Root growth and yield of maize as affected by soil compaction and cover crops Guihua Chen a,b, *, Ray R. Weil b a Department of Land, Air and Water Resources, University of California, Davis, CA 95616, USA b Department of Environmental Science and Technology, University of Maryland, 1109 H.J. Patterson Hall, College Park, MD 20814, USA 1. Introduction The ability of plants to obtain water and mineral nutrients from the soil is related to their capacity to develop extensive root systems. Soil compaction, especially in subsoil layers, may restrict deep root growth and adversely affect plant access to subsoil water from the middle to late growing season when rainfall is usually sparse and evapotranspiration is high. The resulting increase in drought stress may limit plant growth and yield. Deep ripping has been used to alleviate soil compaction (Schmidt et al., 1994), but the benefits of deep tillage may be short-living (Calonego and Rosolem, 2010; Hall et al., 1994) and costly in terms of energy and time. Use of deep tillage to alleviate compaction also disrupts the surface mulch that develops after years of no-till management, increasing the soil’s susceptibility to erosion and sealing (Wier- mann et al., 2000; Zhang et al., 1998). Crop rotation is an important tool for maintaining long-term productivity and environmental quality (Ball et al., 2005). The crop rotation system chosen may profoundly influence soil physical properties, especially with respect to the development and distribution of root channels. The possibility of using ‘‘plant roots as tillage tools’’ was first proposed by Elkins (1985). More recently, Cresswell and Kirkegaard (1995) suggested the term ‘‘biological drilling’’ to describe the process by which root channels left by previous crops may ameliorate the effects of subsoil compaction on subsequent crop root growth. Among the few studies published (Materechera et al., 1992; Merrill et al., 2002), there is general agreement that roots with greater diameter (often tap-rooted dicots) are more capable of penetrating compacted soil layers than roots with smaller diameter (usually fibrous-rooted monocots), although the mechanisms for this difference are not clearly understood (Chen and Weil, 2010; Clark et al., 2003). Rasse and Smucker (1998) found that maize after alfalfa achieved a higher number of roots in the subsoil than maize after maize, a finding which is in agreement with Materechera et al. (1991). However, Cresswell and Kirkegaard (1995), after finding that a canola (Brassica rapa L.) crop did not improve rooting depth in a following wheat crop, suggested that perennials might be more capable of Soil & Tillage Research 117 (2011) 17–27 A R T I C L E I N F O Article history: Received 1 April 2011 Received in revised form 29 July 2011 Accepted 1 August 2011 Available online 27 August 2011 Keywords: Brassica cover crops Bio-drilling Root penetration No-till A B S T R A C T The yield of rainfed crops is commonly limited by the availability of soil water during the summer growing season. Channels produced by cover crop roots in fall/winter when soils are relatively moist may facilitate the penetration of compacted soils by subsequent crop roots in summer when soils are relatively dry and hard. Our objective was to determine the effects of fall cover crops on maize (Zea mays) growth and soil water status under three levels (high, medium, and no) of imposed traffic compaction. The study was conducted on coastal plain soils (fine-loamy Typic/Aquic hapludults and siliceous, Psammentic hapludults) in the mid-Atlantic region of the United States from 2006 to 2008. Cover crop treatments were FR (forage radish: Raphanus sativus var. longipinnatus, cv. ‘Daikon’), rapeseed (Brassica napus, cv. ‘Essex’), rye (cereal rye: Secale cereale L., cv. ‘Wheeler’) and NCC (no cover crop). Maize under high compaction achieved more deep-roots following FR and rapeseed than following rye or NCC. However, maize had greater yield following all cover crops than NCC control regardless of compaction levels and soil texture. Compaction reduced maize yield only under the high compaction in the lightly textured soils. During 24 June–24 July 2008, soils at 15 and 50 cm depths were drier under no compaction than high compaction and drier following FR than other cover crop treatments. Our results suggest that FR benefited maize root penetration in compacted soils while rye provided the best availability of surface soil water; rapeseed tended to provide both benefits. However, as rapeseed is relatively difficult to kill in spring, a mixture of FR and rye cover crops might be most practical and beneficial for rainfed summer crops under no-till systems in regions with cool to temperate, humid climates. ß 2011 Elsevier B.V. All rights reserved. * Corresponding author at: Department of Land, Air and Water Resources, University of California, Davis, CA 95616, USA. Tel.: +1 240 643 3251; fax: +1 530 554 2692. E-mail address: gchen06@gmail.com (G. Chen). Contents lists available at ScienceDirect Soil & Tillage Research jou r nal h o mep age: w ww.els evier .co m/lo c ate/s till 0167-1987/$ – see front matter ß 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.still.2011.08.001