Correlating Field, Greenhouse, and Laboratory Measurements of Nitrogen Release By Controlled-Release Fertilizers.

Turfgrass managers often apply controlled-release fertilizers (CRFs) to deliver sufficient nitrogen (N) to the turfgrass stand while minimizing N losses via volatilization, surface runoff, and/or leaching. In order to determine the longevity of a CRF, N release curves are often generated in controlled laboratory conditions in a water dissolution test; at present, however, there is a lack of research correlating data collected from these experiments with data collected under actual or simulated field conditions. Therefore, the objectives of this research were to generate N release curves in field, greenhouse, and laboratory settings and to correlate N release rates across multiple methods and environments. Nitrogen release was evaluated on four polymer-coated sulfur-coated CRFs with an estimated N release timing of 45, 90, and 120d. Five studies were completed from 2016 to 2017. A field study was conducted from 29 June 2016 to 29 April 2017 on a stand of perennial ryegrass (Lolium perenne L.). Two greenhouse studies were conducted on Kentucky bluegrass (Poa pratensis L.) and bermudagrass (Cynodon dactylon L.). For Kentucky bluegrass, temperatures were set to a day/night of 24/18^oC. For bermudagrass, temperatures were set to a day/night of 32/27^oC. Two water dissolution tests were conducted at a constant room (18^oC) and elevated (60^oC) temperature with continuous agitation at 100rpm. For both field and greenhouse studies, prills were placed in a mesh bag at a rate of 1 g per bag and incorporated into the turf canopy.