Luther C. Carson1, Monica Ozores-Hampton1 and Kelly T. Morgan2, (1)Horticultural Sciences, University of Florida, Immokalee, FL (2)Soil and Water Science Department, University of Florida, Immokalee, FL
Controlled-release fertilizers (CRFs) are soluble fertilizers encapsulated in sulfur, polymer, or a sulfur covered fertilizer coated with a polymer. Manufactures measure CRF nutrient release duration as 75% nitrogen (N) release at 75°F. Increases or decreases in temperature increases or decreases CRF N release; thus, coated fertilizer may release more rapidly than expected during the fall season when soil temperatures in polyethylene mulched tomato production can reach 104°F. The purpose of this study was to evaluate N release rates of CRFs under polyethylene mulch tomato production in south Florida during the fall season. Fiberglass mesh pouches (5 × 5.5 inches) containing CRFs [Environmentally Smart N (ESN/44N-0P-0K), 90 day release (DR); Duration-urea (43N-0P-0K/D120U) and Duration-NPK (19N-2.6P-10.8K /D120NPK), 120 DR; and Duration-urea (43N-0P-0K/D180U), 180 DR] from Agrium Advanced Technologies Inc. were buried 4 inches below the bed surface in a tomato crop grown using commercial production practices. A data logger collected soil temperature 4 inches below the bed surface. Pouches were collected and N content was measured eight times through the fall season. A nonlinear regression model was fit to the data to determine N release rate. Average, maximum, and minimum soil temperatures were 78.9, 104.2, and 61.2°F during the season. Environmentally Smart N had the greatest release rate compared to D120U, D120NPK, and D180U, which were not different. Nonlinear regression fit all CRF’s N release (R2≥ 0.94). Season total N release for ESN, D120U, D120NPK, and D180U was 93.8%, 91.1%, 90.2%, and 91.5%, respectively. The 75% CRF N release for ESN, D120U, D120NPK, and D180U was 41, 56, 57, and 59 days after placement, respectively. Nitrogen release from all CRFs was faster than expected due to high fall bed temperatures. Therefore, based one year study a CRF with 180 DR or higher should be recommended for the fall season.