CRR, PRR increased the soil carbon pool activity and carbon pool activity index; RRI and CRI increased the soil carbon pool index; and CRI, RRI, and PRR significantly increased the soil carbon pool management index by 17.30%-33.49% (P < 0.05). The economic benefits of PRR and CRI increased by 12.05% and 9.86%, respectively (P < 0.05). There was an extremely significant positive correlation between rice yield and microbial biomass carbon (P < 0.01), and the correlation coefficient between the soil carbon bank management index and active organic carbon was the highest, with a significant positive correlation (P < 0.01). In summary, each cropping pattern is beneficial for increasing crop yield and changing the content of soil organic carbon and its components. Among them, Chinese milk vetch-early rice-sweet potato||late soybean and potato-early rice-late rice have better comprehensive effects, which can be popularized and applied in the middle reaches of the Yangtze River.