Growth and Yield Responses of Soybean to Row Spacing and Seeding Rate

Published in Agron. J. 103:123–128 (2011) Published online 22 Nov 2010 Available freely online through the author-supported open access option. doi:10.2134/agronj2010.0316 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 growers in northern latitudes plant soybean in 0.38 m instead of 0.76 m rows because of consistent yield increases at latitudes north of 43 N (Lee, 2006), and increased prevalence of split-row planters allowing soybean planting in 0.38 m rows and corn (Zea mays L.) planting in 0.76 m rows with the same planter (De Bruin and Pedersen, 2008b). Lambert and LowenbergDeBoer (2003), however, concluded that planting soybean in 0.19 m rows with a grain drill was more economical in an annual corn–soybean rotation in the NorthCentral United States, based on a summary of studies showing a 4.8% yield advantage for drilled (<0.25 m rows) compared with 0.38 m rows. Furthermore, Kratochvil et al. (2004) reported that drilled soybean in 0.19 vs. 0.38 m rows yielded the same or more in 47 of 48 cultivar/row spacing comparisons in a 3-yr study for full-season and double-cropped soybean in Maryland. Consequently, it is not clear if growers should plant soybean in 0.38 m rows with a row crop planter instead of 0.19 m rows with a grain drill in northern latitudes, especially if growers still plant wheat with grain drills. Bertram and Pedersen (2004) reported a 5% yield increase for soybean in 0.19 vs. 0.76 m rows in southern Wisconsin, an 8.7% increase in central Wisconsin, and a 9.6% increase in northern Wisconsin in a 3-yr study. In the same study, however, soybean in 0.19 m rows yielded the same as in 0.38 m rows in central and northern Wisconsin and 4.7% less than in 0.38 m rows in southern Wisconsin. In a 4-yr study in southern Wisconsin (Pedersen and Lauer, 2003), average yields did not diff er among the three row spacings, but an interaction with years was observed with soybean in 0.19 m rows yielding greater in 2 yr and soybean in 0.38 m rows yielding greater in 1 yr. Janovicek et al. (2006) reported soybean in 0.19 m rows yielded 13% more compared with 0.76 m rows under moldboard plow and no-tillage systems, but yielded only 4% more under moldboard plow and the same under no-till compared with 0.38 m rows in a 3-yr study at three locations in Ontario, Canada. In an Indiana study at three locations (Hanna et al., 2008), soybean in 0.19 vs. 0.38 m rows yielded 9% more in the absence of wheel-track damage associated with postemergence pesticide applications, but yielded the same in the presence of wheel-track damage. Results from the more recent studies in northern latitudes indicate no consistent yield advantage for drilled soybean in 0.19 m rows compared to 0.38 m rows. Consequently, DeBruin and Pedersen (2008b) advocate the adoption of 0.38 m row spacing, based on a 5.6% yield increase in 0.38 vs.0.76 m rows in a 3-yr study at fi ve locations in Iowa, where grain drills are not prevalent because wheat is not a major crop. Split-row planters compared to grain drills may allow for reduced soybean seeding rates and seed costs because row crop planters result in more uniform seed depth and distance between seeds in a row, improving emergence and uniformity of fi nal stands (Bertram and Pedersen, 2004). Some studies (Weber et al., 1966; Oplinger and Philbrook, 1992) in northern latitudes, however, have reported row spacing by seeding rate interactions with soybean responding more positively to higher seeding rates in narrow vs. wide rows. Other studies in Ohio (Beurelein, 1988) and Ontario, Canada (Ablett et al., 1991) reported no row spacing by seeding rate interactions with ABSTRACT Some growers in northern latitudes plant soybean [Glycine max (L.) Merr.] with a row crop planter in 0.38 m rows, but an economic analysis concluded that drilled soybean in rows <0.25 m was optimum in the North-Central United States. We planted two varieties in 0.19, 0.38, and 0.76 m rows at 321,000; 371,000; 420,000; and 469,000 seeds ha−1 in New York in 2008 and 2009 to evaluate how soybean compensates to wide rows or low seeding rates in the Northeast United States. Soybean had limited compensation in biomass, pods, and seeds plant−1 at wider rows so row spacing had linear responses for biomass accumulation (598, 554, and 497 g m−2 in 0.19, 0.38. and 0.76 m rows, respectively) and leaf area index (LAI, 3.64, 3.47, and 3.16) at seed initiation; pod (1012, 935, and 875 pods m−2) and seed density (2272, 2230, and 2072 seeds m−2, respectively) at harvest; and yield (3.37, 3.12, and 2.86 Mg ha−1, respectively). Compensation in biomass, pods, and seeds plant−1 at lower seeding rates resulted in similar biomass accumulation (528–570 g m−2), LAI (3.38–3.46), pod (921–965 pods m−2), and seed densities (2123 to 2234 seeds m−2) across seeding rates. Nevertheless, yield showed a quadratic response to seeding rate (3.04, 3.25, and 3.12 Mg ha−1 at 321,000; 420,000; and 469,000 seeds ha−1, respectively) with no row spacing interaction. Soybean compensated more at lower seeding rates than at wider rows, but fi eld-scale studies are being conducted to evaluate the economics of both practices.