Responses of Maize Hybrids to Twin-Row Spatial Arrangement at Multiple Plant Densities

Published in Agron. J. 104:1747–1756 (2012) doi:10.2134/agronj2012.0231 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. T continuous increase in maize grain yield in the world’s primary growing areas during the last decades was mainly driven by the development of crowding stress tolerant hybrids that allowed for dramatic increases in plant population and, therefore, in production per unit area (Russell, 1984; Tollenaar and Wu, 1999; Duvick, 2005). Maize grain yields in the United States have also increased due to earlier planting dates (Kucharik, 2008) and more extensive use of irrigation (Cassman, 1999). Sustaining maize grain yield increases into the future requires continued reconsideration of current agronomic practices. Decreasing row spacing at equal plant density promotes more equidistant plant spacing, theoretically reducing plant-toplant competition, while improving plant resource capture and utilization (Duncan, 1984; Andrade et al., 2002; Barbieri et al., 2008) and decreasing weed competition through earlier canopy closure (Bullock et al., 1988). Nonetheless, sharply contrasting conclusions have been reported regarding grain yield response to narrow rows (Nielsen, 1988; Porter et al., 1997; Barbieri et al., 2000; Farnham, 2001; Ma et al., 2003; Andrade et al., 2002; Shapiro and Wortmann, 2006; Yilmaz et al., 2008), and the grain yield benefi t from the implementation of this practice may not warrant the additional machinery investment required. Th e spatial confi guration known as twin rows (Karlen and Camp, 1985) is not a new concept. Twin-row planting systems have proven to be advantageous to soybean [Glycine max (L.) Merr.] yields vs. the single-wide-row alternative of 76-cm spacing (Janovicek et al., 2006) and have gained renewed interest for U.S. maize production in the past decade. Th eoretically, twinrow maize planting systems appears to be an opportunity to derive the benefi ts of narrow rows without need of major changes in harvest, nutrient, or pest application equipment. While the distance between consecutive maize plants within a row at around 85,000 pl ha–1 is around 15 cm for 76-cm planting row widths, in a precisely distributed twin-row arrangement with a 20-cm distance between paired rows, plants ought to be approximately 25 cm from their closest neighbors. Twin-row research has been performed across the United States with varying success, but recent studies showed no consistent grain yield benefi t from twin-row over single-row confi gurations at the same plant densities in the states of Alabama, Iowa, Missouri, or Nebraska (Elmore and Abendroth, 2007; Nelson and Smoot, 2009; Balkcom et al., 2011; Novacek, 2011). In conditions without major nutrient or water limitations, maize grain yield depends most on radiation interception and radiation-driven photosynthetic conversion effi ciencies around ABSTRACT Twin-row planting systems in maize (Zea mays L.) have been proposed as an alternative spatial arrangement that should theoretically decrease plant-to-plant competition, alleviate crop crowding stress and improve yields. Uncertainty remains, however, as to whether twin rows are a feasible option to increase plant densities and improve grain yields. Th ree hybrids (DKC62-54, DKC61-19, and DKC57-66) were grown from 2009 to 2011 to evaluate the individual and interacting eff ects of plant density (PD1 = 69,000; PD2 = 81,000; PD3 = 93,000; and PD4 = 105,000 plants [pl] ha–1) and spatial confi guration (conventional single 76-cm row width vs. 20-cm twin rows spaced 76-cm between paired-rows) on dark prairie soil in WestCentral Indiana. Th e primary research objectives were to determine (i) whether the twin-row spatial arrangement permits higher optimum plant densities, (ii) whether hybrids vary in their response to a twin-row arrangement, and (iii) diverse morphophysiological trait responses to density and spatial treatments. Twin rows never yielded signifi cantly more than single rows at any plant density or hybrid combination in any year of this study. Furthermore, there was no evidence that grain yield-optimizing plant densities were any higher with twin vs. single rows in any hybrid. Twin rows slightly increased leaf area index (LAI) at silk emergence stage in 2010 (mean LAI = 4.8) and 2011 (mean LAI = 4.0), but not in 2009 (mean LAI = 4.4). Despite higher plant spacing variation, radiation interception was initially favored by earlier canopy closure with twin-row planting, but the relative radiation-interception advantage declined as plant density increased and at a later vegetative stage.