Wind

Wind erosion occurs more frequently than the visible evidence, such as dust storms and sand piled against fence lines, may suggest. Wind erosion causes a change in the soil texture, with mostly the smaller particles being removed. There are three main processes that move soil particles during wind erosion, depending on the size of the particles.

Suspension - small particles

Particles smaller than 50 µm go into suspension in the air and can move long distances before returning to land or water.

Creep - large particles

Particles larger than 1 mm roll or creep across the soil surface.

Saltation - medium size particles

Particles ranging from 50 µm to 1 mm are forced into the air by either high wind speeds or impact from other sand grains.

Factors involved in Wind Erosion

1. Erosivity of the wind:

   • The wind speed threshold for sand movement is 4.5 m/s. In Australia, potential wind erosion is greatest in October and least in April. The southern and coastal parts have the highest wind erosivity. (4.5 m/s relates to sand size of 0.3 mm).

2. Vegetation:

   • Loss of vegetation through clearing, burning, or overgrazing can dramatically increase wind erosion.

3. Soil type:

   • Sands and sandy loams are much more susceptible to erosion than loams and clays. If more than 35% of aggregates are greater than 0.85 mm in diameter, then wind erosion is considerably reduced. If more than 60% of aggregates are greater than 0.85 mm diameter then erosion is negligible.

4. Surface roughness:

   • Standing stubble at more than 20 stalks/m² (0.6 t/ha) provides good protection from wind erosion. The stalks absorb most of the wind's momentum, thereby protecting the underlying soil.
   • Ploughing to create wind ridges also increases the surface roughness. However, the ridges themselves are susceptible to erosion and hence wind ridging is of dubious benefit.

5. Cultivation:

   • Cultivation increases wind erosion in all soil types except clays. For sandy soils, just one cultivation will do most of the damage - hence the benefits of minimal tillage.

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