Nutrient Release from Controlled-release Fertilizers in Acid Substrate in a Greenhouse Environment: I. Leachate Electrical Conductivity, pH, and Nitrogen, Phosphorus, and Potassium Concentrations

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  • 1 University of California, Riverside, Botany and Plant Sciences, 4118 Batchelor Hall, Riverside CA 92521
  • | 2 University of California, 669 County Square Drive, Suite 100, Ventura, CA 93003
  • | 3 U.S. Horticultural Laboratory, U.S. Department of Agriculture, Agricultural Research Service, 2001 S. Rock Road, Ft. Pierce, FL 34945

Release characteristics of four types of controlled-release fertilizers (Osmocote, Nutricote, Polyon, and Multicote) were studied during a 47-week simulated plant production cycle. The 2.4-L containers containing a low-fertility, acid-based substrate were placed in an unheated greenhouse and subjected to environmental conditions often used for production of azaleas and camellias. Leachate from containers was collected weekly and monitored for pH, electrical conductivity, and concentrations of NH4+ N, NO3N, total P and total K. Leachate concentrations of all nutrients were relatively high during the first 10 to 20 weeks of the study, and then gradually decreased during the remaining portion of the experiment. Differences were observed among fertilizer types, with Multicote often resulting in higher concentrations of N, P, and K in leachates compared to the leachates from the other fertilizer types during the first half of the study. Concentrations of NO3 and P from all fertilizer types were often above permissible levels as cited in the federal Clean Water Act.

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