Using biodiversity to link agricultural productivity and profitability with environmental quality: Results from three field experiments in Iowa

Background/Question/Methods

Agriculture in the U.S. Corn Belt is under increasing pressure to produce greater quantities of food and fuel while better protecting environmental quality. Key environmental problems in this region include water contamination by nutrients and herbicides emitted from cropland, a lack of non-agricultural habitat to support diverse communities of plants and animals, and high dependence on petrochemical energy in the dominant cropping systems. Additionally, projected changes in climate for this region, which include increases in the proportion of precipitation coming from extreme events, could make soil and water conservation in existing cropping systems more difficult. To address these challenges we conducted three cropping systems projects in central Iowa: the Marsden Farm rotation experiment, the Science-based Trials of Row-crops Integrated with Prairies (STRIPS) experiment, and the Comparison of Biofuel Systems (COBS) experiment. 

Results/Conclusions

Results from these experiments generate three broad conclusions: (1) Diversification of simple cropping systems can permit substantial reductions in chemical use without compromising yields or profitability. In a comparison of a conventionally managed corn-soybean system with a corn-soybean-oat + red clover system during 2006-2011, the latter system used 96% less herbicide, 89% less synthetic N fertilizer, and 60% less fossil energy, yet had corn and soybean yields that were 3% and 10% greater, respectively, and net returns that were equivalent (958 vs. 954 $ ha^-1 yr^-1). (2) Conversion of small amounts of cropland to native perennial cover can provide disproportionately large improvements in conservation of soil, nutrients, and wildlife. In a comparison conducted during 2008-2011 of watersheds cropped entirely with corn and soybean versus watersheds containing 90% crops and 10% reconstructed prairie, the latter system reduced soil, N, and P losses by >90%, while increasing bird and plant species richness by 20% and 340%, respectively. (3) Native perennial species can generate large amounts of liquid fuel, while offering substantial environmental benefits relative to corn- and soybean-based systems. Data collected during 2008-2011 indicated that a multi-species mixture of prairie plants receiving 84 kg N ha^-1 yr^-1 could produce as much liquid fuel as a conventional corn-soybean system, while emitting 94% less N to drainage water and producing >500% more root dry matter and belowground C. Taken together, these results indicate that increasing biodiversity through the strategic integration of additional crop and non-crop species can be a viable strategy for reducing reliance on purchased inputs and for increasing agroecosystem health and resilience in the U.S. Corn Belt.