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Earth and Environmental Science 11–12 · Year 11

Effect of salinity on seed germination and seedling growth

Module 4: Human Impacts

PracticalLow risk

The idea

Dissolved salt lowers the water potential of soil water, so germination and growth fall as salinity rises, the mechanism behind lost production on salinised land.

What you need

  • wheat or radish seeds, 20 per dish, five petri dishes with filter paper per group
  • sodium chloride solutions 0, 3.5, 7, 17.5 and 35 g/L (the last is close to the salinity of seawater); distilled water for the control
  • conductivity meter, ruler, labels, a lit bench at 20 to 25 °C

How to do it

  1. Measure the conductivity of each solution and record it in dS/m.
  2. Place 20 seeds on the paper in each dish, add 10 mL of the assigned solution, seal and label.
  3. Count germinated seeds daily for 7 days and measure root and shoot length on day 7.
  4. Plot germination (%) and mean shoot length against conductivity.
  5. Compare the conductivities with the FAO irrigation water classes (no restriction below 0.7 dS/m, severe above 3.0 dS/m) and with the salinity map for NSW.

What you should see

Germination and shoot length fall as salinity rises; the 35 g/L dish gives few or no seedlings after 7 days. Total dissolved solids run from 0 to 35 000 mg/L across the series, so every salt dish, from 3.5 g/L (3500 mg/L) up, is in the FAO severe-restriction class for irrigation water (above 2000 mg/L, or above 3.0 dS/m), and the learner reads the threshold for the crop from their own curve.

What changes

What you change
salt concentration (conductivity, dS/m)
What you measure
germination (%) and shoot length (mm) on day 7
What you keep the same
  • seed type and number
  • solution volume
  • temperature and light
  • day of measurement

Common misconceptions

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

  • Plants die in salt water because salt is a poison (the main effect is water stress).
  • Salinity only affects coastal land.

Safety card

Low riskLearners carry it out

Hazards

  • mould on sealed dishes

Controls

  • discard mouldy dishes unopened
  • wash hands

Note

No hazardous chemicals or heat sources: record the activity in the school's RiskAssess risk assessment, following the NSW Department of Education Science safety and compliance page; the Chemical Safety in Schools package is not triggered.

Curriculum references

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

  • Earth and Environmental Science Stage 6 Syllabus (2017), NESA; current, replaced by the 11–12 Syllabus (2025) from 2028EES11-11EES11/12-1EES11/12-2EES11/12-3
  • Earth and Environmental Science 11–12 Syllabus (2025), NESA; to be implemented from 2028, not yet taughtEES-11-03
  • Investigating Science Stage 6 Syllabus (2017), NESA; currentINS11-9INS11/12-2
  • Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

  1. www.nsw.gov.au/education-and-training/nesa/curriculum/science/earth-and-environmental-science-stage-6-2017
  2. www.nsw.gov.au/education-and-training/nesa/curriculum/science/investigating-science-stage-6-2017
  3. www.soilquality.org.au/factsheets/salinity-nsw
  4. www.fao.org/4/t0234e/T0234E01.htm
  5. practicalbiology.org/environment/factors-affecting-plant-growth/investigating-the-effect-of-minerals-on-plant-growth.html

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