Soil compaction - Soil Essentials: Managing Your Farm's Primary Asset - page 126

Compacted soils are more difficult to cultivate (causing higher fuel costs), take
more time to work, and increase wear on soil cultivation machinery.
Compacted soils set harder, which means they are workable for a shorter time
than uncompacted soils.
What causes soil compaction?
There are a number of causes of soil compaction:
Excessive mechanical cultivation, leading to damaged soil structure.
Trafficking by machinery and stock - especially when soil is wet.
Loss of organic matter from the soil - especially the humus that binds soil particles
into a crumb structure.
Heavy rainfall on, or irrigation of, cultivated soils, or soils low in organic matter.
Some soil chemical reactions can cause cemented layers to form, for example
silcrete, ferrocrete or calcrete.
The chemical make-up of the soil, usually comprising too much sodium or not
enough calcium.
How to prevent compaction
Avoid unnecessary stock or machinery traffic on wet soil, especially if plant cover
is poor.
Direct drill crops, or at least use minimum till methods of cropping.
Maintain good pasture cover as much as the farming system will allow. Pastures
should contain a high component of deep-rooted species such as grasses, and
preferably some perennials.
Avoid excessive trampling of wet soils by stock, especially sheep and cattle as their
feet exert very high pressures on the soil. This applies particularly to heavy soils.
Avoid use of implements such as rotary hoes, disc ploughs and disc cultivators.
These implements cause more damage to soil structure than tyned implements
and rapidly break down soil structure.
What are the effects of soil compaction?
Water penetration into the soil is reduced, leading to less soil water stored and
increased runoff, with increased erosion and loss of plant nutrients.
Pores between soil crumbs that contain air are smaller or collapsed. This leads to
unfavourable conditions for plant roots and soil organisms.
Reduced penetration to depth by plant roots, thus limiting nutrient uptake.