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Grade 8 Intermediate About 15 min Version 1 Awaiting review Premium

Which soil holds the most water?

Plants need water held in the soil around their roots. How much water a soil keeps depends on the size of its particles. Sand has large grains with big gaps between them, so water drains through quickly. Clay has tiny particles with very small gaps that hold water tightly. Loam, a mixture of sand, silt, clay and humus, holds a useful amount of water while still letting extra water drain.

What you will learn

  • Compare how well different soils hold water.
  • Relate water retention to the size of soil particles.
  • Plan a fair test with equal amounts of soil and water.

Before you start

  • Know what soil is made of. Try "What is soil made of? The soil jar test" first.

Materials

  • Sandy soil, garden loam and clay soil (50 g each)
  • Water (100 mL for each soil)

Equipment

  • 3 beakers
  • 3 conical flasks with funnels and filter paper

Procedure

  1. Each funnel holds 50 g of a different dry soil: sandy soil, garden loam and clay soil.
  2. Pour 100 mL of water from each beaker into the funnel of the same letter.
  3. Measure how much water collects in each flask.
  4. Work out how much water each soil held: 100 mL minus the water collected.

How this simulation is simplified

  • All the water that will drain has drained straight away. Real clay soil drains very slowly.
  • Each soil holds a fixed amount of water per gram: sand 0.2 mL/g, loam 0.7 mL/g and clay 1.2 mL/g.