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Soil Compaction Risk Greater with Wet Soils

Posted: May 3, 2011

Cool, wet spring weather has given us few good days to do field work, increasing temptation to work soils when they are still too wet. Resist that temptation if at all possible. Our soils are more susceptible to compaction than most. Working when soils are too wet can cause surface compaction in the topsoil layer that lasts throughout the current growing season, and deeper subsurface compaction that lasts for many years.

An ideal soil volume for crop production contains about 25 percent water and 25 percent air by volume. The air and water fill the pore spaces between and among actual soil particles and aggregates. The remaining 50 percent of the volume consists of mineral soil particles and organic matter. Soil compaction reduces the pore spaces in that soil volume. Tillage and wheel traffic that reduces pore space results in a dense soil with poor internal drainage and reduced aeration. Plant roots don't grow well in dense soil. Inadequate moisture and nutrients reach the plant, and yield is reduced. Generally, the higher the clay content of a soil, the more compaction reduces the yield.

 

Research in the Midwest has shown that surface compaction can be alleviated by tillage that goes deeper than the area of compaction. However deeper subsurface compaction is relatively permanent. Tire inflation pressure has the biggest impact on surface compaction.  Subsoil compaction is due to axle load.  Axle loads should be limited to less than 6000 pounds per axle. Our friends in dairy and field crop production generally use bigger, heavier equipment such as manure spreaders, grain wagons and combines that can easily go over those axle limits.  But even in vegetable growing equipment used today is larger than it was years ago. Lime trucks, and other equipment can push or exceed those limits. 70% of surface compaction occurs on the first pass over the field so as much as possible it is better to run in the same track to minimize compacted areas.

 

The only real solution is to avoid, as much as possible, field practices that cause compaction. Do not travel on wet soil unless it is absolutely necessary to do so. Try to avoid excessive axle loads, which cause deep compaction. Eliminate unnecessary tillage operations. Keep tire pressures on the low end of the recommended range.

 

 This information taken from the following publications on the subject: 1) “Soil Compaction, Causes, Effects and Control” University of Minnesota Extension, DeJong-Hughes, Moncrief, Voorhees, Swan. 2) “Understanding and Managing Soil Compaction” Iowa State University, Hanna and Al-Kaisi. 3) “Soil Compaction: The Silent Thief” University of Missouri, Frisby and Pfost. 4) “Effects of Soil Compaction” Penn State College of Agricultural Sciences, Duiker.