Soil Pits: Can You Dig It?

Soil Pits Unveil Secrets About Soil Structure and Health

Matt Wilde
By  Matthew Wilde , Progressive Farmer Crops Editor
Mike Petersen, an agronomist with Orthman Manufacturing, stands in a soil pit on Grant and Tana Guetzko's farm near Delhi, Iowa. He and a colleague dug the pit as part of a soil health field day to show the Guetzkos and attendees how soil structure is affected by crop production practices. (DTN photo by Matthew Wilde)

DELHI, Iowa (DTN) -- One of the best ways to measure soil health and the effectiveness of crop production practices is several feet underground.

Mike Petersen gave his 1,755th soil pit talk at Grant and Tana Guetzko's farm near Delhi, Iowa. Standing in a hole about 3 feet deep and 2 feet wide near one of the Guetzkos' cornfields, the agronomist and soil scientist found layers of soil compaction several inches deep, limited earthworm activity and few soil pores. All three hinder root development and water infiltration and holding capacity.

The findings surprised Grant Guetzko. He switched from conventional tillage to 100% no-till three years ago, but the ill effects of past tillage practices in the sandy loam and glacial-till soil are still present. The longtime farmer said that, prior to the switch, it was common to chisel plow, field cultivate and run a soil finisher before planting.

"I thought by now we may have gotten rid of compaction and the soil would have more pores," Grant Guetzko said. "It takes time in a no-till situation to (improve it). It's a good thing we switched."


Petersen, a former NRCS employee who is now Orthman Manufacturing's national and global agronomist, has been digging and analyzing soil pits for 45 years. The Guetzko pit talk was part of a soil health field day sponsored by the Iowa Corn Growers Association and the USDA Natural Resources Conservation Service (NRCS). About 40 area farmers attended.

Pit talks always give farmers a "gold mine" of information, according to Petersen. For growers interested in digging a pit themselves, he recommends doing it as close to plants as possible to reveal roots.

For corn, Petersen said the best time to dig is prior to tassel while roots are still growing. However, digging a pit after tassel and outside of a field is still helpful.

"It gives the producer an idea of their soil resources and potential," Petersen said. "Not just yield potential, but the potential to absorb and store water and roots to take up nutrients. And the potential (for the land to be productive) for their grandchildren.

"Farmers get a better idea what they can do with their soil and current limitations," he continued. "There's some limitations in (the Guetzkos) soil profile, but nothing they can't overcome."


The Guetzkos believe no-till farming will improve soil structure and health but it takes time. They have no doubt the practice will help the environment and eventually boost yield potential.

"It's a work in progress ... to get the soil working again," Grant Guetzko said.

Conservation tillage and no-till, along with other practices such as cover crops and extended crop rotations, help build resilient soil. Collectively, the practices mitigate soil erosion and nutrient loss, improve soil structure and organic matter, increase water infiltration and holding capacity and reduce soil compaction.

Mitigating soil erosion and nutrient run-off, primarily phosphorus, were main reasons why the Guetzkos converted to no-till. The 700 acres of rolling hills the couple farms drain into Silver Lake on the edge of Delhi. The Guetzkos and other area farmers decided several years ago to do what they can to reduce sediment and pollutants from entering the lake, an important community resource and recreation spot.

Erosion problems all but stopped on the farm after implementing no-till, Grant Guetzko said. Corn is the primary crop grown. Yields initially dropped about 20 bushels per acre, on average, when they started no-tilling. But yields returned to normal last year -- 200 bushels per acre or more -- and Grant expects production to increase as soil health improves.

He said finding out more about his soil by hosting the field day, with a pit talk, is part of the process. For area farmers who attended the event, Petersen said they can learn valuable information as well.

"I hope everyone starts thinking about their soil and re-evaluating practices," Petersen said. "Consider looking at your soil profile to see if you're doing anything harmful to the bottom line."


Conventional tillage has many benefits. It can break up topsoil compaction, size and incorporate residue, control weeds and create a warm, dry and smooth seedbed for planting.

However, tilling has drawbacks. It can lead to soil erosion, nutrient loss, fewer earthworms and less biological activity, and soil aggregate degradation. Earthworms create channels for water and roots to infiltrate the soil. Soil pores help hold water, which is especially beneficial in dry years.

As soil structure breaks down due to tillage, organic matter is lost, and soil becomes denser, making it more prone to compaction. That limits root development, which reduces yield potential.

Petersen said a soil pit unveils the ability of dirt to support robust roots to branch out and go more than 5 feet deep in the case of corn. This bolsters water and nutrient uptake so plants can thrive.

"It (soil pit) really tells the story of what potential a corn plant has in a soil profile," Petersen said.

In the Guetzkos case, Petersen said a soil compaction layer 3 to 6 inches deep is an issue but not bad. In some cases, Peterson said, soil compaction will reduce corn yields by 30% to 40%.

Petersen said no-till will eventually break up compaction as soil becomes more mellow, earthworm activity increases and soil aggregate stability improves. But there is another option for conservation-minded farmers.

Strip-tilling can break up compaction with minimal ground disturbance to prepare soil for planting, Petersen said. The machine has shanks or coulters to till a strip about 10 inches wide where seed and fertilizer are placed, and the rest of the field is left undisturbed.

Strip-till combines the benefits of tillage and no-till. "Only 30% of the ground surface is disturbed with strip-till. It can improve water infiltration and help develop bigger root systems quicker," Petersen said.

"Good soil health will make the soil purr. That's what we're after," he concluded.

Watch a soil pit talk by Paul Gross, a Michigan State University Extension educator:

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Matt Wilde