February 22, 2001

NDSU Ag Engineer Says Soil Compaction Is a New Management Concern in Region

As heavy farm equipment and early tillage and planting operations combine to increase the chance of soil packing, soil compaction is becoming a new management concern for producers, according to a North Dakota State University agricultural engineer.

"Actually, an optimum level of soil compaction is needed for maximum yields. If soil is either very hard or very loose, crop yield will probably be reduced," says Vern Hofman of the NDSU Extension Service. "We’re beginning to see problems where soil is packed to the point of reducing crop yields. The optimum level of compaction will depend on the crop, characteristics of the soil and climatic conditions during the growing season. For best crop production, seed should be placed in a warm, moist and firm seedbed."

Typically, problems arise when wheel traffic from tractors and equipment firms soil beyond optimum conditions. The problem usually occurs when working wet soils, the major cause of soil compaction in the northern plains. "Waiting until soils dry to proper levels and using low-pressure radial tires or tracks can reduce soil compaction considerably," Hofman says.

"Operating tractors with radials at air pressures below 10 psi or track type tractors can help reduce the problem considerably. This spreads the weight of the tractor over a larger area, reducing the force on the soil surface," Hofman says. The pressure in the tire is very closely related to the pressure applied to the soil surface. For example, if you operate a radial tire at 8 pounds per square inch (psi), the pressure being applied to the soil surface is about 8 to 9 psi.

Radial tires can be operated at pressures down to 6 psi, but as tire pressure is decreased, load carrying capacity of the tire goes down as well, he notes. Be sure to follow manufacturers’ charts so you do not exceed the load carrying capacity of the tire at that pressure.

"Also, when operating a tire at low pressures, be sure to check tire pressures more often so the pressure does not drop below recommended levels. If this happens, tire damage can occur very quickly," Hofman says..

Bias ply tires should not be operated at low pressures, he cautions. The lowest operating pressure for most bias ply tires is 14 psi.

Using track-type tractors is another excellent way to reduce soil compaction, Hofman notes. The long track spreads tractor weight over a large area, reducing the pressure on the soil surface.

An Ohio study comparing a four-wheel drive tractor to a track type tractor of equal size found the highest and the lowest soil compaction with the four-wheel-drive. The most compaction was found with the four-wheel-drive operating at a tire pressure of 24 psi. The four-wheel-drive also had the lowest compaction with a tire pressure at 7 psi. The track type tractor created soil compaction that was between the extremes of the four-wheel-drive tractor.

Hofman says spreading tractor weight over a larger area usually increases tractor performance by reducing slippage. This occurs with both low-pressure radials and track type tractors.

"If you want to reduce soil compaction by lowering tire pressure, check the tire charts to see if the pressure on your tractor tires can be lowered. To lower pressure, a larger tire may be needed. This can be expensive on an existing tractor, as new tires, rims and wheel hubs may be needed. Adding a larger dual or a triple tire may be an option. It is usually best to buy the correct tire size on a new tractor so it can operate at a lower pressure," Hofman says.

###

Source: Vern Hofman, (701) 231-7240, vhofman@ndsuext.nodak.edu
Editor: Tom Jirik, (701) 231-9629, tjirik@ndsuext.nodak.edu