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Competency Area 4: Soil health and compaction

PO 31. Understand the relation between soil compaction and the following factors. Understand each factors' relation to plant growth and important soil chemical and biological processes.

  1. Aeration
  2. Aggregation/Structure
  3. Soil Strength
  4. Runoff and Erosion
  5. Drainage


Soil compaction reduces pore volume, especially of the larger pores. This reduces air-filled porosity and aeration. This affects root function, because most crop roots start malfunctioning below 10% air-filled porosity. A poorly aerated soil leads to greater denitrification losses. Iron oxides will be reduced to ferric iron (Fe2+), which is colorless and mobile. The soil will take on the color of the soil matrix (usually gray). Many soil organisms will suffocate and die in poorly aerated soils. The microbial community may go predominantly anaerobic.


Soil structure will degrade upon compaction. Most damage is done when soils are trafficked or tilled in their liquid state, therefore when these soils dry out they tend to become hard. Roots will have problems penetrating this hard soil. Water will tend to stagnate, causing aeration problems.

Soil Strength

Soil strength increases in a compacted soil. Roots will have difficulty penetrating compacted soil.

Runoff and Erosion

 Runoff and erosion will increase as an effect of compaction because of the reduced pore volume and especially macro-pores.


Drainage will be compromised because of the reduced pore size and subsequent water percolation rate in compacted soils.