Revisiting Crop Rotation

Wired:

Liebman, inspired in part by a pioneering Iowa farmer named Dick Thompson, wanted to bring integrated pest management back, but augmented with technology’s new tools. On 22 acres at Marsden Farm, his team planted three plots with different rotations of crops. The first followed a two-year rotation, alternating between corn and soybeans, as is customary in the region. It was managed the usual way, with lots of chemicals.
For the second plot, the researchers rotated over three years between corn, soy and oats, with red clover planted in winter. The clover, which absorbs atmospheric nitrogen, was planted between crop rows and plowed under as soil-replenishing “green manure” in spring. On another plot, instead of red clover the researchers planted a fourth-year crop of alfalfa, which can be used to feed livestock. The animals’ manure came back as fertilizer.
On these fields, the researchers still used herbicides and pesticides, but not the usual way. Rather than spraying them routinely over large areas, Liebman’s team applied them only when necessary. “We use low-dose products in the smallest quantities possible,” he said. “We’re not against their use. What we’re arguing for is using them as carefully deployed tactical options.”
Liebman called these applications “therapeutic measures.” Therapy wasn’t often needed. Having different crops with different life cycles made it harder for weeds to grow. What might flourish among corn and soy, for example, was disrupted by oats. When red clover and alfalfa were mowed, weeds were chewed up before they flowered. As for insect problems, low pesticide use, along with habitat provided by cover crops, allowed pest-eating bugs and birds to flourish.
After eight years, Liebman and Davis used eight times less herbicide in the three- and four-year rotations than in the conventional plot, they report in the new study. Ecotoxicity in surrounding water was two orders of magnitude lower. Thanks to clover and alfalfa, the experimental plots also used 86 percent less synthetic fertilizer.
Most important of all, the experimental plots were as productive as the conventional.

My old neighbor Woodie ran a four crop rotation almost his entire life.  My neighbor up the road uses corn, soybeans, wheat followed by hay, which he pastures in the fall and winter, chops in the spring, then tears up and plants corn which he chops or picks.  The problem with implementing such a rotation in many places is that most farmers don't want to do all that work, and don't want to have the livestock around to provide the manure.