Forages Agronomy Journal  Volume 101, Issue 4  2009 989 Published in Agron. J. 101:989–995 (2009). doi:10.2134/agronj2008.0236x Copyright © 2009 by the American Society of Agronomy, 677 South Segoe Road, Madison, WI 53711. 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. B ahiagrass is the primary pasture grass for beef cattle (Bos spp.) and horses (Equus caballus ) in Florida, and it is grown on more than one million hectares. It produces 85 to 90% of annual herbage yield during April through September (Mis- levy and Everett, 1981; Kalmbacher, 1997). Bahiagrass forage production is reduced when nighttime temperatures are below 15°C (Mislevy, 1985). Diploid bahiagrasses such as Pensacola and Titon 9 generally produce more early- and late-season herbage than tetraploid cultivars like Argentine that initiate growth later in the spring (Chambliss and Adjei, 2006). Commonly used bahiagrass cultivars such as Pensacola and Titon 9 are sensitive to short daylengths, which induces a reduc- tion in aboveground growth during the late summer and autumn (Sinclair et al., 1997). During this time, remaining live herbage continues to photosynthesize, but instead of using photosynthate to produce new aboveground tissue, plants accumulate storage organ mass and store photosynthate as nonstructural carbo- hydrates in stem bases and rhizomes (hornton et al., 2000). his response allows plants to efectively prepare for winter survival and early spring regrowth, periods when photosynthetic production is inadequate to meet growth demand (hornton et al., 2000). Limited bahiagrass herbage accumulation during November through April has occurred even when temperature, soil moisture, and soil fertility were adequate for substantially greater growth, supporting the conclusion that daylength sensi- tivity contributes signiicantly to the lower herbage production observed (Sinclair et al., 1997). Breeding and selection has resulted in development of PCA bahiagrass lines with potential to extend the grazing season and reduce winter feed costs (Blount et al., 2001). Greater produc- tion of the PCA Cycle 4 during November through April has been documented (Blount et al., 2008). Of concern is whether the greater cool-season production of PCA types will afect their long-term persistence and productivity when defoliated. his issue has not been explored with bahiagrass, but for alfalfa (Medicago sativa L.) fall dormancy has oten been used to predict cultivar diferences in winter hardiness (Volenec et al., 2002). here are no known studies evaluating yield and nutritive value responses of PCA bahiagrass breeding lines to defoliation management. Characterization of PCA response to a range of defoliation treatments is needed to assess its itness for use by producers. herefore, the objectives of this study were to determine the efects of harvest frequency and stubble height on total and seasonal DM yield and herbage nutritive value of a PCA bahiagrass breeding line relative to existing cultivars. MATERIALS AND METHODS Experimental Site his ield study was conducted at the University of Florida Beef Research Unit, northeast of Gainesville, FL (29°43´ N, ABSTRACT Bahiagrass (Paspalum notatum Flügge) cultivars are daylength sensitive and have minimal cool-season production. A new bahia- grass breeding line is less daylength sensitive and more cold tolerant, but its dry matter (DM) yield and nutritive value responses to defoliation treatments are unknown. A 3-yr ield experiment studied efects of two stubble heights (4 and 8 cm) and two harvest frequencies (7 and 21 d) on diploids ‘Pensacola’, ‘Titon 9’, and the less photoperiod-sensitive, cold-adapted (PCA) Cycle 4 bahiagrass; and the tetraploids ‘Argentine’ and Titon 7. Stubble height had minimal efect on responses measured. When har- vested every 7 d, Cycle 4 had the lowest and Argentine the greatest yield (8.4 vs. 11.8 Mg DM ha –1 ). When harvested every 21 d, Cycle 4 yield was similar to the other diploids (10.6 Mg DM ha –1 ) and less than the tetraploids (12.6 Mg DM ha –1 ). Cycle 4 yield distribution was similar to other diploids and generally greater in spring but less in summer than the tetraploids. Across defolia- tion treatments, Cycle 4 in vitro digestible organic matter (IVDOM) averaged 546 to 562 g kg –1 and was greater than all entries in 2006 and all but Titon 9 in 2005. hese data indicate that Cycle 4 was less productive than other bahiagrasses when harvested every 7 d during the warm season, as productive as other diploids at 21-d harvest intervals, and slightly more digestible than other currently used bahiagrasses. Inferior yield under frequent harvest may imply less defoliation tolerance, thus persistence of PCA Cycle 4 should be studied further. S.M. Interrante, he Noble Foundation, 2510 Sam Noble Pkwy., Ardmore, OK 73401; L.E. Sollenberger and K. Liu, Agronomy Dep., Univ. of Florida, Gainesville, FL 32611-0500; A.R. Blount, North Florida Research and Education Center, Marianna, FL 32446; U.R. White, Natural Resource Conservation Service, Wauchula, FL 33873; S.W. Coleman, USDA-ARS Subtropical Agricultural Research Station, Brooksville, FL 34601-4672. Received 21 Dec. 2008. *Corresponding author (lesollen@ul.edu). Abbreviations: CP, crude protein; DM, dry matter; IVDOM, in vitro digestible organic matter; PCA, less photoperiod-sensitive, cold-adapted. Defoliation Management of Bahiagrass Germplasm Affects Dry Matter Yield and Herbage Nutritive Value S. M. Interrante, L. E. Sollenberger,* A. R. Blount, U. R. White, K. Liu, and S. W. Coleman