Agriculture and Food 7–12 · Years 9–10

Field soil texture by the bolus and ribbon test

Plant Production 1

PracticalLow risk

The idea

How a moist ball of soil holds together and how long a ribbon it forms between thumb and finger estimates its clay content, and clay content controls how much water and nutrient a soil holds.

What you need

soil samples from at least three sites or depths, about 100 g each, in labelled bags
2 mm sieve
wash bottle of water
ruler graduated in millimetres
printed field texture table from the soilquality.org.au fact sheet
disposable gloves

How to do it

Remove gravel, roots and organic matter larger than 2 mm by sieving or by hand.
Take enough soil to fit comfortably in the palm, moisten it and knead it into a ball (bolus) for 1 to 2 minutes, adding soil or water until it no longer sticks to the fingers and its plasticity stops changing.
Hold the bolus between thumb and forefinger and slide the thumb across it to push out a ribbon about 2 mm thick and 1 cm wide.
Measure the ribbon length with the ruler at the point where it breaks, and note whether the soil feels sandy, silky or smooth.
For ribbons longer than 75 mm, roll the soil into rods; if the rods fracture, the soil is lighter than a medium clay.
Repeat three times for each sample and use the middle value to assign the field texture grade and approximate clay content from the table.

What you should see

Sand forms no ribbon (under 10% clay); a sandy loam gives a 15–25 mm ribbon (10–20% clay); a loam about 25 mm (about 25% clay); a clay loam 40–50 mm; a light clay 50–75 mm (35–40% clay); a medium clay over 75 mm with moderate resistance (45–55% clay), according to the soilquality.org.au table adapted from the Australian soil and land survey field handbook. The three ribbons from one sample fall in the same texture grade. Sandier samples will hold less water, as the water availability fact sheet explains. The learner knows it worked when repeat ribbons agree and the grade order of the samples matches the soil jar test.

What changes

What you change: sampling site or depth
What you measure: ribbon length (mm), field texture grade, approximate clay content (%)
What you keep the same: gravel removed
bolus worked until plasticity is stable
ribbon about 2 mm thick
same operator for the three repeats

Common misconceptions

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

Dark-coloured soil is always clay.
Adding compost for one season changes a sandy soil into a clay soil.
Soil texture and soil structure mean the same thing.

Safety card

Low riskLearners carry it out

Hazards

soil may contain sharp objects, animal droppings and bacteria

Controls

gloves when collecting and handling soil
wash hands after the practical

Note

No hazardous chemicals. General laboratory rules in 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)AG5-6 AG5-11 AG5-12
Agriculture Technology 7–10 Syllabus (2024), new syllabus, implementation from 2027AGT5-APG-01
Australian Curriculum v9AC9TDE10K04AC9S10I03

Sources

The pages the author read to write this activity.

All Concept Studio activities