Can Growth Potential Models be Used for Planning Turf Fertilization in Florida?.

Concern about non-point source pollution and impairment of surface and ground water is common place throughout the United States.  In Florida, measures to mitigate these pollutants are promulgated and enforced at the local municipality or county level. Florida’s commercial fertilizer applicators must now follow Best Management Practices (BMPs) for the Green Industries in Florida and possess a state fertilizer license issued by Florida Department of Agriculture and Consumer Services.  However, more restrictive local ordinances which exceed the BMPs continue to be implemented throughout Florida – many of which are not based on sound science. Growth Potential (GP) models are being developed to predict turfgrass growth at specified temperatures and then assigning a numerical value to that prediction. The GP value can then be linked to nutrient demands of turf and the predicted amount of nutrient that a grass will use during a specific period of time can be determined. In an effort to refine fertilization practices across Florida, GP was calculated for various Florida cities across the climatically diverse state. One outcome resulting from the GP modelling is a proposed rule change in Florida fertilizer labeling laws allowing for higher rates of slow release nitrogen on a per application basis.  Florida law currently restricts the use of slow release fertilizer to rates ≤ 49 kg N ha^-1. The GP model coupled with nutrient fate research demonstrated that rates ≤ 98 kg N ha^-1 from certain slow release nitrogen sources have limited leaching when applied to healthy turf prior to the peak of GP.