Managing wind erosion risk on sandy soils in a dry season
With the dry start to the season in many areas crop establishment has been slow, variable or, unfortunately, non-existent.
Those soils most affected by poor establishment are water repellent sands and pale sands with low clay content.
Repellent sands typically have variable wetting and it can take considerable rain over time for them to slowly wet up, and the pale sands have poor water holding and the topsoil can dry out quickly, especially when disturbed by seeding or other tillage operations.
These dry sandy soils are at high risk of wind erosion when there is minimal stubble cover from last season.
Wind erosion can result in:
- a loss of topsoil and associated nutrients
- make paddocks uneven
- bury or damage infrastructure such as fences or farm tracks
- can result in sandblasting of crop seedlings or emerging crops
- can result in blowouts.
Blowouts are one of the most serious consequences of wind erosion and these areas can cause long-term problems in future seasons.
Options for minimising wind erosion risk can be limited when there has been insufficient rain to adequately wet the topsoil for germination and plant establishment.
Avoid driving or having livestock on sandy, high risk soils
Sands that do not have good stubble cover can still form an ‘armouring layer’ at the soil surface, which acts as weak soil crust and consists of larger sand grains that may be partially interlocked and weakly cemented with each other.
This layer can resist wind erosion provided it is not disturbed.
Disturbance can break up the surface soil allowing sand grains to start blowing across the soil surface which dislodges further sand grains, starting the erosion process (saltation).
Bare sandy areas on exposed hill tops or hill sides can be particularly vulnerable.
Establishing a cover crop
Where sown crop seed is still viable avoiding traffic on sandy areas and waiting for crops to establish when rains come is an option.
In some cases however seed may have germinated but failed. In these cases seeding a cereal cover crop on bare areas after rain may be necessary not only to get immediate cover but also to generate some dry matter to protect the soil over summer.
Where a break crop has failed pre-emergent herbicides may prevent seeding of a cereal.
In these cases and for smaller areas it may be necessary to allow weeds to germinate and grow and cover the soil and then sprayed out before they set seed.
Spreading subsoil
One of the most effective but also a more expensive option is to spread clay-rich subsoil or gravel or gravelly loam using a heavy duty multi-spreader.
The subsoil needs a clay content of 30% or more.
Rates of 50-75 tonne per hectare are often adequate to prevent erosion but rates of 75-120 t/ha or more may have lasting benefits to reduce topsoil water repellence, depending on the quality of the subsoil used.
At these rates there is still minimal need for deep incorporation of the clay leading into next season and the action of the seeder or a scarifier would likely be adequate.
Spreading the material through a multi-spreader is the ideal option for evenness of spread and cover and speed but other more intensive approaches could be used for smaller areas.
At the lighter rates of clay it would still be important not to traffic the soil too much – until it is wet and a cover crop can be seeded.
This approach is expensive but may still be helpful to target or prevent patches at risk of blow-out which could be an ongoing problem for many years to come and difficult (and very expensive) to rehabilitate.
Prioritise
When protecting sands from wind erosion it will often be necessary to prioritise areas.
Identify and target bare sands that are exposed and at risk of becoming a blowout.
Where options are limited avoid disturbing the soil surface and monitor the site after strong wind events.
For more information contact Steve Davies, Research Officer, Geraldton on +61 (0)8 9956 8515.