The rapid expansion of ethanol production from maize grain necessitates a better understanding of the factors that influence ethanol yield.  Especially important is the relationship between yield enhancement and ethanol production efficiency, and little is known about how crop management influences ethanol productivity.  Our research is addressing these issues by evaluating the impact of major crop management practices on ethanol productivity using whole-grain near-infrared spectroscopic methodologies developed by Pioneer Hi-Bred International.  Management practices examined include: location, hybrid selection, N fertilization, plant population, and previous crop.  At all sites and for all management practices, there was always more variability in grain yield than in ethanol yield.  Average ethanol yield varied 5.2% between 22 on-farm trials distributed over four states (IN, IL, IA, MN) in 2006, while in-field spatial variation averaged 7%.  The maximum variation between the highest measured value (463 L/Mg) and the lowest value (407 L/Mg) in this data set was 14%.  Ethanol yield varied by 4% between the lowest and highest entries among a group of 17 commercial hybrids grown at the same location.  Nitrogen fertilizer had a negative effect on ethanol yield, which decreased from 444 L/Mg to 433 L/Mg (2.3%) as the N supply went from deficient (no applied N) to excessive (280 kg N/ha).  Conversely, increasing plant population had a positive but small effect on ethanol yield which increased from 436 L/Mg to 440 L/Mg as plant population increased from 70 to 100,000 plants/ha.  Ethanol yield was higher for continuous than rotated corn, but this effect was also of small magnitude, particularly at high N rates and for hybrids of high ethanol yield.  Our research shows that hybrid selection and N supply can exert measurable impacts on potential ethanol production from maize grain and that N should be carefully managed to avoid over fertilization.