Release Rates of Phosphorus, Ammonium, and Potassium in Clinoptilolite‐Phosphate Rock Systems

Abstract

Abstract Controlled release of P, NH 4 , and K can be accomplished in synthetic soils through dissolution and cation‐exchange reactions by phosphate rock (PR) and the zeolite mineral, clinoptilolite (Cp). The power‐function equation has previously been found to adequately describe transport kinetics of the nutrient release process. Research was conducted to evaluate factors affecting P, NH 4 , and K release rates in Cp‐PR systems. Data was collected using a continuous‐flow thin‐disk technique. Results were evaluated with the power‐function equation. Materials included a Texas Cp and North Carolina and Tennessee PRs. Variables examined included the Cp/PR ratio, the mole fraction of NH 4 and K on the Cp, and the type of PR. The power‐function model indicated that initial release rates and cumulative nutrient release in Cp‐PR mixtures were increased by using a higher Cp‐PR ratio and by using a more reactive PR. Nutrient release rates were also affected by changes in the proportion of NH 4 and K occupying Cp exchange sites and reflected ion‐selectivity characteristics of Cp. The results indicate that Cp and PR may be used to obtain a controlled release of NH 4 , P, and K in a synthetic soil.