Soil Compaction and Wet Soils

FOR IMMEDIATE RELEASE
October 16, 2009

Most producers know that going into a wet field with equipment will cause soil compaction. However, faced with a later harvest season and high soil moisture in most of the state, many will take compaction as a lesser evil. Soils at field capacity will allow the greatest amount of compaction to occur. If compaction occurs this fall, it will probably still be noticeable during the next growing season. Uneven plant growth, ponded areas in wheel tracks or evidence of stress during dryer times may be seen.

Duane Friend, University of Illinois Extension natural resources management educator, says there are still some considerations that will reduce the amount of compaction that may occur.

Whenever possible, restrict traffic to specific tracks or lanes. The first trip through the field creates the greatest amount of compaction. Secondary trips over the same lanes do not significantly increase the amount of compaction in those areas. When unloading the combine, use the combine's previous wheel tracks. Never cross the field diagonally. If you cannot park the semi trucks on the adjoining road, keep them on the headlands.

Research indicates that high surface contact pressure, such as from over-inflated tires, concentrates loads onto smaller areas and compacts soil. Using larger wheels and tires for floatation of a given load allows lower inflation pressures. Although less conclusive, research also suggests that large axle loads (greater than 10,000 to 15,000 pounds) may cause some compaction in subsoil, even if surface pressure is relatively light (e.g., 10 to 15 psi).

Once a soil is compacted, time will be needed to reduce it. Wetting/drying and freezing/thawing will diminish compaction over time but should not be expected to correct problems by the next season. Some research suggests that only well-defined, compacted soil layers deeper than four inches below the soil surface are candidates for loosening, or sub soiling.