Evaluation of Nitrogen Management Strategies On Nitrate Leaching and Quality of St. Augustinegrass Turf.

Nitrogen (N) application is very important to maintain the aesthetic quality of turf. However, the frequent arguments about the possible chances of water pollution through nitrate-nitrogen (NO₃-N) leaching have focused attention on N application in turf. This research was conducted at Citra, Florida to determine an environmentally friendly approach to N management in St. Augustinegrass. Ten fertilizer treatments comprised of different N sources (soluble and controlled release), timing (with and without summer application) and doses (0, 146, 195, and 244 kg^.ha^-1) were laid out in randomized block design with four replications. Drainage lysimeters (57 cm diameter) were installed below the turf to collect leachates which were analyzed for NO₃-N. NO₃-N concentration and NO₃-N load of the leachate were low in relation to the fertilizer applied. The nitrate-N concentration of the leachate was always less than 0.3 mg/L irrespective of the season and amount of fertilizer applied. The annual cumulative NO₃-N leached was (0.319 kgha^-1N) for CRF applied @195 kg^.ha^-1 and this mean was not significantly different from the means with other treatments. This result indicates that NO₃-N leaching from the St. Augustinegrass is minimal (<0.2% of fertilizer applied), even at a high rate of fertilizer (244 kgha^-1). The quality (rating of color from 1 to 9) of the grass is highly correlated (0.97) with the amount of fertilizer applied. The no-fertilizer (control) treatment had a quality value (4.7), lower than the minimal acceptable value (6.0) whereas the rest of the treatments resulted in significantly higher quality than the control and also above the minimal limit. CRF fertilizers applied at higher dose (244 kgha^-1) resulted in highest quality value (7.39) with annual nitrate leaching load equivalent to control treatment. Thus the results indicate that fertilization is necessary to maintain the quality of the grass and rate of fertilization was not associated with increased NO₃-N leaching if the N was applied to healthy turfgrass.