Soil Compaction

by Steven P. Graber, Resource Conservationist
Natural Resources Conservation Service
Dodge City, Kansas

Soil compaction occurs on nearly every farm in the United States. The results of compaction can be evident in crop growth. Careful thought should be given to planning your tillage operations. Just how many passes will be needed to prepare your seedbed? The trend has been toward reduced, or no tillage, mainly due to the cost of fuel. However, there is something else besides fuel savings. Every trip across the field compacts the soil forming zones where crop growth is impaired.

Soil compaction can manifest itself in a couple of different forms. Compaction caused by the wheel traffic and compaction from the tillage implement itself. Research has shown that the first pass of the tractor causes the most soil compaction. This is without a doubt the major cause of soil compaction.

The weight of tractors has increased from less than 3 tons in the 1940s to approximately 20 tons today for the big four-wheel-drive tractors. This is of special concern because spring planting is often done before the soil is dry enough to support the heavy planting equipment. Greater axle loads and wet soil conditions increase the depth of compaction in the soil profile. Compaction caused by heavy axle loads (greater than ten tons per axle) on wet soils can extend to depths of two feet or more. Continuous sweep plowing or disking at the same depth year after year will cause serious tillage pans just below the depth of tillage in most soils. The tillage pan is generally relatively thin (two to four inches thick), and can have a significant effect on crop production. This can be alleviated by varying depth of tillage over time or by special tillage operations.

Compaction causes reduced yields and may worsen other problems that reduce yields such as disease and low nutrient supply because of reduced root distribution. Assessment of the severity of compaction problems is best done by inspection of the soil and crop roots. If root growth is restricted due to compaction, deep tillage such as subsoiling may be warranted.

The depth of yield-limiting soil compaction will determine the required depth of tillage and tillage tool selection. If compaction occurs in the top six to eight inches of the soil, tillage tools such as a chisel plow can be used to shatter the compacted layer. However, if compaction is below eight to ten inches, tillage tools such as a subsoiler, ripper, or paraplow may be needed. The key is to operate the tillage tool no deeper than necessary, one to two inches below the bottom of the tillage pan. Also, the soil needs to be dry in order for the operation to shatter the tillage pan.

The alleviation of the compacted soil is not easy. Although subsoiling or chiseling can alleviate compaction immediately, the second pass by a single vehicle or implement may nullify the effort. The use of different strategies will be the best shot at solving the problem. Reducing tillage, increasing organic matter, controlling traffic, and if necessary, subsoiling will all benefit the soil improving soil quality and increasing crop production.

You might think that one pass across the field will not hurt much, but that one pass with the wrong soil conditions may be one too many. Be careful and think, is this tillage pass really necessary? If you plan your tillage operations and stay out of the field as much as possible, you will save fuel and your crops might just produce better yields.

For more information about soil conditions, please contact your local Natural Resources Conservation Service (NRCS) office or conservation district office located at your local county USDA Service Center.

For more information about NRCS programs, visit the Kansas NRCS Web site at www.ks.nrcs.usda.gov.

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Last Modified: 12/21/2007