Factors Affecting Successful Establishment of Aerially Seeded Winter Rye

Published in Agron. J. 105:1868–1877 (2013) doi:10.2134/agronj2013.0133 Copyright © 2013 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. D the last quarter of the 20th century, a 2-yr corn–soybean rotation became the dominant agricultural land use in the Upper Midwest (Randall, 2003; Karlen, 2004). Recent research has shown that this agronomic practice can degrade soil quality (Karlen et al., 2006) and contribute to significant losses of NO3 to ground and surface waters (Dinnes et al., 2002; Oquist et al., 2007). One mitigation strategy to maintain soil quality and reduce NO3 loss is to incorporate cover crops into the rotation, which can increase the amount of time the land is covered in growing vegetation. Cereal rye is especially effective at reducing NO3 leaching (Ditsch et al., 1993; McCracken et al., 1994; Strock et al., 2004; Fisher et al., 2011). Furthermore, rye has many other advantages, such as adding soil organic matter (Kuo and Jellum, 2002) and erosion control (Langdale et al., 1991; Kaspar et al., 2001). Additionally, rye residues suppress weeds in the spring when used as a mulch (Barnes and Putnam, 1983; Leibl et al,. 1992; Dhima et al., 2006). The benefits of cover crops have been known for many years (Odland and Knoblauch, 1938; Beale et al., 1955), although adoption has been minimal. For example, Singer et al. (2007) estimated that only 18% of farmers in the U.S. Corn Belt had used cover crops in the past. Two obstacles to adoption are the lack of knowledge about the practice and concern about various risks, particularly reports of rye negatively affecting subsequent crops. Johnson et al. (1998) reported that in Iowa, corn yields were reduced following winter rye but not after oat (Avena sativa L.). Tollenaar et al. (1993) suggested that winter rye caused a delay in corn development and a yield loss in the subsequent harvest. In both studies, the researchers hypothesized that allelopathy from the rye may have played a role in yield reductions. Researchers in Illinois found that soybean yields were reduced due to low soybean stand when rye was killed immediately before planting (Leibl et al., 1992). In contrast, corn yields were actually improved with cover cropping compared with yields without a previous rye cover crop (Ball-Coelho and Roy, 1997; Ball-Coelho et al., 2005). Certain management practices can reduce the yield losses of corn and soybean following winter rye. Ritter et al. (1998) and Andraski and Bundy (2005) concluded that rye cover crops grown on loamy sand will not reduce subsequent corn yields if irrigation is used. Additionally, soybean and corn yields after winter rye were not reduced when the rye was killed one or more weeks before planting (Leibl et al., 1992; Strock et al., 2004; Ball-Coelho et al., 2005; Duiker and Curran, 2005; Krueger et al., 2011). There are also uncertainties about the additional costs associated with planting and killing a secondary crop. In Minnesota and Missouri, soybean yields following a rye cover crop were comparable to yields following winter fallow, but overall economic returns were usually reduced with the cover crop (Reddy, 2001; De Bruin et al., 2005). One avenue to increase cover crop adoption is thus through cost sharing in conservation programs. While ABSTRACT Establishing cover crops in a corn (Zea mays L.)–soybean (Glycine max L.) rotation in northern climates can be difficult due to the short time between harvest and freezing temperatures. Aerial seeding into standing crops is one way to increase the time for germination and growth. Field studies were conducted to characterize the physical and chemical properties that affect winter rye (Secale cereale L.) establishment in corn and soybean, while a germination experiment was designed to determine optimal temperature and surface soil moisture content needed for successful germination. In the field study, 31 field-scale sites (22 corn and nine soybean) were aerially seeded in southeastern Minnesota during late August to early September 2009, 2010, and 2011. Aboveground biomass was collected before the ground froze, and multiple regression analysis was used to relate biomass to multiple soil and weather conditions. Total N uptake also was determined. Overall, precipitation the week after seeding was the most important factor in determining rye establishment, although our model accounted for only 43% of the variation in biomass. The germination study characterized winter rye germination on the surface of three different soils equilibrated to –50, –200, and –500 kPa water potential placed in three low-temperature incubators at 10, 18, and 25°C. Total germination was decreased by decreasing water potential in the sandy loam but not the clay or silt loam, suggesting that moisture content may be more important than water potential at the soil surface. Generally, germination was drastically reduced below a moisture content of 0.083 g g–1.