Retard farming can be done in a variety of different ways; here is one of the more rustic examples:
Step 1: Buy a farm.
Step 2: Collect retards from government programs.
Step 3: Put said retards on farm.
Step 4: Allow them to graze the lands in a retarded stupor.
Step 5: Collect government money and become filthy fucking rich.
Farmer 2: "Well I heard Farmer Eveland lost his whole stock! They dun' got trapped in the barn while in burnt down. Yep, siree! Them retards dun' been so stupid they couldn't figure out how to open the barn door!"