Organic acids can affect phosphorus (P) sorption. In order to evaluate the effect of citric acid and oxalic acid on phosphorus sorption characteristics in calcareous soils, five different soil samples (0-30 cm) were collected in West Azerbaijan province. Soil samples (2.5 g) were equilibrated with solutions of KH2PO4 containing 0 to 20 mg P l-1. Five mM organic acids were added to each tube and sorbed P was calculated. The sorption data were fitted to Langmuir, Freundlich and linear equations. The results showed phosphorus sorption data were well described by the Freundlich and linear equations. The average values of Kf (distribution coefficient), n and equilibrium buffering capacity (EBC) of linear equation in citric acid treatment were reduced to 29, 12 and 17 percent, respectively and for oxalic acid reduced to 43, 27 and 14 percent, respectively. Maximum sorption was reduced significantly by oxalic as compared to citric acid. Standard phosphorus requirement (SPR) was decreased by 57 % as a result of organic acids additions compared to control condition. It is concluded that organic acids additions to soils containing more calcium carbonate and high amount of clay can decrease P sorption.

Keywords: Sorption characteristics, Citric acid, Oxalic acid, Phosphorus, Calcareous soil

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