Soil capability assessment for expanding irrigated agriculture in 2019-05-28¢  Soil capability assessment

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  • Soil capability assessment for expanding irrigated agriculture in the Irwin focus area and surrounding lands

    Resource management technical report 408

  • Soil capability assessment for expanding irrigated agriculture in the Irwin focus area and surrounding lands

    Resource management technical report 408

    Ted Griffin, Angela Stuart-Street and Peter Tille

  • © Western Australian Agriculture Authority (Department of Primary Industries and Regional Development), 2019

    ISSN 1039-7205

    Cover: Red loamy earth soil close to the Irwin River (photo: L van Wyk)

    Unless otherwise indicated, Soil capability assessment for expanding irrigated agriculture in the Irwin focus area and surrounding lands by Department of Primary Industries and Regional Development is licensed under a Creative Commons Attribution 3.0 Australian Licence. This report is available at dpird.wa.gov.au.

    The Creative Commons licence does not apply to the State Crest or logos of organisations.

    Recommended reference Griffin, EA, Stuart-Street, A & Tille, PJ 2019, ‘Soil capability assessment for the expansion of irrigated agriculture in the Irwin focus area and surrounding lands’, Resource management technical report 408, Department of Primary Industries and Regional Development, Perth.

    Disclaimer The Chief Executive Officer of the Department of Primary Industries and Regional Development, and the State of Western Australia accept no liability whatsoever by reason of negligence or otherwise arising from the use or release of this information or any part of it.

    Copies of this document are available in alternative formats upon request.

    Department of Primary Industries and Regional Development 3 Baron-Hay Court, South Perth WA 6151 Telephone: +61 (0)8 9368 3333 Email: enquiries@dpird.wa.gov.au Website: dpird.wa.gov.au

    https://creativecommons.org/licenses/by/3.0/au/ https://creativecommons.org/licenses/by/3.0/au/ https://www.dpird.wa.gov.au/ mailto:enquiries@dpird.wa.gov.au http://www.dpird.wa.gov.au/ https://creativecommons.org/licenses/by/4.0/

  • iii

    Contents Acknowledgements .................................................................................................. iv Summary .................................................................................................................... v 1 Introduction ....................................................................................................... 1

    1.1 Midlands Water for Food ...................................................................................... 1 1.2 Irwin survey area .................................................................................................. 4

    2 Survey area assessment .................................................................................. 6 2.1 Field survey procedure ......................................................................................... 6 2.2 Sampling and lab analyses .................................................................................. 7 2.3 Soil-landscape mapping review ............................................................................ 8 2.4 Land capability analysis ....................................................................................... 9

    3 Geology ............................................................................................................ 12 3.1 Generalised depositional history ........................................................................ 12 3.2 Irwin survey area ................................................................................................ 13 3.3 Hydrogeology ..................................................................................................... 16

    4 Geomorphology and soil-landscapes ........................................................... 17 4.1 Geomorphology .................................................................................................. 17 4.2 Soil-landscapes .................................................................................................. 17 4.3 Main soils ........................................................................................................... 20

    5 Land capability for horticulture ..................................................................... 27 5.1 Very high (Class 1) to high (Class 2) capability land ........................................... 31 5.2 Fair capability land (Class 3) .............................................................................. 31 5.3 Low (Class 4) to very low (Class 5) capability land ............................................. 32 5.4 Soil salinity and crop tolerances ......................................................................... 33 5.5 Conclusion ......................................................................................................... 34

    Appendixes .............................................................................................................. 35 Appendix A Land capability assessment .............................................................. 36

    A1 Land quality codes used in ratings tables ........................................................... 36 A2 Land capability ratings tables ............................................................................. 37 A3 Example of proportional map unit capability ratings ............................................ 39 A4 Irrigation salinity hazard ..................................................................................... 40

    Appendix B Description of soil-landscape subsystem map units ...................... 43 Appendix C Chemistry results from deep drilling sites ....................................... 45 Appendix D WA soil groups and representative soil profiles .............................. 49 Appendix E Predicted crop yield reductions at varying levels of soil salinity

    in sand, loam and clay .................................................................................... 62 Shortened forms ...................................................................................................... 64 References ............................................................................................................... 65

  • iv

    Acknowledgements Funding through Royalties for Regions made this investigation possible. The Department of Primary Industries and Regional Development (DPIRD), through the Midlands Water for Food Project, conducted this study, which aims to support the expansion of irrigated agriculture in the Northern Perth Basin.

    We would like to thank the local landowners who provided access to their land and invaluable knowledge of agricultural enterprises in the area. In particular, we thank landholders and managers who permitted us to access their land for our investigations, including Peter Kupsch, Tim Macnamara, Geoff Crabb and Sally O'Brien.

    We also thank DPIRD staff Leon van Wyk, Russell Speed, Tim Pope, Nick Wright and Adele Killen for collaborating on the field survey, and John Bruce for GIS support and information sourcing. Noel Schoknecht and Don Bennett gave peer review comments, and KB Editing and Angela Rogerson edited the report.

  • v

    Summary 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 34 000ha.

    This report details the soil-landscapes in the Irwin survey area and provides related information, including:

    • descriptions of geology, geomorphology and the soils • 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 1:250 000 soil-landscapes of the survey area at the more-detailed scale of 1:100 000. 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 (Table A, Figures A and B), with the following limitations:

    • The available water is unsuitable for irrigation. Exploratory drilling found that the groundwater contains brackish water of more than 1500 milligrams per litre (mg/L) total dissolved solids, which exceeds the tolerances of many commercial horticulture crops and is likely to cause long-term structural degradation and irrigation salinity. This would be a significant issue for the fertile clays of the alluvial plains.

    • 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 allu