Closed-system farming, where basically everything is recycled - nutrients, water, biomass (except what goes onto people's tables) - is theoretically possible and this article describes what looks like a successful system. This is also the kind of thing you'd need on a large spaceship or Martian colony (where human feces/urine would also need to be recycled). However, the increase in labor needed shouldn't be underest…
I don't think it would be so radical. For one thing, only about 1% of us work in agriculture now, so even if it takes 10x that's still only 10%.