South Eastern Zone of Ancient Drainage

Posted on Mar 13, 2015


South Eastern Zone of Ancient DrainageLandResources

A smooth to irregularly undulating plain dominated by salt lake chains in the main valleys with duplex and lateritic soils on the uplands. Mallee vegetation on duplex soils, Proteaceous vegetation on gravels and sands.

SWCC Strategic Priority

Threats to be addressed:

  • water erosion
  • land salinisation
  • soil structure decline and/or compaction
  • loss of soil carbon

DAFWA – Report Card (September 2013) The South Eastern Zone of Ancient Drainage, for the purposes of DAFWA’s Report Card, is included in the Agricultural Soil Zone 8. Southern Wheatbelt (along with the South Western Zone of Ancient Drainage). Agricultural Soil Zones are based on repeating patterns of soil and land types. The Ag Soil Zones are used for reporting on the following themes:

  • Soil acidity
  • Wind erosion
  • Water erosion
  • Soil organic carbon
  • Soil compaction
  • Water repellence
  • Nutrient status (phophorus)

Hydrozones are based on grouping areas with similar hydrology and are used for reporting on:

  • Dryland salinity and
  • Acidification of inland waterways.

The South Eastern Zone of Ancient Drainage is identified on its own as a hydrozone.

Key Findings for this Zone

Soil Acidity

Soil Acidity

Summary – A large proportion of soils are below target, and the trend shows continuing deterioration.

Condition and Trend – Poor and Deteriorating (confidence in condition and trend: limited evidence or limited consensus in both).

This zone is dominated by duplex soils with deep sandy duplexes and alkaline shallow duplexes comprising over 40% of the area. Acidity in the surface soil is extreme. More than 80 and up to 89% of samples collected had pH below the recommended target for the layer. Unless surface soil pH is increased, the subsurface soil layers will continue to acidify and restrict productivity.

The subsurface layers of alkaline shallow duplexes and the saline wet soils are at lower risk. However, for the deep sandy duplexes and the gravels that make up 38% of the area, the risk of low soil pH increases, with 40% to 50% of the samples collected from the 10-20 cm layer being below the recommended target and around 30% of the samples from the 20-30 cm layer samples also below the target.

A summary of the percentage of samples below target for depths 0-10 cm, 10-20 cm and 20-30 cm for the Ag Soil Zone 8. Southern Wheatbelt (DAFWA Report Card, 2013).

A summary of the percentage of samples below target for depths 0-10 cm, 10-20 cm and 20-30 cm for the Ag Soil Zone 8. Southern Wheatbelt (DAFWA Report Card, 2013).

Source: Gazey C, Andrew J and Griffen E (2013). ‘Soil Acidity’. In: Report card on sustainable natural resource use in agriculture, Department of Agriculture and Food, Western Australia.

To find out more about Soil Acidification in the south-west of Western Australia go here.

Wind Erosion

Wind Erosion

Summary – More reliable rain produced good crops and stable ground covers. Areas close to salt lakes were poorer.

Hazard and Trend – Low (meaning 1 yr in 4 below target hazard – yrs 2009-12) and variable (confidence in hazard: adequate high-quality evidence and high-level of consensus; confidence in trend: limited evidence or limited consensus).

Click on the image below to enlarge. Table below (from the DAFWA Report Card) shows that in 2011, there was a high average wind erosion hazard for the zone (Zone 8 – Southern Wheatbelt).

Wind Erosion – Hazard Summary for 2009-12 (DAFWA Report Card, 2013)

Wind Erosion – Hazard Summary for 2009-12 (DAFWA Report Card, 2013)

 

Source: Carter D and Laycock J (2013). ‘Wind Erosion’. In: Report card on sustainable natural resource use in agriculture, Department of Agriculture and Food, Western Australia.

To find out more about Wind Erosion in the south-west of Western Australia go here.

Water erosion

Water erosion

Summary – Good condition but increasing intensity and frequency of summer storms in the east remains a concern.

Hazard and Trend – Low and deteriorating (confidence in hazard and trend: limited evidence or limited consensus in both).

Source: Galloway P and van Gool D (2013). ‘Water Erosion’. In: Report card on sustainable natural resource use in agriculture, Department of Agriculture and Food, Western Australia.

To find out more about Water Erosion in the south-west of Western Australia go here.

Soil organic carbon

Soil organic carbon

Summary – SOC levels declining along west to east rainfall gradient. Little data in driest areas.

Abundance and Trend – Moderate and unclear trend (confidence in abundance: limited evidence or limited consensus; confidence in trend: evidence and consensus too low to make an assessment).

Source: Griffen E, Hoyle F and Murphy D (2013). ‘Soil Organic Carbon’. In: Report card on sustainable natural resource use in agriculture, Department of Agriculture and Food, Western Australia.

To find out more about Soil Organic Carbon in the south-west of Western Australia go here.

Soil compaction

Soil compaction

Summary – Grey clays with declining soil structure are prone to collapse and compaction.

Hazard and Trend – High (meaning soil hazard generally high and current land use likely to cause compaction) and deteriorating (confidence in hazard and in trend: limited evidence or limited consensus).

Source: Carter D, Davies S and Schoknecht N (2013). ‘Soil Compaction’. In: Report card on sustainable natural resource use in agriculture, Department of Agriculture and Food, Western Australia.

To find out more about Soil Compaction in the south-west of Western Australia go here.

Water repellence

Water repellence

Summary – Majority of low rainfall areas have no problems. There are some problems on grey sands in the south of the zone.

Condition and Trend – Fair (meaning water repellence of low abundance) and stable (confidence in condition and in trend: limited evidence or limited consensus).

Source: Carter D, Davies S Blackwell P and Schoknecht N (2013). ‘Water repellence’. In: Report card on sustainable natural resource use in agriculture, Department of Agriculture and Food, Western Australia.

Dryland Salinity

Dryland Salinity

Summary – Salinity is extensive and will continue to expand, albeit at a slower rate. Variable trends in groundwater levels, but water levels in upland bores are still rising.

Risk and Groundwater Trends – Moderate (Likelihood of occurring: likely; consequence: major) and variable (confidence in condition: limited evidence or limited consensus and in trend: adequate high-quality evidence and high level of consensus).

A large number of bores are now showing stable groundwater level trends; however, rising trends can still be observed in upland areas and in areas of valley hazard in the southern portion of the zone where rainfall is highest. It is likely that salinity will continue to develop into the future, albeit at a reduced rate due to more dry seasons. The impact of future salinisation is expected to be moderate in the north-east of the zone, and major in the south.

Source: Simons J, George R and Raper P (2013). ‘Dryland Salinity’. In: Report card on sustainable natural resource use in agriculture, Department of Agriculture and Food, Western Australia.

To find out more about Dryland Salinity in the south-west of Western Australia go here.

Nutrient status (phosphorus)

Nutrient status (phosphorus)

Summary – Soil P fertility well in excess of optimal range. Ceasing P application would see P levels slowly decrease to optimal levels.

Condition and Trend – Well in excess (meaning P fertility index > 1.5) and stable (confidence in condition and in trend: limited evidence or limited consensus in both).

Source: Weaver DM and Summers RN (2013). ‘Nutrient status (phosphorus)’. In: Report card on sustainable natural resource use in agriculture, Department of Agriculture and Food, Western Australia.

To find out more about Nutrient status (phosphorus) in the south-west of Western Australia go here.

Acidification of inland waterways

Acidification of inland waterways

Summary – There are extensive areas of acid, saline groundwater. Baseflow acidity has occurred but there is limited data to determine extent or trends.

Condition and Trend – Poor and trend unclear (confidence in condition: limited evidence or limited consensus and in trend: evidence and consensus too low to make an assessment).

Source: Ruprecht J (2013). ‘Acidification of inland waterways’. In: Report card on sustainable natural resource use in agriculture, Department of Agriculture and Food, Western Australia.

Projects:

SWCC has developed two videos to help you get started with soil health. Part 1 describes a process for investigating soil health and identifying what constraints to manage first. Part 2 answers some common soil health questions, such as how to manage soil organic matter and soil biology, impacts of synthetic fertilisers on soil biology, and organic soil amendments such as compost and biochar.

Source:

  • Department of Agriculture and Food 2013, Report card on sustainable natural resource use in agriculture, Department of Agriculture and Food, Western Australia.
  • N. Schoknecht, P. Tille, B. Purdie (2004). Soil-landscape mapping in south-western Australia. An overview of methodology and outputs.
  • Van Gool, D., Vernon, L. and Runge, W. (2008). Land Resources in the South-West Agricultural Region. A shire-based summary of land degradation and land capability. Department of Agriculture and Food Western Australia.

 

Header and thumbnail images supplied by Peter Clifton.

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