Minimizing Interspecific Competition in Soybean by Optimizing Cover Crop Self-Seeding

Published in Agron. J. 103:1186–1191 (2011) Posted online 25 May 2011 doi:10.2134/agronj2011.0045 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. C crops provide important environmental functions that include reducing soil erosion (Zhu et al., 1989; Kaspar et al., 2001) and nitrate leaching (Kladivko et al., 2004; Kaspar et al., 2007), nevertheless, cover crop adoption in agronomic farming systems is low (Singer et al., 2007b). In the northern United States, producers are often harvesting cash crops during the ideal cover crop planting period. Furthermore, the short-term costs associated with cover crops are difficult for producers to justify when profit margins are narrow. Reddy (2003) reported a net return for no-tillage soybean with a rye cover crop at $29 ha–1 compared with 84 and $87 ha–1 for conventional and notillage without a rye cover crop. These treatments yielded similarly, but the added costs for rye seed, planting, and dessication lowered the profitability compared with the standard no cover crop system. Innovative cover crop management systems can reduce cover crop costs and maintain the profitability of the cash cropping enterprise if the cover crop does not decrease main crop yield. Results from relay intercropped soybean in winter wheat in Missouri found that soybean yield, averaged across 3 yr, was reduced 12% compared with a no-wheat full-season soybean. In this study, soybean was planted in 80 cm row widths when wheat was at Feekes growth stage 10.3 and no N was added (Reinbott et al., 1987). In self-seeding winter cover crop systems where management of the cover crop is not dependent on yield, it may be possible to reduce soybean yield loss further. Singer and Kohler (2005) reported from 30 to 60% yield loss in soybean using mechanical control to suppress a rye cover crop at second node, boot, and anthesis growth stages. In their study, the four rows of rye planted between each 0.76 m soybean row were highly competitive with soybean. Singer et al. (2007a) quantified the effect of wheat, rye, and triticale self-seeding systems on soybean production using various cover crop planting configurations. They reported that four rows of cover crop spaced between 0.76 m soybean rows combined with a late application of glyphosate to remove the two cover crop rows adjacent to soybean provided the least competition, lowering soybean yield 19% on average compared with a no cover crop control. The authors concluded, however, that additional gains were likely to minimize soybean yield loss in self-seeding systems because cover crop seed production was not optimized. Wheat, which exhibited the greatest self-seeding, produced 212 and 52 times more seed than resulted in new plants during the 2-yr study (Singer et al., 2007a). The objectives of this study were to quantify growth, seed production, seed viability, self-seeding, and competitive effects of winter wheat, triticale, and rye cover crops using different establishment seeding rates and mature seed dispersal systems while growing concurrently with soybean.