Relationship between Phosphorus Sorption and Soil Acidity as Affected by Bicarbonate and Silicate Ions

Abstract

The aim of this article was to establish a relationship between phosphorus (P) sorption and pH and phosphorus concentration of soil solution in the presence of specifically sorbed anions such as bicarbonate and silicate. Phosphorus sorption isotherms were obtained at different pH values of equilibrated soil solutions for three surface soil samples, namely Typic Haplustept, Calcic Chromustert, and Ultic Paleustalf, in three different systems, namely bicarbonate (0.001 M), silicate (0.001 M), and a system without any bicarbonate and or silicate, all having a common concentration of 0.1 M sodium chloride (NaCl). Phosphate sorption data at different pH values could be fitted very closely to a modified Freundlich equation of the form X/m=K Ha Cb, where, X/m is the amount of phosphate sorbed at solution phosphate concentration C and hydrogen ion concentration H. The values of a and b were positive fractions found to vary with soils and ionic medium. A silicate system more effectively reduced P sorption, particularly at lower pH values. The differences in P sorption in different media gradually decreased in all the soils as pH increased.