Factors Affecting Nutrient Availability, Placement, Rate, and Application Timing of Controlled-release Fertilizers for Florida Vegetable Production Using Seepage Irrigation

This publication summarizes the factors influencing controlled-release fertilizer (CRF) nutrient release, CRF placement, CRF rate, and CRF application timing for the two major seepage-irrigated vegetable production systems (plasticulture and open-bed) in Florida. One of several best management practices for vegetable production, CRF helps growers achieve total maximum daily loads (TMDLs) established in Florida under the Federal Clean Water Act. Several factors intrinsic to CRF and to the vegetable production systems affect CRF nutrient release, making implementation of CRF fertility programs challenging. Increasing or decreasing soil temperature increases or decreases nutrient release from CRF. Soil Moisture required for uninhibited plant growth is within the soil moisture range for optimum CRF nutrient release. CRF substrate affects nutrient release rate, which is inversely related to coating thickness and granule size. Soil microbes, soil texture, and soil pH do not influence nutrient release rate. Field placement of CRFs in seepage-irrigated, plasticulture, and open-bed production should be in the bottom mix at bed formation and soil incorporated or banded at planting, respectively. In plasticulture production systems, soil fumigation and delayed planting for continuous harvest may add a 14- to 21-day lag period between fertilization and planting, which along with different season lengths will influence CRF release length selected by growers. Using a hybrid fertilizer system in plasticulture production or incorporating CRF at planting in open-bed production allows for up to a 25% reduction in the nitrogen (N) rate needed.