Agronomic, Economic, and Environmental Performance Characteristics of Conventional and More Diverse Cropping Systems in the U.S. Corn Belt.

Conventional corn and soybean production in the U.S. Corn Belt typically occurs in short rotations or monocultures and relies heavily on the use of mineral fertilizers, herbicides, and fossil energy. To test the hypothesis that cropping system diversification allows large reductions in chemical inputs while maintaining or improving yields, profits, and environmental performance indicators, a 9-ha field experiment was conducted in Boone Co., IA, over a 12-year period by a multi-disciplinary team of investigators. Systems compared within the experiment included a conventional 2-yr corn/soybean rotation and two more diverse systems: a 3-yr corn/soybean/small grain + red clover rotation, and a 4-yr corn/soybean/small grain + alfalfa/alfalfa rotation, both of which received cattle manure. Mineral N fertilizer use was 81% and 87% lower, and herbicide use was 88% and 91% lower in the 3-yr and 4-yr systems, respectively, than in the 2-yr system. Mean corn yield was 4% greater (p<0.01) and mean soybean yield was 11% greater (p<0.0001) in the more diverse systems compared with the conventional system. Weed biomass in corn and soybean crops was low (≤20 kg ha^-1) in all systems. Incidence and severity of sudden death syndrome, a key disease affecting soybean in the Corn Belt, were both markedly lower (p<0.0001) in the longer rotations compared with the 2-yr rotation. Estimated soil erosion was 28% lower, fossil energy consumption was 59% lower, and freshwater toxicity associated with herbicide use was two orders of magnitude lower in the more diverse systems than in the conventional system. Net return to land and management did not differ among systems (p=0.68, mean=$812 ha^-1 yr^-1), though it tended to rise as rotation length increased. Results of this study indicate that diversification of conventional corn-soybean systems can lead to decreased dependence on chemical inputs and to less environmental damage, while maintaining profitability and improving productivity.