Last summer, Mark Watson found himself in a deep hole. The Nebraska Panhandle grower was 4 ft. down in a soil pit, face to face with the consequences of his farming practices. What he saw surprised him.
After more than a decade of no-till production, his clay-loam soil had regained much of its original structure. The topsoil was dark with organic matter and dense with active roots, even at the surface. Earthworm burrows, old root channels and pore spaces were abundant.
More surprising, Watson says, were all the roots extending down into the soil 4 ft. or more. But most arresting of all was a comparison soil pit in another grower's field. That pit showed how the soil's native structure had been destroyed by continuous tillage.
“It was an eye-opener to me — what no-till is doing for our soil structure,” says Watson, who farms near Alliance, NE, with his brother Bruce.
Soil pits are a good way to check on how your management is affecting the soil and root growth, says Jodi DeJong-Hughes, University of Minnesota Extension soils specialist. A simple, 4-ft.-deep trench spanning several rows in the field reveals a wealth of useful information about your soil's health, she says. You'll see the soil structure — or lack of it — water infiltration and absorption capacity, compaction layers, rooting depth, wheel traffic, water table movement, erosion and other features that affect crop performance.
“Producers have spent a lot of time looking at their crops above ground,” says Paul Jasa, an agricultural engineer at the University of Nebraska who did more than a dozen soil pit demonstrations last season. “We tell them they should spend some time looking below ground.”
Mike Hubbs, formerly a Natural Resources Conservation Service (NRCS) national agronomist and now the NRCS Kentucky state conservationist, has talked soil-quality improvement nationwide. He likes soil pits because they let growers actually see and feel what's happening underground.
The first thing Hubbs looks at in a soil pit is soil structure. “Continuous tillage tends to destroy soil structure, break down natural aggregates and lose pore spaces in soil for water and air movement.” Plate-like layers, clods and fine, powdery texture are all signs of damaged structure.
Hubbs also looks at organic matter content. “If you're doing a lot of tillage, you start to see organic matter decrease,” he says.
Root depth is another thing to check out in your soil pit, he adds. “Are roots going at a 90° angle? Are there compaction issues that obstruct root growth?” Flat, ribbon-like roots signal compaction, DeJong-Hughes says. “Pick around with a knife and see where roots are having trouble penetrating and look at how deep soybean nodules are.”
Check pit walls for earthworm burrows and old root channels — both signs of a healthy soil, Jasa says. He tells about the time he picked up a soil clump that had a root sticking out either end. He showed growers how he could pull the root from both sides. “Think of how little energy that root expended to go down a hole that was already there,” he says.
Soil pits also reveal the effects of wheel traffic and heavy axle loads, Jasa says. “I'm a firm believer in controlled traffic.” He suggests growers dig two comparison soil pits: one in a non-traffic area — maybe near a fence or in a non-tilled place such as a windbreak — and another in a trafficked area of the field. The differences can be startling, he says.
If you have an area of the field that's not producing well, a soil pit can be a useful diagnostic tool, DeJong-Hughes says. Recently, she worked with a no-till producer who had problems with late emergence. “We dug into the soil and discovered that his planter smeared the seed furrow as it laid down seed.”
Soil pits are especially helpful in making tillage decisions. She says, “The most common reason I get asked to do a soil pit is to answer the question, ‘Do I need to use a deep ripper?’”
That's why Dan Bradow dug a soil pit. He farms with his father Don on the edge of the Red River Valley near Fergus Falls, MN. They grow corn, soybeans, wheat and sugarbeets. In 2005, the Bradows began farming a quarter section of heavy-soiled, low-lying ground that had been exceptionally wet for several years.
In 2006, field conditions were drier, so he deep-tilled the new piece of ground. Then he started to worry about what he'd done. He was concerned because “after I ripped it at 12 in., I was still hitting a pan farther down. Should I try to break that up?”
To get answers, he and DeJong-Hughes dug a soil pit in the new field. Bradow saw that the cycle of freezing and thawing, shrinking and swelling, was forming vertical cracks that allowed water and roots to penetrate the soil. He decided that he “probably won't do any more deep ripping there for a few years.”
Ray Ward of Ward Laboratories in Kearney, NE, a soil-testing service, often participates in soil pit demonstrations. “The amazing thing to me is how many growers have no idea what their soil looks like below the surface,” he says.
Mark Watson, the Nebraska Panhandle grower, admits he never used to give his soil much thought. “The only time we paid attention to the soil was having it probed to see how much commercial fertilizer was required.”
He and his brother grow corn, wheat, millet and dry edible beans and peas on 900 acres of irrigated ground and 2,100 acres of dryland. In 1994, they switched to no-till to cut input costs, Mark says. It was only later that they realized how much this management change had altered their soils.
The changes were obvious in last summer's soil pit, Watson says. For example, the topsoil had a nice dark color, reflecting more organic matter. “Organic matter on our dryland acres was 0.6%, and our irrigated acres were 0.8% before we began no-till farming,” Watson says. “After 13 years of no-till, we have improved our dryland organic matter to 2.3% and our irrigated organic matter to 2.8%.”
Another big change was the development of vertical, prism-like columns of well-aggregated soil — attributes of good structure. “This allows water to flow down through the soil evenly,” Watson says. And the soil aggregates create air spaces that increase the soil's ability to absorb and store the water.
Although an old tillage compaction layer could still be felt in Watson's soil pit, plant roots were pushing through it, he says. After seeing how deep root development was, Watson began soil sampling for nitrogen down to 36 in. “because roots penetrate that far down.” He cut both his fertilizer and irrigation water use.
A pit in a nearby field with the same soil type revealed layers of compaction caused by as many as eight tillage operations per season, Watson says.
Compaction layers had squeezed root growth sideways, he says. The fine channels created by roots and earthworms had been pulverized, and the soil particles were “tightly packed, without much room for water to get through.”