A soil pit demonstration by Alliance Tire Americas at the North American Manure Expo in Chambersburg, Pa., highlighted the difference in soil compaction between bias-ply and radial flotation tires—a roughly 50-percent difference in the depth of the compaction.

Alliance compared two types of tires on the same 7,250-gallon Diller manure tank—conventional bias-ply R-3 tires on one side of each of the rig’s two axles and radial flotation tires on the other.

Lines Tell The Story

The 50,000-pound load was rolled over a four-foot-deep pit that had been excavated, then re-filled with layers of soil and sawdust to highlight the effect of forces pressing into the ground. Beneath the bias-ply tires, the layers revealed heavy compaction extending 12 to 16 inches into the soil—four layers deep. Beneath the radial tires, only the first layer was distorted by the weight of the truck.

On the soil surface, the wheel ruts told a similar story. The rut left by the bias-ply tires was a full inch deeper than the track left by the radials—a difference of about 25 percent.

A video of the process and the results is available on YouTube at https://www.youtube.com/watch?v=QtocU7Vn9sg.

Pressure and Footprint

Steve Vandegrift, Alliance Tire Americas product manager, outlined the key factors that led to the differences in performance between the tires:

  • Tire shape. “Bias-ply tires tend to crown in the center of the tread, so they concentrate compaction force in a smaller area of the footprint,” he explained. “Radial tires have a longer, wider, flatter footprint, so the load is spread much more evenly over a larger surface.”
  • Inflation pressure. “For this 50,000-pound tank operating at 25 miles per hour, the bias-ply tires had to be inflated to 40 psi, while the radials could run at 26 psi,” Vandegrift notes. “The inflation pressure of the tire corresponds within one or two psi to the compaction pressure in the soil. That means the bias-ply tires applied about 35 percent more force to the soil.”

Infiltration Illustration

A light rain the night after Alliance conducted the experiment provided a great illustration of the problems soil compaction can cause. By 7:30 am, the rain had soaked into the clay-rich soil in the track left by the radial tires. In the rut left by the bias-ply tires, water pooled for hours afterwards, infiltrating much more slowly into the compacted soil.

“That’s one of the problems soil compaction can cause for years,” Vandegrift pointed out. “Reducing water infiltration can increase runoff during heavy rains, delay fieldwork or planting, and decrease the amount of water that is available to the crop later in the season. Compaction also squeezes water and air out of the root zone and makes it difficult for roots to penetrate into the soil. It’s a devastating problem, and when the damage is deep in the soil, it can take years to heal.

“This is the product of just one piece of machinery rolled backwards and forwards once over the soil,” he added. “Imagine what happens in the field when machinery is driven across the soil over and over again over the course of years.”

Minimize Compaction

“It was exciting to see such a significant difference in this soil pit demonstration,” said Vandegrift. “The farmers and custom applicators at Manure Expo immediately saw the impact, and gained a greater appreciation for the effects of inflation pressure and tire construction on the health of the soil.”

Vandegrift offers tips to help farmers and applicators minimize soil compaction:

  • Before driving onto a field, ask yourself if you really need to be out there.
  • Decide whether conditions are appropriate for traffic, or if it would be better to wait until the soil is dryer. (Wet soils are significantly more prone to compaction.)
  • Consider running a partial load to spare your soil the weight of a full manure tank, grain cart or combine.
  • Remove excess weights from your tractor if they’re not needed.
  • Avoid driving across wet spots if you can.
  • Outfit your equipment with tires that have the largest, most even footprint possible.
  • Minimize inflation pressure. Set the lowest recommended pressure for the load and speed you’re carrying. If you have transported a heavy load down the road—which requires higher inflation pressure—take the time to bleed the tires down to a lower pressure for working in the field at lower speeds. It could save you years of heartache and compacted soils.

Those tips and others are available from Alliance Tire in a white paper on soil compaction. Download the paper free at http://bit.ly/1Osh49X or contact Alliance Tire at (800) 343-3276 to request a copy.

Learning about soil compaction—and learning more about selecting among a growing number of purpose-built tires to meet the unique needs of your farm or business—is important, Vandegrift notes.

“We know that soil compaction is just one thing farmers and applicators have to worry about, and just one variable when it comes to choosing tires,” he says. “The size and weight of the equipment, the speed of operation, how much time the machinery spends on the roads vs. in the fields, the types of soil they run on—all those elements factor into what sort of tire, tread design, and speed rating they need. That’s why we make such a wide range of tires, and why it’s so important to consult a knowledgeable tire dealer to find the right tire for the job.”