Nitrogen Rate Required for Acceptable St. Augustinegrass and Associated Nitrate Leaching.

Recommended nitrogen (N) rates for St. Augustinegrass vary in Florida depending upon location.  The objectives of this research were to determine the minimum N rate necessary to produce acceptable quality ‘Floratam’ St. Augustinegrass (Stenotaphrum secundatum [Walt.] Kuntze.) and to determine the influence of N rate and irrigation rate on NO₃-N leaching.  This research was conducted in Ft. Lauderdale, Citra, and Jay, FL from 2006 to 2008.  Nitrogen was applied in Ft. Lauderdale, Citra, and Jay at rate of 98, 196, 294, and 588; 49, 196, 343, and 490; and 49, 98, 196, and 294 kg N ha^-1 yr^-1, respectively.  Irrigation treatments  consisted of applying 2.5 mm daily and 13.0 mm three times weekly, in Fort Lauderdale, and 13 mm applied twice weekly and 26 mm applied once weekly in Citra and Jay.  In Ft. Lauderdale and Jay, lower than recommended N rates produced acceptable St. Augustinegrass during most cycles but not all.  The 196 kg N ha^-1 in Ft. Lauderdale and the 98 kg N ha^-1 in Jay were the lowest N rates that produced acceptable turf during each cycle.  In Citra, 60% more N was required than the current recommended minimum to produce acceptable turf.  Nitrate-N leaching from each N rate was similar to the lowest N rate except when N rates exceeded recommended rates or when turf grass exhibited stress.  The high irrigation rate increased NO₃-N leaching by 2-fold compared to the low rate in Ft. Lauderdale, but had no influence on NO₃-N leaching in Citra or Jay.  Current minimum recommended N rates for St. Augustinegrass may be lower than necessary in Citra, more than necessary in Jay, and appropriate in Ft. Lauderdale to produce acceptable turf under normal environmental conditions.  However, when turf was stressed, N rates provided no benefit to turf quality and increased NO₃-N leaching.