Nitrate leaching from soluble nitrogen applied to ‘Floratam’ St. Augustinegrass and common centipedegrass during dormancy

Fertilizer bans in Florida prevent turf managers from applying nitrogen (N) fertilizers during periods of active turf growth and may encourage fertilization in fall and winter. Nutrient applications during fall or winter may pose an increased risk to nitrate N (NO₃-N) leaching. A 3-yr field lysimeter study was conducted in Jay, FL, to determine the effect of N rates on NO₃-N leaching from ‘Floratam’ St. Augustinegrass (SA) [Stenotaphrum secundatum (Walter) Kuntze] and common centipedegrass (CE) [Eremochloa ophiuroides (Munro) Hack.] during turfgrass dormancy. Treatments consisted of urea applied as a foliar spray every 45 d beginning in October at rates of 0.0, 6.0, 12.5, 24.0, or 49.0 kg N ha^-1. Leachate was collected weekly and analyzed for NO₃-N. Elevated NO₃-N levels were observed for 105 d after initiation (DAI). No differences in NO₃-N leached were detected among N rates until the late winter cycle of 2008 when rainfall exceeded historic levels by 268 mm. The 49.0 kg N ha^-1 treatment resulted in more NO₃-N leached than untreated turf during 2008, with 12.5 and 1.3 kg NO₃-N ha^-1 leached, respectively. These findings suggest that N rates ≤24.0 kg ha^-1 applied to dormant or semidormant warm-season turf do not pose an increased threat of NO₃-N leaching even when rainfall is excessive. Soluble N rates >24.0 kg ha^-1 should be avoided during dormancy when excessive rainfall is imminent. The benefits, if any, need to be investigated further before fertilization of dormant warm-season turf is recommended.