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Cut Compaction by Reducing Axle Loads, Psi

If Jodi DeJong-Hughes, an Extension educator at the University of Minnesota, could have her way, there would be a sign at the entrance to each field stating, “Weight Limit: 10 Tons Per Axle. Inflation Pressure Max: 10 psi.”

While she realizes this may be unrealistic, she wants farmers to aim for these numbers and to focus on these numbers instead of overall weight, number of tires, or tracks. 

“The higher the psi, the deeper the compaction. Think of the psi as the intensity of the compaction,” explains DeJong-Hughes. “The axle load determines the depth of compaction. The intensity can increase the depth because of the psi.”

The depth of compaction increases as the weight on the axle goes up. The biggest culprit is no surprise – the grain cart. A typical 1,200-bushel grain cart packs 35 to 40 tons on one axle. The simplest solution is to opt for a two- or three-axle grain cart. Then watch where you drive it. Don’t go diagonally across your field. If at all possible, stay on the headlands or follow in the previous pass of the combine.

Next, take a look at the inflation pressures on your equipment.

A study by Ohio State University compared a four-wheel-drive tractor with properly inflated duals at 6 psi, overinflated duals at 24 psi, 24-inch tracks, and 36-inch tracks. The properly inflated tires caused the least amount of compaction. Slightly worse were the 36- and then the 24-inch tracks. The overinflated tires decreased porosity the most. This highlighted a common misconception: Tracks don’t necessarily compact soils less than tires, according to the study.

“If you pay attention to your tires, you can make them work very well,” says DeJong-Hughes. “If you aren’t going to pay attention to tires and have them properly inflated, you might as well go with tracks.

“Flotation and compaction are different,” she adds. “Tracks have better flotation, but don’t confuse that and think they aren’t causing compaction.”

The tire industry continues to bring innovations that allow you to reduce inflation pressures.

Improved flexion (IF) and very high flexion (VF) tires are now offered by most manufacturers. The tires can carry 20% to 40% higher loads, respectively, at the same inflation pressure as a standard radial tire or carry the same load at 20% to 40% lower inflation pressure.

On-board tire-inflation systems, like those available from Precision Inflation or Tire Boss, allow you to fine-tune and lower inflation pressures from the tractor cab. There has been slow adoption of these systems in the U.S., but a few farmers are experimenting with air-inflation systems on their center-fill planters.

“The center-fill planter has brought a visual to farmers on compaction because the corn is lower in the middle of the planter and yielding less,” says DeJong-Hughes. “If you’re going down the road with a center-fill planter, you need to be fully inflated from 70 psi to 110 psi. That is incredibly compactive in the field, especially with the right soil conditions. In the field, you could lower the psi down to 30.” This becomes possible with an air-inflation system.

“I was seeing different heights in the corn plants and noticing a delay in the growth behind the planter,” says Eric Jahn, who invested in a Precision Inflation system three years ago for his farm near Clarkfield, Minnesota. “I think I’m getting better yields due to the system.”

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