You're not going to plant anything that will get ahead of Johnson Grass except maybe kudzu. I have 1 field that I've been fighting since I bought my place. It used to be thick 6'-8' tall. JG is a prolific reseeder, but it will also survive the winter and resprout from rhizomes. I started spraying it with a hot mix of gly to get it under control (sprayed with a tractor with boom sprayer). After several years I have it mostly knocked back but still have to spot spray every time I'm at the camp during summer.
One thing that is very important is try your best not to spread the JC seed. If you mow a field with JC, stop at the exit and sweep your mower and tractor off the best you can. An ounce of prevention is worth a 55 gallon drum of glyphosate... err I mean a pound of cure.
