Prediction of fertilizer phosphate requirement using the Langmuir adsorption maximum

The phosphate adsorption maximum as calculated by the Langmuir equation was used to predict the fertilizer P requirement of wheat (Triticum aestivium, cv. Caldwell) on both virgin and cultivated Decatur clay loam (clayey, kaolinitic, thermic, Rhodic Paleudult) and Hartsells sandy loam soils (fine-loamy, siliceous, thermic, Typic Hapludult). Soils with higher adsorption maximum were found to require more fertilizer P than soils with lower adsorption maximum. For soils 25% saturation of the adsorption maximum gave the optimum dry matter yield. This corresponded to equilibrium P concentration of 0.45 mg L⁻¹ for Decatur cultivated and 0.31 mg L⁻¹ for Decatur and Hartsells virgin soils for optimum dry matter yield. These values are within the range of those reported previously by other investigators working with different soils.