Compaction decreases crop yield potential by restricting root growth and creating a less desirable root environment. Increased surface water runoff on compacted soil also reduces yield potential as well as accelerates topsoil erosion. The increasing trend toward conservation tillage, which requires fewer tillage operations, has the potential of greatly reducing the possibility of traffic compaction of soils. This benefit of conservation tillage can be reduced, however, by the trend toward larger, heavier tractors in recent years. Hammel points out that, depending on implement widths, about 60 to 90 percent of the soil surface in the field may be traversed by tractor wheels during conventional tillage production of small grains.
Additional compaction occurs from the combine, particularly if the soil is wet at harvest.
Each track made by the equipment contributes to compaction of the soil. Hammel explains that the average weight of a wheel type tractor in the early 1950's was 3 tons. In general, the greater the load applied to the soil surface, the greater the degree and depth of soil compaction. Compaction below the normal tillage zone is of particular concern because correction, if possible, is difficult and expensive, A deep subsoiling operation maybe required. In some cases, however, deep soil compaction may only be reduced by years of rooting action from deep-rooted plants.