No-till-driven crop diversity is revealing that some crop sequences can produce benefits exceeding those attributed to rotation alone.

“When cropping is diversified, there is often a rotation effect, but crop synergism goes beyond that,” says Randy Anderson, a USDA Agricultural Research Service agronomist based in Brookings, S.D. “We’ve found that some crops can improve the use of resources, such as water and nitrogen, in continuous, long-term no-till situations.”

Anderson first noted the crop-synergism impact while conducting a rotation experiment in northeastern Colorado, where annual rainfall is about 16 inches.

Five years into the study, which included 15 different rotations, he noted an increase of water-use efficiency for wheat when corn and dry peas (terminated 7 weeks after planting) were included in the rotation.

When the rotation effect was factored out of his data, it was clear there was something extra going on in sequences utilizing corn and dry peas, he says.

Yield Advantages. In a 7-year study, corn following dry peas yielded 11% more than corn following soybeans across the entire period — but the yield gain was significantly higher during dry years. Anderson says the synergies he identified are most apparent during crop stress.

In another trial, grain yield was reduced 75% by foxtail millet interference when corn followed soybeans or spring wheat, but by only 50% when the corn crop was preceded by dry peas. In this 3-year study, corn yields varied from 95 to 150 bushels per acre in weed-free plots, but 11% yield benefit was consistent…