Pinjarra Zone

Posted on Dec 23, 2014


Pinjarra ZoneLandResources

Alluvial deposits (early Pleistocene to Recent) between the Bassendean Dunes Zone and the Darling Scarp, colluvial and shelf deposits adjacent to the Darling Scarp. Clayey to sandy alluvial soils with wet areas.

SWCC Strategic Priority

Threats to be addressed:

  • land salinisation
  • acidifcation
  • loss of soil carbon

DAFWA – Report Card (September 2013) The Pinjarra Zone, for the purposes of DAFWA’s Report Card, is included in the Agricultural Soil Zone 5. Swan to Scott Coastal Plains (along with the Coastal Dune Zone, Bassendean Zone, Scott Coastal Zone and the Donnybrook-Leeuwin 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 Pinjarra Zone is identified along with the Coastal Dune and Bassendean Soil Zones as the hydrozone, Coastal Plain.

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

Soil acidification and resulting poorer root growth and nutrient use is likely to be more important in coastal zones because of the implications for nutrient leaching and eutrophication of waterways. Increased testing and awareness of subsurface soil acidity is recommended as well as consideration of lime quality when calculating appropriate rates.

This coastal zone is dominated by four main soils accounting for about 70% of the area. Surface soil acidity is extreme. From 70-81% of samples collected had pH below the recommended target layer depending on soil type. Subsurface acidity in the 10-20cm layer is also an issue, although fewer subsurface samples were collected from this region, probably due to the dominance of pasture and decreased need to access deeper soil moisture because of the higher rainfall.

Soil Acidification 5 Swan Coastal Plain to Scott Coastal Plain

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 5. Swan Coastal Plain to Scott Coastal Plain (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 -Wind erosion hazard was not monitored for this zone.

Hazard and Trend – Not assessed.

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 –Largely stable. Enterprises in the north are exposed to erosion from flooding of major rivers.

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 related to wide rainfall range. Very high levels often associated with irrigated, fertilised pastures. Decline in SOC under intensively cultivated horticultural systems.

Abundance and Trend – High to very high and unclear trend (confidence in hazard: 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 – No extensive cropping or use of heavy machinery. Soils not vulnerable.

Hazard and Trend – Low (meaning soil hazard generally low and current land use unlikely to cause compaction) and stable (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 – Most of the aeolian (wind deposited) sandy areas are severely water repellent. No problems where alluvial soils occur.

Condition and Trend – Very poor (meaning water repellence widespread) and stable (confidence in condition: Adequate high-quality evidence and high level of consensus; 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 very minor; future development possible in the north, but with low impact. Mostly stable trends in groundwater levels.

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

Groundwater is shallow over much of the plain but trends are stable, responding to seasonal rainfall. Salinisation on the coastal plain is limited to poorly drained areas on the Pinjarra Plain and coastal swales. The salinity risk is low. Expansion of the area affected is possible but with minor consequences depending on whether high intensity land uses move into poorly drained areas. Increasing salinity is likely in surficial aquifers. Widespread soil salinity occurs in the south-west irrigation areas but is not included in this analysis.

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 slowly decrease to optimal levels.

Condition and Trend – Excess (meaning P fertility index > 1.1 – 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.

 

Header and thumbnail images supplied by Peter Clifton.

 

 

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