Optimizing Cropping Systems for Resilience to Stress: Role of Maturity Group Selection and Cover Crops on Yield, Weeds, Insects, and Microbes

For farmers, high grain crop yields are critical to profit margins, however, yields are reduced each year due to diseases and weeds. Herbicide resistance has complicated cropping system management. For example, a USDA analysis reports a $22.53/ acre reduction in returns for soybean acres reporting glyphosate resistance compared to non-resistant acres (Livingston et al. 2015). Lower returns per acre is due to reduced yields and increased herbicide costs. This has driven farmers and researchers to look for novel solutions to manage these complex systems. As one such solution, cover crops have potential as an IPM tool for managing herbicide resistant weed populations (Krutz et al., 2009; Wiggins et al., 2015). Additionally, more than half of soybean diseases causing yield loss in Nebraska are caused by pathogens that dwell in soil (Pythium, Phytophthora, Fusarium, Rhizoctonia, Diaporthe, and Macrophomina). Among all types of diseases in Nebraska, these pathogens accounted for over 24% of yield loss in 2011, which is an estimated loss of 2.84 million bushels (Bradley & Koenning, 2012). These organisms survive in soil without causing disease until the plant is under stress. Many farmers have increased interest in using cover crops to provide rotational benefit to soybean grown in a continuous soybean or soybean-corn rotation (Chen et al., 2005; SARE, 2014; Sarrantonio & Gallandt, 2003). Incorporating cover crops into grain crop systems across the North Central Midwest may provide multiple benefits, but to fully realize these benefits, the systems must be economically robust (Blanco et al., 2015, Weil and Kremen, 2006). Despite the potential benefits, the primary challenge of integrating cover crops into grain crop systems is timely establishment of cover crops (Bich et al., 2014; Hively & Cox, 2001; Johnson et al., 1998; Wortmann et al., 2012). We propose a novel cropping system that could benefit grain crop farmers. Planting shorter season grain crop varieties or hybrids may increase cover crop establishment success in these systems, along with improving resistant weed management, reducing disease and nematode damage, and providing forages (Mirsky et al., 2011; Franzluebbers & Stuedemann, 2014). We propose the rotational benefits from this cropping system could help improve economic resilience for grain crop farmers (Reeves, 1994). Utilizing soybean as a model grain crop system, our goal is to determine the yield potential of soybean varieties from different maturity groups grown at six unique Midwest and upper Midsouth locations. Further we will evaluate how effectively cover crops could be integrated to maximize the economic benefit of the entire cropping system. The proposed research will focus on soybean yield; cover crop biomass production and forage value; stand establishment and yield of the subsequent rotational grain crop; weed management potential; and cropping system effects on seedling pathogens and cyst nematodes. Our hypothesis is that grain yield trade-offs from shorter-season maturity groups could be offset by the increased cover crop/forage production and potential for reduced herbicide input as well as providing a rotation benefit to subsequent crops. Specific objectives are to: (1) identify the potential soybean grain yield relative to maturity group differences, (2) substantiate economic efficiency of integrating cover crops into different soybean maturity groups, and (3) identify the impacts of an integrated soybean/cover crop system on weed management, forage production, soybean seedling pathogens, soybean cyst nematode, and beneficial/antagonistic microbial communities.