Crop rotation is the most effective pest control practice available to crop producers. The sequence of crops grown in a field affects the productivity of each crop. Research from most Midwest states indicate that a soybean crop following a crop other than soybeans will usually yield about 10 percent more grain, on average, than when soybeans follow soybeans. Many of the crop disease and insect problems currently experienced in Ohio are due to short crop rotations or no crop rotation. If all our crops were produced in a four-year crop rotation, yield loss to disease and insects would be near zero rather than at the 8 to 12 percent we currently experience. The effect of crop rotation on yield has been thoroughly investigated by most land-grant universities. Researchers at the University of Wisconsin conducted a crop rotation study with corn and soybean. Averaged across 29 years by location environments, corn and soybeans in their corn-soybean rotation resulted in 13 percent and 11 percent greater yield than the respective monoculture. Kansas State University conducted a 20-year crop rotation study in which the soybean yields were 20 percent greater when rotated with wheat or grain sorghum than without rotation. Results of a Canadian crop rotation study show that soybean yields from a wheat-corn-corn-soybean rotation were 7.1 percent higher than in a corn-corn-soybean rotation. Results of a 10-year crop rotation study conducted in northern Ohio indicated that continuous corn yielded only 89 percent as much as corn in a corn-oats-hay rotation, and corn in a corn-soybean rotation yielded 94 percent of the corn-oat- hay rotation.
Economics often dictate crop sequence, but where choices are available, soybeans should follow crops other than soybeans. Corn or other grass crops can make good use of the nitrogen left by legume crops. The effect of the length of a crop rotation on yield can be seen in Figure 5-1.
Figure 5-1. Effect of length of crop rotation on percent crop yield.