Calculated Cover Crops
Fine-tuning diversified rotations helps one North Dakota farmer overcome yield-limiting conditions.
By Susan Winsor
Progressing Farmer Contributing Editor
Weather, soil and economic limitations have crushed many a farmer, but Rocky Bateman decided to turn those challenges into opportunities.
Financial stress moved the New Salem, North Dakota, farmer to no-till 18 years ago. Bateman's management decision has resulted in higher yields from the improved soil health.
"Low prices and drought have demonstrated soil health's value," he said.
Bateman readily admitted farming "some of the poorest soils in Morton County" is challenging. Add to that a 90-day frost-free growing season, frigid winters and 14 inches of annual rainfall, and the deck's stacked against him. But, building soil organic matter to 5% has provided the same yields as recorded on the best nearby soils.
Even with the 2017 Plains drought, Bateman and other no-tillers were among the few farmers in the region to get a crop, thanks to high soil organic matter and drought-resilient soil that stored moisture, he said.
Bateman credited replicating the prairie ecosystem by adopting a four- or five-crop rotation, having living roots and residue ground cover year-round, minimal soil disturbance, plant diversity and incorporating livestock into the operation.
"I've farmed for 43 years, and I'm more excited than I've ever been because this system works. The first 25 years, nothing worked because I was fighting Mother Nature," he said.
Strategic crop-rotation sequences have improved his yields by building and diversifying the fields' soil biology. But, for many Plains farmers, the hardest sequence is knowing which crop should follow sunflowers.
To determine what works best, Bateman worked closely with retired USDA scientist Don Tanaka, who led a research team at the USDA-ARS Northern Great Plains Research Lab that developed a free online crop-rotation sequence calculator.
Bateman learned that corn is the best crop to follow sunflowers because corn roots follow sunflowers' leftover deep taproot channels. Those channels also improve soil drainage and air and water circulation.
Following sunflowers with corn contradicts conventional wisdom of following sunflowers with wheat or other cool-season grasses.
Tanaka speculates another reason for the winning corn-after-sunflowers sequence may be because corn is a high-mycorrhizae crop. Sunflowers help to establish root-zone conditions favorable to this beneficial fungus that make nutrients more plant-available, he said.
IMPACT OF PRICE
Tanaka offered another example of the calculator's use. "Right now [September 2017], lentils, chickpeas, dry peas and dry beans happen to be at a relatively high price, so producers could plug in their circumstances and see if they fit into their rotation."
One example is Mandan spring wheat. Yields for the crop jumped by 30% in a dry year when following dry peas compared to continuous spring wheat. This kind of synergy can result from diverse water-use depths and timing, and/or from diversified soil organisms. "We still don't have all the answers on crop synergies and antagonisms, but it's based on more than water use," Tanaka explained.
The USDA-ARS calculator quantifies the efficiency/financial boost from various rotations among 10 crops (corn, spring wheat, sunflowers, buckwheat, canola, chickpeas, dry peas, grain sorghum, lentils and proso millet.) Cropping systems need to be more than three years to capitalize on crop diversity. Yields were more stable over time, and precipitation-use efficiency increased.
Bateman's rotation alternates warm- and cool-season grasses with warm- and cool-season broadleaf crops when possible. When determining rotations, he also considers market prices, amount of crop residue (to maintain adequate soil coverage to feed microbes) and rotating herbicide modes of action to slow weed resistance.
He said he still hasn't found a satisfactory cool-season broadleaf to include in his rotation, which includes:
-- soybeans (warm-season broadleaf) that do extremely well on his sandy soils
-- spring wheat (cool-season grass) benefits from soybeans' nitrogen
-- sunflowers (warm-season broadleaf)
-- corn (warm-season grass).
Bateman tried canola and flax, two other cool-season broadleaf rotation options, but they didn't grow well except as part of a cover-crop mix. Also, canola requires expensive inputs. "I'm trying to grow my own nitrogen instead of buying it," Bateman said. "I also hate to have too many crops in that late-harvest category, vulnerable to snow and rain," he added.
He's moving to a five-year rotation, inserting a full-season, 11-species forage cover-crop mix. Besides broadening the microbial habitat, they're forage for his daughter and son-in-law's cattle.
This mix includes four clovers, radishes, turnips, oats, millet, annual ryegrass, kale and soybeans. The variation provides free nitrogen, "biologic tillage" (via the radishes) and a variety of root depths and life cycles. For $27 per acre, Bateman is mimicking the diversity of the original prairie ecosystem.
Why Broaden a Rotation?
By Susan Winsor
Progressive Farmer Contributing Editor
Diversifying your rotations is like fine-tuning a factory. Broad rotations that increase crop residue feed beneficial soil organisms. They also improve your nutrient recycling and soil structure, and gradually build soil organic matter, the magic sponge that makes soils more resilient in wet and dry years.
Higher soil organic matter also increases soil pore space. These "soil highways" circulate vital air and water among roots, store water for dry spells and even out water storage in wet ones.
Soils that absorb water faster and efficiently translate into quick recovery from intense rainfalls and storing water in pore spaces for drought. Research finds that 20% of yield loss occurs 80% of the time because of water availability.
In other words, a soil's ability to drain or store water efficiently correlates strongly with yields, said Jerry Hatfield, lab director, USDA's National Laboratory for Agriculture and the Environment, located in Ames, Iowa. Abundant soil microbes, fed by diverse crops, improve organic-matter turnover and nutrient cycling. This, in turn, improves soil structure and water availability, he said. This all results from having a year-round stable food source for your soil microbes, he added.
Research shows with each 1% increase in soil organic matter (i.e., soil carbon), soil's water-holding capacity increases by 3.7%.
Diverse crop rotations also expand beneficial soil-microbe populations. A handful of soil contains more soil microbes, working on your behalf than there are people living on the earth, according to USDA studies.
These "underground livestock" recycle residue into nutrients and carbon, and make nutrients more plant-available. By choosing crop rotations with nearly yearlong living roots underground, you maximize your "soil microbe factory."
For More Information:
USDA Crop Sequence Calculator: bit.ly/2h1FP3z
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