The Density of Compacted Soil

Soil Compaction and Soil Density

• Soil density is an important factor is recognizing a soil compaction problem. Accurately quantifying soil compaction is difficult. However, measuring the change in a soil's bulk density and using this change to represent the degree of compaction that a soil has undergone is one way. As a soil becomes compacted, the pores in between soil particles become smaller, making for a more dense soil. The higher a soil's bulk density, the more it is compacted.

Positive Effects

• Soil compaction's effects on plant growth are not all negative. According to the University of Minnesota's comprehensive guide to soil compaction, noncompacted soils with a density of 1.2 grams per cubic centimeter favors root structure development but is not dense enough to support root branching or secondary root formation. A soil with a higher density due to light compaction supports this more extensive root development. The key is for the lightly compacted soil, as heavily compacted soils have harmful effects on overall root development.

Negative Effects

• The space between soil particles is reduced in compacted soil, creating smaller pores in the soil. It is through these pores that water drains out of soil and new water is introduced from rainfall, irrigation or other sources. These two factors combine, creating a soil that is dry and does not drain well enough to support healthy plant growth. Nutrient transfer between different soil particles is also diminished, as are gas exchanges, leading to more aeration-related problems in the compacted soil.

Other Considerations

• The use of heavy farming equipment, particularly those pieces of equipment weighing more than 10 tons per axle, is the leading cause of problematic soil compaction. Since equipment this massive is almost never used in home gardening, compaction is much more common problem in agricultural plots than home gardens. Many natural and manmade factors contribute to compaction including rate of rainfall, erosion, tillage, crop rotation, so home gardeners face soil compaction problems.