There are several ways to measure the costs and benefits of crop rotations. Weed population changes, soil organic matter building or depleting, yield bumps or total energy used are all different ways of gauging the relative advantages of different rotations. Dr. Perry Miller, professor at the University of Montana, has done extensive work into crop rotation diversity, energy use and economics.
At the recent Farming Smarter conference, Debra Murphy interviewed Dr. Miller (who originally hails from Saskatchewan) to gain his insight into some of the barriers to more robust crop rotations in the west, as well as the costs and benefits of including green manure in a rotation.
If you cannot see the embedded video, click here.