Reduced axle load lowers tractor impact

Soil compaction research finds no advantage to tracked tractors over conventional machines

Tracked tractors don’t reduce soil compaction, says an Alberta government official.

Lawrence Papworth of Alberta Agriculture’s livestock production and energy section said many producers think tracks will limit the problem, but research shows otherwise.

“In general, there is no difference between soil compaction with track tractors and wheel tractors,” he told a Jan. 20 Manure Management Update in Lethbridge.

Papworth said pressure spike is the key to compaction.

Each axle on a conventional wheel tractor causes a pressure spike. When a tracked tractor travels, each axle and each roller on that track causes a pressure spike because the track is flexible.

Papworth said reduced soil compaction was a selling point when tracked units first came out.

“Research has shown that that’s not true.”

Tracked tractors have advantages in flotation and pulling power, while those with wheels have the advantage in steering and cost.

However, he said compaction levels are comparable.

Axle load is the first consideration to limit compaction because pressure goes deeper into the soil layers as the load increases,.

“It’s very important to keep axle loads down so that you can avoid subsoil compaction because subsoil compaction is very hard to rectify,” said Papworth.

“The research has shown that you should limit axle loads to 10 tons (9.1 tonnes), and I read in some cases even six tons (5.4 tonnes).”

One way to do that is to increase the number of axles.

Contact pressure is another facet of compaction. The pressure is typically one or two pounds per sq. inch higher than the tire pressure.

Flotation tires, which can be operated at a lower pressure, could reduce compaction.

“You’re getting more surface compaction with a narrower tire because it’s at a higher pressure, and you also could get some compaction in the subsoil too, depending on the weight and the pressure that that tire is operating at.”

Papworth said 10 pounds per sq. inch is the pressure at which compaction can be kept to a manageable level.

Contact pressure can be reduced by:

  • Using the lowest allowable tire pressure based on the load.
  • Using flotation tires to spread out the weight.
  • Using radial instead of bias-ply tires.
  • Using larger diameter tires for bigger footprint front to back.
  • Using tractors with four wheel drive, front-wheel assist, tracks or duals instead of conventional single axle.

Papworth also reminded producers to check tire ballast.

“Many tractors that are used for multi purposes, they are ballasted to pull heavy tillage equipment, but when you’re using them to pull a manure spreader, it doesn’t take a lot of force to pull it so you could probably remove some of that ballast,” he said.

“It might be worth doing it. You’ll save a lot of fuel and soil compaction, but if it’s liquid ballast in the tires, it’s pretty hard to do.”

Travelling over a smaller percentage of the field can reduce compaction.

A vertical beater spreader that covers a wider area is preferable when spreading manure.

It may require a slower speed to get desired coverage, but equipment tramples less of the field.

Papworth also said a hose drag system is better than large, heavy manure tanks when it comes to compaction.

An automatic air inflation-deflation system for tires is another option to consider.

barb.glen@producer.com

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