Agriculture and Food 7–12 · Years 9–10

Salt tolerance of crops at germination

Plant Production 1

PracticalLow risk

The idea

Salt in soil water makes it harder for seeds and roots to take up water, and crops differ in salt tolerance, which is why barley can be grown on land where faba beans fail.

What you need

untreated seed of barley, wheat and faba bean, 100 of each per salt level
sodium chloride and deionised water
conductivity (EC) meter reading in dS/m, calibrated
paper towel and clear plastic bags for rolled-towel germination; 20 mL syringe
ruler graduated in millimetres

How to do it

Make five solutions by adding sodium chloride to deionised water while reading the EC meter: 0 (deionised), 2, 4, 8 and 12 dS/m. Record the actual readings.
For each crop and salt level, set up four replicates of 25 seeds on paper towel wetted with 20 mL of the solution (more for the large faba bean seeds), rolled and sealed in a bag.
Keep all bags at room temperature and count germinated seeds on days 3, 5 and 7; measure the radicle length of 5 marked seeds on day 7.
Express germination at each salt level as a percentage of that crop's 0 dS/m result.
Plot relative germination against EC for the three crops on one graph and compare the ranking with the crop salinity table in the NSW fact sheet.

What you should see

Germination and radicle length fall as EC rises for all three crops. What the class tests is whether the germination ranking matches the yield ranking in the NSW salinity fact sheet, not that it will. That fact sheet's Table 1 gives the root-zone salinity causing a 5% yield decline (barley grain 8.0, wheat 6.0, faba bean 1.8 dS/m) and says nothing at all about germination, and salt tolerance at germination and emergence is a separate trait from tolerance during growth: germination is generally the most salt-sensitive stage, so the two rankings can differ and a crop that tolerates salt well through the season need not tolerate it well as a germinating seed. The two scales differ as well. The class reads the EC of the solution it makes; the table figures are ECe, the EC of a saturated paste extract of soil, which is a different measurement, and the fact sheet gives no factor for converting one to the other. The class's dS/m settings therefore cannot be compared with the table's numbers at all, and only the order of the three crops can be compared. The learner knows it worked when the 0 dS/m controls germinate well and the four replicates at each level agree; a germination ranking that differs from the yield ranking is a result to report, not an error to correct.

What changes

What you change: salinity of the solution (0, 2, 4, 8, 12 dS/m) and crop
What you measure: germination at day 7 as a percentage of the control; radicle length (mm)
What you keep the same: seeds per replicate
solution volume
temperature
counting days

Common misconceptions

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

Salt only harms plants when it lands on the leaves.
Every crop is damaged by the same amount of salt.
Salinity is a problem only near the coast.
A crop's salt tolerance is one number that applies at every stage of its growth.

Safety card

Low riskLearners carry it out

Hazards

salt solutions sting cuts and eyes
treated seed if untreated seed is not used

Controls

eye protection when making solutions
use untreated seed
wash hands afterwards

Note

NSW Department of Education, Chemical Safety in Schools (CSIS) 2021 Technical Update: Section 1 (general information for all staff) and Volume 2 Appendix D (generic risk assessment advice for each chemical). Complete a CSIS or RiskAssess site-specific risk assessment before the lesson.

Curriculum references

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

Agricultural Technology Years 7–10 Syllabus (2019)AG5-8 AG5-11 AG5-12
Agriculture Technology 7–10 Syllabus (2024), new syllabus, implementation from 2027AGT5-ENV-01 AGT5-APG-01
Australian Curriculum v9AC9TDE10K04AC9S9I02

Sources

The pages the author read to write this activity.

All Concept Studio activities