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Crusting

Crusting | Waterlogging | Trafficability | Compaction | Cultivation/Tillage for Broadacre Cropping

What does a soil crust look like?
A soil crust on soil is like a bread crust on bread. It is a thin layer of dense and tough material. It is considerably more compacted and packed than the underlying material. A soil crust tends to look smooth and even when compared to freshly exposed soil.


A developing soil crust




Photographs showing surface soil crusts

As can be seen from these images, porosity declines. Water permeability and air permeability is restricted. Seedling emergence is also reduced.

How do crusts form?
Rain impact on exposed soil is probably the main method of crust formation. A lack of ground cover (e.g. stubble retention) to protect the soil surface can result in soil crusts forming following a rainfall event.
Cultivation and trafficking (by both stock trampling and vehicle movement) can severely disturb and disrupt the soil surface and make them especially susceptible to separation, repacking and compaction by rain drops.

Soils of low
aggregate stability are generally more susceptible to crusting. These will be soils with one or more of the following characteristics: low levels of organic matter; sodic; dispersive; and of generally low cohesive forces between particles.

Sodic soils are highly susceptible to crusting when exposed.

What is the effect of a soil crust?
Crusts block soil pores and increases
soil strength. Soil crusts decrease permeability of the soil surface to water and air. Soil crusts can inhibit seedling emergence.

Soil crusts can negatively affect production by limiting water intake, poor drainage,
waterlogging, low aeration, poor seedling emergence, and subsequent cloddiness.

Plant available water down the soil profile will also be limited by soil crusts as water will not penetrate readily into the soil.

Is crusting common to any soil type or region in Victoria?
Sodicity is a key characteristic of soils prone to crusting, and more than 60 % of the 20 million hectares of cropping soils in Australia are sodic (Rengasamy 2002). In Victoria, approximately 70 % of the soils in the cropping area of the Wimmera and southern Mallee regions are affected by sodicity and high pH (Ford et al. 1993).

This 40 mm thick crust caused failed crop emergence.

Crusting affects major soil types including Sodosols, Vertosols and Calcarosols.

Sodosols are a specific kind of sodic soil with a clear or abrupt texture change between the surface soil (A horizon) and subsoil (B horizon), which is not strongly acid and has an exchangeable sodium percentage (ESP) of 6 or greater in its upper part. The B horizons are usually clayey with restricted hydraulic conductivity caused essentially by the dispersive nature of the sodic clay. An ESP of 6 is the critical limit for the sodicity to have an adverse affect on productivity of the soil (Land and Water Australia 2001).


What can I do to prevent crusting of my soils?
Increase
organic matter levels at the soil surface.
  • Keep soils covered (e.g. stubble retention)
  • Minimise cultivation and other mechanical disturbance.
  • Minimise traffic.
  • Managing sodic soils and dispersion.
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