Soil structural recovery processes in diversified soybean-based systems and their relationship with soil organic matter

Soil organic matter (SOM) is widely recognized as a key driver of soil resilience. This study evaluated the effects of soybean-based production systems managed under no-tillage, with contrasting levels of crop diversification, on soil physical recovery and its relationship with SOM. The systems assessed included soybean monoculture–fallow, soybean in succession with ruzigrass, and a diversified rotation comprising soybean, sunn hemp, maize intercropped with ruzigrass, and ruzigrass. Undisturbed soil samples were collected from the 2.5–5.0 cm soil layer. Soil compaction and physical recovery were evaluated under controlled laboratory conditions by applying a uniaxial stress of 300 kPa, followed by successive wetting–drying cycles. Soil bulk density (Bd), air-filled porosity (εa₁₀), and air permeability (ka₁₀) were quantified before compaction, immediately after compaction, and after one to four wetting–drying cycles. SOM contents were higher in the succession and rotation systems than in the monoculture (53.7, 56.6, and 42.3 g kg^-1, respectively). Although Bd, εa₁₀, and ka₁₀ did not differ among systems prior to or immediately after compaction, wetting–drying cycles promoted partial structural recovery, particularly in the rotation system, where Bd decreased from 1.26 to 1.22 Mg m^-3 and εa₁₀ increased from 0.09 to 0.13 m³ m^-3 relative to the monoculture system. Despite higher SOM contents under diversified systems, soil recovery rates were not significantly correlated with SOM concentration. These findings indicate that SOM quantity alone may be insufficient to explain soil physical resilience in the short term, underscoring the importance of SOM quality, spatial organization, and its interaction with pore structure when assessing soil resilience.