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Soil Compaction, Is it good or bad?

Soil compaction occurs when the soil structure is compressed, thus reducing the number and size of the pore spaces between the particles, which causes a decrease in the availability of air and oxygen for the plants as well as a saturation of the pores with water. Soil compaction in urban areas often occurs when heavy equipment during construction is used and by constant human traffic during periods when the soil is wet.

Figure 1. No compressed vs. compressed soil. Courtesy Univ. of Minnesota Extension

Figure 1. No compressed vs. compressed soil. Courtesy Univ. of Minnesota Extension

Compacted soils provide a stable foundation for homes and streets, but they are not ideal for plant growth or water movement. Typically, a good soil has 50% solids, 25% water and 25% air. Because a compacted soil has less pore space for air (porosity), the water infiltration will decrease, and runoff and soil erosion will increase.

Soil compaction also increases resistance to root penetration, making it difficult for roots to grow deeper through the soil. This can lead to the development of a shallow root system, poor plant growth, increased need for irrigation and fertilization. A plant under stress is also prone to attack by pests and diseases.

Figure 2. Plant under good soil vs. compressed. Courtesy University of Minnesota Extension

One way to quantify soil compaction is by measuring bulk density which is the mass of dry soil per unit volume (e.g., grams per cubic centimeter). As the pore space decreases, the bulk density increases. Soils with a higher percentage of clay and silt (for example Georgia’s soils) naturally have more pore space and lower bulk density than sandier soils (Florida’s soils). Bulk density may range from normal (approximately 1.4 g cm-3) to extremely compacted (2.2 g cm-3) in urban soils.

Figure 3. Bulk density comparison: 2.66 gr/cm3 is higher than 1.33 g/cm3. Courtesy of Soil Resources, Spring 2011

Figure 4. Courtesy of Bulk Density, Sustainable Agriculture

How to avoid soil compaction:

Remember that the soil is the most important resource for developing a healthy landscape. The following practices are recommended to avoid soil compaction:

  • Eliminate or reduce pedestrian and heavy equipment traffic
  • Spreading a thick layer of mulch over planting areas during construction
  • Avoid working on the soil when it is very wet

Other available practices:

1.- Tilling: The idea is to break up soil compaction and create more pore space. This can be done with a rototiller to avoid damage to irrigation and utility lines. The incorporation of compost is also recommended to increase the content of organic matter, thus improving water retention.

Figure 5. Shallow tillage (6″) using roto-tiller. Courtesy IFAS

2.- Plug aeration: Used in golf courses and sport fields by lawn aerator machines.

Figure 6. Lawn aeration. Courtesy of Wright Outdoor Solutions

3.- Air aeration: Uses compressed air from a high-speed gun (AirSpade®) to eliminate soil compaction mainly around trees located in parking lots, streets and other locations.

Figure 7.Air aeration using AirSpade. Courtesy of Shelter Tree Care

In conclusion, planning will prevent many problems with compaction. Preventive practices, including limiting the extent of disturbed areas, manipulating soil only when dry and restricting traffic, are more effective and less expensive than practices to alleviate compaction after it occurs.

 

 Literature:

Soil Compaction, University of Minnesota Extension,  https://extension.umn.edu/soil-management-and-health/soil-compaction

Shober, A., et. al. Soil Compaction in the Urban Landscape, IFAS, EDIS

https://edis.ifas.ufl.edu/ss529

Urban Soil Compaction, USDA/ NRCS

https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_053278.pdf