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Soil's pan layer critical to yieldSoil's pan layer critical to yield

June 5, 2002

6 Min Read

Walk into a brick wall and you have a general feeling of what your crops are going through when they hit the hardpan. Know your soils and what to do to correct the hardpan, and your soils will repay you with production. Pay attention to their names and consider their properties and bring them to life under your feet.

It may sound like an evangelistic call, but it's more akin to prophetic knowledge.

Looking out over a field, George Naderman sees three dimensions. First, he sees the lay of the rows, then the width of the field and its topography, whether flat or rolling. But he also knows there is a “depth dimension.”

Although he can't visually detect what's underground, he knows from 28 years of practical field research the third dimension can be highly variable and can make or break crops. And he has looked lots of places at this all-important depth dimension, simply using a shovel or the “auger” of soil professionals.

It's called the pan layer.

Whether the farmer is using no-till or conservation-tillage, the pan layer has a tendency to develop and harden in the light colored soils of the Coastal Plain, thereby restricting root development and ultimately yields. Therefore, in such soils there is often the need for deep tillage to break up that rooting limitation, even in reduced-tillage situations.

Naderman, a retired North Carolina State University Extension soil specialist, believes the key to dealing with the pan layer is to gain a working knowledge of soil properties lying across your fields below the topsoil layer.

Research in several Southeastern universities has shown that the light, sandy soils of the Coastal Plain are prone to hardpan formation. The “tillage pan” is a dense layer beginning six to 10 inches below the surface. Naderman says that in places it is only a couple of inches thick while in other soils it may extend to 12 to 16 inches below the surface.

Any soil that has the word sand and loam in its description of the layer or “horizon” just below the soil surface can benefit from deep tillage. Also, this is especially true for those soils that are described as “well or “moderately well” drained. This information can be found in the Soil Survey for your county. You can usually get it from your local Soil Conservation District.

“Notice I use the term ‘deep tillage,’” Naderman says. “I mean something deeper than coulters. All forms of strip-tillage involve essentially a subsoiler, either under the row or near the row.”

In-row subsoilers are available in various brand names. These place the ripper directly under each row-planted crop. However, the DMI, which has winged points and Unverferth, Terra Max and Paratill (made by Tye and Bigham Brothers) are somewhat different forms of deep tillage, which may offer benefits or weaknesses, depending on their design features and the crop and farm situation, Naderman says.

When pan layers are present, deep tillage not only shatters the hardpan, it also benefits the growth of the crop. For example, a six- to 12-bushel increase in soybean yields has been attributed to the breaking of the pan layer. In corn, typical yield increases of 15-25 bushels per acre when a definite pan layer is broken up. In cotton, it's common to increase yields 50-125 pounds of lint per acre. The response to shattering the hardpan is less marked in peanuts.

“Strip-tillage is at home in the South, especially on sandy soils of the Coastal Plain, because of the frequent presence of the pan layer,” Naderman says. In many operations, however, there are also major areas of the fields where subsoilers typically run at depths of 10 or 12 inches, causing an uplift of heavy, sticky clay layers. These layers often cause problems in the seed zone, with variable seed/soil contact and even exposed seed and skippy stands. “This is especially common with cotton and strip-tillage, and results in stand skips,” Naderman says.

In his capacity as a soil scientist, Naderman urges farmers to know their soils. “One of the greatest challenges in talking about soil is to get people to think in three dimensions. There's a vertical dimension to soil. Go out and just dig a small hole under a crop row in the field and you can see the variation. While you're at it, take a screwdriver and prick out the roots on the face of your soil point and look at the rooting depth.”

In many fields this soil variation is not handled very efficiently by most of the current deep-tillage implements, Naderman points out.

He believes, however, there's a new machine just on the market this season that brings promise of a better way. It's a strip-tillage implement that can vary the subsoiler depth on-the-go by hydraulic rams. No other mechanical adjustments are needed while the implement prepares the row zone throughout the field.

He points to one implement developed by a North Carolina farmer.

Agricultural engineers and soil scientists in the Southeast have long considered ways of detecting differing soil conditions and making adjustments.

“But I believe we should start with what is already known by the soil's name itself, and the subsurface properties that go along with each and every soils name in the modern Soil Survey,” Naderman says.

Then, with the soil map in hand, and the farmer's knowledge of the crop performance he's seen in certain areas of each field, he could design a more efficient plan with a good, practical agronomist for using this new type of deep tillage/strip-tillage tool.

Clifton Dixon, a Pitt County, N.C., farmer has developed and is marketing an implement that can be hydraulically adjusted to match the depth of the pan layer.

“This is a design that has been needed for at least 25 years,” Naderman says. The advent of this equipment and others like it to come presents an exciting challenge and opportunity for farmers. “Watch for this new technology.

“To take advantage of this type of equipment, the farmer will need someone such as a crop consultant, a Natural Resources Conservation expert, or Extension people working with him to determine where the hardpan variability is in the field,” Naderman says. It will involve paying closer attention to soil surveys and maps already available.

The variable-depth ripper opens the door to precision agriculture applications. It could be developed with GPS and soil maps already available, the farmer's tractor could adjust the depth of the subsoiler on-the-go, Naderman says. It depends on the degree of success in the market. “Technologically, it could be done and it would be widely applicable in the Southeast.”

Talking about the future of farming, Naderman believes this modern equipment we're getting now is doing an excellent job of conserving crop residue. “Combined with the use of cover crops, we can improve soil tilth, soil quality, enhance our rainfall capture, catch some soil nitrogen and phosphorous in the small grain cover crops before these nutrients move toward our ground or surface water — and even tie up some of the troublesome “greenhouse gases” produced mostly by the rest of our society today,” he says.

Such technology, however, would only benefit the farmer if he understands the soil properties in his fields. “I would like to see crop consultants become more knowledgeable about using soil maps so they could help farmers determine specifically what problems they have with hardpans,” Naderman says. In light sandy soils of the Coastal Plain, the hardpan is a given. Knowing in what soils and what depth it is likely to occur gives farmers a heads up on shattering the wall to yields. New technology may add an element of precision to that operation in the near future.

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