Agronomy Journal • Volume 103, Issue 6 • 2011 1827 Biofuels Planting Date Affects Biomass and Brix of Sweet Sorghum Grown for Biofuel across Florida J. E. Erickson,* Z. R. Helsel, K. R. Woodard, J. M. B. Vendramini, Y. Wang, L. E. Sollenberger, and R. A. Gilbert Published in Agron. J. 103:1827–1833 (2011) Posted online 29 Sept 2011 doi:10.2134/agronj2011.0176 Copyright © 2011 by the American Society of Agronomy, 5585 Guilford 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. S orghum is a unique C 4 grass in that it is capable of high biomass, grain, and sugar yields (Rooney et al., 2007; Zhao et al., 2009). hus, it has received considerable attention in recent years for use as a biofuel crop (Amaducci et al., 2004; Gof et al., 2010). Sweet sorghum, in particular, ofers potential advantages over other candidate biofuel crops because it stores readily fermentable sugars in the stalk that can be converted to liquid fuels and bio-based products with current technologies. It is also an annual crop that can be integrated into existing crop rotations, and it is readily established from seed. More- over, it does not have to compete directly with food or feed. Despite these potentially attractive features, relatively little is known about the production of sweet sorghum for bioenergy use in the southeastern United States, as it has traditionally been grown on limited acreage primarily for syrup production in the transition area of Kentucky and Tennessee. hus, there is a need for a better understanding of the yield potential of cur- rently available, commercial sweet sorghum cultivars, especially with regard to ratoon crop yields for sweet sorghum production at low latitudes in the United States. Sweet sorghum biomass yields have been variable within and across studies due to cultivar, environment and management practices. Wortmann et al. (2010) reported dry stalk yields from 8 to 48 Mg ha –1 across a range of N fertilization rates, three cultivars, and multiple plant populations in Nebraska. Soileau and Bradford (1985) reported dry biomass yields rang- ing from 6 to 18 Mg ha –1 across a range of fertilization and liming treatments in northern Alabama. Similarly, Tamang et al. (2011) reported total dry matter yields of 9 to 18 Mg ha –1 for ‘Della’ and M-81E sweet sorghum cultivars across a range of N fertilization rates in the Southern High Plains. Miller and Ottman (2010) reported no efect of irrigation frequencies on M-81E sweet sorghum dry matter yields, which ranged from 20 to 31 Mg ha –1 in the southwestern United States. Although sweet sorghum biomass yield data are abundant for some growing regions, estimation of commercial-scale etha- nol yields from sweet sorghum is complicated by not always knowing the fraction of total soluble solids (brix) that are fer- mentable sugars and the sugar recovery eiciency during mill- ing. Miller and Ottman (2010) measured juice sugars directly with high performance liquid chromatography (HPLC) and reported an average ethanol yield of 2726 L ha –1 . When total stalk nonstructural sugars were measured directly (i.e., not expressed juice), estimated ethanol yields for M-81E sweet sorghum ranged from 3533 to 5414 L ha –1 (Zhao et al., 2009). Tamang et al. (2011) estimated ethanol yields of 1968 to 2700 L ha –1 from measured brix values for a single crop of two sweet sorghum cultivars over 2 yr without irrigation in Nebraska. hese studies indicated that sweet sorghum ethanol yields from a single crop may be comparable to maize (Wortmann et al., 2010). Moreover, sweet sorghum has been shown to use less water and N than maize for similar ethanol yields (Keeney and DeLuca, 1992; Geng et al., 1989). Although sorghum is better adapted to the southeastern USA than maize (Zea mays L.), use of sweet sorghum as a ABSTRACT Sweet sorghum [Sorghum bicolor (L.) Moench] is a potential bioenergy crop that is capable of high biomass and sugar yields, but production for biofuel in the Southeast is not well understood. he present study examined the efects of planting date (three dates from mid-March to mid-June) on primary and ratoon crop fresh biomass, brix, and estimated sugar yield of three sweet sorghum cultivars (‘Dale’, ‘Topper 76-6’, and ‘M-81E’) grown at three sites from North (29°24¢ N) to South Florida (26°40¢ N). Across all treatments, primary crop fresh biomass, brix and estimated sugar yields were 70 Mg ha –1 , 148 g kg –1 , and 5.69 Mg ha –1 , respectively. Primary crop yields were greatest for the two earliest planting dates (mid-March to mid-May), and for our southern- most site. he yield potential for ratoon crops was in general only about half as much as the primary crop across all years, sites, and cultivars for the earliest planting date. An exception, however, was ratoon crop yields at the southernmost site, which were in some cases equal to or greater than primary crop yields. Low primary crop brix values were found for all cultivars on the muck soils in South Florida compared to the other two sites, and for M-81E compared to Dale and Topper 76-6. hese low brix values were correlated with greater fresh biomass production. Further research is needed on planting dates for optimizing primary and ratoon crop yields along with varietal development with improved ratoon crop yields. J.E. Erickson, K.R. Woodard and L.E. Sollenberger, Agronomy Dep., Univ. of Florida, Gainesville, FL 32611; Z.R. Helsel, Dep. of Plant Biology and Pathology, Rutgers Univ., New Brunswick, NJ 08901; J.M.B. Vendramini, Range Cattle Research and Education Center, Ona, FL 33865; R.A. Gilbert and Y.Wang, Everglades Research and Education Center, Belle Glade, FL 33430. Received 8 June 2011. *Corresponding author (jerickson@ul.edu). Abbreviations: BG, Belle Glade; CIT, Citra; PD, planting date.