RZWQM Simulations of Nitrate Loss to Subsurface Drains from a Midwest Bioenergy Production System.

Goals have been established to replace 30% of U.S. transportation fuels that are currently derived from petroleum with biofuels by 2030. The allowable quantity of first-generation, corn (Zea mays L.) grain-based biofuel (i.e., ethanol) has been capped at 15 billion gallons, thus requiring 16 billion gallons of second generation, biofuels to be derived from various cellulosic feedstock sources. Due to global demand for corn grain, not only for biofuel but also as an animal feed, food, and export commodity, the crop has been planted in the U.S. on an average of 88.9 million acres each year between 2005 and 2015. From a sustainability perspective, increased corn production has had positive economic benefits, but environmentally, corn production is a “leaky” process that has resulted in substantial loss of nitrate to surface and groundwater resources and thus created tensions between rural and urban sectors of our society. Incorporating a cover crop such as cereal rye (Triticale cereale L.) into current cropping systems, water quality concerns can be mitigated and demands for corn grain, stover, and other cellulosic feedstock can be met. The Root Zone Water Quality Model (RZWQM) was used to estimate the effects of corn production with and without a winter rye cover crop on shallow groundwater quality. We used a calibrated and tested version of RZWQM to estimate N loss in subsurface drainage (1.2 m) assuming a sustainable amount of corn stover (~1.7 tons/acre or 50% of the residue from a 175 bu/acre crop) is harvested and a winter cover crop is grown. Simulated nitate-N dynamics with or without harvesting the cover crop will help determine if both economic and environmental sustainability goals can be met.