Re-acidification of limed soil alters aggregate stability and soil carbon turnover in an agroecosystem

Soil acidification adversely influences the soil structural stability and carbon sequestration. The current study exploited a unique 75 year liming experiment established in 1949 on Retisols in Lithuania to evaluate how historically generated soil pH gradients (pH 3.82, 3.98, and 5.52), maintained after 19 years without liming (2005-2024), influence soil aggregate stability and aggregate-associated carbon and nutrient pools. Soil samples were collected from 0-10 and 10-20 cm depths and separated into four aggregate size classes: macroaggregates (MACA, 8.00-2.00 mm); mesoaggregates (MESA, 0.630-0.200 mm); microaggregates (MICA, 0.063 mm); and the silt-clay fraction (SCF, <0.063 mm) by dry sieving. Increasing the soil pH from 3.82 to 5.52 substantially improved the soil structural integrity at both soil depths. Under pH 5.52, the proportion of MACA increased from 45.63% to 52.45% at 0-10 cm and from 46.86% to 55.13% at 10-20 cm. The highest mean weight diameter (2.78 and 2.99 mm) and geometric mean weight (1.17 and 1.19 mm) were recorded under pH 5.52 in surface and subsurface soils, respectively. Soil organic carbon increased significantly across all aggregate fractions with increasing pH, with the maximum SOC concentration (22.95 g kg^-1) observed in the SCF at pH 5.52 in the surface soil. Permanganate-oxidizable carbon showed the strongest response in MACA, increasing by 54.66% at pH 5.52 compared with strongly acidic soil (pH 3.82). In contrast, water-extractable organic carbon was consistently highest in MICA, reaching 333.66 mg kg^-1 at pH 5.52. Total nitrogen and total phosphorus also increased significantly with increasing pH across aggregate fractions and soil depths. Correlation analysis revealed strong positive associations between soil pH, aggregate stability, and carbon and nutrient pools. Conclusively, increasing soil pH to moderately acidic conditions (5.52) promoted MACA formation, enhanced aggregate stability, and increased both stable and labile carbon pools, highlighting long-term liming as an effective strategy for restoring soil structure and improving carbon and nutrient retention in Retisols.