Agroclimatology Agronomy Journal  Volume 101, Issue 1  2009 193 Published in Agron. J. 101:193–200 (2009). doi:10.2134/agronj2007.0393 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. S weet corn is a warm-weather crop that is grown in most of the United States. In 2004, Florida, California, New York, and Georgia were the leading fresh-market producers, contribut- ing to 21, 19, 12, and 11% of the total production, respectively. Te southeastern USA is the most important sweet corn producer for the winter season fresh market (USDA-ERS, 2005). With the advance of the season, the production moves to the northeastern states, mainly due to changes in local weather conditions. Sweet corn is planted in a wide planting date window to allow for a regu- lar supply to the fresh market (Tracy, 2001). As a result, the crop is exposed to major weather risks, including low temperatures during early planting and drought for all planting dates. Changes in the planting date modify the radiative and thermal conditions during the growing season (Cirilo and Andrade, 1994) due to the normal variation of the weather conditions throughout the year. Tis ultimately impacts the time required to reach maturity due to the variation in air and soil temperatures (Kwabiah, 2004). Local environmental factors play a large role in good crop estab- lishment. For instance, a combination of a warm soil temperature (20–30°C), soil moisture at or above feld capacity, and a soil aggre- gate distribution with a geometric mean diameter between 1.0 and 6.8 mm, has been reported as favorable for rapid maize emergence (Schneider and Gupta, 1985). On the other hand, a combination of a low soil temperature (<12.5°C) and high soil water content can cause poor maize stand establishment (Dwyer et al., 2000). Field studies have demonstrated that the diurnal growth rates of maize (Benoit et al., 1990; Cirilo and Andrade, 1994) and sweet corn (Williams and Lindquist, 2007) are infuenced signifcantly by daily maximum and minimum air temperatures. As a strategy for the crop to use the entire growing season, Lauer et al. (1999) recommend for the northern U.S. Corn Belt to plant full-season hybrids early. Such a strategy could allow for the crop to reach physiological maturity before growth stops due to frost. However, the intraseasonal weather varia- tion could cause a delay in planting, which would reduce the number of potential growing days. Producers, therefore, might consider using short-season hybrids (Soler et al., 2007). Because of their fast leaf appearance, short-season hybrids could provide an early canopy closure and better seasonal light interception (Begna et al., 2001). Short-season hybrids might also be pre- ferred if an early harvest is desired (Howell et al., 1998). ABSTRACT Sweet corn (Zea mays L. var. rugosa) is a warm-weather crop that is grown in most of the United States. Normally, it is planted over an extended planting window to provide a continuous supply for the fresh market. However, this planting window exposes the crop to various stresses and weather risks. Te objective of this study was to determine the efect of planting date on early growth of sweet corn with di ferent maturities for di ferent environmental conditions in Georgia, USA. Tree yellow sweet corn genotypes, including a full homozygous sugar enhanced (se), a super sweet (sh2), and a standard or normal (su), were compared in 2004, 2005, and 2006 in two locations in Georgia. Te experiment consisted of one planting date in 2004, six in 2005, and four planting dates under two water regimes in 2006. Plant growth variables that were measured included leaf area index (LAI), canopy height, and aboveground biomass from emergence to the beginning of tasseling. Te growth rate as a function of thermal time (TT) was used to determine the impact of planting date on growth of sweet corn. A base temperature (T b ) of 6.6°C for the three genotypes, obtained from experimental data, was used. Days to emergence varied from 4 to 12 for the warmest and coolest growing seasons, respectively. Te growth of the three sweet corn genotypes showed a clear response to planting dates as LAI, canopy height, and aboveground biomass and the individual plant components, including stem, sheath, and leaves were signif- cantly (P < 0.05) diferent at the beginning of tasseling. For all experiments, the longer the maturity group, the higher the total aboveground biomass. Signifcant di ferences (P < 0.05) for growth rate were found between planting dates, genotypes, plant components and their interactions. Te short-season hybrid tended to have a faster overall plant growth rate of all individual plant components during the warmer seasons. In contrast, the mid- and full-season hybrids tended to have a higher growth rate during the cooler seasons. For rainfed conditions, the short-season hybrid had higher leaf and sheath growth rates than the mid- and full-season hybrids, resulting in a higher stem growth rate. Tese results indicate that the efect of planting date on early growth of sweet corn is of signifcance, as it may lead to identifcation of an optimum planting window for this crop. Dep. of Biological and Agricultural Engineering, Te Univ. of Georgia, 1109 Experiment St., Grifn, GA 30223-1797. Received 10 Dec. 2007. *Corresponding author (axelg2@uga.edu). Abbreviations: BRF, Bledsoe Research Farm; LAI, leaf area index; se, sugar enhanced; SIRP, C.M. Stripling Irrigation Research Park; sh2, super sweet; su, standard; T b , base temperature; TT, thermal time. Impact of Planting Date and Hybrid on Early Growth of Sweet Corn Axel Garcia y Garcia,* Larry C. Guerra, and Gerrit Hoogenboom Published January, 2009