Planting the same crop in a field year after year depletes the soil of nutrients that crop relies on and allows pest populations specialized to that crop to build up season over season. Rotating in a legume crop, which fixes atmospheric nitrogen into the soil, restores nitrogen levels while also starving out pests that cannot survive on the legume. A farmer who rotated corn with soybeans, a legume, every other year for a decade applied, on average, 40% less synthetic nitrogen fertilizer than a neighboring farmer who planted corn continuously on comparable soil, and also reported far fewer corn-rootworm infestations, a corn-specialist pest.