Effect of Low Molecular Weight Organic Anions on the Adsorption of NO3 − by Variable Charge Soils

Abstract

Low molecular weight organic acids exist widely in soils and have been implicated in many soil processes. The results in the present paper showed that the presence of organic anions led to a decrease in the adsorption of NO3 −. The effect of citrate was much larger than that of oxalate and malate. Among different soils, the effect for Hyper-Rhodic Ferralsol and Rhodic Ferralsol was larger than that for Haplic Acrisol, which was related to the content of iron oxides in these soils. The effect of organic anions decreased with the increases in pH value and the amount of organic anions added. The organic anions depressed the adsorption of NO3 − through two mechanisms, the competition of the organic anions for adsorption sites with NO3 − and the change of soil surface charge caused by the specific adsorption of organic anions.