Check Soil Health With Soil Pits

Can You Dig It?

Matt Wilde
By  Matthew Wilde , Progressive Farmer Crops Editor
Mike Petersen (in the soil pit), Orthman Manufacturing agronomist, uses soil pits to demonstrate to farmers the importance of good soil health and root development. (Matthew Wilde)

One of the best ways to measure soil health and the effectiveness of crop-production practices is several feet underground.

Standing in a hole about 3 feet deep and 2 feet wide near one of Grant and Tana Guetzko's corn fields in Delhi, Iowa, Mike Petersen jabs an orange-handled knife into the soil about 3 inches from the top of the pit. He then sinks the blade of another knife, its handle bound in weathered leather, into the black dirt several inches below the first blade.

Farmers hovering above Petersen gathered closer to the hole to see why the agronomist and soil scientist violently stabbed the earth.

"There's some soil compaction between 3 to 6 inches," Petersen proclaims, using the knives to highlight the area. "If you have soil that's compacted, you are losing 30 to 40% of your corn yield potential. That's pretty harsh. A lot of farmers won't be happy."

Grant Guetzko's concerned look as Petersen analyzes his soil indicates he isn't thrilled with the findings. Besides some compaction, Petersen found limited earthworm activity and few soil pores. All three hinder root development, water infiltration and holding capacity.

Guetzko 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 says 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," Guetzko adds. "It takes time in a no-till situation to improve it. It's a good thing we switched."

DIG A LITTLE, LEARN A LOT

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. He estimates he has given 1,755 pit presentations.

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). The soil specialist says farmers can learn valuable information by attending a pit talk or digging one themselves.

The best time to dig a soil pit near or in a corn field is prior to tassel while roots are still growing, Petersen explains. However, digging a pit after tassel and outside of a field is still helpful. He recommends digging it as close to plants as possible to reveal roots.

"It gives the producer an idea of their soil resources and potential," Petersen says. "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 continues. "Consider looking at your soil profile to see if you're doing anything harmful to the bottom line."

ON THE RIGHT TRACK

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 says.

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 help reduce soil compaction.

Decreasing soil erosion and nutrient runoff, primarily phosphorus, were main reasons why the Guetzkos converted to no-till. The 700 acres of rolling hills the couple farms drains into Silver Lake, on the edge of Delhi. They 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 confirms. 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.

TILLAGE AND SOIL STRUCTURE

Conventional tillage has benefits. It breaks up topsoil compaction, sizes and incorporates residue, controls weeds and creates a warm, dry and smooth seedbed for planting.

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

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

Petersen says 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 explains.

Strip-Till Offers Soil Health Advantages:

Mike Petersen, Orthman Manufacturing's national and global agronomist, says 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 says. 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 says.

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

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For More Information:

-- Orthman Manufacturing: https://orthman.com/…

-- Watch a Soil Pit Talk by Paul Gross, a Michigan State University Extension educator: https://www.canr.msu.edu/…

-- Follow Matt on Twitter @progressivwilde

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