What is Soil Compaction?


In agriculture, soil compaction is a complex problem in which soil, crops, weather and machinery interact. 

External pressure due to the use of heavy machinery and inappropriate soil management can lead to the compaction of subsoil, creating waterproof layers within the soil that restrict water and nutrient cycles. This process can cause on-site effects such as reduced crop growth, yield and quality as well as off- site effects such as increased surface water run-off, soil erosion, greenhouse gas, depletion of oxygen in water, reduced groundwater recharge and a loss of organisms in environment.

Top soil compaction is considered partly reversible and its occurrence controllable. Subsoil compaction, however, is regarded as the major problem because it can be permanent, meaning the pore (minute opening) functions can potentially not be restored after deterioration. 

Since farmers in modern intensive agriculture depend on heavy machinery and therefore cannot completely avoid compaction, soil compaction management approaches focus on mitigation. 

Attempts to mitigate soil compaction include biological, chemical and technical approaches. Long-term public policies can tackle the underlying reasons for soil compaction. For instance, subsidies for low-tech agriculture may decrease heavy machinery use on the field, and educational programs aiming at slowing population growth can lower the pressure on agriculture caused by population size.

Image: HR45 footprint - Compaction occurs below the surface of the soil.

Soil Compaction: Then and Now

Soil compaction is not a recent issue. Before the beginning of mechanised agriculture, the usage of plough-pans was associated with soil compaction. However, multiple studies have shown that modern farming techniques increase the risk of harmful soil compaction. 

The historic data basis for global soil compaction is generally very weak as there are only measurements or estimates for certain regions/countries at certain points in time. 

In 1991, it was estimated that soil compaction accounted for 4% (68.3 million hectares) of anthropogenic (influence of human) soil degradation (distress) worldwide. 

In 2013, soil compaction was regarded a major reason for soil degradation (distress) in Europe (approx. 33 million ha affected), Africa (18 million ha), Asia (10 million ha), Australia (4 million ha), and some areas of North America. 

When soil compaction occurs the bulk density of the soil in the compacted layer increases. Compaction typically occurs to a depth of about 30 to 40cm due to traffic by machinery and/or animals. The type of tyre, the air pressure in the tyre, the weight of the vehicle and, most importantly, soil moisture, all have a bearing on soil compaction by vehicles.

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