What about the farming activity concentrated in California, Florida, Texas, etc. It's not even close to being in one place, it's a matter of what is grown where.
I think that what needs to be examined here is why is there a concentration of money in a single (or handful) of districts?
My first guess is going to be a concentration of land ownership by a small group of people/corporations/partnerships. The landowner makes the money, not the farmer.
Take a drive and ask around as to who is buying up the farmland. You'll find a very short distance between the two points of corporate farms and chemical/seed companies.
What do YOU reckon most of that money is going to be spent on?
I think when Congress thinks about farming they think about corn and beans.
The money is going to be spent on new pickup trucks, farm equipment, and property taxes. At least that is how it works in my small part of Minnesota. Farms are bigger it is true, but most of the corporate farming is partnerships of area farm families who have been here for decades.