Physical and Chemical Properties of Soil

Physical and Chemical Properties of Soil

By the end of this chapter, you will be able to:

(a) identify the types of soils.

(b) determine soil constituents and identify their properties.

(c) understand that different soil samples having different properties; water rotation, drainage, capillarity and PH values.

(d) carry out experiments to find the percentage of air, water, and humus in the soil sample.

(e) understand the importance of air and water in soil to other living things.

Introduction

In this chapter you are going to learn more about soil. Remember that soil is the covering of the earth surface in which plants grow and some animals and micro organisms live.

You are going to identify types of soil, determine soil constituents and identify their properties and also be able to understand that different soil samples have different properties such as porosity, drainage, water retention, and pH.

You will carry out experiments to find the percentage of air, water and humans in the soil sample. You are expected to understand the different constituents and the amount of each one in the given sample. you will then be able to appreciate competence.

1.1 Types of soil

Activity 1.1 Identifying types of soil

Key question

What are the main types of soil?

What you need

Soil samples of clay, loam and sand.

Biology/Geography/Agriculture textbooks.

Computer connected to the internet.

What to do In your group,

1. Study the three main different types of soil.

2. State the main features of each soil types.

3. Research on how suitable each soil type is for growing crops.

4. Find out other uses of the different soil types.

5. Present your findings to the rest of the class.

Soils are grouped according to the proportion of the different sized particles they contain. There are three basic types of soil: sand, clay and loam soil. Each type of soil has its own characteristics different from others which determine the types of plants to grow on. After studying types of soil, you should be able to understand which crops should be grown on certain types of soil.

1.2 Soil layers

Soil differs from place to place to place. if you touch soil samples from different places, you will observe that sand is the largest particle found in soil, clay is the smallest particle found in soil whereas loam, on the other hand consists of the two, making this type of soil the best for growing plants.

In nature the consists of different soil layers which can distinguished by their difference in colour, composition and size of particles.

Figure 1.2 Soil layers

Activity 1.2 Finding out the layers formed when soil is mixed with water

What you need

Soil samples: preferably loam soil

Measuring cylinder

Notebooks/pens Water Rulers

What to do

In pairs or small groups, put dry loam soil samples in a measuring cylinder to cover at least a quarter of it.

Mix with water thoroughly and leave to settle.

Observe how many layers have been formed.

Measure the height of each layer in mm.

Draw the diagram showing arrangement of layers in the soil.

Discuss why it is important to maintain soil layers in their natural positions.

Identify the different kinds of soil particles from the list below (Note that this list is not in any order). Gravel – small stones and pieces of rock with a diameter larger than 2mm.

Humus– pieces of dead plant and animal matter

Clay – tiny particles suspended in water.

Course sand – particles with a diameter between 0.2 – 2.0mm.

Silt – very small fine particles that settle on the bottom.

QUESTIONS

1 . What sort of particles are floating on top of the water?

2. Where are the smallest particles?

3. Where are the biggest particles?

4. Why do some types of particles settle before others?

5. What approximate proportions of each kind of soil particle contained in soil?

6. Present your findings to the rest of the class.

1.3 Characteristics of each soil sample

Soil types are identified by their characteristics into clay, sand or loam. These characteristics include – particle size, crumb structure, and texture. These affect plants that grow in the soil and animals that live in it.

Activity 1.3 Identifying characteristics of different soil samples

Key question

How are characteristics of clay, sand and loam identified?

What you need

Clay soil, sand soil, and loam soil

Plastic trays

Magnifying glasses / hand lens

Notebooks, pens, and textbooks of Biology/computer with internet

Water

What to do

1. In pairs or small groups, put dry soil samples (clay, sand and loam) on different plastic trays, and observe the colour of each soil sample.

2. Carry out investigations on the characteristics of the soils that can be used to identify them.

3. Which particles of the soil sample don’t cling together in the presence of moisture?

4. Which particles of the soil sample cling together easily and form balls which don’t break.

5. In your groups record your observation of each soil sample in Table 1.1.

6. Using textbooks of Biology/ Computer with internet, research and discuss other characteristic of different soil types.

7. Present what you have discussed in your group to the rest of the class.

Differences between clay, sand and loam soil

Table 1.1: Table of observations

Characteristics	Clay	Loam	Sand
Colour of the sample
Types of materials with their colours
Size of particles
Texture – smooth or rough
Forms balls or not
Human content

1.4 Constituents of soil

If you look down at the soil under your feet, you cannot tell what soil is composed of. You need to observe clearly a sample of soil got from different places with vegetation.

Soil varies in its composition and the structure of its particles, and these factors are closely examined by farmers, who need appropriate soil for planting crops, as well as engineers who may need to understand how soil is going to hold under different demands.

In this study, you will observe that soils vary in some properties but all of them have basic components.

Activity 1.4 Identifying components of soil

Key question

What are materials that make up soil?

What you need

Hoes and trays

Textbooks/computer with internet connection

Notebook and pens/ pencil Hand lens / magnifying glass

Source of heat

Water Beaker/suitable container

What to do

1. In small groups, move out of your class to the compound and look for a place where there is much vegetation. Dig deep the ground and obtain a handful of soil.

2. Discuss how you are to identify the components of soil using the materials provided.

3. Display the soil on the tray and observe it through a magnifying glass. Identify any living organisms present in the soil.

4. Identify decaying things (organic matter).

5. Heat a soil sample while placing a dry test tube above. What do you observe? What does it show?

6. Place a soil sample in a beaker and pour water to cover it. What do you observe? What does this show?

7. Using biology textbooks/computer, research about other components that you may not have been observed in that soil you got from the compound.

8. Research and discuss the importance of each soil component.

9. Present your findings to the rest of the class.

Components of soil are materials that make up the soil and these include; living things, organic and inorganic materials.

The non-living components are air, water, and weathered rocks. The living components are living organisms such as bacteria, fungi, nematodes and arthropods.

Non- living components include rock particles and humus. The combinations of these determine the soil’s properties and each component is important for supporting plant growth, micro organisms and chemical decomposition.

1.5 Properties of soil

Activity 1.5 Investigating soil samples for the properties of soil

Key question

What are the properties of soil?

What you need

Soil samples from different habitats of the school

Computer connected to internet

Biology textbooks

Universal indicator

Measuring cylinders

Stiring rod

Filter funnels

Water

pH scale

Beakers

Test tubes

What to do

1. In groups make a research on the different soil properties and record them in your notebooks. What are the different soil properties?

2. Design experiments you would carry out to investigate the properties discovered on the internet/biology books.

3. Write out a report in a suitable design in your group.

4. Report your findings to the rest of the class.

1.6 Water retention and drainage

Soil has some amount of water inside it in form of moisture. soil which is usually a thin film around the soil particles. The Soil texture determines the water holding capacity of the capacity of a soil to hold water is important for the growth of various crops. Even dry soil has some water in it.

Water moves across and out of the soil as a result of the force of gravity. Different soil samples have different rates of drainage. Drainage ensures that the soil is well aerated, excess water or stagnant water reduces air content of the soil which affects plant growth.

Activity 1.6(a) Investigating water retention in dry soil samples

Key question

How is the amount of water retained in the dry soil determined?

What you need

Dry soil samples of sand, clay and loam soil

3 measuring cylinders

Three filter funnels

Cotton wool/filter paper

What to do

1. Stop clock Water soil samples above. In pairs or groups, prepare experimental setups using different

2. Leave water to drain through without disturbing the apparatus. Note the time taken for the water to drain through each.

3. When dripping has stopped in all the three setups, read the volume of water in the measuring cylinders. This is the volume of water that has drained through. Record your results in Table 1.2

4. Present the findings in your group to the rest of the class.

Table 1.2: Table of results

Questions

1. Which soil has the highest rate of drainage?

2. Which soil has the lowest rate of drainage?

3. Which soil sample retains more water and why?

4. Give the order of water retention in the three soil samples.

5. Research more about importance of drainage in the soil.

Activity 1.6(b) Investigatingthe rate of drainage in dry soil samples

Key question

How is the rate of drainage in the soil determined?

What you need

Dry soil samples of sand, clay and loam soil

3 measuring cylinders

Three filter funnels

Cotton wool/filter paper

Water.

Stop clock.

What to do

1. Set up the apparatus again as for water retention and start the clock.

2. For each soil sample, determine the volume of water passing through every one minute in mm3.

3. Record your results in the Table 1.3.

4. Present your findings to the rest of the class.

Table 1.3: Volume of water drained in the soil samples

Time/ min	Volume of water drained	Sand	loam	clay
0
1
2
3
4
5

1.7 Capillarity of soil

Capillarity is the process by which water rises in a cylindrical column. This is the cause of rise in a straw placed in a soda bottle.

In nature water rises from deeper soil layers to the surface layers by capillarity to replace water absorbed h the root hairs.

Activity 1.7 Investigating the rise of water (capillarity) through different types of soil

Key question

How is the capillarity of different types of soils determined?

What you need

Three wide glass tubes of the same size

Cotton wool, dry soil samples (clay, sand and loam soil)

Three retort stands

Graph paper

A large beaker of water

What to do

1. In pairs or groups, set up the experiment as described in the following procedure.

2. Take three long, wide glass tubes same size and plug them loosely at one end with cotton wool. 3. Hold the tubes vertically with the plugged end downwards. Then fill each with dry soil of one type above the cotton wool up to half.

4. Half fill the beaker with water.

5. Using a retort stand, clamp the glass tubes upright so that the cotton wool end is dipping into the beaker.

6. Start the clock immediately.

7. Observe the rise in the level of water in each tube at interval of 5 minutes.

8. Record the reading till the rise in the level of water stops. Record your results in Table 1.4.

	SAND	CLAY	LOAM
0
5
10
15
20

1. Use the data from the table to draw a graph of capilarity of each soil sample.
2. which soilshows the greastest rise of water in the early stages of the experiment? explain the resuilts.
3. which soil shows the hiehest rise odf water in the experiment? explain the s\resuilts.
4. why do you think capilariy is an important factor in the soil?
5. present your findings tp the whole class.

1.8 Soil pH

It is a bout the measure of alkalinity and acidity in the soils. pH levels range from 1 to 14 with 7 being neutral, below 7 acidic and above 7 is alkaline. Different plants thrives on different pH. it is also influences soil dwelling organisms, whose wellbeing, in turn, affects soil conditions and plant health.

Activity 1.8 Testing pH of soil samples

key question

how can you tell the pH of soil?

what do you need

 

• Soil samples (clay, sand, loam)
• Universal indicator solution
• Stardard ph chart
• Distilled
• Test tubes
• Glass rod
• Dropper

What to do

1. Put a spatula full of soil in a clean test tube .
2. Add distilled water to cover the soil .
3. Using a dropper add a few drops of universal indicator solution , cover the test tube with a thumb and shake vigorously and leave it for 5 minutes . Tilt the test tube and note colour change .
4. Compare the colour of the universal indicator with the standard pH chart and identify the pH of that soil sample .
5. Record your results in Table 1.5 .
6. Repeat the steps above with other soil samples provided .
7. Present your findings to the whole class .

Questions

1. Which soil samples are acidic ?
2. Which soil samples are alkaline ?
3. What is the importance of soil pH ?

Figure 1.3 : pH colour chart

Table 1.5 : Table of results

soil pH refers to acidity or alkalinity.

Soil sample	colour	pH	Acid/ Alkali/Neutral
clay
sand
loam

1.9 Soil air, water and humus

There are certain things that every living organism needs to live and grow. Just like humans, plants need air, food and water.

If any one of these things is missing, the plant will grow slowly or not at all. on there is to much of something, the plants growth can also be harmed.

Water, soil and air are three natural resources that we cannot live without. Farmers strive to protect, maintain, and restore these valuable assets now and into future.

Activity 1.9 Finding out the percentage of air in the soil.

Key question

How do you determine the percentage of air in the soil?

What you need

Soil samples of clay, loam and sand soils.

Biology textbook/computer with internet

Measuring cylinders

Beakers

Stirring rod

Notebooks/pens

what to do

1.In pairs, put 300 cm3 of water in a large measuring cylinder.

2. Pack tightly sand soil in a beaker or tin of known volume.

3. Pour sand soil into the measuring cylinder with 300cm3 of water and observe what happens. 4 5 6 7 4.Shake or stir well the mixture using a stirring rod until no more air bubbles appear.

5. Note what happens to the level of water immediately and after few minutes.

6.Explain why there was change in the water level.

7.Workout your results by showing; initial volume of water, volume of soil, volume of water plus sand soil, and change in the volume of water plus sand soil at the end of experiment (volume of air).

8. Repeat the experiment with dry clay and loam soil.

9. Record your results in Table 1.6

Table 1.6 Table of results

Soil sample	Volume of soil in cm3	Volume of soil and water before stirring	Volume of water and soil after stirring	Volume of water in cm3	Volume of air in cm3
Sand
Clay
Loam

Formula Percentage of air in the soil = volume of air which has escaped from the soil Divide by volume of the soil × 100

10. Calculate the percentage of air in the sand soil, clay and loam soil.

11 Find out which of the three soils has more air. Explain your answer.

12 Present your findings to the whole class.

13 In your groups research about the importance of soil air to plant.

Activity 1.10 Finding out percentage of water in the soil

key question

How can you determine the percentage of water in the soil?

What you need

Crucible

Beam balance

Soil sample of clay, loam and sand soil

Cooker with an oven (if possible), or stove

Stirring rod

What to do

1 Weigh a crucible and record its weight.

2, Put some soil on the crucible and weigh it again and record.

3. Place the crucible of soil in an oven or heat gently at around 100°C to dry the soil. Stir occasionally. CAUTION Do not touch the crucible or hot soil with bare hands.

4. Let the crucible with soil cool and weigh again.

5. Repeat the heating, stirring and weighing until a constant weight is attained.

6.Calculate change in weight that is, weight before heating- weight after heating, stirring to constant weight.

7. From this deduct the weight of the crucible.

8. Calculate the percentage of water in the soil using the formula given

Formula Percentage of water in the soil = change of weight in soil divide by original weight of soil

9 Record your results in Table 1.7. × 100

10 Repeat the experiment with other soil samples.

11 Which of the soil samples has more water? Explain your answer.

12 Present your findings to the rest of the class.

13 In your groups research about the importance of soil water to plant.

Table 1.7: Table of results

Soil sample	Weight of crucible in g	Weight of soil before heating in g	Weight of soil and crucible after heating in g	Weight of soil after heating in g	Change in weight of soil in g
Sand
Clay
Loam

Activity 1.11Finding out the percentage of humus in the soil

Key question How can you determine the percentage of humus in the soil?

what you need

Crucible

Beam balance

Dry soil samples of sand, loam and clay

Stick/wire Stove

Biology textbook/computer with internet

What to do

1. Weigh the crucible.

2. Add to the crucible few grams of dried soil and heat strongly. Note any change that occur for example colour, smell and smoke

3 Stir the soil gently with a stick, and continue heating until there is no change. Stir the soil gently with a stick, wire and continue more heating until there is no smoke seen. CAUTION Do not touch the crucible with bare hands.

4. When there is no further change, let the crucible cool and weigh it. $

5. Calculate the change in weight by subtracting final weight from initial weight.

6 From this deduct the weight of the crucible.

7 Calculate the percentage of humus in the soil using the formula given.

Formula/ Percentage of humus in the soil = change in weight of soil after strong heating/initial weight of the soil × 100

8. Record your results in Table 1.8.

9. Repeat the experiment with other soil samples

10 Which of the soil sample has more humus? Explain your answer.

11 Present your findings to the whole class.

12 In your groups research about the importance of humus to plant.

Table 1.8 Table of results

Soil sample	Weight of crucible in g	Weight of soil before heating in g	Weight of soil + crucible after heating in g	Weight of soil after heating in g	Change in weight of soil in g
Sand
Clay
Loam

1.10 Extension Learning: Science Project

Growing plants in different soils

Characteristics of each soil type determine the type of crops that grow there. Like animals and humans, plants need water, air and nutrients to grow. They get all of these from their growing medium which is the soil.

In this project you will investigate whether an annual crop like beans, maize, and peas can do well in all soil types and which one is best for their growth. In this study, you will use beans as example of annual crops.

Activity v1.13 Investigating the growth of beans on different soil types

Key question

What effect do soil types have on the growth of bean plants?

What you need

Bean seeds

Measuring tape/ ruler

Flower pots/basins/buckets

Camera (if possible)

What to do

1. Sticks Water jar Water In your groups, prepare soil with different percentage of soil content and fill it in flower pots, buckets/basins. Fill the first pot/bucket with soil which has high percentage of sand, the second with soil that has high percentage of clay, the third with soil of equal percentages of sand and soil with a lot of humus.

2. Label each pot clearly so you know which soil is in each pot.

3. Make sure you plant each seed at the same depth.

4. Plant two seeds per container because one seed may be defective and doesn’t germinate. You can remove the less healthy plant once the second set of leaves appear.

5. Water them all with the same amount of water, and make sure that they all get the same amount of light.

6 Once the beans have started to sprout, provide them with sticks for support.

7 Measure their heights everyday and record for a couple of 00 weeks.

8. Observe and record which plants grow quickly, look the healthiest.

9 Which soil is best for the beans to grow? Explain your answer.

10 Which soil is not good for the beans to grow? Explain your answer.

11 Present your group findings to the whole class.

Chapter summary

In this chapter, you have learnt that:

• There are three basic types of soil that is sand, clay and loam soils.
• Characteristics of types of soil include soil texture, color, and soil structure and particle size.
• Soil is made up of four types of components; soil air, soil water. Living things, organic matter and inorganic materials, each soil component is good for making soil suitable for plant growth.
• Properties of soil and their importance to soil.
• Experiments to find the percentage of air, water, and humus in a soil sample.
• Soil air is important to living organisms in that it provides oxygen which is used for respiration and for seed germination.
• Soil water is important for living organisms in the following ways ;
• It dissolves mineral salts and gases and then makes them readily available to plants.
• It is essential for photosynthesis.
• It makes cells turgid hence provide support to herbaceous plants.
• It is important for seed germination..

Watch the video below to learn more about physical and chemical properties of Soil

You can ask the AI Biology teacher below and get answers to your questions S1-S4