KS2 Science: Which soil holds the most water?

Primary resources > KS2 Science > Experiments in controlled environments

Video summary

Presenters Harry and Cayana have been challenged by a farmer to find out which sample of soil holds the most water.

To test this idea, they compare how quickly water moves through various soil samples.

They place three samples in three filters, add 100 ml of water and then measure how much water has been retained by the soil.

This short film is from the BBC Teach series Experiments in controlled environments.

Teacher Notes

Before Watching

Show your learners some soil. What do they think it is made from? Is all soil the same? Soils vary depending on the rocks from which the soil has come, the climate and terrain of the region, as well as the type of plant life and vegetation present, and human intervention such as adding extra plant material.

After Watching

Before they tested the soils, the presenters looked closely at the three unprepared soil samples, to feel the texture of the soil.All of the samples contained plant material and stones. Therefore, the presenters prepared their soils before they tested them, by sieving them to remove all stones and plant mater. They also ensured that their samples were dry. Ask the children why they prepared their soil in this way before testing which soil holds the most water? This was to make it a fair test, where they were only looking at how much water was absorbed by the soil and not any additional plant matter.

Think about the type of soils that farmers may need for different crops. For example, carrots grow best in light and well-drained soil. Whilst celery needs fertile, moisture-retentive soil that is wet but still well-drained.

Try this investigation out! Every soil sample will be slightly different and you may get different results to those in the film. Ask your children to consider why this might be? Many soils are a combination of sand, clay, chalk and may have silt or peat or lime within it. Each soil type, has a set of characteristics that provide different benefits and limitations for farmers and gardeners to consider when they select and grow their crops.

Ideas for further learning

Investigate the soils near you. Look closely at your soil with a magnifying glass or under digital microscope – what is the soil made from?

Do a soil settlement test to find out which type of soil you have. Fill a jam jar with one quarter soil, three quarters water. Shake vigorously and allow to settle on a flat surface. Observe the settlement over a period of a few days. Sand, silt, clay and organic matter will separate in different layers and at different speeds with the heaviest particles settling first.

Health & Safety:

• Ensure that you only use soil that is free from faeces, sharp objects and rubbish.
• Children should wear gloves when handling soil.
• Always wash hands after gardening and especially before eating.

Key Knowledge

• Soil - soil is a mixture of tiny particles of rock, dead plants and animals, air and water. Different soils have different properties depending on their composition. Soil has many small spaces, called pores, that hold water and air.

  • Sandy soil is pale coloured and has large particles. These create lots of small air gaps. Water drains through them easily so it usually feels dry.
  • Clay soil is usually sticky and has small particles. They contain very few air gaps and water does not drain through it easily._
  • _Chalky soil is a light brown soil. Water drains through it quickly.

• Soil texture – this is an indicator of the nutrient and water holding capacities of soil that is determined by the proportion of sand, silt and clay soil particles. Our presenters assessed the soil texture by feeling the unprepared samples before they tested them.

• Why is soil important? - Soil is an important natural resource, not only does it supply a suitable environment and conditions to grow food, it also protects us from flooding, helps regulate our climate and provides an important habitat for many soil dwelling organisms.

Developing Practical Enquiry Skills

• Comparative test enquiries - comparative test are an opportunity for children to make comparisons. In this case we are comparing soils. To set up a comparative test we change one variable, measure another variable and keep all the other variables the same. It is important that we only change one variable so that we know what caused the effect.

• Measuring how much water the soil retains - 100 ml of water is poured carefully onto the sample. Some water is retained by the soil, the rest is collected in the beaker. The quantity collected is subtracted from the original 100 ml to calculate how much has been retained by the soil.

• To read the volume of a liquid - place the beaker on a flat surface. Look and check the scale on the beaker. Check does the scale increase in 1,10 or larger increments? Read the scale at eye level.

These short film clips support teachers with practical enquiry. They can be both used as a resource for learners to watch at home. Or as a stimulus to support learners to plan and conduct their own science investigations. They link to the UK Science curricula.

Rocks & Soils

• Pupils recognise that soils are made from rocks and organic matter.
• Pupils compare the texture and properties of different soil types.

Science enquiry / Skills for working scientifically

• Pupils should plan different types of scientific enquiries to answer questions, including recognising and controlling variables where necessary.
• Pupils should take measurements, using a range of scientific equipment, with increasing accuracy and precision, taking repeat readings when appropriate.
• Pupils should record data using tables.

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