Illegality
Switchgrass is a viable substitute for hemp, largely because hemp enjoys the dubious distinction of being the only crop that is legal to import into the United States, but also completely illegal to grow. Switchgrass possesses an attractive biomass yield without the political thorniness.
Current Production
Hemp is the number one crop in the world used for ethanol-making biomass, with the most production coming from China and Russia. Hemp has other purposes, which makes it an important and attractive crop for export, but the advantage of switchgrass is that it is a hardy, adaptable plant that is native to North America, meaning that it is ideal for growing within the United States.
Yield Potential
In long-term research trials, switchgrass has been shown to yield, on average, 15 tonnes per hectare. This converts into about 380 liters of ethanol per tonne harvested, which is slightly less than the yield of corn ethanol. Hemp yields about 6 tonnes per hectare, but can be harvested throughout the year, which ultimately makes for a greater output. The advantage of both crops is that they are not as input dependent as another ethanol crop like corn, which means they use acreage much more efficiently and in a more environmentally friendly way, as grasses don't tend to exhaust soil like other types of crops.
Nonfuel Uses
Switchgrass is largely used for ethanol creation, bioplastics and notably to preserve arable soil, as deep root grasses literally hold soil together and prevent desertification, as seen in the dust bowl conditions of the mid-20th century. Hemp is fibrous, which makes it useful for more types of applications in addition to ethanol biomass, which includes processing of fiber for paper and fabric.