New initiative investigates non-wetting solutions

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Research is unravelling the mechanisms underlying soil water repellenceand developing management solutions to tackle a constraint that costs growers millions of dollars in lost production each year

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More than 12 million hectares of agricultural land across southern Australia are at risk of water repellency and more than 10 million of these are in Western Australia.

PHOTO: Evan Collis

More than 12 million hectares of agricultural land across southern Australia are considered at risk of water repellency – a condition that has been estimated to reduce crop yields by as much as 40 per cent, particularly in dry years.

More than 10 million of these non-wetting hectares are in Western Australia and represent over 50 per cent of the WA agricultural area. Non-wetting soils have been rated as a highly significant constraint to crop production by four of the five WA Regional Cropping Solutions Networks (Table 1).

Water-repellent soils are common in south-east South Australia, the Eyre Peninsula and western Victoria. 

Soli Constraint  Albany Esperance
Geraldton
Kwinana West
Kwinana East
Non-wetting
Yes Yes
Yes
 – Yes
pH and acidic soils
Yes Yes
Yes
Yes 
Compaction Yes
Yes
Yes
 – Yes
Subsoil constraints*
Yes
Yes
 – Yes
Yes

*Identified as limitations to water supply

SOURCE: Soil Constraints – West: A GRDC initiative to develop soil management systems for the future.

Soil constraints

Soil constraints rarely exist in isolation. In acknowledgement of this the GRDC has invested $18.2 million in the western region over five years (2014–19) to develop management systems tackling non-wetting soils, soil acidity, compaction and subsoil constraints.

The investment, known as Soil Constraints – West, forms a component of a new GRDC-funded national Soil Constraints Initiative that commenced in 2015.

Soil Constraints – West spans the Western Australian wheatbelt and involves the Department of Agriculture and Food, WA (DAFWA), Murdoch University, CSIRO, and grower and industry groups. The initiative will:

  • further investigate soil water repellence across soil types and WA cropping systems with the aim of delivering the best management options for the range of water-repellent soils that occur on WA farms;
  • coordinate an across-industry effort to effect a step change in the management of soil acidity in the western and southern GRDC regions (the project will revisit the major barriers to adoption of liming by growers and propose solutions to overcome these as well as refining calculators to aid liming decisions);
  • develop ways for growers to confidently predict the severity and extent of subsoil constraints such as nutrient deficiencies/toxicities, acidity, sodicity, waterlogging and compaction; and
  • develop profitable options to better manage subsoil compaction while providing continued support to evaluate the financial and environmental benefits of controlled-traffic farming.

Water repellency is associated with soil organic matter, which is derived mostly from plants and contains a mix of ‘water-loving’ (hydrophilic) compounds and more complex waxy, water-repellent (hydrophobic) compounds, which previously protected the plants from desiccation.

When these waxy, hydrophobic compounds become fused onto the surface of soil particles they create a water-repellent skin around soil particles, rendering them hydrophobic. This results in water flowing over the surface of affected soils until it finds a point of entry such as crack or old root channel. As a result, non-wetting soils are characterised by patchy and delayed plant emergence.

Sandy-textured soils with less than five per cent clay are most at risk of exhibiting water repellence because the soil particles have a relatively smaller surface area than the particles of soil with higher clay content and, as a result, become coated with the water-repellent compounds more quickly.

Adoption of no-till farming has intensified the severity of water repellency in some areas because it leads to an accumulation of soil organic matter and the waxy compounds responsible for water repellency at the soil surface.

Growers have also reported worsening repellency after dry or early sowing when the seasonal break has been weak and unreliable (see Dry seeding puts time pressure on moisture).

More information:

Dr Stephen Davies, DAFWA,
0408 439 497,

stephen.davies@agric.wa.gov.au;

Dr Margaret Roper, CSIRO Agriculture Flagship,
08 9333 6668,
margaret.roper@csiro.au;

Dr Phil Ward, CSIRO Agriculture Flagship,
08 9333 6616,
phil.ward@csiro.au

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Dry seeding puts time pressure on moisture

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Collaborative approach to tackle soil constraints

GRDC Project Code DAW00244, DAW00204, CSP00139

Region West