Grazing exclusion restores soil health in Brazilian drylands under desertification process

Abstract

The Brazilian drylands (Caatinga biome) are facing accelerated soil desertification due to human activities (e.g., overgrazing). However, restoration practices (e.g., grazing exclusion), are promising to curb soil desertification and, eventually, increase soil functioning. However, the understanding of soil health (SH) changes, induced by desertification and restoration in the Caatinga biome remains, poorly understood. Here, the SMAF (Soil Management Assessment Framework) was applied to assess the impact of desertification and long-term grazing exclusion on the SH in the Caatinga biome. Three conditions were assessed: i) native vegetation (NV), ii) degraded soil by overgrazing (DE) and iii) restored soil by grazing exclusion (RE). Soil samples (0–10 cm) were collected in both rainy and dry seasons, and chemical (pH, sodium adsorption ratio (SAR), K+, and P), physical (bulk soil density), and biological (soil organic carbon (SOC), microbial biomass carbon (MBC), and β-glucosidase activity) indicators were analyzed. Then, integrated soil health indexes (SHI) were calculated using the SMAF algorithms. Briefly, DE reduced (0.44 and 0.47 in rainy and dry seasons, respectively) the SHI compared to NV (0.72 and 0.82 in rainy and dry seasons, respectively). Importantly, RE recovered SH after two decades of implantation (0.65 and 0.79 in rainy and dry seasons, respectively). Bulk soil density and SAR were the indicators that presented a higher negative correlation with SH, mainly in DE, while SOC, MBC, and β-glucosidase activity correlated with SH in NV and RE soils. Biological soil health indicators increased in dry season, which may be due to the deciduous behavior of Caatinga vegetation, which could intensify microbial activity. We provided novel evidence that SMAF can be a user-friendly tool to monitor changes in SH under Brazilian drylands soils. In addition, long-term grazing exclusion can restore SH, contributing to curbing the desertification process in the region.