Monday, April 20, 2009

Turf and Landscape - Compaction

Compaction by equipment can have long-term effects on a soil. This spring planting season has seen limited periods where the soil was in perfect condition. Landscapers and turf managers should avoid the tendency to try to get on soils that are too wet. You need to wait until they are dry enough to avoid compaction. The following is a short article on the subject.

Compaction has the effect of re-arranging the soil aggregates to form a denser, less porous soil. Severe compaction will destroy these aggregates further reducing porosity. The denser soil has fewer large pores to conduct water, so increased runoff and ponding in depressions are common symptoms of compaction. The smaller pores hold water tighter resulting in a a wetter soil that dries more slowly. Soil gas exchange is slowed and oxygen can become limiting to roots. In compacted soil, the soil strength increases impeding root growth. Roots cannot easily penetrate dense compacted areas in soils. This leads to more water stress on plants and reduced ability to take up mineral nutrients.

Compaction is most severe when heavy equipment passes over the soil when it is wet because water acts as a lubricant between soil particles. This is why wet soils are more easily compacted. The problem is also worsened as the clay content of the soil increases. This is one of the issues with new developments where soils were handled when wet.

It has been estimated that over 70 percent of the compaction effect occurs in the first pass across the soil. The heavier the equipment, the more severe the effect. Factors such as increased tire size, proper inflation pressure, and the addition of tracks, duals, or tandem axles can offset some of the effect, but in many cases with very heavy construction equipment there will be a limited reduction in compaction.

In a compacted soil, tillage can help to loosen the soil and the use of an aerator can help over time. However, tillage and aeration tools will not re-create structure or the biopores from roots and earthworm activity. These redevelop over time once the site is planted. Natural forces, such as wetting/drying, freezing/thawing, and biological activity will take many years to restore a severely compacted soil. It is interesting to note that the compaction caused by covered wagons in the 1880’s in the West could still be detected over a century later.

The best advice for managing compaction is to avoid compaction. When possible stay off wet soils, operate with lighter loads, and use tracked or high floatation vehicles when possible.

Gordon Johnson, Extension Horticulture Agent, UD, Kent County

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