Soil carbon–compaction relationships in diversified cover crop management systems

Soil compaction is a major constraint in Brazilian grain and pasture systems, and conservation-based practices such as cover crops are used to alleviate compaction and increase soil carbon stocks. This study (FAPESP 2025/17358-2) aimed to evaluate the effects of cover crops grown as monocultures or in mixtures on soil compaction alleviation and soil carbon accumulation under different compaction levels. The experiment was established in 2023 under three soil compaction levels: C0 (no compaction), C8 (eight tractor passes), and C16 (sixteen tractor passes). Subsequently, cover crops were cultivated, including Urochloa ruziziensis as a monoculture, U. ruziziensis intercropped with dwarf pigeon pea, and a multi-species mixture composed of U. ruziziensis, dwarf pigeon pea, and buckwheat. Soil physical attributes and soil organic matter were evaluated to assess structural changes induced by the management systems. The results indicated consistent responses of soil physical properties and soil organic matter to the evaluated cover crop systems. A general trend toward lower soil bulk density was observed in treatments with cover crops, indicating reduced compaction and improved soil structural conditions. Aggregate stability showed increases under conservation-based systems, reflecting stronger interactions between mineral particles and biologically derived binding agents such as roots, microbial exudates, and organic compounds. Higher organic matter levels were associated with reduced bulk density and enhanced aggregate stability, highlighting their structural and functional importance. Overall, the results demonstrate that mixed cover crop promotes synergistic improvements in soil structure and carbon-related attributes, supporting the sustainability of intensive agricultural systems in highly weathered tropical soils.