well, if we're growing more consumable biomass per acre or whatever, we can do something else with land we would have otherwise dedicated to producing the same amount of potatoes.

Not an expert, but read the Omnivore's dilemma which kinda runs through how modern farming works on a high level. Basically you figure out what the chemical building blocks are for what you're trying to grow, and fertilize the soil with that. The plant then pulls that out to actually construct the corn or whatever it is you're trying to grow.

Of course it might not be as delicious and nutritious as what you might be able to grow at home or at a well managed organic farm, but the goal is quantity here.