Significance of Iron Oxides and Calcium Carbonate Particle Size in Phosphate Sorption by Calcareous Soils

Abstract

Abstract Though many soil components are involved in reactions whereby soluble fertilizer P is converted to less soluble and therefore less available forms, the relative influence of each phase in this process is not clearly defined. While both crystalline and amorphous Fe oxides readily react with P in noncalcareous soils, the contribution of these forms to P sorption in calcareous soils has received little attention. Thus, in this study, samples of 20 mainly calcareous Lebanese soils, ranging widely in relevant properties, were equilibrated for 6 d with 25 mL P solutions ranging from 12.5 to 62.5 mg kg −1 . The data did not conform to the conventional Langmuir isotherm. Correlations and regression coefficients with actual P rentention from solution indicated an involvement of oxalate Fe, but there was no effect of CaCO 3 particle size. Removal of Fe prior to equilibration had an inconsistent effect on P retention. The P behavior of calcareous soils may be modified by Fe oxides in such soils.