So what's the question? Why we've gone to highly specialized agriculture over the last 60 years (according to ERS farms producing the most usually produce only one commodity)?
This study shows that a 3 and 4 year rotation using low inputs of synthetic fertilizer can beat the yields of a 2-year corn/soybean rotation. (Not organic, but low input.)
Great news, but what's the problem?
The problem is where's the market for the small grains and clover or alfalfa that are produced in the third and fourth year. In the good old days (and on Amish farms), the answer was horses--they'd eat the oats and hay. In the bad new days, no horses.