Investigating Science 11–12 · Year 11

Growth of radish seedlings watered with saline water

Module 2: Cause and Effect – Inferences and Generalisations

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

Plant growth falls once the salinity of the water a crop receives passes a threshold, and a class trial infers that threshold from its own data before checking it against published secondary data.

What you need

60 radish seeds (Raphanus sativus), 15 pots of 10 cm diameter, seed-raising mix
sodium chloride and tap water, five labelled 2 L bottles, conductivity meter reading in mS/cm (1 mS/cm = 1 dS/m)
balance to 0.01 g, ruler, measuring cylinder, gloves and dust mask for handling potting mix

How to do it

Make five irrigation solutions: tap water only (record its reading), and tap water with salt added until the meter reads 1.0, 2.0, 3.5 and 6.0 dS/m.
Sow four seeds per pot, three pots per solution, and thin to two seedlings per pot after germination.
Water every pot with the same volume of its solution on the same days for 4 weeks.
Harvest, rinse and blot the plants; record shoot height and fresh mass of shoot and root.
Express each treatment’s mean mass as a percentage of the tap-water treatment and plot it against conductivity.
Compare the class curve with the FAO crop salt-tolerance data for radish and write the inference and its limits.

What you should see

FAO Irrigation and Drainage Paper 29 (Table 4) gives radish yield potential against irrigation-water salinity (ECw) of 100 % up to 0.8 dS/m, 90 % at 1.3, 75 % at 2.1, 50 % at 3.4 and 0 % at 5.9 dS/m. Four-week pot seedlings are not field yields, so the class curve is compared with the shape of the FAO relation, which predicts 96 % at 1.0 dS/m, 76 % at 2.0, 47 % at 3.5 and no yield at 6.0 dS/m. The learner reports percentage growth with the range across the three pots and names the differences between the trial and the field data that limit the generalisation.

What changes

What you change: salinity of irrigation water (dS/m)
What you measure: fresh mass of shoots and roots after 4 weeks, as a percentage of the tap-water treatment
What you keep the same: same mix and pot size
same watering volume and schedule
same light and temperature
two seedlings per pot

Common misconceptions

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

A little salt always helps plants grow.
If seeds germinate the water is safe for the crop.
One pot per treatment is enough to draw a conclusion.

Safety card

Low riskLearners carry it out

Hazards

potting and seed-raising mixes can carry Legionella bacteria
wet floors

Controls

dampen mix before use to keep dust down
wear gloves and a dust mask when handling mix
wash hands afterwards

Note

No hazardous chemicals or heat. Potting mix is a biological hazard: record the handling controls in the school’s RiskAssess risk assessment.

Curriculum references

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

Investigating Science Stage 6 Syllabus (2017), NESA; currentINS11-9 INS11/12-1 INS11/12-2 INS11/12-4
Earth and Environmental Science Stage 6 Syllabus (2017), NESA; current, replaced by the 11–12 Syllabus (2025) from 2028EES11-11
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

All Concept Studio activities