But how do you kill the black grass before you plant wheat again. Grazing it will just keep it down until you plant wheat again. Then it will grow up through the wheat
Broadscale monoculture invites its own range of problems, and herbicide-resistant highly-competitive (when in a single-other-species ecosystem) weeds are one such.
If the starting position is 'we must grow the same variety of wheat in the same field every year', then indeed, you're going to have some challenges.
I don't really think its possible yet, (or it might not be possible with the current breeds of wheat)