While it would require some changes, planting cellulosic ethanol feedstocks like switchgrass doesn't require a total agricultural realignment. Switchgrass can grow in in poor soils and with minimal fertilzation.
It's not that simple. Crop rotation must be part of the equation, so twice as much area must be dedicated to the task. The choice of alternative crop to address soil depletion is a critical (beef production?) component of the long term solution.