Climate change and broadacre cropping in Western Australia

Page last updated: Tuesday, 14 July 2020 - 4:31pm

Climate change in south-western Western Australia is a reality – temperatures have increased, annual rainfall has decreased, and climate variability has increased. The projections are that these changes will increase in most areas. The effect of these changes on cropping will vary regionally.

The Department of Primary Industries and Regional Development provides this information to support farm business managers and cropping industry managers in their response to a changing climate in Western Australia.

How has climate change affected broadacre cropping?

During the last 50 years, the 50 parts per million increase in atmospheric carbon dioxide is estimated to have increased wheat yield by 2–8% in WA. Increased carbon dioxide concentrations work to improve plant water use efficiency; this process is called the carbon dioxide fertiliser effect.

Increased temperatures have generally benefited crops during the winter months. The harmful effects of increased spring temperatures have been offset to some degree by earlier sowing, higher temperatures during winter accelerating plant maturity, and using varieties with a shorter growing season.

Declining average winter rainfall has had relatively little effect on yield because winter rainfall generally exceeds plant demand. However, shorter growing seasons and variability in annual rainfall and rainfall distribution and intensity has had a profound effect on crop management.

Wheat yields doubled between 1980 and 2010 with the adoption of improved varieties, technology and management systems, such as reduced tillage, liming, stubble retention, early sowing, precision agriculture and integrated weed control. These changes effectively increased the water use efficiency of wheat at a greater rate than rainfall declined over the period.

The increase in wheat yield was not uniform across the grainbelt. Yield increases were greatest in southern and northern areas and least in central and eastern areas. Yield variability was greatest in eastern and northern areas.

The rate of increase in wheat yield and water use efficiency has slowed since the end of the 1990s. Some possible reasons for this slow down:

  • In response to climate variability, producers are reducing crop inputs (risk), which lowers yields in good years.
  • There is increased variability in yield between seasons as seasonal variability increases.

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How will crop yields be affected by climate change?

Although the effects of climate change will vary with location, soil type and management, experience and climate and production models point to some common projections:

  • Crop yield will be most affected by changes in rainfall, particularly the seasonality of rainfall.
  • Higher temperatures, and to a lesser extent declining rainfall, will hasten development times and reduce the flowering period.
  • Increased carbon dioxide concentrations will offset some of the negative effects of increased temperature and decreased rainfall.
  • It is likely that higher temperatures and less rainfall will reduce average crop yields and profit in drier eastern and northern areas (external link).
  • The risks associated with climate variability will increase, particularly in drier marginal areas.
  • Crop yields may be largely unchanged or increase in wetter western and southern areas (external link), where higher temperatures and reduced waterlogging will benefit crops.
  • The plant available water capacity of soils will become increasingly important in determining yield; yield declines will be greater on clay soils compared to sands, particularly in drier eastern areas.

Note that the projections from climate and crop models are not exact or certain. In addition, crop models generally do not consider the risks associated with extreme weather events, changes in pest and disease risk or the benefits that technology and management improvements may bring.

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How can broadacre crop producers adapt to climate change?

In the short term, incremental changes aimed at improving crop water use efficiency, optimising inputs and managing according to seasonal conditions will cope with climate change. In the longer term (2050–70), producers may need to make transitional or transformative business changes, such as changing enterprises and land use. There are many ways to achieve these adaptations.

Improve rainfall use efficiency of plants

Increase plant ability to access stored soil water

Remove physical constraints to root growth by using:

Remove chemical constraints to root growth by:

  • applying micronutrients and macronutrients
  • liming acid soils to increase soil pH
  • using drainage to reduce sodicity
  • using crop varieties/species with increased ability to explore the soil profile by having:
    • suitable root morphology (deep versus lateral roots)
    • tolerance of chemical soil constraints, such as pH, boron, aluminium, transient sodicity
    • the ability to grow through soil physical constraints, such as hard pan and transient waterlogging.

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Increase volume of plant available soil water

Improve soil water-holding capacity using one or more technologies:

  • increase soil organic carbon content
  • reduce tillage
  • deep-rip
  • apply gypsum to improve soil structure
  • use controlled traffic farming to reduce compaction
  • apply clay (surface application/delving/spading) to reduce non-wetting
  • eliminate water use by weeds using:
    • fallowing based on:
      • controlling summer weeds
      • bare fallow, green or brown manures from the previous growing season.
    • herbicide management
    • cultivation, such as strategic use of mouldboard ploughing
    • herbicide-tolerant crops
    • improved weed germination and subsequent control by ameliorating non-wetting soil using:
      • claying (surface application/delving/spading), generally in high rainfall areas
      • applying surfactants, generally in medium rainfall areas.
    • chaff management
    • crop canopy management.
  • root rip along tree lines
  • reduce evaporation of soil water by using:
    • reduced tillage
    • stubble retention
    • mulching
    • rapid crop canopy development/closure
    • increased deep infiltration of rainfall by using:
      • furrow sowing
      • wetting agent in furrows
      • sowing into previous years furrows (precision agriculture)
      • press wheels to increase run-off into furrow.
    • reduce surface water run-off, using:
      • stubble retention
      • contour sowing
      • minimum tillage
      • claying.

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Use best-adapted crop species and varieties

  • Use crop varieties or species with increased drought resistance, such as stay-green varieties with:

    • physiological tolerance of hot and dry conditions including:
  • Use varieties or species which are better able to exploit the fertilisation effect of increased atmospheric carbon dioxide to improve water use efficiency.
  • Use crop varieties or species that are bred to resist current disease risks and new risks presented by changing climate.
  • Use crop rotation for disease management.

Increase resilience to seasonal variability

Optimise sowing date, crop species/variety and areas sown

  • Use seasonal and long-range weather forecasts to determine rotations and cropping area. Options may be:

    • do not crop heavy land in dry seasons, cull paddocks early
    • opportunistic cropping of marginal land when seasons are favourable.
  • Account for stored plant available water.
  • Early/dry sow:

Manage crop water use to account for plant available stored water and rainfall

  • Manage plant density with:

  • Use seasonal and long-range weather forecasts to manage canopy leaf area index by:
    • tailoring nitrogen fertilisation to season with foliar nitrogen application
    • strategically grazing crops to reduce leaf area index and delay flowering.

Ensure crop access to nutrients as topsoil dries in spring

  • Place nutrients deeper at seeding.

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Reduce frost risk

  • Use varieties or species that are better able to tolerate frost.
  • Time sowing with species and cultivar to minimise frost risk.
  • Reduce frost risk by managing stubbles.
  • Match sowing date and species to topographic location (that is, frost prone areas may need special management).

Optimise inputs

Use decision tools

Use tools, such as crop models, flowering calculators and soil water calculators, to help with making decisions about:

  • sowing date
  • variable rate fertiliser application
  • grain marketing
  • the value of soil amelioration.

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Reduce business risk

  • Focus on reducing risk and maximising profit, not maximising yield ('Adapting Growth for Climate Change on Bungulla Farm' case study)
  • Change enterprise mix:
    • adjust ratio of cropping to livestock according to terms of trade, land capability and long-term climate trends
    • use dual-purpose crops, such as grazing cereals
    • find new markets for existing agricultural residues, such as straw as biofuel
    • diversify by growing new agricultural products.
  • Change enterprise size to:
    • ensure efficiencies of scale
    • reduce local risks by farming over a wider geographical area.
  • Use all-risk insurance policies.
  • Ensure there is access to off-farm income.
  • Undertake training.
  • Maintain information and innovation sharing via networks and links.

Reduce soil erosion risk

  • Reduce wind erosion risk using:

    • reduced tillage
    • stubble retention, such as reduced tillage and stubble burning, livestock management
    • windbreaks on suitable erosion prone sites
    • claying.
  • Reduce water erosion risk using:
    • reduced tillage
    • stubble retention
    • contour farming, including drainage in high rainfall regions
    • claying
    • vegetated buffers along waterways.

While most of these adaptations are currently considered good practice, they vary in applicability across the grainbelt and we recommend analysis of location-specific costs and benefits before making changes.

WA producers have been adopting best practices and are likely to be able to continue adapting to projected climate change in the short to medium term. Producers should continue making incremental changes in the short term and investigate and plan for more transitional and transformative changes for the medium and longer term.

For more information

Download Bulletin 4870 Climate change: impacts and adaptation for agriculture in Western Australia (PDF 4.9MB)

Contact information

Rob Sudmeyer
+61 (0)8 9083 1129