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Solubility and Cation Exchange in Phosphate Rock and Saturated Clinoptilolite Mixtures

Dep. of Agronomy, Oklahoma State Univ., Stillwater, OK 74078

L. R. Hossner

Dep. of Soil and Crop Sciences, Texas A&M Univ., College Station, TX 77840

D. W. Ming and D. L. Henninger

NASA Johnson Space Center, Houston, TX 77058

*Corresponding author.

ABSTRACT

Mixtures of zeolite and phosphate rock (PR) have the potential to provide slow-release fertilization of plants in synthetic soils by dissolution and ion-exchange reactions. This study was conducted to examine solubility and cation-exchange relationships in mixtures of PR and NH₄- and K-saturated clinoptilolite (Cp). Batch-equilibration experiments were designed to investigate the effect of PR source, the proportion of exchangeable K and NH₄, and the Cp to PR ratio on solution N, P, K, and Ca concentrations. The dissolution and cation-exchange reactions that occurred after mixing NH₄- and K-saturated Cp with PR increased the solubility of the PR and simultaneously released NH₄ and K into solution. The more reactive North Carolina (NC) PR rendered higher solution concentrations of NH₄ and K when mixed with Cp than did Tennessee (TN) PR. Solution P concentrations for the Cp-NC PR mixture and the Cp-TN PR mixture were similar. Solution concentrations of N, P, K, and Ca and the ratios of these nutrients in solution varied predictably with the type of PR, the Cp/PR ratio, and the proportions of exchangeable K and NH₄ on the Cp. Our research indicated that slow-release fertilization using Cp/PR media may provide adequate levels of N, P, and K to support plant growth. Solution Ca concentrations were lower than optimum for plant growth.

Received for publication July 24, 1992.