Why diagnose risk?
Because there may be time to do something that will lower the likelihood or damage that wind erosion can cause. Doing something can start years ahead for susceptible paddocks — by planting tree windbreaks or claying — or start the season ahead by retaining enough stable groundcover.
Soils that are susceptible to wind erosion are likely to be susceptible to water erosion.
Factors contributing to wind erosion risk
- Erosive winds: wind speeds of greater than 28 kilometres per hour are needed to move soil particles and lift dust for significant distances. The Bureau of Meteorology provides information on wind speed and direction during the year at all Australian weather stations.
- Exposure of the soil surface: erosive winds must be able to reach the soil surface to cause erosion. Exposure can be prevented in several ways:
- landscape position: sheltered areas include valleys, gullies, downwind of ridges and hills
- tree and shrub windbreaks: native vegetation, tree windbreaks, alley systems, tagasaste plantations
- crop and stubble groundcover: retaining at least 50% groundcover with 30% of that anchored. The critical level is 30–40% groundcover and 50% gives a safety factor. Groundcover of 30–40% is achieved with 750 kilograms per hectare (kg/ha) of cereal stubble and 1500kg/ha of lupin stubble
- pasture groundcover: retaining at least 50% groundcover of annual pasture or perennial pasture.
- Erodible soil surface: to be eroded, the soil surface needs to be detached (disturbed or loose) at the surface. Gravelly or rocky surfaces are less erodible, and large stable clods also provide protection. The soil surface can be detached by:
- cultivation: mouldboard ploughing, spading, tyne cultivation, disc cultivation, deep ripping
- livestock movement: sheep tend to loosen more soil than an equivalent number of cattle
- vehicle movement: harvesting, seeding.
Conditions which contribute to high risk of wind erosion
Conditions that lead to a high risk of wind erosion are obvious — after the event. Being aware of these developing conditions and having a plan to deal with them can help reduce wind erosion:
- Poor seasonal conditions: dry conditions in the previous winter and spring, followed by a long, dry summer usually mean there is inadequate groundcover in late summer and autumn. Dry conditions and strong winds after seeding are hard to treat at the time.
- Grazing stubbles or pastures as the groundcover approaches critical dry matter levels or 50% groundcover; by the time that it looks like time to remove livestock, it is probably too late. Bare patches around watering points, gateways and camping pads can lead to blowouts.
- Paddock burning: full paddock burning, especially if the area has been recently grazed, will leave the soil exposed and erodible.
- Cultivation: this reduces groundcover and loosens the soil surface. Soil inversion — mouldboard ploughing, delving, spading — is the most extreme form of cultivation leading to exposure. Large stable clods or clay brought from the subsoil may reduce erodibility.
- Combinations of the conditions above.
Assessing the current risk
All soils can be eroded by wind in certain conditions, depending on the level of protective cover (exposure) and whether the soil is loose and dry (erodible).
Managers can use the sytem in Figure 1 to diagnose risk of wind erosion.