Golf courses and athletic fields typically see intensive use and require specifically-designed fertilization management programs depending on the turfgrass being grown, the season of the year, and their location within the state. Because of the diversity among turfgrass species, cultivars, soil types, climatic patterns, the intensity of utilization, and the physiological attitudes of turfgrass managers, interpretative soil test information, and subsequent recommendations have not been heavily utilized in the past. But due to economic and environmental reasons, recently more attention has been directed to best management practices for turfgrass management. These best management practices involve the use of soil test information in the formulation of turfgrass fertilization programs. Therefore, the following fertilization recommendations for nitrogen (N), phosphorus (P), potassium (K), and magnesium (Mg) were developed based on the best current soil and turfgrass nutrition research information available.
Because the UF/IFAS Extension Soil Testing Laboratory does not analyze for nitrogen, N fertilization recommendations were based on the turfgrass nutritional requirements. It is recognized that the level of required N will vary based on an array of factors, not the least of them being intensity of play and the turfgrass cultivar being used. Therefore, these N recommendations should serve as guidelines to be adjusted based on the turfgrass manager's experience.
Due to potential negative environmental impacts from over-fertilization, phosphorus fertilization should be based on soil test recommendations. It is typical for mature golf course greens to test high in Mehlich III extractable P; in which case, P fertilization on bermudagrass greens is not recommended. Research has shown that cool-season (overseeded) grasses respond more to P fertilization than warm-season grasses. Therefore, if overseeding is part of an annual maintenance program, it is best to apply P to the cool-season turfgrass when soil tests indicate that P is required.
Potassium is highly mobile in most Florida soils. Therefore, it is common to observe low Mehlich III exchangeable K levels in Florida's sandy soils. As a consequence, many turfgrass managers routinely apply K not based on soil test recommendations. Research has shown that there is a critical minimum Mehlich III soil test level at which a response to K fertilization will be obtained. Therefore, quality turfgrass can be maintained based on soil test recommendations. Deposition of clippings, water, and stress management also influence the turfgrass requirement for K fertilization and should be factored into the overall K fertilization program.
Mehlich III exchangeable Mg level has been shown to directly influence turfgrass growth. When the Mehlich III soil test Mg level drops below 20 ppm, a response to Mg fertilization is anticipated. Nutrient applicators should apply Mg based upon the amount of Mg recommended rather than based upon the ratio of Mg to other cations, such as calcium. The 'balanced cation' approach (otherwise known as 'base saturation') has been proven to be inaccurate and often results in unnecessary nutrient applications (Kopittke and Menzies 2007; Sartain 1993). Apply Mg as either dolomitic lime when the soil pH is low and liming is required, or as magnesium sulfate when the pH is in the desired range.
The recommendations in Table 1 are based on Mehlich III extractable levels of P, K, and Mg. These recommendations are for bermudagrass and overseed cool-season grasses.
References
Kopittke, P.M. and N.W. Menzies. 2007. "A review of the use of the basic cation saturation ratio and the 'ideal' soil". Soil Sci. Soc. Am. J. 71: 259–265. https://doi.org/10.2136/sssaj2006.0186.
Sartain, J.B. 1993. "Interrelationships among Turfgrasses, Clipping Recycling, Thatch, and Applied Calcium, Magnesium, and Potassium". Agron. J. 85: 40–43. https://doi.org/10.2134/agronj1993.00021962008500010008x