Chapter 3: Nature of Soil and Soil Conservation

Nature of Soil and Soil Conservation Introduction

Most of the things we use come from soil. What are the things that come from
soil around you now? Soil has been changing over billions of years. It has been
subjected to environmental changes; calamity and temperature effects. You will
study about causes of soil erosion and how to conserve soil thereby increasing
the yield. In this chapter, you will appreciate soil components and its properties in
relation to their contribution to the life of living things.

3.1: Importance of Soil to Living Things
What do you use soil for in your community? Soil is very vital for the survival of
living organisms. Soil is the upper layer of the earth’s surface. It is a black or dark
brown material as shown in Figure 3.1. It typically consists of a mixture ot organic
remains, clay and rock particles.

Soil is very important to life on earth. By doing Activity 3.1 , you will appreciate the
importance of soil to life on earth.
Activity 3.1: Discussing the importance of soil to living things
What you need: notebooks,stylus, slate, perkins brailler and braille papers.

What to do: In groups;
Study and analyse the pictures shown in Figure 3.2. Answer the questions that
follow.

1. Name the use of soil illustrated in each of the pictures above.
2. List other uses of soil to living organisms which are not shown in figure 3.2
3. Present your work to the class.
4. Individually write or braille the class conclusions.
   3.2: Soil Constituents
   When you closely examine a sample of soil, you will discover it is a mixture of
   many components. Each component of the soil has a role it plays. In Activity 3.2,
   you will identify some of the constituents of soil.
   Activity 3.2: Identifying the components of soil
   What you need: Notebooks, Stylus, Slate, and Perkins brailler and braille papers.

What to do:
The pictures A and B shown in figure 3.3, represent the components which
make up the soil. Study the pictures in groups and provide responses to the
task assigned.

1. Suggest the importance of each of the soil component identified.
2. List other components of soil apart from those shown in the pictures.
3. Describe the importance of the soil components you have listed in (2).
4. Present your findings to the rest of the class.
   Activity 3.3: Performing an experiment to show that soil contains air
   What you need: water, dry soil sample, measuring cylinders (2) , glass rod.
   notebooks, stylus, slate, and perkins brailler and braille papers
   What to do:

In groups;
1. Measure 50 cm30f dry soil in a measuring cylinder and level out the soil.
2. Measure 50 cma of water in another measuring cylinder.
3. Mix the water and the soil together (observe carefully as you pour the water
onto the soil)
4. Allow the mixture to stand until no more bubbles appear.
5. Read and record the final level of water plus soil in the measuring cylinder.
6. Calculate the air content in terms of percentage.
Use the calculations below to find out the amount of air in the soil
cma
Volume of soil = …………………………………. cm³
Volume of water = ……………………………… cm³
Final volume Of water + soil after mixing = ………………………………………………… cm³
Volume of air in the soil = Initial volume of soil + water before mixing – final
volume of water + soil after mixing
Percentage(O/o) Of air in the soil =……………………………………………….. %
7. Explain the importance of soil air to the existence of other living organisms
in the soil.
8. Present your work to the rest of the class.
9. Individually write or braille the class conclusions in your notebooks.

Air is a very important constituent of the soil. It is required by living organisms in
the soil. As observed in the experiment, when the soil was mixed with the water,
air bubbles were evolved. These bubbles show the presence of air in the soil.
Sand soil is the most well aerated soil. It contains the highest percentage of soil
air. This is because sand soil has the largest soil particles. These particles are not
compacted together and therefore allow free circulation of air.

Activity 3.4: Performing an Experiment to snow that soil contains water

What you need: crucible. soil sample. source ot heat. notebooks, stylus. slate.
perkins brailler and braille papers.
What to do
In groups;
I. Weigh as clean evaporating dish recorb its and weight. (Let the weight be X g),

2. Fill the evaporating dish with soil and record the weight of the soil plus the
   evaporating dish. (Let the weight be Y g).
3. Dry the soil by heating it gently over a Bunsen burner flame for about 30 minutes.
4. Heating and weighing is repeated until a constant mass is achieved. (Take
   care not to burn the soil to produce smoke),
5. Re-weigh the soil and the evaporating dish. (Let the weight be Z g).
6. Then calculate the water content in the soil sample as shown
   Note:
   You should cool in a desiccator before weighing. This ensures that no fresh
   vapour enters the soil.
   Use the calculations below to find out the amount of water in the soil
   Questions:
   Weight of the dish = ………………………………. g
   Weight of soil + evaporating dish heating = …………………………………… g
   Weight of soil + evaporating dish after heating = ………………………….. g
   Weight of soil sample = ………………………………………………….. g
   Weight of water in the soil sample = ……………………….. g
   Percentage(%) of water in the soil = …………………………. g
7. Present your work to the rest of the class
8. Individually write the class conclusions in your notebooks.
   Water is an important component of the soil. Processes such as germination are
   possible because of the presence of water in the soil. Water softens the seed coat
   during germination. It also activates the enzymes during germination.

Activity 3.5: Designing an experiment to show that soil contains living organisms
What you need: Muslin bag, top soil, two corks, two test tubes, lime water,
notebooks, stylus, slate, perkins brailler and braille papers.
What to do:
In groups;

1. Collect a hand full of fresh topsoil and divide it into 2 equal portions.
2. Sterilize one portion of the soil sample by heating it strongly on a crucible
   for 30 minutes. Leave it to cool and place it in a muslin bag.
3. Place the remaining portion of the fresh soil sample in another muslin bag.
4. Add equal amounts of lime water or bicarbonate indicator in the test tubes
   and then suspend the muslin bags with soil in the test tubes as shown in
   the set up below.
5. Allow the test tubes to stand for about 2 days and observe the appearance
   of lime water or bicarbonate solution.
   Task:
   a) Record the results and observations of your experiment.
   b) Suggest an explanation for your results in (a) above.
   c) Write a report about your experiment.
   d) In your report include the importance of living organisms in the soil.

Living organisms respire producing carbon dioxide as a waste product. Therefore
to detect that soil contains living organisms bicarbonate indicator/ lime water is
used. You may have observed changes in the colour of these substances in one
of the setup in the experiment. This is an indication that living organisms were
present in the soil.
Activity 3.6: Designing an experiment to show that soil contains humus
What you need: crucible, soil sample, weighing scale, heat source, wire, tripod
stand, pipe clay triangle, notebooks, stylus, slate, perkins brailler and braille papers.
What to do:
In groups;

1. Weigh a clean empty crucible and record its weight (W g).
2. Fill the crucible with soil halfway and record the weight of soil plus crucible
   on weighing scale (X g).
3. Dry the soil by heating it in an oven at 1050C to constant weight (Y g)theloss in weight of soil at this temperature is due to the water driven out byevaporation.
4. Reweigh the soil and crucible and record the weight.
5. Heat the dried soil on a crucible to redness in an oven, then weigh the soil after cooling and record its weight. Repeat this till a constant weight is achieved (Z g).
6. Use the calculations below to determine the percentage of humus in the soil.
7. Weight of crucible = ………………………………………….. g
8. Weight of crucible + fresh soil = …………………….. g
9. Weight of fresh soil = ………………………………… g
10. Constant weight of soil + crucible after heating at 105 oc =………………………….. g

Constant weight of soil + crucible after heating to redness = ……………….. g
Weight of dry soil = ……………………… g
Weight of dry soil after burning off humus = …………………….. g
Weight of humus = …………………. g

Percentage of humus = …………………….. g

Humus is an important constituent of the soil. Humus is the decaying plant an
animal material. It is a dark brown, rather sticky material that gives soil its dark color
Self check
The following experiment was done to find out the percentage of humus in a given
soil sample. The soil sample weighing 120g was heated in an oven kept at 1 OOCC.
The dry soil weighed 1 12g. The soil was then heated slowly to burn away humus.
The weight of soil after all humus had burnt was 106g
a) Why was the soil not heated properly at first?
b) What was the weight of humus in the soil?
c) Calculate the percentage of humus in the soil.
d) How many times was water more than humus?
3.3: Soil Types

Soil is used for a variety of purposes. Some of these include farming, pottery,
building and construction, among others. Soil used for farming may not be the
same type used for making a pot. What are the different types of soil that exist in
nature. Well, in primary science, soil was categorised into different types; which
included; clay soil, sand soil and loam soil. These are shown in figure 3.4. You are
to carryout activity 3.6 to identify the different types of soil.

Activity 3.7: Identifying the three different types of soil
You are provided with specimens, P, Q and R which are different soil samples.
What you need: Three different soil samples, notebooks, stylus, slate, Perkins
brailler and braille papers.

What to do: Individually,
I.Get a small amount of P and moisten it with little water. Rub between your
thumb and fingers.
2.Describe the feel of the specimen P based on the stickiness, and texture
of the soil.
3.Repeat the same procedures (1) and (2) with specimen Q and R
4.Suggest the type of the soil each specimen is.
5.Which of the specimens, P, Q and R is better for cropping?
6.Give reasons for your answer in (5) above.
7.Which of the specimens, P, Q and R is better for pottery?
8.Give reasons for your answer in (7) above.
9.Present your work to the class 10.Individually write or braille the class conclusions.

Different soil types have different texture and stickiness when mixed with water.
This variation is mainly due to the size of the soil particles. For example, clay
soil with the smallest sized particles has the finest texture while sand soil with
the largest particles has a coarse soil texture.
3.4: Drainage and Water Retention by the Soil
Soil has different properties, among which are; Soil water retention, drainage and
capillarity that make it suitable for its different uses on earth.
Soil water retention capacity is the soil’s ability to hold water inside its pores and
hold onto moisture rather than allowing it simply to obey gravity and pour through.
Soil’s ability to effectively retain water is largely attributed to number and size of
open spaces between soil particles and the size of the soil particles.
Soil drainage is a measure of how easily soil allows water to move across, through,
and out of the soil as a result of the force of gravity. In activity 3.8, you will explore
how to determine soil water retention or drainage capacity.

Activity 3.8: Comparing water retention and drainage in different soil sample.
What you need: 2 filter funnels, 2 measuring cylinders, 2 fitter papers, equal
volumes of samples of dry sand, dry clay soil, dry loam soil, water and beakers,
notebooks, stylus, slate, Perkins brailler and braille papers.
What to do:
In groups;

1. Obtain dry soil samples A(sand), B(clay) and C(loam.
2. Obtain equal volumes of soil samples and measure them separately.

PH is the degree of acidity or alkalinity of a given substance. Most of the soils in the
tropics are acidic but some are alkaline. Soil pH affects the rate at which mineral
salts e.g. nitrogen, phosphorous, iron are absorbed by plant roots. Most plants
grow best in slightly acidic or neutral soil.
3.7: Fertile Soil
Crops need nutrients just like people do. A fertile soil contains all the major nutrients
for basic plant nutrition (e.g. nitrogen, phosphorus, and potassium), as well as other
nutrients needed in smaller quantities (for example calcium, magnesium, sulphur,
iron, zinc, copper, boron, molybdenum, nickel). In Activity 3.11, you will discuss
the characteristics of a fertile soil.

Activity 3.11: Discussing the features of a fertile soil.
What you need: Notebooks, stylus, slate, Perkins brailler and braille papers.
What to do:
In groups;

1. Basing on the experiments you have conducted in the previous activities
   (3.2 to 3.10) state the characteristics of a fertile soil.
   Hint: For example you conducted an experiment to determine the amount of air
   in the soil. From this information, you can conclude whether a fertile soil is one
   which has more air (well aerated) or not.
2. Present your work to the rest of the class
3. Individually write the class conclusions in your notebooks.

The fertility of a given soil sample depends on the soil properties investigated in
the experiments in Activities 3.2 to 3.10. These include soil PH, Soil air, soil water
among others. Loam soil is the most fertile soil and suitable for plant growth because
it has the suitable characteristics of a fertile soil.
3.8: Soil Erosion
In primary science, you studied about soil erosion. Take a minute and share with
your neighbour; what soil erosion is all about. There are different types of soil
erosion. Can you identify some of them? In Activity 3.12, you will explore more
about the meaning, types of soil erosion and its causes
Activity 3.12: Discovering the types and agents of soil erosion
What you need: notebooks, camera, Internet connection, slate, stylus, Perkins
brailler and Braille papers.

1. As a class move around in the school and the community with your teacher. If
   you have a camera you can take pictures of the different types of soil erosion.
2. Identify the different types of soil erosion in your school or community.
3. What are the agents of the types of soil erosion you have identified in (2).
4. Which type of soil erosion is most common in your school or community
5. Suggest a reason for your answer.
6. What are the causes of soil erosion in your community?
7. Present your work to the class
8. Individually write or braille the class conclusions in your notebooks

Hint: Types of erosion studied in primary science include gully, rill erosion as shown in Figure 3.6 sheet, splash, wind erosion.

Soil erosion is the washing away of the top soil by agents such as wind, running
water, animals. You should note that the agents of soil erosion are different from
the causes of soil erosion.
3.9: Loss of Soil Fertility
Loss of soil fertility is a common issue affecting most farmers in IJganda. It is
characterized by the soil losing its value year after year. This contributes to poor crop
yields and harvests. Figure 3.7 shows crops poorly growing due to soil infertility.

Food insecurity, hunger and malnutrition are the likely effects of infertility of the
soil. In Activity 3.13, you will investigate about the causes of loss of soil fertility in
your community
Activity 3.13: Assessing the causes of loss of soil fertility.
What you need: notebooks, camera, Internet connection, slate, stylus, Perkins
brailler, Braille papers and a video showing causes of soil infertility.
What to do:
As a class;

1. Listen to a talk from a visiting farmer from your community/ watch a video
   on the causes of loss of soil fertility. Or go to the school community and:
2. Identify the causes of loss in soil fertility.
3. Discuss with the farmer the solutions to the causes of loss in soil fertility.
4. Individually write a report from the farmeös talk/ viewed images.
   From the Activity above, you have been able to identify the different causes of soil
   fertility and remedies to curb soil fertility loss.

From the Activity above, you have been able to identify the different causes of soil
fertility and remedies to curb soil fertility loss.
3.10: Soil Conservation
In most cases, you preserve foods such that they don’t go bad. Soil also needs
to be preserved in order not to lose its fertility. How can we preserve soil? Which
methods of soil preservation do you use in your community? In Activity 3.14, you
will discuss about the various methods of soil conservation
Activity 3.14: Discussing the methods of soil conservation.
What you need: notebooks, camera, Internet connection, slate, stylus, Perkins
brailler, Braille papers.

What to do: In groups;
Carefully examine the pictures in Figure 3.8.
1.Name the soil conservation methods shown by each picture in table 3.3
2. Other than the methods shown in Figure 3.8, mention other methods of
soil conservation.
3. How is each of the methods effective in soil conservation?
4. Which methods of soil conservation are used in:
a) Lake Victoria basin
b) Kigezi highlands
c) Karamoja region
5. Present your work to the rest of the class
6. Individually write or braille the class conclusions in your notebooks.