Planting density and yield per plant and per area · Concept Studio

The idea

Plants in a crop compete for light, water and nutrients, so as density rises the yield of each plant falls while the yield per unit area rises and then levels off.

What you need

radish seed, about 250 (twice the 124 plants kept, to allow for thinning)
20 identical containers, each with a 20 cm by 20 cm surface, filled with the same potting mix (16 plants fit a 4 by 4 grid 5 cm apart)
slow-release fertiliser, the same weighed mass in every container at the label rate for a 400 cm^2 surface, with its N:P:K analysis recorded
ruler, balance reading to 0.01 g
paper bags and a drying oven set to 90–95 °C (the SAPS radish dry-mass method)

How to do it

Sow extra seed and thin after emergence to exactly 1, 2, 4, 8 and 16 evenly spaced plants per container, with four replicate containers per density in a randomised layout.
Give every container the same water and fertiliser, and rotate positions weekly.
Harvest when the roots have swollen (about 4 to 5 weeks), and record fresh mass of each plant.
Dry each container's plants at 90–95 °C to constant mass and calculate dry mass per plant and per container.
Plot both against density, and relate the result to the sowing-rate calculation and the target plant densities in the BCG table.

What you should see

Dry mass per plant is highest at 1 plant per container and falls steadily as density rises. Dry mass per container rises from 1 to the middle densities and then levels off, so extra plants add little at the highest densities. Plants at high density vary more in size, because some are suppressed by their neighbours. The learner knows it worked when the four replicates at each density show the same pattern.

What changes

What you change: plants per container (1, 2, 4, 8, 16)
What you measure: dry mass per plant and per container (g)
What you keep the same: container size
mix
water and fertiliser per container
light
harvest date

Common misconceptions

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

Doubling the number of plants doubles the yield.
The best density is the one that grows the biggest individual plants.
Plants in a crop do not affect one another if each has its own space in the row.

Safety card

Low riskLearners carry it out

Hazards

dust and bacteria (including Legionella) in potting mix
hot drying oven

Controls

dampen potting mix before handling; gloves and a P2 mask
wash hands afterwards
teacher loads and unloads the drying oven

Note

No hazardous chemicals. Oven heat and general laboratory rules: 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.

Agriculture Stage 6 Syllabus (2013)H2.1 H4.1
Agriculture 11–12 Syllabus (2026), new syllabus, implementation from 2028AG-12-03 AG-12-06
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.