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Plant Diversity Builds Biological Activity
After nearly a decade of growing cover crops and a long list of no-till cash crops, Dan Forgey, agronomy manager at Cronin Farms, Gettysburg, South Dakota, sees mounting benefits from plant diversity.
“Adding cover crops to my rotation has given me healthier soil,” he says. “Cover crops feed the soil microorganisms and speed up the formation of organic matter.”
Increasing the diversity of cash crops further helps soil health. “My soils are responding to the diversity in the rotation as well as to the cover crops,” he says. “I’ve gone from planting four kinds of cash crops to as many as 10 different crops.”
Plant diversity enhances the biological activity in the soil. These biologically active soils break down residue readily. This has helped build organic matter, which has increased from 3.2% to 4.1% in 10 years.
Furthermore, the breakdown of residue by the biological activity creates nutrients for the subsequent crop. This decreases the need for some crop inputs while yields remain constant or increase.
This year’s cash crops include spring wheat, winter wheat, corn, sunflowers, oats, field peas, lentils, and flax.
Forage crops for the farm’s 850 beef cows further increase diversity. “I grow teff grass along with sorghum sudan,” says Forgey.
Cover crops grow annually on about 10% of the farm’s 8,000 acres. “I plant about 90% of the cover crops on fields where winter wheat has been harvested,” he says. “I no-till the cover crop mix into the wheat stubble and let frost terminate the cover.”
Some cover crop acres are devoted to fall and winter grazing for heifers. This year’s grazing mix comprises sorghum sudan, oats, millet, grazing corn, buckwheat, radishes, flax, and dwarf Essex rape.
He seeded the mix this summer during the first part of July on ground that had not yet produced a crop in the 2015 season. The heifers will graze the field from late fall through winter.
Dry growing conditions last summer changed the normal sequence of cover crops. Counting on late-summer rain, Forgey’s plan in early August was to plant a cover crop the first of September on fields where lentils had been harvested. The cover crop mix would include cereal rye, oats, turnips, and radishes along with the volunteer lentils.
Tweaking the cover crop mixes to retard residue breakdown is an ongoing process.
“My first cover crop in 2006 was dwarf Essex rape mixed with Indianhead lentils,” he says. “The low carbon-to-nitrogen ratio in the plants caused them to break down too fast, though, leaving little residue behind. In my dry environment, soil needs a lot of residue.”
Forgey has since included in the mix high-carbon crops like cereal rye and oats. “I love oats, and it offers the benefit of a fibrous root,” he says.
Flax is of particular importance in the cover crop blend, partly because of its structure. Like other species in the cover crop mix, flax winterkills. Its stems tend to stand erect overwinter, thus, trapping snow.
“Flax also increases the colonization of mycorrhizal fungi in the soil,” says Forgey.
He credits this activity with a reduced need for applying phosphorus (P). “I maintain high levels of P in the soil even though I apply P at a rate that’s about 50% of the rate I applied five years ago,” he says.
Pesticide is another input that has decreased in recent years. Forgey credits the decrease to plant diversity.
While nitrogen (N) applications have remained constant in recent years, yields have increased, suggesting gains in N-use efficiency.
Fueling these soil processes requires large amounts of crop residue. “My soils have become so biologically active that the residue from the previous crop is 80% gone one year later,” he says. “I really have to pay attention to having a high carbon-to-nitrogen ratio in the crop residue so that breakdown doesn’t occur too quickly.”
Forgey produces and conserves as much residue as possible to build the residue storehouse. Growing tall varieties of crops such as oats and wheat helps.
“Harvesting with a stripper header helps, as well,” he says. “The stripper header leaves the stubble standing, and the tall stubble traps snow, of course. I’ve found that when I straight cut a crop, the residue is broken into small pieces, and these break down too fast.”
To diversify crops further, Forgey has recently planted a few small fields to perennial grasses for both haying and grazing.
“Perennial grasses have the benefit of being really deep rooted,” he says. “My whole focus is on increasing plant diversity and improving soil for the future. I’m farming so that when the next generation of farmers takes over, they’re going to have land that’s on an upward rise in health.”
Forgey chooses cover crop species that are economically priced and that have a proven track record on his farm.
“In my dry environment, it doesn’t always pay to plant a wide variety of exotic cover crops,” he says. “I focus on crops that will grow well in my environment.”
Species of cover crops he tends to plant most frequently include high-carbon cereal crops like oats, millet, and rye along with flax, which is highly mycorrhizal. He also typically includes Indianhead lentils for N and a small amount of brassicas like turnips, radishes, and dwarf Essex rape.
“I’m really cautious about using brassicas,” he says. “In my environment, the brassicas break down residue too fast.”
Of the brassica species, Forgey tends to include in the mix a higher proportion of economically priced dwarf Essex rape seed than the more higher-priced seed from radishes – or turnips, which are used only for grazing.
“Rape produces the same biomass on top of the ground as do radish and turnip,” he says. “Rape tubers are smaller, but they’ll still reach down and break up compaction. I’ve gotten a lot done with dwarf Essex rape for a seed cost of $1 a pound, while radish seed costs $3 a pound and has a third fewer seeds per pound. The same benefits come at a more economical seed cost.”
Forgey continues to include radish in the cover crop mix, but at a decreased rate. He blends into the mix a half pound to the acre of radish seed and the same amount of dwarf Essex rape seed.
“There’s no Easy button to push when it comes to choosing what types of cover crops to grow,” he says. “I have to figure out what works best on my own place.”
Contact Dan Forgey at 605/769-0277 or firstname.lastname@example.org.