A 22-acre field experiment was established in 2001 at the Iowa State University Marsden Farm, in Boone, Iowa to test the hypothesis that diversifying a simple corn-soybean cropping system could allow for substantial reductions in nitrogen fertilizer and herbicide use without compromising crop productivity and profitability. The site lies within a region of intensive rain-fed corn and soybean production and is surrounded by farms with high levels of productivity. Soils at the site are fertile Mollisols: Clarion loam, Nicollet loam, and Webster silty clay loam. Three rotation systems have been evaluated intensively during 2003–2012; a 2-yr corn-soybean system, a 3-yr corn-soybean-small grain + red cloversystem, and a 4-yr corn-soybean-small grain + alfalfa-alfalfa system. The 2-yr rotation is representative of cash grain farming systems in the region, whereas the 3-yr and 4- yr rotations are representative of low-externalinput (LEI) farming systems in the region that include livestock.