A series of experiments were conducted to examine the interactive effects of an organic ligand,a competing cation, and pH on the dissolution of zinc (Zn) from three California soils,Maymen sandy loam,Merced clay,and Yolo clay loam.The concentrations of soluble Zn of the three soils were low in a background solution of Ca(NO3)2.Citric acid,a common organic ligand found in the rhizosphere,was effective in mobilizing Zn in these soils;its presence enhanced the concentration of Zn in soil solution by citrate forming a complex with Zn.The ability of Zn to form a complex with citric acid in the soil solution was dependent on the concentration of citric acid,pH,and the concentration of the competing cation Ca~(2+).The pH of the soil solution determined the extent of desorption of Zn in solid phase in the presence of citric acid.The amounts of Zn released from the solid phase were proportional to the concentration of citric acid and inversely proportional to the concentration of Ca(NO3)2 background solution,which supplied the competing cation Ca~(2+) for the formation of a complex with citrate.When the soil suspension was spiked with Zn,the adsorption of Zn by the soils was retarded by citric acid via the formation of the soluble Zn-citrate complex.The dissolution of Zn in the presence of citric acid was pH dependent in both adsorption and desorption processes. A series of experiments were conducted to examine the interactive effects of an organic ligand, a competing cation, and pH on the dissolution of zinc (Zn) from three California soils, Maymen sandy loam, Merced clay, and Yolo clay loam. These concentrations of soluble Zn of the three soils were low in a background solution of Ca (NO3) 2. Citric acid, a common organic ligand found in the rhizosphere, was effective in mobilizing Zn in these soils; its presence enhanced the concentration of Zn in soil solution by citrate forming a complex with Zn. the ability of Zn to form a complex with citric acid in the soil solution was dependent on the concentration of citric acid, pH, and the concentration of the competing cation Ca ~ (2 +). The pH of the soil solution determined the extent of desorption of Zn in solid phase in the presence of citric acid. The amounts of Zn released from the solid phase were proportional to the concentration of citric acid and inversely proportional to the concentration of Ca (NO3) 2 backg which provides the competing cation Ca ~ (2+) for the formation of a complex with citrate. When the soil suspension was spiked with Zn, the adsorption of Zn by the soils was retarded by citric acid via the formation of the soluble Zn-citrate complex. The dissolution of Zn in the presence of citric acid was pH dependent in both adsorption and desorption processes.