Effects of Low-molecular Weight Organic Acids on Phosphorus Sorption in Some Calcareous Soils

The effect of 0, 2, and 5 mM of citric, malic and oxalic acids on phosphorus (P) sorption was evaluated. In the collected soils, the level of total calcium carbonate stood in the range of 4-28%, clay content at 33-56% and the amount of organic matter recorded within 0.6-2.7%. The results indicated that the addition of organic acids causes reduction in P sorption. Citric acid in most soils, was shown to be more effective in this respect than oxalic and malic acids. The level of P sorption significantly decreased in particular at 5 mM concentration of organic acids. The lowest and the highest P sorption as regards the three organic acids were observed at concentrations of 5 mM in soil No. 5 vs. 0 mM in soil No. 4, and where the soils contained low vs. high clay plus calcium carbonate contents, respectively. Therefore, it is concluded that P adsorption by soils is controlled by the kind and concentration of organic acids content, and as well by soil mineral constituents.