Modeling Surface Water Quality Impacts of Residue Removal for Ethanol Production in Southern Minnesota.

Ethanol production capacity in Minnesota has increased to nearly 3.2 billion liters per year, requiring grain from roughly 25% of Minnesota’s corn acreage.  Ethanol producers in Minnesota are beginning to explore the use of corn residue for cellulosic ethanol.  The objective of our research was to quantify the impacts on water quality of increases in corn acreage and removal of crop residue for ethanol production. There is concern that changes in tillage and nutrient management practices associated with residue removal may increase sediment and nutrient losses to surface waters.  The Soil Water Assessment Tool (SWAT) model was used to evaluate the overall impacts of increased corn acreage and residue removal on water quality in the Le Sueur River watershed due to sediment and nutrient losses.   Water quality impacts were studied with a corn-soybean (CS) rotation in comparison with a corn-corn-soybean (CCS) rotation, each rotation was evaluated with 0, 10, 30 and 60% residue removal rates. Sediment losses (t/ha/yr) increased with percent residue removal (RR) according to the relationship 1.24+2.51RR for the CS rotation and 1.73+2.2RR for the CCS rotation.  Total phosphorus (TP) losses (kg/ha/yr) increased according to the relationship 0.9+1.07RR for the CS rotation and 1.2+RR for the CCS rotation.  Total nitrogen (TN) losses (kg/ha/yr) increased according to the relationship 18.3+4.65RR for the CS rotation and 29.6+7.5RR for the CCS rotation.  These results show that significant degradation in water quality will occur if residue is removed at high rates from a CCS rotation relative to a baseline scenario involving a CS rotation with no residue removal.