Limestone Reapplication and Tillage System Influence Non-Exchangeable Aluminum in Subtropical Oxisol

Liming reduces aluminum (Al) toxicity in acidic soils, but its effects on non-exchangeable aluminum (Al ne ) remain unclear. This study evaluated Al fractions and their relationships with soil chemical properties, soybean ( Glycine max L. Merr.) and wheat ( Triticum aestivum L.) yields. The experiment was established in July 2023 in Paraná State, Brazil, on an Oxisol, using a randomized block design in a 4 × 2 factorial arrangement. Treatments consisted of four limestone reapplication rates (0, 1.0, 1.3, and 1.6 times the rate required to reach 70% base saturation) and two application methods (surface application or incorporation into the 0–0.20 m layer). Nine months after reapplication, soil samples from the 0–0.05, 0.05–0.10, and 0.10–0.20 m layers were analyzed. Liming reduced exchangeable aluminum (Al 3+ ) and increased soil organic matter (SOM) in all layers. Non-exchangeable aluminum decreased only in the 0–0.05 m layer. Conventional tillage reduced SOM and increased Al ne by 18% in the surface layer. Non-exchangeable aluminum was positively correlated with potential acidity (H + Al) and negatively correlated with soil pH and base saturation. Wheat yield was more negatively associated with Al ne than soybean yield. Non-exchangeable aluminum correction remained limited to the surface layer regardless of management. Soil disturbance increased Al extractability, indicating greater exposure of reactive Al forms under conventional tillage. Surface liming and no-till favored SOM stability and moderated Al dynamics in subtropical Oxisols.