Effect of cover crop on soil fertility and bacterial diversity in a banana plantation in southwestern China

A cover crop can be an effective strategy to mitigate soil degradation in crops, such as banana. In this study, soil bacterial diversity, chemical properties, enzymatic activities, and bacterial nutrient-related functional genes were examined in the intercropping area of a banana plantation from 2018 to 2020 that had conventional tillage with bare soil (CT), natural weed cover (WC), which was primarily goosegrass (Eleusine indica (L.) Gaerth), or a cover crop of cultivated Siratro (Macroptilium atropurpureum (DC.) Urb.) (SC). By 2020, SC followed by WC and CT treatments were higher in soil organic matter, available nitrogen, total nitrogen and total phosphorus content as well as increased phosphatase, catalase, invertase and urease activities. Compared to CT and WC treatments, the co-occurrence network of SC treatment had higher modularity index indicating a more stable bacterial community. The composition of community was significantly different between the CT and SC treatments in 2019 and 2020, and the WC treatment in 2020. The relative abundance of fatty acids and lipid biosynthesis genes in the soil bacterial microbiome were significantly higher with SC compared to CT and WC in 2019 and 2020, as well as for carbon and nitrogen functional genes in 2020. However, the relative abundance of nucleoside and nucleoside biosynthesis genes were significantly lower with SC compared to CT and WC in 2020. SC treatment increased the relative abundance of Bradyrhizobium and MND1 related to nitrogen cycle and utilization compared to CT in 2019 and 2020. In general, the major benefits of a Siratro cover crop was increased soil organic matter, nitrogen content, and nitrogen fixing bacteria, as well as a more stable soil bacterial community, indicating that it provided multiple potential benefits to the soil of banana.