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Controlled Release of Fertilizer Minerals by Incapsulating Membranes: I. Factors Influencing the Rate of Release¹

ABSTRACT

The availability of nutrients from inorganic fertilizer salts can be regulated through coating such materials. The release rate was investigated in several elution and leaching experiments. The release approached linearity for a considerable period; thereafter the rate dropped off. The release rate was largely independent of the pH of the elutant and of the soil pH. An increase in temperature from 10° to 20°C. almost doubled the initial release rate. The release could be regulated very efficiently through the coating thickness. There was an effect of ionic species, nitrate and ammonia being given off more rapidly than potassium or phosphates. The release was only slightly reduced under sterile conditions. It was concluded that diffusion is the most likely release mechanism and proposed that discrepancies such as the high Q₁₀ value could be explained through possible changes in membrane properties. Coated fertilizers thus possess the properties required for regulation of the availability of nutrients: they may reduce leaching losses and provide a steady prolonged nutrient supply to plants.

¹ Contribution by the Department of Irrigation and Soil Science, University of California, Los Angeles. Parts of this paper were presented at the Western Society of Soil Science meetings in Davis, Calif., June 22, 1961, and before Div. IV, Soil Science Society of America, Saint Louis, Mo., Nov. 30, 1961.

² Assistant Professor and Associate Professor of Soil Science respectively.

Received for publication February 5, 1962. Accepted for publication July 12, 1962.