Finding out the constituents of soil

Back to: BIOLOGY NEW LOWER SECONDARY CURRICULUM BOOK 2

Key question: What are the constituents of soil?

What you need

• fresh soil sample
• beaker or measuring cylinder
• water               
• hand lens
• stirring rod      
• heat source evaporating dish or any container for heating
• a lid

What to do

1. In groups, dig out a block of soil from
   the nearby garden.
2. Spread some soil on a paper and using a hand lens or low power objective lens of the microscope, take note any living organisms seen in the soil.
3. Place a small amount of the soil sample in an evaporating dish or metallic container, and cover it with a dry lid.
4. Strongly heat the soil sample to about
   100°C, then remove the lid and note
   your observations. Give reasons for
   your observations.
5. Half fill the transparent container (beaker
   or measuring cylinder) with a fresh soil
   sample and then fill the container with water. What do you observe? Give a reason for your observation.
6. Cover the open end of the container
   and vigorously shake to mix. Leave the container to settle for about 20 minutes.
   What do you observe on the surface of
   the mixture?
7. What do your observations in 2, 4, and 5 suggest about the components of soil?
8. Compile a report of your findings and
   present to the rest of the class.

Suggested responses

2. Earthworms, nematodes for example ascaris, filarial worms and soil arthropods.

4.     Water droplets are formed on the underside of the lid. This implies that it has evaporated from the soil.

5.    Air bubbles are seen in the beaker. This is because soil air in the soil sample has been displaced by water. 7. Soil consists of several components among which are; living organisms, water, and air

1.3: Properties of Soil

Guide the learners to understand that different soil samples have different properties, both physical and chemical. Through conducting the experiments in Activities 13(a), 13(b) and 13(c) the learners will investigate soil properties. The physical properties of soil include:

a)   Water retention

Let the learners understand that the soil that retains more water has high water retention while that which retains less water has low water retention. The ability of soil to hold considerable amounts of water is called water retention. The soil type that allows water to pass through it faster has high drainage while the soil type that does not allow water to go through it easily has low drainage.

Water   retention   can   also   be referred to as water infiltration