<![CDATA[Acidic mineral soils are one of the major constraints to peanut cultivation due to the low availability of phosphorus (P), which is caused by fixation with aluminum and iron. Humic acid has the potential to improve phosphorus fertilizer efficiency by enhancing soil chemical properties, thereby increasing phosphorus availability and uptake by plants. This study aimed to evaluate the interaction between humic acid and phosphorus fertilizer on cation exchange capacity (CEC), phosphorus concentration, phosphorus uptake, and selected soil chemical properties in peanut (Arachis hypogaea L.) cultivated on acidic mineral soil. The experiment was arranged in a Completely Randomized Design (CRD) using a factorial pattern consisting of two factors. The first factor was humic acid dosage: A0 (0 kg ha⁻¹), A1 (10 kg ha⁻¹), A2 (25 kg ha⁻¹), and A3 (35 kg ha⁻¹). The second factor was phosphorus fertilizer dosage: P0 (0 kg ha⁻¹), P1 (150 kg ha⁻¹), P2 (300 kg ha⁻¹), and P3 (450 kg ha⁻¹). Data were analyzed using analysis of variance (ANOVA), followed by the Honestly Significant Difference (HSD) test at the 5% significance level. The results showed a significant interaction between humic acid and phosphorus fertilizer on soil cation exchange capacity (CEC), plant phosphorus concentration, and phosphorus uptake. The A3P3 treatment produced the highest CEC (24.14 cmol(+)/kg), phosphorus concentration (0.401%), and phosphorus uptake (0.072 g plant⁻¹). Individually, humic acid and phosphorus fertilizer significantly affected soil pH and soil organic carbon. The application of 35 kg ha⁻¹ humic acid resulted in soil pH of 7.57 and soil organic carbon of 2.40%, while 450 kg ha⁻¹ phosphorus fertilizer increased soil pH to 7.58 and soil organic carbon to 2.18%. The combination of 35 kg ha⁻¹ humic acid and 450 kg ha⁻¹ phosphorus fertilizer is recommended to improve soil chemical properties and phosphorus uptake efficiency in peanut cultivation on acidic mineral soils. Keywords: humic acid, peanut, phosphorus, phosphorus uptake, cation exchange capacity, acidic mineral soil.]]>
