Nitrate Leaching From Warm-Season Turfgrass in the Winter Months.

There are increasing fertilizer regulations restricting timing of lawn fertilizations in Florida. As a result of this, fertilization in many areas is primarily restricted to fall, winter, or spring months, when the grass may not be actively growing. The objectives of this research were to evaluate differences in nitrate-N (NO₃–N) mass flux and turfgrass quality from application of nitrogen at different rates throughout the winter months and to look at differences in NO₃–N mass flux due to month of application. The research was conducted in Citra, FL from 2006-2009. Nitrogen (N) was applied monthly throughout the winter as soluble urea (46-0-0) at 0, 6.1, 12.2, 24.5, 49.0, or 98.0 kg N ha^-1 to ‘Floratam’ St. Augustinegrass (Stenotaphrum secundatum [Walt.] Kuntze.) and ‘UltimateFlora^®’ zoysiagrass (Zoysia japonica Steud). There were differences in yrs 1 and 3 in cumulative NO₃–N leached due to interactions of grass × N rate. St. Augustinegrass tended to have higher leaching only at the highest N rates, while zoysiagrass leaching increased as N rate increased. Where differences existed due to grass, leaching was greater from zoysiagrass. There were also significant month × grass × N rate interactions. With the exception of the first year when grasses had recently been sodded, greatest leaching typically occurred in the winter and spring months prior to spring green-up rather than in the fall months. Turf quality (TQ) and color (TC) were generally below an acceptable score of 6 for all months in all years, although St. Augustinegrass at highest N rates had some color scores at or just above acceptable. Due to increased potential for NO₃–N leaching and little or no improvement to TQ and TC, it is not recommended that lawn grasses be fertilized throughout the winter months, even if fertilization restrictions limit N application during times of active growth.