Thoelen cover crop

MARSHALL, Minn. — If Randy Tholen is a conservationist, it’s because he is convinced good conservation makes economic sense. It’s not maximum yield that is profitable, but getting the best return on your investment. His convincing has come from his own experience.

Randy and his son Ryan have even put together a brochure and a PowerPoint presentation to share what they have found. They call it “Farming Clean and Green.”

“The farming clean part means to eliminate soil and nutrient escape,” Tholen explained. He said that if farmers don’t take steps in that direction, eventually regulations will be forced on them to do so.

“Farming green is to have living roots in the ground as long as possible,” he went on to say. “When you have living roots in the ground you are building soil structure, increasing organic matter, and feeding the biology of the soil, microbes, bacteria — all that stuff.”

When Tholen farmed 1,200 acres while raising 1,000 head of cattle near Tracy, he had no time to indulge his life-long interest in research. When he moved to a quarter-section farm between Balaton and Marshall, he made it a research farm.

“We’ve done a lot of research with a lot of different companies,” he said. “When we do research we do four replications of everything. We’ll have eight rows of the product and eight rows of check repeated four times, (each row extending) all the way across the field. These testings have a lot of integrity and the companies appreciate that.”

For four years he tested biological soil additives from companies around the United States. The result: he found none of the products worked. Only one time did the product even pay for itself. At the same time, he was also attending national no-till conferences and hearing that if we take care of the soil, it will take care of us. Cover crop roots feed the microbes already present. Rather than add products to the soil, feed and take care of what you have. That made economic sense to Tholen, but he had to see for himself.

Instead of testing products, he now tests methods — working with a crop consultant and occasionally the University of Minnesota. In his fifth season of working on building soil health, he has found excellent results using strip till to disturb less of the soil, banding fertilizer in the spring to concentrate it where it’s needed and make leaching and runoff less likely, and interseeding corn and soybeans with cover crops.

While cover crops can provide off-season grazing and prevent erosion, it’s what is going on below the soil that especially interests Tholen.

Earthworms are one sign of soil health.

“The value of earthworms is something farmers have not paid attention to,” Tholen said. “A healthy soil will be home to 25 worms per square foot, down to a depth of nine feet. That amount of earthworms can produce up to 100 tons of excrement of manure including the worm carcass decay at the end of their life cycle. It has only four pounds of nitrogen per acre, but there is 30 pounds of phosphorus, 72 pounds of potassium, 90 pounds of magnesium and 500 pounds of calcium per acre.”

When he moved to his current farm, he allowed an environmental class studying earthworms to do a project on his land. The students from Southwest Minnesota State University dug 20 pits — 18-inches long, 12-inches wide and 12-inches deep. They found earthworms in only three of the pits.

“That has changed tremendously,” Tholen said. Wherever he turns over soil, it is full of worm holes that provide pathways for water and roots.

Earthworms are at the top of the subsoil food chain and indicate the presence of microbial life. And it is roots that provide food for the soil life.

“What microbes do,” Tholen explained, “when you have all these different roots in the ground, they put out something called exudates. They are a kind of sticky substance and that helps hold soil particles together (giving good soil structure). I used to think that when we were planting, if we had a field that looked like powder, that would be the perfect seed bed. But that kind of soil does not absorb moisture. With this kind of soil (that looks like cottage cheese) there is opportunity for moisture to go down.”

All those roots feeding the microbes are the result of cover crops.

In 2015, Tholen hosted a field day for the University of Minnesota. He handed out a sheet about cover crops.

“One farmer looked at it for a while, handed it back to me and said, ‘Why would I want to plant weeds in my corn? It’s going to take my fertility and moisture and cut my yield by a third.’ That prompted me to do a yield test.”

Tholen did his usual four replications: eight rows each of corn across the field, with and without cover crops. There was virtually no difference in yield.

“The thing is, we didn’t take a 10-20 percent hit in yield from having the cover crops. Both areas yielded 216-217 bushel.”

Even Tholen was surprised he could get 60 bushel beans and 200 bushel corn on soil that tested extremely low in fertility — a P of 6 and a K of 135.

“My crop consultant told me that with your cover crops (that feed the soil life), the microbes will activate the natural ability of the soil to create and cycle plant available nutrients. We have a tremendous amount of natural fertility in the soil, but it’s not available to plants.”

In the spring, Tholen sprays to knock down cover crops which survive the winter. By then, their roots have done their job of feeding the soil life and increasing organic matter. He strip-tills his corn and beans, and later interseeds cover crops once the corn and beans have a head start.

Tholen is currently researching nitrogen rates. His spring banding already reduces cost since it requires less nitrogen by concentrating it at the roots and reducing loss through leaching. But could that be reduced further?

“We want to see if by using strip till and cover crops we can cut nitrogen and not affect yield.”

In 2017, using his usual replications, he applied at two rates — the normal rate of 140 pounds per acre, and a reduced rate of 110 pounds per acre.

“We did not take a yield hit for lesser nitrogen,” Tholen said. This year he is experimenting with rates of 135, 100, and 65 pounds per acre. “What we want to do is find the nitrogen rate where we start seeing a lower yield.”

Tholen is constantly seeking to find out what works best. He tries seeding and drilling for cover crops — including seeding cereal rye while combining corn. When he started, he interseeded three species into the corn. This year he’s using eight.

He can recount numerous benefits that have been shown from studies of cover crops.

“Organic carbon and organic nitrogen increase dramatically in fields where diverse cover crops are planted as compared to monoculture — just corn or beans alone. Adding cover crops can increase organic matter 15 times faster than rotations without cover crops. Organic matter is slow to build back up. By adding cover crops we can do that faster.”

Studies show that one percent organic matter will hold 27,000 gallons of water per acre. Typically, Tholen does not find water standing in his fields after a big rain. This wet year has been a real test. While the heavy rains in early July did not drown out any crop, even his already-saturated soil couldn’t swallow all of the water. No gullies were created, but yellow lower leaves showed the beans suffered from water shock.

For Randy Tholen, successful farming is all about building soil health. It’s a long-term vision, “but not as long-term as you might think,” he said. “We’ve seen dramatic improvements in a matter of a few years. That’s why we do what we do. Stop erosion and build healthy soil. Those two go hand-in-hand. I can get more excited about seeing what the cover crops are going to do than seeing what the corn and beans are going to do.”

He’s not only excited about what he’s doing and learning, he is always ready to share it with others through his PowerPoint presentation or a phone call. You can reach him at (507) 993-1803 or by email at