The Southeast is poised to be the leader in energy crop production according to University of Florida Associate Professor and energy crops expert Dr. John Erickson. He has been focusing on research of perennial grasses, mostly C4 grasses in his work with the Agronomy department. These can include sugarcane, energycane, elephant grasses, miscanthus, giant reed, switchgrass and sorghum.
In terms of output, in the short-term, sugarcane and sweet sorghum look promising. Current studies put sweet sorghum on par with corn in higher latitudes where it is a little colder. In the longer-term, cellulosic feedstocks such as energycanes and elephant grasses are producing upward of 40 megagrams per hectare. These grasses are selected for their fiber content – they don’t have high juice or sucrose contents that sugarcanes do but the yield more biomass.
Perennial grasses offer several advantages, said Erickson, including not having to plant the crops every year so you don’t have renewable annual planting costs and they tend to be a little more efficient in water and nutrient use.
If a grower chooses to grow a perennial crop, that becomes the crop for that land area, explained Erickson. Therefore a grower 
must commit to a longer-term commitment when they grow perennial grasses. “Some of that will be dependent on how they incentivize, or even if, they incentivize carbon credits and whether or not agriculture has the potential to be involved in that. And so if that becomes a reality then perennial grasses will be viewed more favorably than something like sorghum. If they don’t, than sorghum may do just as well or better than some of these others because they can be worked into rotation with current existing crops.”
Erickson stressed that the results are still in their early stages and crops typically do better in the second year. It will be a year or so before the final results are published, but in general, he notes that perrienal grasses look like they have good potential as energy crops.
Listen to my in depth interview with John here.