The Midlands groundwater and land assessment is a $4.7 million Water for Food project using Royalties for Regions funding. It is seeking to confirm groundwater availability in focus areas that may form precincts of 2000–3000ha suitable for intensive irrigated horticulture. Irwin is one of these.
The Department of Water identified the Irwin focus area for investigation for irrigated agriculture potential. It covers almost 7000ha to the east of Dongara in the Mid West region of Western Australia.
This report provides the land assessment for the Irwin area. We expanded the investigation to include land outside of the focus area because our review of the regional soil-landscape mapping indicated that this land had potential for irrigated agriculture. This ‘survey area’ covers about 34000ha.
This report details the soil-landscapes in the Irwin survey area and provides related information, including descriptions of geology, geomorphology and the soils, and an outline of the capability of the soil and land for irrigated horticulture.
To provide a better assessment for irrigated agriculture, we remapped the previous 1:250000 soil-landscapes of the survey area at the more-detailed scale of 1:100000. We described 117 soil sites and 15 of these received a significant amount of laboratory analyses.
Our assessment found that over half of the soils in the survey area have moderate to good capability for horticulture, with the following limitations:
• The available water is unsuitable for irrigation.
• The fertile Yardarino Flats have moderate amounts of salt at depth in some areas. While this is not a risk for broadacre agriculture, irrigating these soils may cause the watertable to rise and bring salt closer to the rooting zone. High evaporation may also lead to salt concentrating at the soil surface.
• The alluvial soils have highly sodic subsoils, indicating poor drainage and a risk of waterlogging. The boron levels of some subsoils are high enough to limit root growth of some crops.
• The wind erosion risk is high for most sandy-surfaced soils, so investment in soil management would be required, especially for annual horticulture.
• With the high evaporation and the need to control wind erosion, irrigation in this area has a high water-use requirement.
• The use of poorer quality water for irrigation can also be problematic on the sandy slopes surrounding the clayey alluvial flats, potentially leading to a build-up of salt in the subsoil.
Apart from small, niche opportunities, water of a suitable quality in the quantities required for extensive irrigated agriculture development is not generally available in the Irwin area. Dryland cropping and grazing would be the preferred land uses on the highly productive alluvial flats, and irrigation on the surrounding sandplain would require careful management.
Number of Pages
Irwin, soil capability, soil-landscapes, irrigated agriculture, Midlands
Griffin, EA, Stuart-Street, A & Tille, PJ 2019, ‘Soil capability assessment for expanding irrigated agriculture in the Irwin focus area and surrounding lands’, Resource management technical report 408, Department of Primary Industries and Regional Development, Perth
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