Review of Corn Yield Response under Winter Cover Cropping Systems Using Meta-Analytic Methods

yield of the following crop (Wagger and Mengel, 1993). Winter cover crop residues can affect soil water dynamExtensive research on the use of winter cover crops (WCC) under ics by reducing runoff, increasing infiltration, and reducdifferent agricultural practices in the USA and Canada has shown both negative and positive effects on subsequent corn (Zea mays L.) ing evaporation, all of which may ultimately benefit crop yield. These contrasting results determine the need for a comprehenyield (Unger and Vigil, 1998). Conversely, WCC can also sive quantitative review. The objective of this study was to use metacompete with the crop by using soil water during active analytic methods to summarize and quantitatively describe the effects growth (Munawar et al., 1990). of WCC on corn yield based on peer-reviewed published research. Legumes and grasses have been used extensively as Thirty-six studies were included in the analysis representing different WCC (Frye et al., 1988; Smith et al., 1987; Wagger and regions of the USA and Canada under different agricultural practices Mengel, 1993). In general, at the time of killing, legume (i.e., species, fertilization, kill date, tillage, etc.). The effect-size used WCC provide less biomass with narrower carbon to to compare studies was the response ratio, calculated as yield of corn nitrogen (C/N) ratios than grass WCC (Doran and following WCC over yield of corn following no cover. Biculture WCC Smith, 1991) at the time of WCC killing. Because of their increased corn yield by 21%, but there is greater variation due to the small number of studies in this group. Overall, grass WCC neither narrow C/N ratio, legume residues usually decompose increased nor decreased corn yields and this response was not depenfaster, releasing inorganic N into the soil that becomes dent on the use of N fertilizer. Legume WCC increased corn yield available for the following crop (Varco et al., 1989; Wagby 37% when no nitrogen (N) fertilizer was applied and this benefit ger, 1989). Lal et al. (1991) recognized that weather condecreased with application of N fertilizer. ditions considerably influence biomass production of WCC and subsequent decomposition of the residues, strongly affecting N release. Therefore, N supplied by N resource conservation and profitable farmWCC can be quite variable among studies (Frye et al., ing are essential goals in agriculture. Among con1988). Successful management of the cropping system servation practices, the introduction of WCC to cropinvolves synchrony between release of N from WCC ping systems has been recognized as a management and demand for inorganic N from the following crop option for maintaining and enhancing soil and water (Huntington et al., 1985). quality (Reeves, 1994). In terms of soil quality, WCC Agricultural practices such as N fertilization, tillage, are effective in protecting the soil against erosion (Langchemical desiccation, or mechanical killing of WCC can dale et al., 1991), improving soil structure (Dapaah and affect growth and yield of the following crop (Reeves, Vyn, 1998), and enhancing soil fertility (Latif et al., 1994). Furthermore, the effects are highly variable when 1992; McVay et al., 1989). The use of WCC can also differences among studies, which represent different agimprove water quality and N use efficiency by trapping ricultural practices, locations and years (i.e., different N in the biomass of WCC, thus reducing N losses from soil types and climates) are considered. Thus, different cropping systems (Shipley et al., 1992; Thorup-Krisenvironments and managements are a major source of tensen et al., 2003). The adoption of WCC by farmers variability and have important implications for crop rein the USA is limited, in part, by uncertainty about the sponse to WCC (Power and Biederbeck, 1991). yield response of the crop planted after WCC (Larson The contrasting results and the large volume of eviet al., 1998; Smith et al., 1987). dence of the effects of WCC on corn yield determine Winter cover crops can positively or negatively affect the need for a comprehensive quantitative review (Frye the following crop by their influence on N and water et al., 1985; Huntington et al., 1985; Kuo and Jellum, dynamics (Thorup-Kristensen et al., 2003). Positive ef2000; Larson et al., 1998; Wagger, 1989). To our knowlfects of WCC on yield have been attributed to an inedge, there are few reviews that combine independent crease in soil N availability through a build up of soil studies using quantitative methods to relate the impact organic matter and N mineralization during decomposiof management practices and environmental effects on tion of WCC residues (Frye et al., 1988). On the other crop yield. Ainsworth et al. (2002) evaluated the effects hand, decomposition of WCC residues can lead to imof high CO2 treatments on soybean [Glycine max (L.) mobilization of N, adversely affecting the growth and Merr.] physiology, growth, and yield. Looking at different cropping systems, Marra and Kaval (2000) compared Dep. of Crop Sciences, Univ. of Illinois, 1102 S. Goodwin Ave., Urbana, the relative profitability of organic and no-till with that IL 61801. Received 6 Jan. 2005. *Corresponding author (gbollero@ of conventional systems. These studies used meta-anauiuc.edu). lytic methods that have been widely applied in other Published in Crop Sci. 45:2318–2329 (2005). disciplines, such as the medical, physical, and behavioral Crop Ecology, Management & Quality sciences (Cooper and Hedges, 1994), and recently in doi:10.2135/cropsci2005.0014 the ecological sciences (Curtis and Wang, 1998; Gure© Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA vitch and Hedges, 1999; Osenberg et al., 1999). 2318 Published online September 23, 2005