Diverse cover-crop mix delivers tonnage, healthier soil.
They call it a cover-crop “cocktail” in South America. In North Dakota, it's an exotic seed “salad” that's surprising ranchers, forage growers and even cash grain producers.
In late July or early August, they fill their no-till drills with a mix of seed for six to eight crops. Then they plant it in a single pass without fertilizer through the residue of whatever crop was early harvested or perhaps winterkilled.
Initial results show it producing more than 6 tons/acre of forage by October. It's for grazing, but could be harvested for silage.
Trials began in scorching conditions in July 2006 with a unique series of small test plots, says Jay Fuhrer, Burleigh County NRCS district conservationist in Bismarck. Most of North Dakota was extremely dry that year.
The research crew had seven crop species to plant. One set of plots each had one of each species. The second had two, the next had three, then four, five and six. The last had all seven species in a single plot.
“The more diversity we had, the better it did,” Fuhrer recalls. “By the time we got to seven species, they just flourished. It was lush, it was tall, the leaves were flat open. The monoculture plots were pretty much dead. That's a real eye-opener.”
A year later, brothers Marlyn and Patrick Richter planted a 70-acre cover-crop salad after early harvests of peas and winter triticale. For comparison, they kept a few acres under chemical weed control.
They planted seven types of seed on July 7. Cowpeas, sweet clover and soybeans are later-maturing crops that fix nitrogen; millet and sudangrass use nitrogen. They also chose a cool-season, broadleaf crop (turnips) and a warm-season broadleaf crop (sunflowers).
The brothers grazed 141 cow-calf pairs for 17 days in October. The millet seed heads went first, followed by millet leaves. Soybeans, cowpeas and sunflowers were third choice, followed by the brassica leaves. Then the cattle nosed into the turnip tubers.
The Richters took the cattle off while half the cover crop was still on the field. They saved that to feed to soil organisms.
Average calf gain was 52 lbs or 3.1 lbs/day. They reckoned gross income at $111/acre and net at $66/acre.
The uncovered portion of the field required two herbicide treatments and wind eroded some soil. That winter, snow blew off the open ground but “stuck” on the cover crop side, says Marlyn Richter.
While the cover-crop mixture provided fresh grazing, Richter says some poor native pasture was getting badly needed rest.
On May 5 of this year, Richter planted Roundup Ready corn on the site. Earthworms and microorganisms had greatly reduced the residue. Compared to the other side, the covered side had at least three times as many earthworms and very low weed pressure, he says. It needed one burn-off; the other needed two.
Hal Weiser, a USDA-NRCS soil scientist at Bismarck, took soil cores May 6. He says moisture availability for the next crop was virtually identical on both sides, at 3.11” on the check side and 3.07” on the covered side. But soil from the covered side had better tilth and higher organic content.
“The enhancements they're seeing — especially in so short a period — are new and very exciting,” says Kris Nichols, USDA-ARS soil microbiologist at Mandan. “All of these things work together, even though all of the organisms are living for their own benefit.”
Diversity is a key factor, she says, adding that it seems essential that the mix contain seeds of warm- and cool-season plants, including grasses, legumes and broadleaves, with a variety of rooting depths.
Growth of organisms beside the plant roots is nearly explosive, says Nichols. They consume organic matter, leaking it as plant-available nutrients and reducing water leakage from the roots. They improve the soil's structure so it's able to capture moisture.
On the surface, crop material first prevents evaporation, then as it decomposes it acts like a sponge that collects and holds newly arriving snow or rain.
“The different groups give resiliency to withstand different conditions,” says Nichols. “It isn't just one cycle. The interconnecting cycles are making everything work so much more efficiently.”
One result of the lush fall growth is an increase of soil carbon, drawn from the air by the cover crop.
“Marlyn and others in Burleigh County are reducing the cost of production and improving fertility by requiring plants to grow and give carbon to the soil organisms,” Nichols says. “When that system is cycling very well, you don't have to keep putting in inputs.”
She and colleagues are developing research projects to better understand and support a diversified cover-crop system.
“I believe we're at the beginning of a paradigm shift,” she says. “The system has a tremendous amount of potential, even if you don't have cattle. In the long run, it is going to improve soil health and fertility and even reduce input costs. Cover crops are feeding those organisms in the soil and giving long-term benefits.”
Richter continues to be enthusiastic.
“It was tremendous,” he says. “We grew that cover crop on a difference of 0.04” of rain, and we had 6-8 tons on there. For the amount of forage we got, the amount of organic matter and residue I was leaving on there and grazing my cattle, making $66/acre profit just off the calves, that was a tremendous deal. And what a soil health advantage we have now!
“It's going to be closer to 200 acres this year, and it's going to be (part of the rotation) probably every third year,” he adds. “We can start to build up our soils where they're poor.”