Biological indicators drive soil quality differentiation under contrasting land-use systems in dry tropical sandy soils

Sandy soils in semiarid regions are highly vulnerable to land-use change due to their low water and nutrient retention, yet integrated assessments of soil quality remain limited in these environments, particularly in the Caatinga biome. This study evaluated soil quality using a Soil Quality Index (SQI) across four contrasting land-use systems in the Brazilian semiarid region: native Caatinga vegetation (NV), conventional corn cropping (CC), forage cactus cultivation (FC), and forage grassland (FG). Soil samples were collected at 0–10 and 10–20 cm depths, and principal component analysis to define a minimum data set and construct a SQI. Potassium was the only indicator selected in both soil layers. Biological indicators drive soil quality differentiation, with basal respiration driving variability at 0–10 cm and microbial biomass carbon at 10–20 cm. NV showed the highest SQI values (0.92 at 0–10 cm and 0.97 at 10–20 cm), whereas CC showed the lowest values, with reductions of 27.3% and 20.7%, respectively. Correlation network analysis revealed higher connectivity among soil indicators in systems with higher vegetation cover, indicating stronger functional integration. These findings support conserving native Caatinga vegetation and promoting forage-based systems, particularly forage grassland, as sustainable land-use strategies to improve soil quality in sandy semiarid soils. In parallel, forage-based systems, mainly FG, showed the highest soil quality among managed systems, suggesting that replacing conventional corn cropping with forage-based systems may improve soil physical, chemical, and biological functions in degraded sandy semiarid soils.