Soil microbial indicators and bacterial co-occurrence networks reveal early changes under no-tillage and cover crops in a tropical Oxisol.

Improving soil quality in tropical agroecosystems requires management strategies that enhance soil functioning and ecological processes. This study evaluated whether short-term adoption of no-tillage combined with cover crops induces early changes in soil microbial indicators and bacterial co-occurrence patterns in a tropical Oxisol under soybean cultivation in the Brazilian Cerrado. Conventional plowing was compared with no-tillage systems using maize, millet, Crotalaria spp., Urochloa spp., and intercropped combinations during the off-season. After three years, microbial biomass carbon, enzyme activities, potentially mineralizable nitrogen, and bacterial community structure (16S rRNA) were assessed. No-tillage with cover crops increased microbial biomass and enzymatic activities related to nutrient cycling. Crotalaria enhanced potentially mineralizable nitrogen and dehydrogenase activity, while intercropping increased β-glucosidase activity. Bacterial alpha diversity increased under no-tillage, whereas community composition showed limited variation. Network analysis revealed greater bacterial connectivity and interaction complexity under no-tillage, indicating that microbial interactions are sensitive early indicators of regenerative changes in tropical soils.