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Agriculture and Food 7–12 · Years 11–12

Growing-season rainfall and wheat yield potential

Climate Challenge (HSC elective)

Practical, model not builtLow risk

This site has no interactive model of its own. Where a step or a material names a Concept Studio model, simulation or tool, it has not been built; an external simulation a step names (for example PhET) is not part of this site.

The idea

In southern Australia wheat yield is limited mainly by water, so the rain from April to October, plus some stored summer rain, sets an upper limit on yield that growers compare with what they harvest.

What you need

  • Bureau of Meteorology climate statistics page for the station nearest the school
  • the school's rain gauge records (read at 9 am each day)
  • spreadsheet
  • the soilquality.org.au yield potential calculator
  • district or school farm wheat yields, where available

How to do it

  1. Copy the station's mean monthly rainfall and add January to March and April to October.
  2. Calculate available water and yield potential with the model, then compare the result with the soilquality.org.au calculator, noting the sowing window chosen, because the calculator's page does not state how that setting changes the figure.
  3. Repeat for the current year using the school's rain gauge or the station's monthly totals.
  4. Calculate the growing season's share of annual rainfall.
  5. Compare potential with an actual yield, calculate water-use efficiency (actual yield divided by available water) and list factors besides water that could explain the gap.

What you should see

For Wagga Wagga AMO (station 072150, 1941–2026) mean rainfall is 128.3 mm from January to March and 347.8 mm from April to October, of an annual mean of 571.8 mm, so the growing season supplies 60.8% of the year's rain. Available water is 0.3 x 128.3 + 0.7 x 347.8 = 282.0 mm, and at 20 kg/ha per mm the yield potential in an average year is 5639 kg/ha (5.6 t/ha). A season with only 200 mm from April to October lowers it to 3570 kg/ha. The learner knows it worked when the spreadsheet reproduces these figures for the Wagga Wagga means; any gap from the soilquality.org.au calculator is traced to its sowing-window setting rather than assumed to be an error.

What changes

This activity lists no variables to change, measure and keep the same.

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

  • Annual rainfall is what matters most for a winter crop.
  • Every millimetre of growing-season rain ends up in the crop.
  • A below-potential yield in an average-rainfall year must be the weather's fault.

Safety card

Low riskLearners carry it out

Hazards

  • none beyond normal classroom work and daily rain gauge reading

Controls

  • read the gauge from a safe, level position

Note

Data analysis: no chemicals, heat or animals.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

  • Agriculture Stage 6 Syllabus (2013)H3.4H4.1H5.1
  • Agriculture 11–12 Syllabus (2026), new syllabus, implementation from 2028AG-11-02AG-12-04
  • Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

  1. www.soilquality.org.au/calculators/yield_potential
  2. www.bom.gov.au/climate/averages/tables/cw_072150.shtml
  3. www.bom.gov.au/climate/cdo/about/about-rain-data.shtml
  4. www.nsw.gov.au/education-and-training/nesa/curriculum/tas/agriculture-stage-6-2013
  5. www.nsw.gov.au/sites/default/files/noindex/2025-03/agriculture-amended-st6-syl-2013.doc
  6. curriculum.nsw.edu.au/learning-areas/tas/agriculture-11-12-2026/outcomes

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