Lack of Hybrid, Seeding, and Nitrogen Rate Interactions for Corn Growth and Yield

Published in Agron. J. 104:945–952 (2012) Posted online 1 May 2012 doi:10.2134/agronj2012.0027 Copyright © 2012 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. C with older corn hybrids, modern hybrids require greater plant densities (Tokatlidis and Koutroubas, 2004; Hammer et al., 2009; Tokatlidis et al., 2011) and N fertilizer (O’Neill et al., 2004) to optimize yield. Accordingly, optimum fi nal plant densities, based on university studies in the 2000s, are now greater than in the 1990s in the northern states of Wisconsin (83,300 plants m–2, Stanger and Lauer, 2006), Iowa (∼90,000 plants m–2, Coulter et al., 2010) and Minnesota (∼80,000 plants m–2, Van Roekel and Coulter, 2011). Recommended fi nal plant densities of 70,000 plants m–2 in New York, based on studies conducted in the early 1990s with seven hybrid releases from the late 1980s or early 1990s (Cox, 1997), have not been adjusted upward because studies conducted during the 2000s showed similar results (Cox and Atkins, 2011). An optimum plant density exists for a specifi c genotype within an environment (Tokatlidis and Koutroubas, 2004; Ciampitti and Vyn, 2011), and environments with greater yield potential require greater plant densities to optimize yield (Paszkiewicz and Butzen, 2007). Th e average yield in New York is consistently lower than average yields in Wisconsin, Minnesota, and Iowa (National Agricultural Statistical Service, 2012), so the lack of response in New York to seeding rates above 75,000 kernels ha–1 and fi nal plant densities of 70,000 plants m–2 on silt loam soils may be related to the yield potential of the environment. On the other hand, seeding rate studies in the 2000s in New York (Cox and Atkins, 2011) were conducted at recommended N rates, which may have limited the response to seeding rates. High plant densities (>80,000 plants m–2) and N rates (>140 kg N ha–1) increase the leaf area index (LAI) of corn during vegetative development and at silking (Cox et al., 1993; Cox and Cherney, 2001), which allows greater radiation interception during the late vegetative period (Westgate et al., 1997) and greater plant growth rates (PGRs) during the critical PGR period of ∼2 wk before to ∼2 wk aft er silking (Tollenaar, 1991). Greater PGR around the silking period results in greater kernel set and grain yield per plant (Andrade et al., 1999; Maddonni and Otegui, 2004; Echarte et al., 2004). Genotypes, however, diff er in their threshold PGR around the silking period for kernel set (Echarte et al., 2004; Echarte and Tollenaar, 2008; Borrás et al., 2007; Severini et al., 2011). Also, most genotypes show a curvilinear response of kernel number per plant to PGR around the silking period (Andrade et al., 2002; Echarte and Tollenaar, 2008), but some genotypes have more linear responses (Gambin and Otegui, 2008; D’Andrea et al., 2008; Severini et al., 2011). Greater PGR around the silking period also results in greater biomass accumulation at the R1 (silking) stage (Ritchie et al., 1993), the milk stage of grain fi ll (R3), and physiological (R6) maturity (Cox and Cherney, 2011; Ciampitti and Vyn, 2011), which can promote higher grain yield (Ciampitti and Vyn, 2011). Too high a plant density, however, results in an excessive LAI, which can reduce grain yield in environments where water is a limiting factor (Shanahan et al., 2004). In addition, too high a plant density in favorable environments can increase crowding stress and greatly reduce the PGR around the critical silking period, resulting in kernel abortion or barren plants (Tollenaar et al., 1992, Andrade et al., 1999), which greatly reduces kernel number and grain yield per plant (Borrás et al., 2007; Echarte et al., 2008; Boomsma et ABSTRACT Corn (Zea mays L.) seeding rates have increased because new hybrids purportedly optimize yield at high seeding and N rates. Two hybrids were evaluated in New York at four seeding and two sidedress N rates to determine if recommended rates (74,100 kernels ha–1 and 111 kg N ha–1) still optimize yield. Precipitation from June through August varied (389 mm in 2010 and 198 mm in 2011), so year × hybrid and year × seeding rate interactions existed for yield and yield components, but no twoor three-way interactions existed among hybrid and N and seeding rates. Quadratic regression analysis predicted maximum yield at 88,000 kernels ha–1 in 2010, although yields varied by only 2% between 74,100 (18.5 Mg ha–1) and 98,800 kernels ha–1 (18.9 Mg ha–1). Seeding rate did not aff ect yield in 2011. As seeding rates increased from 61,875 to 98,800 kernels ha–1, kernel number per plant had negative linear decreases in 2010 (818 to 694) and 2011 (567 to 383). Kernel weight had a negative quadratic response to seeding rates in 2010 but a linear response in 2011 (338 to 317 and 312 to 332 mg, respectively, from 74,100 to 98,800 kernels ha–1). A year × N rate interaction existed for kernel weight (320 and 338 mg in 2010 and 318 mg in 2011 at 111 and 167 kg N ha–1, respectively) but not for yield (18.2 and 18.4 Mg ha–1 in 2010 and 11.1 and 11.3 Mg ha–1 in 2011, respectively). Overall, recommended seeding and sidedress N rates achieved close to optimum yield in this study.