200square feet seems too low. This is only 18.5 m^2. I know that the best fields produce 60t of potatoes per hectar, so this field would give 111kg of potatoes. This is not enough calories for a year.
And as far as I am aware potatoes are oje of the densest energy source you can grow.
I find it really unausible that 6 square feet of Lima beans should be enough.
Care to explain?