Release rates of phosphorus, ammonium, and potassium in clinoptilolite-phosphate rock systems

Controlled release of P, NH4, 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, NH4, and K release rates in Cp-PR systems, Data was collected using a continuous-how 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 NH4 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 NH4 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 NH4, P, and K in a synthetic soil.