Long-term effects of low N rates on St. Augustinegrass cultivars

Current recommended nitrogen fertilization rates for St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze] in South Florida range from 4 to 6 lb N per 1,000 ft² per yr, applied throughout the year. Nevertheless, strict fertilizer ordinances are being passed by multiple counties in Florida, setting limits to the amount of N that can be applied to turfgrass areas, and establishing summer blackout periods for fertilizer applications; hence, there is a need to identify the minimum N rates to sustain St. Augustinegrass quality. A 4-yr study was conducted at the University of Florida's Fort Lauderdale Research and Education Center to assess the turfgrass quality of four St. Augustinegrass cultivars (‘CitraBlue’, ‘Floratam’, ‘Palmetto’, and ‘Raleigh’) grown on a Hallandale fine sand (siliceous, isohyperthermic Lithic Psammaquents) and fertilized at either 2.5 or 5 lb per 1,000 ft² per yr. Plots were evaluated monthly for visual turfgrass quality, and yearly for genetic color, leaf texture, spring green-up, and summer density. CitraBlue had the highest turfgrass quality, color, and density. Differences were rarely detected among the other three cultivars. Nitrogen rates had an effect only on summer density, suggesting that St. Augustinegrass grown on Hallandale fine sand with 3.4% organic matter in South Florida could be managed with less N than is currently recommended without detrimental effects.