Geography K–10 · Years 9–10

Salinity and crops: a seedling trial checked against FAO salt-tolerance data

Biomes and food security (ACARA Year 9 sub-strand); NSW Stage 5 focus area Sustainable Biomes (2015 syllabus) and Biomes and sustainable agriculture (2024 syllabus)

Practical, model not builtLow risk

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The idea

Salt in soil water reduces plant growth once it passes a threshold that differs by crop, which is why land clearing that raises saline groundwater cuts food production.

Safety card

Low riskAn adult supervises

Hazards

treated seed (fungicide coating) if the wrong seed is bought
salt solution in eyes
mould on dishes

Controls

untreated seed only; wash hands after handling seeds
eye protection when mixing solutions
dishes kept closed and disposed of sealed at the end

Note

Sodium chloride is the only chemical: check it against the NSW Department of Education Chemical Safety in Schools package and record the practical in RiskAssess (riskassess.com.au). Solutions go to the sink with running water.

What you need

Untreated radish seeds and untreated barley seeds, 300 of each
Non-iodised cooking salt (sodium chloride); kitchen scales reading 0.1 g; five 1 L jugs
30 petri dishes or small takeaway containers with lids, paper towel cut to fit, a 10 mL syringe
Electrical conductivity meter, high range where there is a choice (the NSW Waterwatch SMART 2 kit calibrates its low meter with a 500 µS/cm standard and its high meter with 12.9 mS/cm), rinsed between solutions; distilled water and a 50 mL measuring cylinder for dilutions
Ruler with mm marks, labels, a dark cupboard at room temperature

How to do it

Make 1 L each of 0, 1, 2, 4 and 8 g/L salt solutions in tap water. Measure and record the EC of each in µS/cm (a high-range meter reads mS/cm, which × 1000 is µS/cm) and convert to dS/m (divide by 1000). Where the meter reads 'Or' (over range), dilute as the Waterwatch EC procedure sets out: 10 mL of solution made up to 30 mL with distilled water, read again and multiply by 3 (10 mL to 40 mL and × 4, or 10 mL to 50 mL and × 5, if it still reads 'Or'), so every solution has a number to plot.
Line each dish with two layers of paper towel and wet it with 10 mL of one solution. Make 3 dishes per concentration for each crop (30 dishes).
Place 20 seeds on each dish, close the lid, label, and keep in the dark at room temperature.
Every second day add 2 mL of the same solution to every dish so all stay moist by the same amount.
On day 3 and day 7 count seeds with a root of at least 2 mm (germinated). On day 7 measure the shoot length of 10 seedlings per dish.
Compute germination % and mean shoot length for each crop and concentration; plot both against measured EC and compare the two crops.

What you should see

Germination and shoot length are expected to fall as EC rises, and the class reports the ranking of radish and barley that its own dishes show. The FAO salt-tolerance annex does not predict that ranking: its yield thresholds (1.2 dS/m for radish, 8.0 dS/m for barley) apply only from the late seedling stage to maturity, it marks barley as less tolerant at the seedling stage (ECe at that stage should not exceed 4 or 5 dS/m), and its ECe is a saturated-soil-extract value, not the EC of a solution in a dish (the annex assumes soil water at field capacity holds twice the salt concentration of the extract). The class therefore compares its seedling ranking with the FAO maturity ranking as a separate question. It worked if the 0 g/L dishes germinate well for both crops, showing the seeds were viable.

What changes

What you change: salt concentration (g/L), measured as EC (dS/m); crop
What you measure: germination % at day 3 and 7; mean shoot length (mm) at day 7
What you keep the same: seeds per dish
solution volume
temperature and darkness
paper type
three replicate dishes

Common misconceptions

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

Salt only harms plants when the ground looks white.
All crops respond to salt in the same way.

Curriculum references

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

Geography K–10 Syllabus (2015), NESA; current and taught in 2026, replaced from 2027. The outcome codes are not printed on the NESA landing page for this syllabus, which only links the document, so the url given is the syllabus document itself (geography-k-10-syllabus-2015.docx); the code and its outcome text were read in that document on 23 September 2026.GE5-3 GE5-5 GE5-7
Geography 7–10 Syllabus (2024), NESA; implementation from 2027, not yet taught; code read on this page on 22 September 2026GE5-PRI-01 GE5-MAN-01 GE5-TAP-01
Australian Curriculum v9AC9HG9K02AC9HG9K04AC9HG9S02

Sources

The pages the author read to write this activity.

All Concept Studio activities