Potential feedstocks from crop-based energy production systems range from starchy and sugary tuberous crops to woody, oilseed, or herbaceous crops (including corn, sweet and grain sorghums, and several grasses). An important characteristic of biomass crops is that the ratio of energy of the biomass product be large compared to the energy used to pro­ duce the crop. Because one of the most costly inputs in the latter component is nitrogen (N) fertilizer, any evaluation of potential energy crops must emphasize N inputs. Given its high N requirement, corn is not likely to meet all future ethanol demands. Corn also is limited by the inefficient conversion of starch to etha­ nol and by environmental and conservation considerations such as suitable land use.