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Cheap and Easy-to-Kill Cover Crops

03/21/2014 @ 11:43am

Cheap and easy to kill. That’s how Lee Thelen prefers his cover crops. The St. Johns, Michigan, crop farmer does what it takes to keep the cost down – from planting old corn seed to growing his own oilseed radish and oat cover crop seed.

After a couple of decades experimenting with cover crops on 1,900 acres of farmland, Thelen appreciates their value. He’s taken a more serious approach the past five years, and he annually budgets to invest in new ideas.

Thelen has three reasons why he grows cover crops. “Erosion is a big one,” he says. “Holding my fertilizer in a high profile is second. The third reason is that I feed the microbial activity going on in the soil.”

Cover crops maximize the value of manure (40 tons per acre) he purchases from local dairy farms. They sequester the nutrients high in the soil profile, where they are available to crops the following year. He knows it works because of a trial he conducted many years ago.
“I used wheat for a cover crop one year, and I left strips on purpose without a cover crop,” he says. “In the spring, I went back and tested to see how much nitrogen (N) I was holding up in the profile. With the wheat, I was holding up 17 pounds more N per acre through the winter in the high profile than the soil without the cover crop.”

Later testing indicated oats and radishes held 7 to 12 additional pounds of N.

“It seems like every product that I plant that stays greener longer through the winter will hold more of that fertilizer value up in the profile,” Thelen says.

Combined with no-till farming for 25 years, he has watched his soil’s organic matter increase 3% to 7% over a wide range of soil types.

“That makes no-tilling easier, which makes my job better, which makes higher production,” he says. 

Thlen is so convinced of the cover crop benefits that he budgets $5,000 annually for cover crop experiments, such as aerial-seeding radishes/oats, crimson clover, and rye into corn and soybeans.

Not every experiment works as planned. For example, forage was so dense when he aerial-seeded annual rye into soybeans one year that no rye was growing at harvest. The seed sprouted later that fall and the following year, when Thelen planted the field to corn.

Fortunately, the herbicides he used in corn killed it. However, Thelen has avoided annual rye since then. He sticks to cereal rye, which is easier to kill with herbicides.

“This year, I flew wheat into cornstalks early in September in a 50-acre field. I was about 50% successful on the lighter, sandier ground with a tremendously good stand of wheat. On heavier, lower ground I had to go back in and patch it. I’ll have a good stand of wheat, but the results were a little erratic.”

Challenges

It’s difficult in Michigan for a fall-planted cover crop to mature before winter and then enter the field in spring to kill it. Springtime fields can be difficult to access if they are soft and muddy from cover crops holding moisture.

Thelen focuses on planting cover crops after harvesting wheat, oats, or rye so there is time for plants to establish before winter. Typically, he plants 150 to 250 acres of cover crops on sandy fields and the land he rents.

“My landlords like that approach,” he says. “The dirt isn’t running away. Their hills aren’t eroding. They’re getting crops up on knobs they never had before. They appreciate that I’m trying to help them out.”

Favorite things
Radishes rank high. Seed is expensive, though, so Thelen raises his own radishes for seed and combines it with other seed in a cover crop mix. 

“I like to mix oats and radishes,” he says. “I’ll do 8 pounds of radishes for $1 per pound (compared to $3 per pound purchased) and 2 bushels of oats. That’s $8 worth, and I’ve got a fantastic crop for $16 per acre.”

The 3-inch-diameter, foot-long radish tubers reduce soil compaction, but that isn’t as important as the quantity of organic matter the radishes add to soil. Thelen figures he gets double benefits from the radishes he plants for seeds in May on 5 acres of his poorest soil.

After harvesting the seed, some of the seed germinates and produces a taproot, which grows as a cover crop and improves that soil. Radishes usually stay green until mid-December in Michigan, then they die over the winter.

Thelen uses outdated corn seed and seed left from experimental plots as another cheap cover crop seed source.

“The secret is I drill corn at about 70,000 plants per acre with an 8-inch drill,” he says. “I could broadcast it and cover it with a light dragging, too.”

He plants the corn in August, and it usually grows 3 to 4 feet tall before frost turns it translucent and tips it over. “By spring I can drill and plant right through it,” Thelen says.

Another one of his favorite cover crop techniques typically lands on November 14, the day before Michigan’s deer rifle season.

“I take cereal rye in a spinner box and spread it in the cornstalks (about 200 acres) and walk away. By spring, the stuff underneath the snow will be 4 inches tall with a bright red color, and it will take off growing to 2 feet before I spray it. If I drill it in October, it would be 4 to 5 feet tall and by spring, I would hardly be able to manage it. At 2 feet, I can stay with it and kill it off quick enough to go plant into it.”

Besides creating organic matter and holding nutrients high in the soil profile, the rye’s allelopathic properties help eliminate weeds.

Whether it’s corn or soybean stubble left after harvest, it’s aerial-seeding, or it’s planting cover crops, his goal is to keep something on as much of his farmland as possible.

Fun to experiment
Each year, he plans experiments and side-by-side trials. “I’m always doing something that costs a little bit of money to see if it’s worthwhile or not,” he says. “And it’s fun. My advice to anybody is that there aren’t any dumb ideas. Just try it. If you are going to try it, make sure you have a test strip next to it. You’ve got to do a field of checks so you can see what you could have got and what you are getting. There’s no way you can make a conclusion without a check.”

His only regret is that there isn’t more time and money in the budget for more cover crop experimentation.

“I’m big on what it costs, so the cheaper, the better. If it’s cheap and dies in the winter, I’m good,” he says.

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