LAUSR

ABSTRACT Understanding the role of organic acids on phosphorus (P) sorption capacity of soils is very important for its economic and friendly management. Combining P application with low-molecular weight organic acids could result in its higher plant availability for prolonged time. Therefore, citric and oxalic acid (at the rate of 1.0 mM kg−1 soil) were evaluated for their effect on P sorption capacity and its plant availability in two different textured calcareous soils. Organic acids decreased P sorption capacity and organic carbon partition coefficient (Koc) whereas increased Gibbs free energy (ΔG) of P. Organic-acid-treated soils required lesser quantity of P fertilizer to produce soil solution P concentration optimum for plant growth (external P requirement [EPR0.2]), that is, 0.2 mg L−1. Citric acid was efficient than oxalic acid in the above effects. P sorption parameters of Freundlich model were negatively correlated with lime potential and ΔG whereas had positive correlation (P < 0.05) with EPR0.2 and Koc. Incubation with oxalic acid increased available P in loamy sand and loam soil by 20% and 30%, respectively. Thus, organic acids could help reduce application rate of P fertilizer through lowering its adsorption in highly P-fixing soils without compromise on yield.