Soil microbiology in integrated livestock-forest systems under different spacings and forage crops in the semi-arid region of Brazil

Abstract Improving soil productivity in the Brazilian semi-arid region remains a major challenge. Integrated livestock–forest (ILF) systems represent a promising strategy for agricultural intensification with lower environmental impacts, as they enhance soil microbial functioning and support soil organic carbon (SOC) stocks accumulation. However, studies on how ILF systems affect soil biological properties and SOC dynamics in tropical semi-arid regions, particularly in the Caatinga biome, remain scarce. This study assessed soil microbiological properties in ILF systems established for six years in the Brazil’s semi-arid region. Four ILF systems were evaluated, each cultivated with sorghum (ILFSo), forage cactus (ILFFc), massai grass (ILFMg), and buffel grass (ILFBg), at spacings of 7 m (S7), 14 m (S14), and 28 m (S28) between strips of native trees. A native vegetation (NV) area served as a reference. Soil analyses included microbial biomass carbon (MBC), basal respiration, β-glucosidase activity, easily extractable glomalin (EEG), and SOC. ILFMg and ILFBg were the most effective systems for maintaining microbial biomass, activity, and SOC levels. ILFFc and ILFSo increased MBC but did not promote SOC accumulation. The spacing S7 resulted in the highest MBC, microbial quotient, and SOC, and the lowest metabolic quotient. ILFSo and NV showed the highest β-glucosidase activity at 0–10 cm, while ILFFc had the lowest. At 10–20 cm, β-glucosidase activity was greatest in ILFMg and ILFBg. EEG activity was similar among systems in the surface layer, whereas in the 10–20 cm layer the highest values occurred in ILFSo and ILFBg, and the lowest in ILFFc. Overall, ILF systems with grasses demonstrated superior soil microbiological activity and SOC accumulation, indicating that high-biomass forage crops should be prioritized in Brazil’s semi-arid region.