Nitrogen is the most important nutrient that will directly affect the grains starch content.
High ethanol content is inversely related to grain nitrogen i.e. low grain nitrogen (or protein) is an indication of high starch content, and hence potentially high bioethanol yield per tonne. If the grain is grown specifically for ethanol then nutrient management practices should be adjusted accordingly. Nitrogen should be applied early in the growing season preventing any late nitrogen applications to increase grain protein content.