That wonky dystopia. We have no food but we got sci-fi weaponry.
And if the soil and water is contaminated with radiation or god-knows-what else, you sure as hell wouldn't want to eat the crops you grew even if they you could.you can do like rimworld "build underground or in (mountain) farm with artificial light"
Which does absolutely nothing to remove radioactivity. You might remove some heavy metals, which is surely helpful, but the water is still contaminated. There's a reason why things like reverse osmosis is used for water treatment.purify water is really easy to do just evaporate and condensate it.
Which will still be contaminated by tilled top soil from you digging into it. And would require you to remove tons of dirt.And soil not contaminated is the easiest to find dig a bit the earth you will find it especially marsh soil is the best one.