Evaluation of Nitrogen Release Patterns From Controlled-Release Fertilizers Under Seepage Irrigation.

Potential benefits of controlled-release nitrogen fertilizers compared to conventional fertilizers include increase fertilizer use efficiency, and reduce N loss to the environment. Two field experiments were conducted in spring seasons of 2006 and 2007 at University of Florida at Immokalee, FL. Four different  N sources were applied in two bands on soil beds covered with plastic mulch or distributed in the bed in a completely randomized design replicated four times. Treatments were tested without plants under field conditions according to typical production practices. Soil samples were collected weekly 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 the feasibility of controlled-release nitrogen fertilizers use in commercial production. Objectives of the study were: 1) to verify the release pattern of N from sources under the growing conditions 2) to find out which products exhibit suitable N release rates under seepage irrigation conditions. For soil samples taken under the fertilizer band, 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 in the 10-20 cm soil depth which indicates movement of NO₃-N. For soil samples taken from the bed center, data indicated that there was an increase in both NH₄-N and NO₃-N from CRFs N fertilizers compared to soluble fertilizers. 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.