Crop rotations influence yield and some soil properties because of changes in availability of nutrients and water, physical properties, and incidence of pests and weeds. A crop rotation study was started in 1979 to assess the effects of various cropping sequences on crop yield and on the response of corn to nitrogen (N) fertilization. The rotations under study are continuous corn for grain and for silage, continuous soybean, several corn-soybean sequences with one to three corn crops for every soybean crop, and corn-corn-oats/alfalfa. Alfalfa is undersown with oats, oats grain is harvested the first year, and alfalfa is harvested the second year. Tillage practices are chisel plowing in the fall and field cultivation in the spring. The N treatments are 0, 80, 160, and 240 lb N/acre and are applied only for corn. Granulated urea is applied in the spring before planting corn and is incorporated by a field cultivator. This report summarizes average grain yields of corn, soybean, and oats for the 1979–2004 period and for the last four years (for a complete cycle of the 4-year rotations).