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A typical soil is about half solid material and half gaps (pores). In a typical soil, about 45% is minerals from broken rock, 5% is organic matter, 25% is air and 25% is water.

The mineral part comes from rock that has been broken down by weather, water and living things. This rock is called the parent material. Soil forms over hundreds to thousands of years.

Scientists sort the mineral grains by size. Sand grains are the biggest (2 mm down to 0.02 mm), silt is smaller, and clay particles are the tiniest, smaller than 0.002 mm.

Experiment: Fair test: which soil drains fastest?

1. Line each holed cup with a coffee filter and stand it on an empty cup.
2. Fill each lined cup to the same level with one type of soil. Do not press it down.
3. Predict: through which soil will the water drain fastest?
4. Pour exactly 100 ml of water onto the first soil and start the stopwatch.
5. Stop the watch when water stops dripping out, or after 5 minutes. Measure how much water came through.
6. Repeat with the other soils. Keep the cups, the amount of soil and the amount of water the same.

Soil	Time to drain (s)	Water collected (ml)
Sand	Prediction
Clay soil	Prediction
Compost / loam	Prediction

Questions

1. Name the four parts that make up a typical soil, with their rough percentages.

2. Which soil drained fastest in your test? Explain why using the word 'spaces' or 'pores'.

3. Draw and label the soil horizons O, A, B and C.

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4. Clay holds water well. Is that good or bad for a garden? Give one good and one bad point.

Sources for every fact on this sheet: echoesof.science/school/soil/sources/

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