Before all the land was cleared for crops and livestock quite a bit of
the US was covered by native bamboo (canebrake)
Much nicer than the Norway maples my neighbors insist upon or the other
invasives like turfgrass which has taken over the nation' consumed
resources, and fouled both ground and suface water with it's
mismanagement.
Have you seen any 10 acre stands of bamboo? Or even one acre stands if
it is so invasive?
As for building new soil, anytime you use the energy of the sun to make
new carbohydrate and protein from the gases in the air you will improve
the soil.
Kenaf and bamboo might be even better sources of fiber than hemp in the
long run.