Back to: biology new curriculum notes senior two
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
(a): Comparing the water retention capacity of sandy, clay, and loam soils.
Key question: What is the difference in the water retention capacity of soils?
What you need
- measuring cylinders (3)
- funnels (3)
- water
- filter papers or pieces of cotton
wool soil samples: sandy soil, clay soil, and loam soil
What to do
- In groups, using the materials you have been provided with design an experiment to compare the water retention capacity of loam, sandy, and clay soils.
- Conduct the experiment you have designed and write a report on your investigation.
3. Present your report to the rest of the class using a graph or a table.
Observation: Water passes through sandy soil faster than it does in loam and clay soils. Sandy soil gives the first drop of water and clay soil gives the last drop. So much water is collected in the cylinder with sandy soil and the least water is collected in the cylinder with clay soil.
Conclusion: Clay soil holds more water than loam and sandy soils.
Explanation: Sandy soil has larger air spaces which enable water to pass through more rapidly and on the other hand, clay soil retains more water than sand and loam soils. This is because clay soil has many small particles with small air spaces thereby retaining more water. Loam soil has medium retention.
b) Water drainage
Help the learners understand that rainwater seeps to the bottom layers of soil and in places where this is impossible there: is flooding (Figure 1.4). Ask the learners to share their experience about floods, then guide them to understand that drainage is the ability of a soil water to pass through it and that it varies in different soils.
b): Comparing the drainage of sandy, loam and clay soil samples
Key question: What is the difference in the water drainage properties of the different types of soil?
What you need
- measuring cylinders (3)
- funnels (3)
- water
- filter papers or pieces of cotton
wool soil samples: sandy soil, clay soil and loam soil
What to do
- In groups, using the materials you
have been provided with, the design of an experiment to compare the drainage properties of loam, sandy, and clay soils.
- Conduct the experiment you
Have designed and then write a report about your investigation.
- Present your report to the rest of the class.
Suggested responses
Observation: Water passes faster through sandy soil than through loam and clay soils. Sandy soil gives the first drop of water and clay soil gives the last drop. So much water is collected in the cylinder with sandy soil and the least water is collected in the cylinder with clay soil.
Conclusion: Sandy soil drains faster than loam and clay soil.
Explanation: Sandy soil has larger air spaces which enable water to drain through more rapidly and on the other hand, clay soil retains more water than sandy and loam soils. This is because of clay soil . has few air spaces and small particles. Loam soil has medium drainage.
c) Capillarity
Stimulate the learners’ thinking by asking them how they are able to sip a soda through a straw!
Let them relate it to the rise of water from the bottom layers of the soil to the top layers through soil particles. This is called soil capillarity. Guide them to investigate this in activity 1.3(c).
c): Comparing the capillarity of water of different soil samples
Key question: What is the difference in the capillarity of the different types of soil?
What you need
- glass tubes (3)
- petri dishes (3)
- piece of cotton wool
- ruler or any other instrument for length
determination - soil samples: sandy soil, clay soil and
loam soil
What to do
- In groups, using the materials available at your school and in the environment, design an experiment to compare the capillarity of water in loam, sandy, and clay soils.
- Conduct the experiment you have designed and then write a report on your investigation.
- Present your report to the rest of the class.
Observation: Water rises faster but to a lower level in sandy soil while in clay soil, water rises slowly but to higher levels. In loam soil water rises moderately to a moderate level.
Conclusion: Clay soil has the highest capillarity while sandy soil has the lowest capillarity and loam soil has medium water capillarity.
Explanation: Water rises fastest during the early stages of the experiment in sandy soil because sand has large spaces that enable water to rise more rapidly. Clay soil has the highest rise of water hence the highest water capillarity because it is composed of tiny soil particles that present a large surface area over which water molecules cling. Water rises at a slow rate in clay soil because clay has small spaces between its particles.
Application of knowledge: Trigger the learners to share their local experience of how the study of physical properties of soil have been put to use in their community. That knowledge can be used while preparing activities such as pottery and making of clay masks as shown in figure 1.5
Thanks