Sustainable Soil Management Through Liming: Effects on Soil pH, Carbon Stabilization and Aluminium Transformations

Soil pH is a key regulator of soil chemical processes, organic matter transformation, and ecosystem functioning in acid soils. This study examines how pH gradients induced by long-term liming affect soil chemical properties, aluminum dynamics, and soil organic carbon (SOC) stabilization in Retisols under plant-derived organic inputs. The study was conducted at six soil pH levels (pHKCl from 3.9–4.0 to 6.5–6.7), which reflect a gradient of acidity conditions. Soil chemical parameters, SOC content and fractions, humic substance composition, aluminum forms, and soil respiration (CO2 release under laboratory conditions) were analysed. Increasing soil pH significantly reduced aluminum concentrations (by up to 59%) and improved nitrogen and phosphorus availability, indicating a gradual reduction in chemical limitations associated with soil acidity. Soil pH strongly controlled both SOC content and quality. The highest SOC content was observed at pH 6.0–6.1, and strongly acidic conditions favored the accumulation of more labile carbon forms. As the pH increased, there was a clear shift towards more stable organic matter, as indicated by higher humic acid content, an increased HA/FA ratio, and a threefold increase in the organic carbon stability index. At the same time, the reduced water-extractable organic carbon content indicated reduced carbon mobility and improved physicochemical stabilization. Microbial activity increased with increasing pH, but showed a nonlinear response, reflecting a balance between increased mineralization and carbon stabilization processes. These data indicate that soil pH primarily determines SOC stabilization pathways, rather than just total carbon accumulation. These results suggest that soil pH may influence SOC stabilization through changes in aluminum dynamics, organo-mineral interactions, and microbial processes, supporting previously reported mechanisms of carbon stabilization in acid soils. The optimal pH range of 5.5–6.1 promotes favorable interactions between nutrient availability, microbial processes, and organic–mineral associations, supporting long-term soil functionality. This study highlights liming as a key strategy for regulating soil biogeochemical processes and improving the sustainability of acid soil management.