Multiyear productivity and nitrate-nitrogen loss from corn and prairie bioenergy cropping systems

Though corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] are widely grown and readily accepted into commodity markets and biofuel facilities, heavy reliance on seeds of those two crops for bioenergy production has been linked to environmental degradation, including nutrient discharge to water, and to constraints on food production. Alternative biofuel feedstock systems might better address this “food–energy–environment trilemma.” Using data from a 9-ha field experiment in Iowa, we evaluated yields from a 14-year period for four bioenergy feedstock systems: stover harvested from corn grown with and without an unharvested rye cover crop, and prairie vegetation grown with and without fertilizer. We also assessed sub-surface drainage flows and NO₃-N concentrations and discharges in leachate from those cropping systems. The continuous corn systems produced mean grain yields of 11.0–11.5 Mg ha⁻¹ year⁻¹, while also yielding about 4 Mg ha⁻¹ year⁻¹ of stover. Mean harvested biomass from the fertilized prairie was 83% greater than from the unfertilized prairie and was superior to stover production in the two corn treatments in 11 out of 14 years. Nitrate-N losses in drainage water from the corn systems averaged 12–14 kg NO₃-N ha⁻¹ year⁻¹, whereas both the fertilized and unfertilized prairie systems almost eliminated NO₃-N loss. Cover cropping with rye reduced NO₃-N loss in only one out of 13 years and had variable effects on corn yield. Adoption of prairie-based biofuel systems might be driven by placing perennial feedstocks on environmentally sensitive sub-field areas and by government policies that favor perennial feedstocks over annual crops like corn.