Fluorine in Sodic Soils

Effect of varying levels of exchangeable sodium percentage (ESP) on the solubility and adsorption of fluorine in a soil was studied in the laboratory. Water‐extractable F of 25 differentially gypsum treated and uniformally cropped field plots increased linearly with increase in soil ESP ( r = 0.93) and pH ( r = 0.95). Incubation studies revealed that a major portion of the added F was immobilized within the 1st 8 days. A relatively lesser quantity of added F was immobilized in soil of higher ESP and pH. Fluorine adsorption by these soils was describeable by Langmuir isotherm up to an equilibrium soluble‐F concentration of 0.6 mmol/liter. Beyond this limit the adsorption pattern seemed to reflect immobilization through precipitation. At any equilibrium soluble F concentration, there was a decrease in adsorption of F with increase in soil ESP or pH. Addition of amendments, like gypsum, to these soils which reduce ESP and pH will also simultaneously result in a reduction of water‐extractable F.