Soil compaction results in compression of pores that would otherwise transport water and air. This impedes root growth and can cause oxygen deficiency. Soil compaction can lead to a severe decrease in yield.
Soil compaction by definition means that the density of the soil increases when it is compressed. In other words, the soil becomes denser and every litre of soil weighs more when the pores are compressed. It is often easy to understand and gauge the effects of soil compaction from watching a tractor tyre roll over loose soil in wet conditions.
What happens to the roots when the soil is compacted?
Soil compaction results in root growth being restricted and affects root development in two ways:
- Compaction decreases the number and size of pores. As a result, there are fewer pores with diameter larger than roots in which the roots can grow freely, without resistance.
- Compaction increases the resistance of the soil through pressing soil particles more closely together.
Water can’t move freely
Soil compaction also restricts the movement of water down through the soil. This causes water saturation in the upper layers, which in turn can lead to oxygen deficiency for the roots according to image below.
Air is essential: Guideline values for soil air-filled porosity: >25 percent air means good aeration, 10-25 percent air an result in limitations in certain conditions, and <10 percent air is characteristic of oxygen deficiency
In addition, soil aeration status affects the availability of various plant nutrients, e.g. nitrogen and manganese. Under anaerobic conditions, denitrification can lead to severe loss of nitrogen in the form of nitrogen oxide or nitrogen gas to the atmosphere. Soil compaction can thereby decrease nitrogen availability in the soil.
How to make things better?
To avoid soil compaction, it is important to employ remedial measures that can contribute to better soil structure in the long term. Such measures include drainage, structure liming, keeping the soil covered with vegetation and supplying external organic material. These measures, which result in the soil being drier, decrease soil compaction at depth.
Reduce number of passes
Cropping system and soil tillage are also critical for soil compaction. The most important consideration is to avoid tillage when the soil is too wet. A dry soil has greater bearing capacity for loads, while a wet soil is compressed under a similar pressure.
A large contact area with the help of broad tyres or dual wheels results in a lower wheel load
Number of passes is also important, as is keeping the total weight of field equipment as low as possible.
The yield decreases with greater soil compaction.