Land use impairs soil quality in a Histosol: a comparative study between conventional cultivation and secondary forest

Histosols provide key ecosystem services, including carbon storage, hydrological regulation, and biodiversity support; however, the effects of conventional agriculture on their quality in tropical regions remain poorly understood. In this study, we evaluated the effects of different land-use systems on a Sapric Thionic Histosol in a coastal plain of Rio de Janeiro, Brazil, by comparing a conventional cropping system with a secondary forest under natural regeneration, both with approximately 25 years of contrasting land use. Soil chemical, physical, and biological attributes were evaluated, including bacterial diversity, macrofauna, arbuscular mycorrhizal fungi (AMF) spore density, glomalin-related soil proteins (GRSPs), β-glucosidase and arylsulfatase activities. A subset of representative soil attributes was selected to compose a Minimum Data Set (MDS) and integrated into chemical, physical, and biological sub-indices and an overall Soil Quality Index (SQI). Conventional cultivation was associated with lower soil pH, organic carbon, and fertility, whereas physical properties showed no significant differences. Significant shifts in bacterial community structure and lower bacterial richness and diversity were also observed under conventional cultivation. Functional predictions suggested differences in pathways associated with stress responses and sulfur metabolism under conventional cultivation. Biological indicators, including Oligochaeta abundance, AMF spore density, GRSP concentrations, and enzymatic activity, were notably reduced under cultivation. Overall, soil quality indices were significantly lower under conventional cultivation, indicating that agricultural use of tropical Histosols is associated with chemical and biological degradation and pronounced shifts in bacterial community structure, with potential implications for ecosystem functioning and stability.