CROP SCIENCE, VOL. 53, MAY– JUNE 2013 WWW.CROPS.ORG 1179 RESEARCH P lant–soil ecosystems are described as either open or closed with regards to nutrient recycling and retention. Most are open with regards to N fertilizer inputs, with losses occurring via water movement (leaching and runof) and as a gas (volatilization and denitrifcation). Due to the vast acreage planted to tur fgrasses (Emmons, 2008) and their high profle in urban environments, considerable public concern and scrutiny have focused on NO 3 - leaching and water pollution from turfgrass fertilizers (Baier and Rykbost, 1976; DeRoo, 1979; Flipse et al., 1984; Geron et al., 1993; Petrovic, 1990; Trenholm et al., 2012). While most studies have found relatively low potential for NO 3 - leaching (Cohen et al., 1999; Duf et al., 1997; Erickson et al., 2001; Gold et al., 1990; Kunimatsu et al., 1999; Lee et al., 2003; Pannkuk et al., 2011), some report higher concentrations and amounts, resulting from heavy irrigation (Brown et al., 1977; Modsdell and Schmidt, 1985; Morton et al., 1988; Roy et al., 2000; Snyder et al., 1984; Starr and DeRoo, 1981), heavy fertilization (Brown et al., 1982; Mangiafco and Guillard, 2007; Petrovic et al., 1986; Rieke and Ellis, 1974; Sheard et al., 1985; Snyder et al., 1981), sandy soil (Brown et al., 1982; Petrovic, 1990; Rieke and Ellis, 1974), and age of the turf (Frank et al., 2006; Petrovic, 1990; Porter et al., 1980). Unlike many traditional row crops, established turfgrass systems, particularly when young, are remarkably efcient at Nitrate Uptake Rates of Kentucky Bluegrass Genotypes and Their Efect on Nitrate Absorption under Competitive Conditions Chenxi Zhang, Thomas W. Rufty, Grady L. Miller, and Daniel C. Bowman* ABSTRACT Nitrate leaching from turfgrasses continues to be a concern. It is proposed that selecting turfgrass genotypes with higher NO 3 - absorption abilities could reduce NO 3 - leaching. This study examined the intraspecifc difference in NO 3 - absorption among Kentucky bluegrass (Poa pratensis L.) genotypes and how such a difference affects N absorption when roots are in competition for soil N. A nutrient solution screening procedure was used to identify Kentucky bluegrass genotypes having high vs. low NO 3 - uptake capacity. Tillers of 60 Kentucky bluegrass cultivars were rooted and transferred to a continuous fow solution culture system. After establishment, plants were treated to develop moderate N defciency. Isotopically labeled ( 15 N) KNO 3 was introduced at high (1 mM) and low (0.05 mM) concentrations to screen for differences in NO 3 - uptake. After a brief uptake period, plants were harvested, dried, and analyzed for 15 N content to determine N uptake rate. There were signifcant differences among genotypes for uptake rate at both high and low N concentrations. The 60 genotypes exhibited a wide range of uptake rates, with strong correlation between rates at high and low N. The cultivars Julia and Midnight were selected as representing cultivars with effcient and ineffcient NO 3 - uptake, respectively. Julia had NO 3 - uptake rates averaging 56% higher than Midnight. A subsequent lysimeter study examined whether higher NO 3 - uptake capacity would translate into increased N absorption under competitive conditions. Tillers of the two cultivars were planted as a mixed stand in soil or sand column lysimeters. After establishment, 15 N-labeled KNO 3 solution at high (2 or 1mM) and low (0.05mM) concentrations was applied to each column. After an uptake period, individual plants of each cultivar were harvested for 15 N analysis. Results indicated that Julia absorbed 20 to 50% more NO 3 - than Midnight at the high N concentration and 25 to 71% more NO 3 - more than Midnight at the low N concentration. Most differences were statistically signifcant. This indicates that differences in NO 3 - absorption by Kentucky bluegrass identifed in solution culture translate into differences in absorption of soil N. Dep. of Crop Science, North Carolina State Univ., Campus Box 7620, Raleigh, NC 27695. Received 18 Oct. 2012. *Corresponding author (dan_bowman@ncsu.edu). Abbreviations: C m , uptake compensation point; K m , afnity factor; PPFD, photosynthetic photon fux density; PVC, polyvinyl chloride; V max , capacity factor. Published in Crop Sci. 53:1179–1188 (2013). doi: 10.2135/cropsci2012.10.0597 © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA 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. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Published April 16, 2013