Determining Nitrogen Fertilizer Cost Using Turfgrass Response

Numerous nitrogen (N) sources are used in turfgrass management and vary from soluble to slow-release. Determining the least expensive N source can be confusing for consumers. Price per ton and price per pound N are common price comparison methods. An improved approach could use longevity of the N source to balance the price. The objective of this study was to determine the longevity of turfgrass response to N sources and to determine the cost to achieve such responses. This study was conducted in Ft. Lauderdale and Jay, FL, from 1 Jan. to 31 Dec. 2018 on ‘Riley’s Super Sport’ (Celebration®) bermudagrass (Cynodon dactylon). Treatments included nontreated turfgrass, urea, ammonium sulfate, stabilized urea, methylene urea, ureaformaldehyde, two natural organics, sulfur-coated urea, and two polymer-coated urea fertilizers. Treatments were arranged in a split-plot design with N sources as whole plots and N rate (N applied at 49 and 98 kg·ha−1 every 4 months) as subplots. Turf quality was recorded on a scale of 1 to 9, where 1 = dead/brown turf and quality, 6 = minimal acceptable, and 9 = optimal healthy/green turf. Turf quality ratings were recorded weekly and used to determine response longevity (days quality ≥6.0) and area under the turfgrass response curve (AUTRC). Urea resulted in response longevity greater than or equal to other N sources during each season except when applied at 98 kg·ha−1 of N during the fall fertilizer cycle in Jay. Natural organics were ≈6-fold more expensive than urea in Jay and Ft. Lauderdale using turfgrass response longevity and AUTRC. Urea and sulfur-coated urea were the least expensive soluble and slow-release N source, respectively, using dollars per pound N, dollars per acre per day, and dollars per acre per quality-day during each fertilizer cycle and annual average in Jay and Ft. Lauderdale. No evidence was found supporting the use of turfgrass response as a more effective method of determining fertilizer cost than dollars per pound N.