Spatial arrangement of livestock-forest integration systems enhances soil organic carbon associated with aggregates in a Cambisol in the Brazilian semi-arid region

Land-use changes associated with agricultural activities can disrupt soil aggregates, expose soil organic matter and lead to losses of soil organic carbon (SOC). This study evaluated the effects of integrated livestock–forest (ILF) systems with different crops and spacings between strips of native vegetation (NV) on SOC stocks associated with soil aggregates in the Brazilian semi-arid region after six years of system establishment. Four ILF systems cultivated with sorghum, forage cactus, massai grass, and buffel grass were implemented between native tree strips (NTS) with spacings of 7 and 28 m, using the Caatinga as a reference area. Soil samples were collected from the 0–10, 10–20, 20–30, and 30–50 cm layers. Water-stable aggregates were separated into macroaggregates (>2.00 mm), mesoaggregates (2.00–0.25 mm), microaggregates (0.25–0.053 mm), and aggregates associated with the silt and clay fraction (<0.053 mm). SOC was determined by dry combustion using an elemental analyzer. The 2.00–0.25 mm aggregates were the main contributors to SOC stocks, followed by the <0.053 mm fraction, representing 24.2–55.8% and 13.7–44.6% of total SOC, respectively. Conversion from NV to ILF systems altered the distribution of aggregate fractions and the associated SOC stocks. Compared with NV, ILF systems with sorghum and buffel grass under 28 m (S28) spacing increased SOC stocks in macroaggregates (>2 mm) by 55% and 46%, respectively, in the 0–10 cm layer. Crucially, the S28 spacing shifted the carbon dominance from mesoaggregates to macroaggregates, resulting in significantly higher macroaggregate-associated SOC stocks compared to the narrower 7 m spacing. These results indicate that ILF systems can improve soil structure and promote SOC stabilization, representing a sustainable land-use strategy for the Brazilian semi-arid region.