AgMemo - Grains news, October 2019

Page last updated: Wednesday, 27 November 2019 - 9:07am

Please note: This content may be out of date and is currently under review.

Plan to manage your ground cover now to reduce erosion risk

sand or dust blowing in a paddock with little or no stubble
Some paddocks are already blowing as a result of the poor season

Many grainbelt properties have experienced poor crop and pasture growth this year, which could bring about an increased chance of overgrazing and, therefore, increased risk of wind and water erosion. 

Decisions are best made early in the season about managing erosion through the dry period. Producers considering grazing failed crops will be reviewing the amount of feed likely to be on offer, the stock numbers to be carried and whether there will be sufficient plant cover to protect the soil from erosion.

Wind erosion occurs when three conditions are met.

  1. Insufficient ground covers (<50% of the surface covered by non-erodible elements - stubble, pasture residues, gravel or very coarse sand).
  2. Loose, dry soil at the surface.
  3. Wind strong enough to initiate sand movement. The wind velocity that causes sand movement is about 28 km/h.

When cover is reduced below 50 per cent, loosened soil starts to move and the blowing sand lifts the dust, which is made up of clay, organic material and nutrients, transporting the dust out of the paddock. The majority of soil nutrients are stored in the top few centimetres of soil. Research indicates that an 8mm loss of top soil in pastures can result in a 16 per cent reduction of the following crop yield.

Now is a good time to think about whether paddocks are likely to be exposed to strong winds over the drier months, and to check paddocks to assess if the soil is dry, loose or disturbed, and if they have enough cover. Consult DPIRD’s diagnosing wind erosion risk page for tips on how to assess your paddocks.

Stable ground covers are the major wind control mechanism 

The level of cover to minimise wind erosion is about 50 per cent of the surface covered by non-moveable residues (i.e. anchored stubble). For cereal stubbles this is about 750 kg/ha of straw and for lupins and canola about 1500kg/ha of straw. This is from crops yielding about 500 kg/ha for cereal, 650 kg/ha for lupins and 800 kg/ha of canola. The corresponding critical level for pastures is about 500 kg/ha of dry residues.  The images below can provide an idea of what a good cover looks like on a paddock.

An oblique view of 1400 kg/ha of cereal stubble, with about 10 % cent standing and 80% prostrate.  More than enough to minimise erosion.
An oblique view of 1400 kg/ha of cereal stubble, more than enough to minimise erosion.
A vertical view of 1400 kg/ha of standing cereal stubble.  About 50% of the white sandy surface is visible.  More than enough to minimise erosion
The 0.25 quadrat in this vertical photo represents 1400kg/ha of stubble.
An oblique view of 1000 kg/ha of standing and prostrate cereal stubble covering about 40% of the ground.
An oblique view of a trial plot representing 1000 kg/ha of cereal stubble, enough to resist wind erosion. This amount of stubble represents about 40% ground cover.
A vertical view of 1000 kg/ha of standing cereal stubble. About 60% of the white sandy surface is visible.
The vertical view of a quadrat represents 1000kg/ha of stubble or about 40% ground cover
An oblique view of cereal stubble covering about 20% of the ground.  Not enough to resist erosion
This paddock is highly prone to wind erosion as it contains only 400kg/ha of cereal stubble, not enough to resist erosion.
A vertical view of cereal stubble covering about 20% of the ground.  Not enough to resist erosion
The area in this quadrat shows the lack of cereal stubble to resist wind erosion.

Strategies to manage ground cover

Managing stubbles begins at harvest. By adjusting harvest settings appropriately, stubble levels can be maximised and spilt grain minimised. The Harvesting short patchy crops page has more information on this topic. By reducing the spilt grain at harvest, the paddock has little feed value. For paddocks that have been cropped this year and are not grazed, stubble management options for seeding in the coming season need to be considered at harvest. If stubbles are burnt to manage weed seeds, harvester settings will need to be set-up to enable the burning of windrows only rather than the whole paddock. Burning whole paddocks leaves the soil surface vulnerable to blowing from strong autumn pre-frontal winds.

If there is likely to be insufficient cover either for livestock or erosion control, there are a number of options to reduce grazing pressure and erosion risk. These options may include grazing vulnerable paddocks for the least time possible, minimising vehicle movement to reduce soil disturbance, use of feedlots or stable refuge areas, agistment, or selling excess stock. Grazing native vegetation is discouraged for a number of reasons including potential breach of clearing regulations.

More detailed information can be obtained from the dry seasonal conditions article and the Managing wind erosion page. Alternatively you can contact Paul Findlater, senior research officer, Geraldton, on +61 (0)8 99568 535 or Justin Laycock, research officer, South Perth, on +61 (0)8 93683 832.