Western Darling Range Zone

Posted on Jan 9, 2015


Western Darling Range ZoneLandResources

Moderately dissected lateritic plateau on granite with deeply incised valleys; includes the Darling Scarp on the western margin. Soils are formed in laterite, lateritic colluvium, granite weathered in-situ and gneiss.

SWCC Strategic Priority

Threats to be addressed:

  • water erosion
  • land salinisation

DAFWA – Report Card (September 2013) The Western Darling Range  Zone, for the purposes of DAFWA’s Report Card, is included in the Agricultural Soil Zone 6. Darling Range to South Coast (along with the Eastern Darling Range Zone and the Warren-Denmark Zone). 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

The Western Darling Range zone is identified on its own as a hydrozone.

Key Findings for this Zone

Soil Acidity

Soil Acidity

Summary – With nearly 90% of surface soils below target, subsurface soils will continue to acidify.

Condition and Trend – Poor and Deteriorating (confidence in condition: adequate high-quality evidence and high level of consensus and in trend: limited evidence or limited consensus).

The historical dominance of pastures compared to cropping is likely to have contributed to greater acidification of the surface soil. This zone is dominated by gravels, comprising 63 percent of the area. Nearly 90% of top soils samples collected had a pH 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 6. Darling Range to South Coast (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 6. Darling Range to South Coast (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 – Some areas of high erosion hazard in dry years with high stock numbers on poor pastures, however the region is of moderate hazard grade.

Hazard and Trend – Moderate (meaning 2 yr in 4 below target hazard – yrs 2009-12) and variable (confidence in condition and 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 very high average wind erosion hazard for the zone (Zone 6 – Darling Range to South Coast ).

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 – Stock enterprises present erosion risk from summer storms. Irrigated farms are managing erosion risk.

Hazard and Trend – Low and stable (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 vary with rainfall gradient. SOC maintained in conservation areas and areasof reliable rainfall. RIsk of SOC decline with increased cropping.

Abundance and Trend – Moderate to high 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 – Forest soils resilient to compaction due to gravel content. Also there is limited cropping in this zone.

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 – Forest soils mow in crop (previously pastures) have severe water repellence problems.

Condition and Trend – Poor (meaning water repellence is common) and deteriorating (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 – Extent of salinity minor, with low risk of expansion because groundwater levels are mostly rising.

Risk and Groundwater Trends – Low (Likelihood of occurring: possible; consequence: minor) and improving (confidence in condition and in trend: limited evidence or limited consensus in both).

Surveillance monitoring of groundwater levels is limited in this zone as it is mostly forested or has been reafforested, As a result, grundwater levels are falling at the majority of sites. The salinity risk is low; expansion of salinity is possible at a local scale, with minor consequences.

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 in excess of optimal range. This could change to well in excess with continued P application; however, ceasing P application would see P levels very slowly decrease to optimal levels.

Condition and Trend – 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.

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.

 

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