Effects of low-molecular-weight organic acids on phosphorus sorption characteristics in some calcareous soils

Authors: NEDA MORADI, MIRHASAN RASOULI SADAGHIANI, EBRAHIM SEPEHR, BABAK ABDOLLAHI MANDOULAKANI

Abstract: Understanding the role of organic acids in phosphorus sorption in soils is very important for economic and environmentally friendly management of soil P. Thus, calcareous surface soils (0-30 cm) from West Azerbaijan Province, Iran, were sampled to study the effect of different organic acids on P sorption. Soil samples (2.5 g) were equilibrated with 25 mL of 0.01 M CaCl_2 solution containing 0-20 mg P L^{-1} and 5 mmol L^{-1} of different organic acids (citric, oxalic, and malic acid). The sorption data were well fitted to Freundlich and linear equations but not to the Langmuir equation. The standard P requirements (SPRs) were lower in soils treated with organic acids than in untreated soils. The minimum and maximum values of calculated parameters (extent of sorption, energy of sorption, equilibrium buffering capacity, equilibrium P concentration, and SPR) by Freundlich and linear sorption isotherms were observed in soil 5 (sandy) and soil 4 (clayey-calcareous), respectively. Generally, organic acids decreased the amount of sorbed P and other sorption parameters in the studied soils. Oxalic acid was the most effective reagent for reducing the P sorption.

Keywords: Low-molecular-weight organic acids, phosphorus, sorption equations

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