Take all this with a grain of salt, this is my first year for a dedicated food plot, but Ive ton a ton of research on here, and I didnt stay at a Holiday Inn last night.
First off, this thread was extremely helpful to me:
http://deerhunterforum.com/index.php?threads/dbltrees-getting-started-threads.869/, its not all about food.
Again everyone on here needs to remember there might be a fair amount of difference between "here" and "there". What works in one place might not in another. Also scale is different in different parts of the country, for you a small plot might be 4 acres, for someone in NY for example, a spot the size of a big garden might be huge. Generally speaking about an acre or more is usually enough of each type of plot to support a good sized deer herd
The root systems of the different plants are what make it tough, bluegrass has a massive rootsystem, which is great when its growing, but trying to do any tillage or even plant right into it in the spring is almost impossible. Most "weeds" dont have the fiborus root system like bluegrass so by looking at your plot after disking you would be alright, here a bluegrass field wouldve had baseball and softball sized clumps of grass and dirt everywhere, even after multiple diskings.
Here we usually try to kill sod in the late fall time, after mowing it the last time, let it get some growth and hit it hard with some roundup and something with some residual action, if youre unfamilar with chemicals and spraying, its best to get an expert. Then let it lay all winter where the freez/thaw action and the rotting of the sod roots will make a nice mellow seedbed but not loose like tillage, perfect for notilling with a planter or drill. But that might not work as well in South OK with the milder temps.
What I would do now is hit it hard with Rup might throw some 2-4D in and make sure everything is dead, the 2-4D will give you about 4-6 weeks of residual on broadleaves IIRC. Then plant the buckwheat, kill it later this fall, should be able to do it with a roller or anything that will knock it down and plant a oat/rye/crimson clover mix in it. Then next spring depending on what you want to plant, you can kill it with a shot of Rup again or let it grow.
4 acres is a heap plenty of one crop, I like the idea of a bunch of different things in each plot, it gives them variety depending how they feel or what they need, but I see your thinking.
Some other ideas for you to think about too. Milo will be more drought tolerant than corn and cowpeas would be a more drought tolerant than soybeans. Those would make a nice mix together in a plot, the cowpeas would climb the milo, lots of CPs grown in OK, but I dont think any are RR (roundup ready). If you wanna save some money, maybe put a CL add out or ask at your local COOP looking for leftover soybeans, milo, or corn, thats what I use, just leftover seed from planting that we cant send back, usually any opened bags or some that was left when changing hybrids, you could save some from this year in airtight 5 gal buckets from home depot in a basement and use it next year.
Any other questions feel free to ask!
