Biology 11–12 · Year 11

Restoring degraded soil: earthworm response to a soil improver in a choice chamber

Module 4: Ecosystem Dynamics (Future Ecosystems)

PracticalLow risk

The idea

A change to an abiotic factor in soil shifts where soil animals are found, and a choice chamber lets earthworms show which amended soil they prefer or avoid, which decides whether an amendment used to restore degraded soil will be accepted by the soil biota.

What you need

Compost worms (Eisenia fetida or Eisenia andrei, the species named in the source) from a worm farm, 10 per chamber
Plain potting soil or compost; biochar ground to fine grains (or another soil improver such as gypsum or compost) mixed at 2 percent and 4 percent by mass
Plastic containers with a removable central divider, 3; lids with air holes; balance; gloves; dust mask for grinding

How to do it

Fill one half of each chamber with plain soil and the other half with soil containing 2 percent (chamber A) or 4 percent (chamber B) improver by mass; chamber C has plain soil on both sides as the control.
Remove the divider and place 10 worms along the line, cover, and keep at room temperature in the dark for 48 hours.
Replace the divider and count the worms on each side; repeat the whole test three times with fresh soil.
Test the counts against an even split with a chi-squared test (critical value 3.841 for one degree of freedom at the 0.05 level), and read the result as indicative only: worms follow one another's burrows and mucus trails, so ten worms in a chamber are not ten independent choices. The chamber is the unit of replication and the three repeats are the sample size the conclusion rests on.
Return the worms to the worm farm; record soil pH and moisture of each treatment.
Relate the outcome to choosing amendments for a degraded site.

What you should see

The control chamber splits close to 5 and 5; in treated chambers the worms shift toward or away from the amended side, and a shift as large as 9 to 1 out of 10 gives a chi-squared of 6.4, above 3.841, so it is unlikely by chance, while 7 to 3 gives 1.6, which is not. Those thresholds hold only if each worm chose on its own; because worms aggregate, a 9 to 1 split can come from two or three group decisions, for which the two-tailed exact probability is 0.5 or 0.25 rather than 0.02 (computed), so agreement in direction across the repeats is the stronger evidence. The learner knows it worked when the control shows no preference and the replicates of a treatment agree in direction.

What changes

What you change: concentration of soil improver (0, 2, 4 percent by mass)
What you measure: number of worms on the amended side after 48 hours
What you keep the same: worm species and number
soil type and moisture
temperature and darkness
time

Common misconceptions

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

Any organic amendment improves soil; some amendments are avoided by soil animals at high concentration.
A 7 to 3 split proves a preference; with ten animals that split arises by chance often enough that a statistical test is needed, and because worms aggregate the test is read against the repeats rather than the individual animals.
Restoration is about plants only; the soil biota drive nutrient cycling that plants depend on.

Safety card

Low riskLearners carry it out

Hazards

Soil microorganisms
Dust from grinding biochar

Controls

Gloves; wash hands with soap and hot water after handling soil or worms
Grind in a fume cupboard or wear a dust mask
Return animals promptly to their original environment

Note

The Department's Animals in Schools framework sets out a school's animal welfare obligations (https://education.nsw.gov.au/teaching-and-learning/animals-in-schools); every animal here is held only for as long as the activity needs and is returned to where it came from. Soil handling per RiskAssess (https://www.riskassess.com.au/).

Curriculum references

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

Biology Stage 6 Syllabus (2017), current: Year 11 taught to the end of 2026 and Year 12 to Term 3 2027BIO11-11 BIO11/12-1 BIO11/12-2 BIO11/12-5
Biology 11–12 Syllabus (2025), Year 11 focus area Evolution and ecosystems; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-11-03
Biology 11–12 Syllabus (2025), Year 11 Working scientifically; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-11WS-01 BI-11WS-02 BI-11WS-05
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

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