Nitrogen rate required for acceptable St. Augustinegrass and associated nitrate leaching

The recommended N rates for St. Augustinegrass (Stenotaphrum secundatum [Walt.] Kuntze.) vary in Florida. This research, conducted in Fort Lauderdale, Citra, and Jay, FL, (2006– 2008), aimed to determine the minimum N rate necessary for acceptable St. Augustinegrass and to determine the influence of N and irrigation rate on NO₃–N leaching. Urea was applied in Fort Lauderdale, Citra, and Jay at 98, 196, 294, and 588; 49, 196, 343, and 490; and 49, 98, 196, and 294 kg N ha^-1 yr^-1, respectively, based on best management practices. Irrigation was 2.5 mm d^–1 and 13.0 mm three times weekly in Fort Lauderdale; 13 mm twice weekly and 26 mm wk^–1 in Citra and Jay. In Fort Lauderdale and Jay, lower than recommended N rates mostly produced acceptable turfgrass. Applications of 196 kg N ha^-1 (Fort Lauderdale) and 98 kg N ha^-1 (Jay) were the lowest rates producing acceptable turf. In Citra, 65% more N was required for acceptable turf than the recommended minimum . Leaching from all N rates was similar, except when N rates exceeded recommendations or when turfgrass exhibited herbicide stress. The high irrigation rate doubled NO₃–N leaching compared to the low rate in Fort Lauderdale; irrigation frequency had no influence on leaching in Citra or Jay. The predicted minimum N rate for acceptable turf in Fort Lauderdale was <98 kg N ha^-1 yr^-1 (lower than in Citra; more than in Jay). In stressed turf, additional N conferred little benefit to quality and increased leaching.