A green patch is bait placed in a specific location by man to lure game into gun or bow range.
You had me until you said this^^^
Green fields, except for on the best of the best places, are not placed in specific locations. They are where they are. Most of the time they are in the worst place possible for deer hunting. MOST are planted with the purpose of killing a deer standing in them though.
That said, unless you're CNC, there is more effort in food plotting than just throwing seed on the ground like you can a bag of corn.
JK of course crimson