Farmers Field in public land

First to start off last year I decided a month before the season started that it was time to try my hand at bringing home some deer meat. So I got a new rifle, squeaked in under the line for time to get my hunters education course done and found a spot of public land to hunt. For the spot to hunt I ended up going to a spot that a co-worker advised as a good place next to his property. Needless to say I did not fire a single shot and learned the lesson of patience as the first day I would have gotten a three point had I sat still for another 20 minutes. And on the last day learned the lesson of not hunting near any roads where local duck hunters can get pissed off and drive down the gravel road at break neck speeds pushing the deer to the other side of the field where they are killed by another hunter....but I digress.

So fast forward to this year and I have been out shooting more then a few times and have the gun sited in to where I'm comfortable taking a shot at 300 yards. I have gone through and removed all scent from my hunting gear and have them five times bagged with a pound of sage to help mask anything left. I hit every bargain sale after the season ended and went from BDUs to actual hunting gear. I have taken to driving the back roads once a week in search of signs of good bucks. I also have found every source there is to be found for locating and identifying the BLM land. And picked the mind of every hunter I could find in the hope of gleaming just a little more of a chance of scoring my first buck.

That brings me to my question. As the lines are well defined as to where the BLM land ends and the private ends, what is the law regarding hunting a portion of a farmers land that crosses into public land.

You can't hunt on private land without permission.

"Go hunt for meat at Walmart."

The spot I picked to hunt from is way to far from the field its self to ever take a shot with my rifle. I guess it was just more of a general question. I looked into the plat and what it has for the geo lat and long, and he without a doubt has a 1/3rd of an acre in public lands. In that case is that potion...(And that portion only)... something that for future hunts I could use to my advantage? When I called the farmer to ask permission he said there were already to many hunters with permission to hunt his land...