Nitrogen Release Patterns From Controlled-Release Fertilizers Under the Growing Conditions of Southwest Florida.

            Controlled-release fertilizers (CRFs) are recognized as one of the main nutrient BMPs for vegetable crops grown with seepage irrigation. Potential benefits of controlled-release nitrogen fertilizers compared to conventional fertilizers include increase fertilizer efficiency, and reduce N loss to the environment. Two field experiments were conducted in spring seasons of 2006 and 2007 at University of Florid at Immokalee, FL. Six different N sources were applied in spring of 2006 and four different sources were applied in 2007 in a completely randomized design replicated four times. Treatments were tested under field conditions using plastic mulched raised beds, and seepage irrigation according to typical production practices except no plants were grown. Soil samples were collected weekly directly under the fertilizer band and at the center of the bed at three different depths (0-10, 10-20 and 20-30 cm). Soil samples were analyzed for NH₄-N and NO₃-N concentrations. The goal of the study was to determine which products exhibit suitable N release rates under seepage irrigation conditions for further evaluation. Objectives of the study were: 1) to determine the release pattern of N from sources under the growing conditions of south Florida 2) to understand the feasibility of controlled-release nitrogen fertilizers for use in commercial production. Data indicated that there was a decrease in both NH₄-N and NO₃-N from soluble N fertilizers in the top soil layer while there was increase in NO₃-N from soluble N in the 10-20 cm soil depth which indicates movement of NO₃-N. In general, for the CRFs N sources there were two peaks of N release at weeks 2 and 7 after fertilizer application. More NH₄-N was found in the top soil layer than NO₃-N. The extended release time for N from CRFs fertilizers can enhance the use efficiency of the fertilizers and reduce the potential leaching losses.