Without question, cover crops can improve soil health—and better soil health means more efficient use of resources and the potential for higher yields. But failing to select the right cover crop will waste money as surely as dense, crusted soil wastes rainfall.
It’s not difficult to find farmers who skimped on the planning process and wound up disappointed with their cover crop. There are plenty of successful cover crop users, too. Their experiences can help you choose the cover that will set your soil on the road to better health.
“What stands out with successful cover crop users, versus those who struggle, is the successful ones had an objective,” says Farm Journal Field Agronomist Ken Ferrie. “They thought through all the steps of growing and managing their cover. That makes the odds of success go way up.”
Goals: Address Compaction to Increase Yields
Recently acquired by the operator; corn/soybean rotation; significant amount of highly erodible land; no-tilled for years by former tenant
To understand why yields weren’t up to par, Ferrie dug soil pits. Beneath the surface, substantial compaction or density layers from long-ago horizontal tillage were restricting root growth.
Deep vertical tillage would have removed the dense layers fairly quickly, but tillage was not acceptable to the landowner. The operator needed a cover crop that would function like a subsoiler—penetrate dense layers and leave biochannels for roots to grow and water to infiltrate.
When evaluating cover crop options, use a source such as the Midwest Cover Crop Council (www.mccc.msu.edu), Ferrie says. “You’ll probably find a number of crops that can penetrate dense soil layers, but only a few that will fit your climate and your time windows in the fall and spring,” he adds. “Not only must you get the crop planted in the fall, but to be most effective, many covers also need to grow in the spring. The amount of growth you see above the ground reflects the size of the root system.”
The planting window becomes shorter, and your cover crop options more limited, as you move from south to north.
In this case, the operator, who farms in central Illinois, could have used cereal rye, annual ryegrass, radishes or sweet clover to achieve his objective. Farther north, his options might have been limited to cereal rye, which can be planted later in the fall.
The farmer realized lengthening his planting window would increase his chances of success. So he switched from his 111-day corn hybrid to a 104-day hybrid and planted it first. Although it meant he had to use artificial drying, he harvested the hybrid at 27% to 28% moisture.
The cost of the cover crop included not only seed but potentially lower yield from the shorter-season hybrid and drying expense. However, it gave the farmer enough time to plant a mixture of cereal rye and radishes. Because the next crop was soybeans, the cereal rye had some time to grow in the spring, as well as in the fall. (The radishes winter-killed.)
After soybeans, the farmer considered the challenges of planting corn into cereal rye, and decided oats and radishes were a better choice. It’s best to plant as close to harvest as possible, or even before harvest.
“To lengthen his planting window, he may want to fly the cover crop seed into growing soybeans,” Ferrie says. “Our experience with aerial seeding has been hit and miss. Success depends on getting rain within two weeks of seeding.”
The farmer makes sure to have his cover crop seed on hand and a person designated to plant it while he’s still combining.
“Although we are not conducting side-by-side trials, our infiltration tests show water infiltration is getting better,” Ferrie says.
Goals: Store Nutrients, Protect Soil
Continuous corn, which the operator chops for silage; knifes in liquid manure
This operator has two objectives for his cover crop: capture and store excess nutrients, especially nitrogen, which he applies in early fall, and protect the soil surface from erosion.
In this farmer’s location, he could plant barley, annual ryegrass, cereal rye, millet, oats or wheat, perhaps with some radishes added to the mix. “With mixtures, just make sure everything that’s included accomplishes one of your objectives,” Ferrie says.
To smooth the surface after manure application, the operator tills about 7" deep—using a modern hybrid chisel that provides full-width shattering at shallow depths—and levels with a vertical harrow. Then he broadcasts the cover crop seed. “If the weather is dry, he incorporates the seed with his vertical harrow,” Ferrie says. “But if he has good moisture, he doesn’t need to.”
If there is good growth in the fall, it gives the farmer a cattle grazing option. “In wet weather, he has to be careful the cows don’t compact the soil,” Ferrie notes. In the spring, the operator kills the cover with a herbicide or chops it for silage.
Grazing or chopping the cover probably won’t be allowed if you’re enrolled in a USDA program, Ferrie points out. “Some would say you should leave the cover crop residue to improve soil health,” he says. “But that was not this grower’s objective. Even though he harvested the crop in the spring, his soil was still protected from erosion, and he received a good return on his cover crop investment.”
Goal: Rebuild Soil Structure
Recently acquired farm; corn/soybean rotation
Soil fertility in this field is good, and digging revealed no density layers. But yield failed to match similar farms in the area. Poor soil structure from abusive tillage had broken down the aggregate stability, so the surface sealed when it rained and water ran off.
“This grower wants to rebuild his soil structure, creating macropores between soil particles for water and air,” Ferrie says. “Grasses, such as annual ryegrass, cereal rye, barley, wheat and sorghum-sudangrass, as well as sweet clover, can improve soil structure.”
Timing is an issue because it’s difficult to build soil structure unless your cover crop develops plenty of growth and root mass. “The ideal solution, with the fastest structural improvement, would be to plant this type of field to a perennial grass crop for four or five years—and that’s what this grower did,” Ferrie says. “Fortunately, he had a neighbor who was willing to purchase his grass hay. Since his row-crop yields in this field were low, it was less of a sacrifice to switch the field to hay production.
“If hay was not an option, the grower’s best bet would have been to add barley or wheat to his crop rotation,” Ferrie says. “That would require finding a market, which could include chopping the crop and selling it to a livestock feeder. Chopping would remove the carbon in the forage, but it’s the root mass that builds soil structure. Wheat and barley not only build soil structure, but they grow better than corn or soybeans in poorly structured soil.”
Goals: Manage Density, Nutrients and Erosion
Sandy soil; rotate seed corn and commercial soybeans; under center-pivot irrigation
There’s lots of wheel traffic with seed corn production, and the crop is harvested early. Seed corn also removes fewer nutrients than commercial corn. So this farmer needs a cover crop or combination that manages density issues, improves infiltration, scavenges nutrients and prevents erosion, mostly from wind.
“With irrigation available if it fails to rain, and plenty of sunlight hitting the ground thanks to the detasseled corn crop, aerial application will likely be successful,” Ferrie says. “Some cover crop options include cereal rye, annual ryegrass and an oats/radish combination. The operator can let the cover crop grow in the spring, providing good erosion protection, and then plant soybeans into it.
“Following soybeans, the operator can plant annual ryegrass to avoid planting cereal rye ahead of seed corn. He also can add a legume to produce nitrogen for the corn crop,” he adds.
If you grow seed corn, make sure the company you grow for permits cover cropping ahead of seed corn. You might be limited to a cover that winter-kills, such as oats and radishes.
Before Proceeding With Cover Crops
Incorporating cover crops into a cash-crop rotation requires planning and a lot of thought. In every situation, some considerations apply:
- Let everybody involved, including the landowner and your crop insurance agent, know you plan to grow a cover crop.
- Make arrangements with suppliers, especially the one who will kill the cover crop, well in advance. Plan how to kill it and when. “This is especially important if your herbicide supplier lacks cover crop experience,” Ferrie says.
- Discuss the herbicide program for your cash crop, including rescue treatments, with your supplier. This is especially important with in-season applications becoming more common—and in light of your desire to plant your cover crop as early as possible. Make sure re-cropping intervals are observed, so herbicide residues don’t kill your cover crop.
- Buy your cover crop seed early.
- Have your cover crop planting team ready to roll the day you begin to harvest. If you use a custom applicator, don’t choose someone with a busy harvest schedule. “If you have to wait for someone to plant your cover crop, you may wind up spending money on cover crop seed that, in the end, won’t help your soil all that much,” Ferrie says.
- If you apply cover crop seed aerially, watch for drift onto neighboring fields. “If that occurs, discuss it with your neighbor and arrange to kill the cover in his field,” Ferrie advises. “I’ve seen situations like this in which the neighbor doesn’t know how to kill the cover crop, and it gets out of control.”
- Do your homework. Consult sources of cover crop information for your region. Get pointers from neighbors who are successfully growing cover crops.
- Start slowly. Planting your first cover crop simply to gain experience might be the smartest first step you can take.