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October 4, 2002

Soil compaction not always grounds for deep tillage

WEST LAFAYETTE, Ind. – Crop fields are taking the 2002 season hard, but it might not require a deep tillage operation to loosen them up.

The wild weather extremes that compelled many farmers to plant into wet soils in late spring and then baked the earth with excessive heat and drought this summer did more than damage potential crop yields. Those hasty field operations and subsequent rainy/dry periods also laid the groundwork for compacted soils.

Farmers anxious to break up tough soil layers to prevent crop losses in 2003 should first determine the extent of the compaction problem, said Tony Vyn, Purdue University Cooperative Extension Service cropping systems specialist. Although it might be tempting to pull a deep ripping implement across their fields, farmers shouldn't underestimate the soil loosening power of nature.

"We can't necessarily assume that planting operations when surface soils were too wet resulted in deep compaction," Vyn said. "It may very well be that the bulk of the compaction was actually quite close to the soil surface, and that the compaction can be alleviated by natural processes like soil wetting and drying, earthworms and crop rooting activity. Compaction can be alleviated even further by frost activity over the winter."

Compaction occurs when heavy farm machinery presses down on soil as the equipment travels over a field. Compacted soils can make it difficult for crops to grow properly if plant roots are unable to penetrate dense soil layers except through weaker cracks or large pores.

Generally, only well-defined, compacted soil layers deeper than 4 inches below the soil surface are candidates for loosening, or subsoiling, Vyn said.

Careful evaluation of soils will help farmers identify deep compacted layers. Vyn suggests performing a soil evaluation when the ground is uniformly wet to a depth of two feet or more. A farmer should dig a 20- to 24-inch deep hole, exposing a vertical soil profile. Then, using constant pressure, try pushing a pocketknife blade from the surface down to the maximum depth of the blade. If the farmer has a harder time sliding the blade through a particular area a few inches wide, a compacted layer might be present.

Such soil evaluations should be done at four or more random areas in fields of 50-plus acres, Vyn said. Farmers also should note crop rooting patterns. If a significant number of roots have grown sideways before finding a crack in the soil and growing down again, it may be a sign of compaction.

When subsoiling is warranted, it should be done when soils are dry.

"Typically, we suggest that loosening operations be done when soils are reasonably dry, because we tend to get more shattering of the soil between the shanks of a ripper or subsoiling tool," Vyn said. "If rains cause very damp soil conditions, then it's possible to create a greater problem using a subsoiling tool through smearing as the tool is pulled through the soil."

In some cases, subsoiling makes a bad situation worse, Vyn said.

"What tends to happen after a ripping operation is you have one or more passes with tractors and tillage implements, which can result in a re-formation of a dense soil layer at the depth of the next tillage operation, or at even greater depths if there are high axle loads with the tractor," he said, adding that excessive loosening can lead to harvest delays the following year under wet fall conditions.

"We need to be conscious about limiting traffic on these fields after loosening. One way to do that is strip tillage. Another way is to use a combination tillage operation in the fall so that it's possible to use a stale-seedbed planting system the following spring."

Vyn said farmers should be mindful of other issues when addressing compaction:

• Subsoiling should be done no deeper than 1-2 inches below the compacted soil zone, and never based on available tractor horsepower or the maximum depth a tillage tool can go.

• There is less benefit to deep loosening in fields high in organic matter, or in those with a history of manure application or regular forage crop production.

• Deep loosening can expose soil to erosion, especially if the subsoiling operation produces a large area of disturbed soil with little remaining residue cover.

• Subsoiling costs a farmer money in fuel, time and equipment use. Costs can increase if soil ripping brings up large clods, which then must be broken down by additional tillage passes.

As harvest nears an end, Vyn recommends farmers refrain from field activities that could cause soil compaction next year.

"Avoidance is always the best management practice when we deal with compaction," he said. "Avoid imposing a load on the soil when soils are too wet for that operation. Avoid doing tillage when soils are wet. Avoid planting when soils are wet. Avoid, where possible, imposing high axle loads with a combine or grain carts at harvesttime when soils are too wet.

"Also, try to avoid the creation of ruts in the field, unless it is absolutely essential in order to remove a crop prior to snowfall in the fall."

Writer: Steve Leer, (765) 494-8415, sleer@purdue.edu

Source: Tony Vyn, (765) 496-3757, tvyn@purdue.edu

Ag Communications: (765) 494-2722; Beth Forbes, bforbes@aes.purdue.edu; http://www.agriculture.purdue.edu/AgComm/public/agnews/

Related Web sites:
Purdue Extension tillage articles
Purdue University Department of Agronomy

Purdue News Service: (765) 494-2096; purduenews@purdue.edu


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