Longer rotation schemes require less herbicide and reduce frequency of sudden death syndrome in soybean. Crop rotation can alter the soil environment, affecting plant physiology, and may impact insects, like soybean aphid. With the support from North Central Region – Sustainable Agriculture Research and Education Program and collaboration with agronomists at Iowa State University, we are investigating how conventionally managed 2-year corn-soybean rotation compares to a 3-year rotation (corn-soybean-small grain+ red clover), and a 4-year rotation (maize-soybean-small grain + alfalfa-alfalfa) affects the soybean aphid’s use of soybean as a host plant. We artificially infested soybeans with aphids in each of the rotation schemes, caged them to control for predation, and recorded populations over a 14-day period. Population growth rates were calculated for each caged plant, and mean growth rates generated for each rotation scheme. Aphid population growth rates were estimated at multiple stages of the soybean plants growth. Overall, we found soybean aphids had significantly higher population growth rates when infested on soybean in a 2-year than 3-year or 4-year rotation at the late vegetative growth stage. We hypothesized continued use of these rotations affected the soil such that the plants grown within these plots were physiologically different, affecting their value as a host for the aphid. In 2018, we measured macronutrient concentrations within soybean from each rotation as an indicator of host quality. Our results suggest soybeans grown in an extended rotation have a different profile of macronutrients, which may influence the plants value as a host for soybean aphid.
What does it mean for farmers: Crop rotation provides benefits such as reduction in nutrient runoff, improved soil structure, and a reduction in sudden death syndrome in soybean. Our results suggest that longer rotations could protect soybeans from aphid outbreaks.