1 Te objectives of this research were to evaluate nitrate N (NO 3 –N) leaching and turf response to nitrogen rate (NR) and irrigation regime (IR) in ‘Floratam’ St. Augustinegrass (Stenotaphrum secundatum [Walt.] Kuntze.) and ‘Empire’ zoysiagrass (Zoysia japonica Steud). Te research was conducted in Citra, FL, from 2005 through 2007. Nitrogen (N) was applied at annual rates of 32, 64, 128, and 196 kg ha -1 in 2005, and at 49, 196, 343, or 490 kg ha -1 in 2006 and 2007. Irrigation treatments consisted of 1.3 cm applied twice weekly or 2.6 cm applied once weekly. In general, NO 3 –N leaching was greater from zoysiagrass. In 2007, annual NO 3 –N leached varied due to the interaction of NR, IR, and grass. Tere was little association between NR and increased NO 3 –N leaching in St. Augustinegrass in any year. While St. Augustinegrass had no diferences in NO 3 –N leached within NR due to IR, there were some diferences in NO 3 –N leached from zoysiagrass at some N levels, with greater NO 3 –N leached from the more frequent irrigation regime. Turf quality (TQ) was generally above an acceptable level in St. Augustinegrass at all but the lowest NRs and at all NRs in zoysiagrass with the exception of the spring fertilizer cycle (SFC) in 2007, when high NR treatments resulted in disease. Maintenance of a healthy turfgrass cover is an important strategy for reducing potential nutrient movement from fertilizer application. Te current recommended rates for St. Augustinegrass provide good turf cover and health, and result in minimal NO 3 –N leaching. Zoysiagrass N rates may need to be revised downward to reduce disease, improve turf cover, and reduce NO 3 –N leaching. Nitrate Leaching and Turf Quality in Established ‘Floratam’ St. Augustinegrass and ‘Empire’ Zoysiagrass Laurie E. Trenholm,* J. Bryan Unruh, and Jerry B. Sartain W ith increasing urbanization, there are concerns that urban turf fertilization may contribute to nonpoint-source pollution of ground and surface waters. To this end, there are some who support a cessation of or placement of severe restrictions on turf fertilization, although numerous research reports have clearly documented that many factors can infuence N leaching from turf areas. Tese factors include N application rate (Brown et al., 1977; Shuman, 2001; Easton and Petrovic, 2004; Frank et al., 2006), N source (Geron et al., 1993; Easton and Petrovic, 2004), irrigation management (Starrett et al., 1995; Morton et al., 1998), maturity of the grass (Frank et al., 2006), and root architecture (Bowman et al., 1998; Bowman et al., 2002). Frank et al. (2006) observed a range of 0 to 0.08 kg ha -1 labeled fertilizer N in leachate from established Kentucky bluegrass (Poa pratensis L.) that received urea N at 98 kg ha -1 annually compared with 0.01 to 0.73 kg N ha -1 leached from turf fertilized with 245 kg urea N ha -1 annually. Te authors concluded that the 2 yr of research indicated that application of the low NR provided minimal potential for groundwater pollution, but that the high rate, particularly when applied as a single application, water soluble N source, may result in nitrate N (NO 3 –N) levels in excess of the USEPA safe levels of 10 mg NO 3 –N L -1 . Te authors cited a need for subsequent years of research to verify these fndings. Morton et al. (1988) reported greatest annual fow-weighted NO 3 –N concentration (4.02 mg L -1 ) in a mixture of Kentucky bluegrass and red fescue (Festuca rubra L.) that received high N (244 kg ha -1 yr -1 ) and excessive irrigation (3.75 cm wk -1 , regardless of rainfall). Annual N losses for this treatment totaled 32 kg inorganic-N ha -1 . Te authors concluded that inorganic N leaching losses from appropriate home lawn care practices would not contribute to groundwater contamination, but that care should be used when fertilizing lawns in coastal watersheds. Easton and Petrovic (2004) reported greater NO 3 –N leaching losses from a mixture of Kentucky bluegrass and perennial ryegrass (Lolium perenne L.) treated with soluble urea than from an untreated L.E. Trenholm, Dep. of Environmental Horticulture, Univ. of Florida, PO Box 110670, Gainesville, FL 32611; J.B. Unruh, West Florida Research and Education Center, 4253 Experiment Dr., Jay, FL 32565; J.B. Sartain, Dep. of Soil and Water Sci., Univ. of Florida, PO Box 110510, Gainesville, FL 32611. Assigned to Associate Editor Pamela Rice. Abbreviations: ESFC, early summer fertilizer cycle; ET, evapotranspiration; FFC, fall fertilizer cycle; HDPE, high-density polyethylene; IR, Irrigation regime; IR1, applied twice weekly; IR2, applied once weekly; LSFC, late summer fertilizer cycle; MDL, minimum detection limit; N, nitrogen; NO 3 –N, nitrate N; NR, nitrogen rate; SFC, spring fertilizer cycle; TQ, turf quality. Copyright © 2012 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. J. Environ. Qual. doi:10.2134/jeq2011.0183 Received 23 May 2011. *Corresponding author (letr@uf.edu). © ASA, CSSA, SSSA 5585 Guilford Rd., Madison, WI 53711 USA Journal of Environmental Quality GROUNDWATER QUALITY TECHNICAL REPORTS