Fields rutted by wheel tracks during soybean harvest are a common sight in the grain-producing areas of Kentucky. The ruts look bad, but may or may not be as damaging as they look.

Even though combines can compact soil, the physical condition of the soil must be right for compaction to be severe. When soils are dry enough that they could be tilled properly, little compaction is likely to occur because shear strength of soil is great enough to withstand the pressure. This is the usual condition under which we harvest.

As the soil becomes wetter, they are easier to compact because the soil aggregates and individual particles become lubricated with water which reduces the shear strength. The large pores are filled with air and the small ones filled with water. The large pores collapse with pressure and compaction is formed. Compacted ruts are formed.

As the soils become wetter, all pores are filled with water and the soils can not be compacted but the shear strength of the soil is reduced to near zero. This causes large, deep, muddy ruts with little or no compaction.

So there are two kinds of ruts, compacted and uncompacted. Both of these can exist in the same field.

Uncompacted ruts

These look the worst and have large raised ridges on each side of the track. There is a lot of mud. There is no compaction in these ruts or a small amount at the bottom of the rut. The soil structure was damaged but can be easily corrected.

How to correct: The rutted areas need to be smoothed for future production. No-tillage helps reestablish the soil structure. The ruts can be smoothed two ways. One is with a roller (such as a rice roller) when the soil is still saturated. The soil moves back into place and the saturated soils prevent any compaction from the process. It does negatively affect the structure but can be quickly corrected. For most people, it will require waiting until the area has dried and using surface tillage to fill and smooth the ruts.

Compacted Ruts

These ruts don’t look too bad. They have little or no lip on the rut and are mostly a compressed track. In these ruts the compacted zone usually starts 1 to 2 inches below the bottom of the rut and is compacted for several inches. The depth of the compaction can range from 4 to 10 inches.

Compaction can also be severe and deep on the ends of edges of the fields where grain hauling was done. These areas may need special attention.

The amount and depth of compaction can easily be checked by probing with a penetrometer, a steel rod 1/2 to 3/4 inches long or a long screwdriver. When pushed into the soil, the compaction can be easily felt by resistance. With this information (depth and amount of compaction), you can select the tillage tool needed for repair.

How to correct: The rutted areas need to be smoothed and the compaction area broken. If the bottom of the compacted layer ends within 8 to 9 inches of the soil surface then a tillage tool such as a chisel plow could be used. For deeper compaction, a subsoiler would need to be used. If only the top 6 inches of soil was tilled to remove the compaction and the compaction below 6 inches remains, the area would produce 80 percent to 85 percent of its production potential.

If we get too anxious about this tillage in the spring, we could cause additional compaction. Compaction caused by spring tillage of wet soils can be severe and more costly than that caused by the combine at harvest. Any time soils are tilled wet, the potential for serious compaction exists. It is important that we wait for the soils to dry enough for proper tillage and shattering.

SOURCE: Corn & Soybean News, University of Kentucky.
By Lloyd Murdock, Plant and Soil Sciences
University of Kentucky