Soil phosphate adsorption and desorption in 0.01m calcium chloride electrolyte

Abstract

Using the soil samples of long‐term fertilization experiments started 25 years ago, the factors that determine the phosphorus (P) supply in plants were examined: actual, readily available P content of the soil, soil solution P supply, and P‐adsorption and ‐desorption by the soil. The experiments suggest that the P‐binding (adsorption) is fairly different in soils with different soil properties which fact has to be considered when a growing site specific fertilization is applied. The experiments introduced show that the P‐adsorption can well be monitored with the Fox‐Kamprath method under constant ionic strength (0.01M CaCl₂). In the investigated concentration range both the Van Huay equation and the Freundlich isotherm are suited to the description of the experimentally determined P‐adsorption. The adsorptive isotherms of the soil are characteristic of the adsorption determined by soil qualities and make the assessment of fertilizer doses needed to ensure the critical concentration of equilibrium soil solution possible. The desorption curves prove that considerable amounts of the phosphates accumulated in the soil can be mobilized. The results of the desorption investigations show that beside characterizing the actual supply, the single time extraction P values in 0.01M calcium chloride (CaCl₂) can also express the P supply potentials. Not only plant available, labile soil‐P can be characterized by the 0.01M calcium chloride extractable P but the excessive and environmentally undesirable P levels as well.

Notes

Project N* OTKA T5377 State Scientific Research Fund of Hungary and ERB CIPA CT 94–0221 EC Contract.