Nitrogen Recovery and Loss from Kentucky Bluegrass Fertilized by Conventional or Enhanced-Efficiency Urea Granules

Easy handling and low unit N cost make prilled urea (46-0-0) a popular fertilizer. While incomplete recovery of granular urea applications by turfgrass is documented, field evaluations of NH3 volatilization mitigation by coatings or bioinhibitor efficiency enhancements are limited. Meanwhile, NH3 emissions reduce air quality and contribute to nutrient loading of water resources. Our objectives were to quantify 3- and 6-d ammonia emission and 9-week turfgrass recovery of unincorporated granular fertilizer application to turfgrass. In 2014 and 2015, commercial urea-N fertilizers were broadcast over a mature Kentucky bluegrass (Poa pratensis L. ‘Midnight’) lawn at 43 kg ha−1. Treatments included conventional urea and three enhanced-efficiency fertilizers; a blended fertilizer with 25% of its urea-N supplanted by polymer- and polymer-/sulfur-coated prills, or two stabilized urea fertilizers both amended by N-(n-butyl) thiophosphoric triamide (NBPT) and dicyandiamide (DCD) inhibitors. Using a 51% ‘trapping-efficiency’ flux chamber system under the field conditions described, 23.1 or 33.5% of the conventional urea-N was lost as NH3 over the respective 3- or 6-d period following application. Alternatively, dual amendment by NBPT and DCD resulted in approximately 10.3 or 19.6% NH3-N loss over the respective 3- or 6-d periods, and greater fertilizer-N recovery by the turfgrass over the 9-week experiments