New initiative investigates non-wetting solutions
GroundCover™ Supplement Issue: 118 | 31 Aug 2015 | Author: Dr Margaret Roper and Dr Stephen Davies
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
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.
|pH and acidic soils
*Identified as limitations to water supply
SOURCE: Soil Constraints – West: A GRDC initiative to develop soil management systems for the future.
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,
Dr Margaret Roper, CSIRO Agriculture Flagship,
08 9333 6668,
Dr Phil Ward, CSIRO Agriculture Flagship,
08 9333 6616,
GRDC Project Code DAW00244, DAW00204, CSP00139
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