Can a Cropping System with Only Corn and Soybean be Sustainable?.

The two-year rotation of corn (Zea mays L.) and soybean [Glycine max (L.) Merrill.] is the predominate cropping system in the U.S. Midwest. This system developed rapidly as soybean replaced small grains and forages as dairy-based rotations declined beginning in the 1940s; by 1980 these two crops together occupied more than 80 percent of the cropped area in the Corn Belt. Even so, concerns remain that these two crops grown in sequence fail to produce the economic and environmental stability that a longer, more complex rotation might provide. Our analysis of results of a number of crop rotation studies designed to compare continuous corn, corn-soybean, corn-soybean-wheat (Triticum aestivum L.) and other crop sequences in Illinois and Wisconsin does not support the idea that crop sequences consisting of only corn and soybean lack inherent stability. In long-term studies at Monmouth, IL and Arlington, WI, adding wheat into the corn-soybean rotation increased both corn and soybean yields by 5 to 10%, but did not affect yield stability of corn and soybean as measured by standard error. However, the 3-crop rotation provided substantially lower returns than did the corn-soybean rotation. These two crops together produce the quantity and quality of nutrients needed to sustain both livestock and people; replacing either of them on a large scale is likely to occur only if the replacement better meets these nutritional requirements. Economic considerations may well change the proportion of corn and soybean grown by producers in the coming decades, but we consider it likely that crop sequences that include only corn and soybean will continue to dominate in this region.