Hairy Vetch Varieties and Bi‐Cultures Influence Cover Crop Services in Strip‐Tilled Sweet Corn

Published in Agron. J. 104:629–638 (2012) Posted online 29 Feb. 2012 doi:10.2134/agronj2011.0360 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. H vetch is a vining legume native to Eurasia. Of all the species in the genus Vicia (150+), hairy vetch is reported as the only one that can survive moderate to harsh winter conditions when sown in the fall (Undersander et al., 1990). Because of its winter hardiness and its ability to provide large amounts of N to subsequent crops through biological nitrogen fi xation (BNF), hairy vetch has received much attention as a potentially valuable cover crop in many cropping systems. Depending on planting density and climate, hairy vetch may fi x up to 300 kg N ha–1 (Ledgard, 2001) with typical rates in the northern United States ranging from 50 and 190 kg N ha–1 (Teasdale et al., 2004). As a winter cover crop, hairy vetch also provides: (i) a C source to build soil organic matter and improve soil physical properties; (ii) ground cover during a time period when fi elds are without crops and are prone to soil erosion; and (iii) suppression of weed growth through allelopathy and mulch eff ects (Clark, 2007; Hill et al., 2006; Teasdale and Mohler, 2000). Crop yields following hairy vetch and rye–vetch mixtures have generally been comparable or greater than bare soil, although results vary depending on factors including the level of N fertilization as well as tillage and weed management practices used in bare soil controls (Carrera et al., 2004; Hanson et al., 1993; Miguez and Bollero 2005). Despite these potential benefi ts, widespread adoption of hairy vetch has been limited by several management challenges. Problems associated with hairy vetch include overwinter mortality (Jannink et al., 1997), regrowth following mechanical termination resulting in competition with subsequent crops (Aarssen et al., 1986; Teasdale and Shirley, 1998) and rapid mineralization of residues resulting in N losses prior to crop N uptake (Rosecrance et al., 2000). Cover crop competition with cash crops due to regrowth is a well-established potential problem in cropping systems (Moschler et al., 1967). Indeed, hairy vetch is considered a problematic weed especially in winter annual crops like wheat (Triticum aestivum L.) and in perennial tree fruit (Aarssen et al., 1986). Hairy vetch regrowth can be particularly problematic in reduced tillage systems in which mechanical means of termination including mowing or roller crimping are used. For example, Boydston and Williams (2011) report that yields in reduced tillage dry bean (Phaseolus vulgaris L.) production were lower where hairy vetch was roller crimped due to competition from vetch that regrew. Hairy vetch regrowth in subsequent grain crops may necessitate extra herbicide applications (Hanson et al., 1993). Since regrowth of vetch following mowing or roller crimping is reported to be minimized when vetch has reached full fl owering and early pod set (Mischler et al., 2010), earlyfl owering varieties may be terminated earlier in the spring with reduced risk of regrowth. Estimates in the literature regarding the appropriate time to mechanically terminate (e.g. fl ail mow) ABSTRACT Hairy vetch (Vicia villosa Roth) cover crops provide a wide array of ecosystem services including erosion protection, weed suppression, and N fi xation. However, adoption has been hindered by risks including overwinter mortality and regrowth following mowing or crimping. Early-fl owering vetch varieties and mixed stands of vetch and cereal rye (Secale cereale L.) have the potential to reduce these risks, but little is known about their impact on N fi xation. In fi eld trials in Central Michigan, two early-fl owering hairy vetch varieties (Purple Bounty and Purple Prosperity) and one later-fl owering variety (‘Oregon’) were grown alone and in mixtures with cereal rye, prior to strip-tilled sweet corn (Zea mays L. var. rugosa). Vetches grown in mixture with rye had equal or greater overwinter survival and earlier fl owering than vetches grown in monoculture. Nitrogen fi xation of early-fl owering varieties was not aff ected by mixture with rye. However, N fi xation of Oregon was lower when grown in monoculture than when grown in mixture in 2009. Purple Bounty and Purple Prosperity fl owered earlier than Oregon, exhibited comparable survival, and had equal or greater levels of N fi xation. Despite diff erences in the timing of fl owering, there were no diff erences in regrowth of hairy vetch following mowing. Nor were any diff erences in sweet corn yield or quality detected. Th ese results demonstrate that rye–vetch mixtures can increase overwinter survival, accelerate fl owering, and increase N fi xation relative to vetch monocultures. Observed varietal diff erences in fl owering time, N fi xation, and response to bicultures may be exploited to optimize cover crop use in agroecosystems.