Determinants of soil aggregate stability in a long-term experiment under different tillage intensity and crop management systems

Soil aggregate stability (AS) is a critical indicator of soil physical quality, yet its long-term drivers in vulnerable silty soils remain inadequately quantified. This study analyzed the determinants of AS over 25 years (1999–2023) in a long-term field experiment on a temperate silty Luvisol, comparing four cropping systems: conventional (CON), low-input (LI), organic (ORG), and conservation agriculture (CA). Aggregate stability was assessed biennially using Le Bissonnais tests targeting distinct disaggregation mechanisms, alongside soil organic carbon (SOC), quantitative management indicators (intensity of crop sequence, grass-to-legume ratio, crop diversity and carbon biomass, and nitrogen inputs), and climatic variables. Mean AS remained low in frequently tilled systems (CON, ORG), reflecting the legacy of mechanical disturbance. In contrast, CA achieved a stable, high-AS state after approximately six years, which persisted. Intermittent tillage in LI prevented long-term recovery, underscoring a non-linear response to disturbance frequency. While SOC accumulation was associated with improved aggregate stability, it was insufficient to explain AS dynamics on its own. Long-term aggregate stability was primarily associated with cumulative indicators of crop diversity and below-ground biomass, whereas short-term variations responded more strongly to recent management factors such as crop sequence composition, nitrogen inputs, and rooting continuity. Precipitation exhibited dual effects, with recent rainfall promoting aggregate disruption, particularly in the Slaking test, whereas antecedent moisture conditions were generally associated with increased aggregate stability. Among the tests evaluated, Micro-cracking proved particularly sensitive to management and environmental drivers. The study demonstrates that sustained reduction of mechanical disturbance is the primary prerequisite for restoring aggregate stability in silty agroecosystems. Complementary management practices become effective determinants of soil structure only once mechanical constraints are alleviated. These findings provide a hierarchical framework for prioritizing soil management strategies to enhance the physical health and resilience of cultivated silty soils.