South Dakota farmer Dwayne Beck uses cover crops in his farming practice, and rotates alfalfa with continuous corn.
Dwayne Beck admits right away that his farm “is research.” Why else would he alternate alfalfa with continuous corn? Say what? That’s a sampling of the different farming approach he takes at the Dakota Lakes Research Farm, Pierre, S.D. The producer-owned farm, also part of South Dakota State University’s ag research program, is led by Beck’s no-till-or-nothing approach. He takes conservation farming to the next level.
He recommends that fellow growers work a strong cover crop cocktail into their corn and soybean production. In his continuous-corn studies, he uses a cocktail mix of cool-season winter annual grasses and broadleaf crops planted in the fall. For soybeans following corn, he uses just a cool-season grass mix.
“Cocktails can be any number of plants depending on what they are trying to accomplish,” Beck says. This includes sorghum, flax, millet, mung beans, cowpeas or black-eyed peas, field peas, hairy vetch, chickling vetch, sunn hemp, turnips, lentils, canola, ryegrass and rapeseed.
“In continuous corn, you need legumes and non-legumes,” he says.
In a 2011 dryland test of corn following winter wheat (see chart), a check field yielded 119 bu./acre with no added N and 153 bu. with a 75-lb. N application. However, fields with cover-crop cocktails planted following the previous year’s wheat harvest had yields up to 15 bu./acre higher. Yields from fields with no N application ranged from 122 bu. to 143 bu.
“The cocktails help to turn excess water into something beneficial by scavenging soil N so it doesn’t get lost, and fix additional N from the air. They also grow beneficial soil microorganisms and host beneficial insects,” Beck says.
“Cover-crop cocktails also produce residue, vital carbon to the soil. The right mix will cycle diseases and temper high-carbon residue into more benevolent forms. Moisture used in this process is replenished by the time it’s needed for the following crop because of enhanced snow catch and better water infiltration and storage characteristics in the soil.”
But alfalfa? “Why not under irrigation or in wet climates,” Beck says, noting that a perennial alfalfa crop in continuous corn can reduce corn’s N requirements. “It cycles deep water and nutrients better and produces a resilient seedbed.
“We know that non-legume plants in cover-crop cocktails can source N from the legumes through thevesicular arbuscular mycorrhiza network. (The arbuscular mycorrhiza fungus penetrates the cells of roots to capture soil nutrients such as N, P, sulfur and micronutrients. This highly evolved mutualistic relationship between fungi and plants, the most prevalent plant symbiosis, is found in 80% of vascular plant families.)
“We think corn and alfalfa polycultures will work the same way. Manufacturing, transporting and applying 150 units of N requires energy equivalent to 30 gal./acre diesel. That’s expensive.
“You can’t manage the ecosystem if you till,” Beck says.