Temporal Yield Variability under Conventional and Alternative Management Systems

Year to year variation in yield is an inherent risk associated with crop production and many growers rely on intensive mechanical or chemical inputs to preserve crop yield in the face of fluctuating environmental conditions. However, as interest grows in alternative crop management systems which depend less on external inputs, determining the degree to which management systems can impact the temporal yield variability will help the development of sustainable agroecosystems. This study assessed average crop yields and temporal yield variability over a 12-yr period in four agricultural management systems that are part of a long-term cropping systems experiment at the W.K. Kellogg Biological Station (KBS) Long Term Ecological Research (LTER) site in southwestern Michigan. The four systems follow a corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and winter wheat (Triticum aestivum L.) 3-yr rotation under conventional (CT), no-till (NT), low-input (LI), or organic (ORG) management, and each crop phase was present in the rotation four times from 1993 to 2004. Yields were measured each year and crop yield variability was estimated using the coefficient of variation calculated separately for each crop phase. Averaged over the study period, yields in the CT and NT systems were similar across all crop phases of the rotation and of higher magnitude than the LI system only in the winter wheat phase of the rotation. Compared to the other three management systems, yields in the ORG system were lower in the corn and winter wheat phases of the rotation. Yields in the soybean phase were similar across the four management systems. Temporal yield variability differed among management systems and rotation phases and was highest in the ORG system during the soybean (CV 5 48%) and winter wheat (CV 5 33%) phases of the rotation. Compared to the CT system, yield variability was 40% lower in the LI (corn phase), 33% lower in the NT (soybean phase) and similar in the NT (corn and winter wheat phases) systems. Results of this study suggest that yield and temporal yield variability under alternative management systems such as no-till and low-input can be comparable to that in conventional systems. However, temporal yield variability can be as high or higher in organic cropping systems without external inputs of manure or compost. Y VARIATION IN CLIMATE can be substantial and can interact with biotic and abiotic factors such as pest pressure, topography, soil properties, and management practices in determining crop performance (Porter et al., 1998; Andresen et al., 2001; Kravchenko et al., 2005; Mallory and Porter, 2007). To reduce the effects of variability on crop production, many growers rely on external inputs of fertilizers, pesticides, and tillage (Varvel, 2000). However, growing awareness regarding the ecological and economic impacts of intensive reliance on synthetic chemicals and tillage has driven interest in identifying alternative cropping systems. A major goal of these alternative cropping systems is to lessen the need for intensive management practices while maintaining or enhancing the economic and environmental sustainability of the farming enterprise (Robertson and Swinton, 2005). Agricultural management systems have been shown to have substantial impacts on many aspects of agroecosystems, including soil biochemical properties (Drinkwater et al., 1995; Kladivko, 2001; Sanchez et al., 2004; Grandy et al., 2006), soil faunal composition and diversity (Wardle et al., 1999; Scheu, 2001; Menalled et al., 2007), and weed community structure (Buhler, 1995; Menalled et al., 2001; Davis et al., 2005). Thus, it is reasonable to expect that management systems may also have substantial impacts on ecosystem processes that contribute to annual crop yield variability (Altieri, 1999; Kravchenko et al., 2005). Alternative management practices that maintain or enhance crop yields while reducing inter-annual yield variability have the potential to decrease the risk associated with crop production. Enhanced yield stability is of particular importance to the sustainability of agriculture under future global climate change scenarios which predict that variation in precipitation patterns will increase (Southworth et al., 2000; Tilman et al., 2001; Lotter et al., 2003). Despite the potential benefits to growers of decreasing temporal yield variability, there have been relatively few studies that explicitly address the impact of management systems on year-to year yield variability within row crop agroecosystems typical of the Midwest. However, several recent studies incorporating data from long-term cropping systems experiments suggest the significant role that management systems may play in affecting yield variability. For example, Kravchenko et al. (2005) observed that over a 6-yr period spatial yield variability was higher in a zero chemical input system during low rainfall years compared to systems that received chemical fertilizers. In contrast, Smith and Gross (2006) found that over a 4-yr period, corn yields in an organically managed rotation that included soybean and winter wheat were less temporally-variable than yields of continuous corn under conventional management. Clearly, additional studies that focus explicitly on temporal variability and incorporate a time period long enough to capture a R.G. Smith and F.D. Menalled, Dep. of Land Resources and Environmental Sciences, Montana State Univ., Bozeman, MT 59717; and G.P. Robertson, Dep. of Crop and Soil Sciences and W. K. Kellogg Biological Station, Michigan State Univ., Hickory Corners, MI 49060. R.G. Smith, current address: USDA-ARS, Exotic and Invasive Weeds Research Unit, 800 Buchanan St., Albany, CA 94710. Received 15 Mar. 2007. *Corresponding author ([email protected]). Published in Agron. J. 99:1629–1634 (2007). Cropping Systems doi:10.2134/agronj2007.0096 a American Society of Agronomy 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: CT, chisel-plowed treatment with conventional chemical inputs; CV, coefficient of variation; KBS LTER, W.K. Kellogg Biological Station Long-Term Ecological Research Project; LI, chiselplowed treatment with low chemical input and a winter legume cover crop; NT, no-tillage treatment with conventional chemical inputs; ORG, organic-based chisel-plowed treatment with zero chemical input and a winter legume cover crop. R e p ro d u c e d fr o m A g ro n o m y J o u rn a l. P u b lis h e d b y A m e ri c a n S o c ie ty o f A g ro n o m y . A ll c o p y ri g h ts re s e rv e d .