A validation of Iroquois farming methods can be read in this press release from Cornell University.

The Iroquois planted what has come to be termed "the three sisters", beans, corn and squash, in a polyculture.

"Corn provides protection from weeds and insects and acts as a scaffold to support twining bean plants. The beans, in turn, produce nitrogen, essential for plant growth. Adding squash to the mix also controls the growth of weeds, and recycling crop residues (the "leftovers" of a harvest) back into the soil promotes fertility."

The format also means if disease strikes one plant, it won't wipe out all three species.