HS903 Controlled-Release Fertilizers for Vegetable Crops Grown in Florida in the BMP Era1 Eric Simonne and George Hochmuth2 1. This document is HS903, one of a series of the Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Publication date: January 2003. Please visit the EDIS Web site at http://edis.ifas.ufl.edu. 2. Eric Simonne, assistant professor, George Hochmuth, center director, NFREC-Quincy, Horticultural Sciences Department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611. The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office. Florida Cooperative Extension Service/Institute of Food and Agricultural Sciences/University of Florida/Christine Taylor Waddill, Dean. This publication is one of a series entitled Fertilizer and Irrigation Management in the BMP Era. This series is divided into nine principles described in the Introduction Chapter (HOS-897). This publication is part of Principle 2, "Soil Test and Follow the Recommendations." BMP implementation requires a global approach to production management. However, for presentation purposes, each aspect of vegetable production is described in a separate publication. Controlled-release fertilizers (CRF) are an alternative to conventional soluble fertilizers where nutrient release into the environment is of concern (especially nitrate nitrogen). In theory, CRFs allow the grower to better synchronize nutrient release with the crops nutritional requirement, thereby reducing the risk of leaching between time of application and plant uptake. Most CRFs are in the granular form (prills), but some liquid formulations are now available. Due to high manufacturing costs, CRFs have been mainly used with high-value ornamental crops. Recently, CRFs have been included in the citrus BMPs for Florida. The renewed interest in CRFs for vegetable production has stimulated on-going research efforts which should increase the amount of available information and grower use. Working Definition Granulated CRFs are sphere-like prills made of a water-soluble fertilizer covered by a degradable coating, which degrades based on soil temperature and/or moisture. The time of release is determined by coating composition and thickness as well as the soil condition (mainly temperature). Planning Things to Do Test the soil for nutrient availability before using CRFs. Know your CRF: grade, form of N once released (urea, ammonium, nitrate) and factors influencing time of release (usually soil temperature). Match the CRF release time with the crop nutrient needs. Consider blending soluble fertilizers and CRFs, and/or several CRFs together to ensure adequate and continuous nutrient supply to the crop.
Controlled-Release Fertilizers for Vegetable Crops Grown in Florida in the BMP Era 2 Match the release temperature with the actual soil temperature for temperature-based release CRFs by using soil temperature records. Incorporate or band CRFs in the soil. Monitor crop nutritional status using leaf analysis, sap testing, or both. Application Things to Do Apply CRFs as other fertilizers would be applied: with a fertilizer spreader for granulated formulations, by banding (knifing-in), or in the irrigation water for liquid formulations. Consider using rates lower than the recommended rate for soluble fertilizers since the same production results may be achieved as the CRFs are slowly released. Extrapolation from other crops suggest that under appropriate release time, 60 to 75 lbs of N from a CRF will have the same effect on the crop as the 100 lbs of N from a soluble fertilizer (urea, ammonium nitrate, 10-10-10). Things to Avoid: Potential Pitfalls Do not exceed the soil test-based recommended rate. Do not place CRFs on the soil surface. Other Considerations CRFs with a 1:1:1 ratio provide equal amounts of N, P2O5 and K2O. The application rate of a 1:1:1 fertilizer should be made based on the element (among N, P and K) that is the least required according to soil test results otherwise, excessive application rates will occur. Most coatings and technology of CRF manufacturing are proprietary. Hence, users must rely on and follow the product label. The most common materials are sulfur-coated urea (SCU), polymer-coated ureas, isobutylidene diurea (IDBU) and crotonyldiene diurea (CDU). Stay updated on CRF-related issues (formulation, cost, recommendations, and other breakthroughs) as new information is likely to become available in the near future. Plant a cover crop following the cash crop to help trap residual fertilizer. Additional Readings Slow-release Fertilizer, Virginia Coop. Ext., Dept. of Horticulture, Virginia State Univ. http://www.ext.vt.edu/departments/envirohort/articles/ misc/slowrels.html Controlled Release Fertilizer-properties and Utilization, S. Shoji (Ed.), 1999, Konno Printing Co., Sendai, Japan.