Geography and Environment

By the end of this unit, you must be able to determine the relationship between different types of soils and human activities.

Unit objectives

By the end of this unit, you must be able to:
(a) define soils
(b) state factors responsible for soil formation
(c) identify soil properties and constituents
(d) identify types of soils
(e) state the importance of soils
(f) outline the effects of soils on human activities.

Definition of soil

Work in groups of four.
1. Go outside your classroom.
2. Collect soils from different parts of the school compound.
3. Observe and describe the soil samples collected.
4. In your own words attempt to give a definition of soil.

Soil refers to the top layer of the earth’s surface on which plants grow. Soil consists of rock and mineral particles mixed with decaying organic matter, water and air.
Soil can also be described as a naturally occurring thin layer of loose materials. The loose materials overlie crustal rocks. Soils are important for the existence of many forms of life on earth.

Soil formation processes

(a) Weathering of rocks

Work in pairs.
Study the photographs in Figure 7.1 and answer the questions that follow.

                                 Fig 7.1

1. Describe what you can see in each picture.
2. Identify the weather conditions that lead to the condition observed in pictures (a) and (c).
3. Give the importance of the process that is taking place in picture (a).
4. Why do you think there are different colours on picture (c)?

Weathering is the process through which the rocks of the earth’s crust are broken down. They are broken into smaller particles through mechanical or chemical processes hence forming soils.

(b) Leaching

This is the process by which water removes minerals and other soluble constituents from the soil.
The minerals are usually removed from the upper to the lower horizons of soil. This happens when the water percolates into the soil.

(c) Eluviation

This is the process that involves the washing through of solid materials from the upper soil horizons as a result of leaching. This process encourages the formation of different soil horizons.

(d) Illuviation

This process follows eluviation. It involves the accumulation of materials into the lower
layers of the soil.

(e) Salinisation

It is a process by which water soluble salts accumulate in the soil. This accumulation is caused by high rates of evaporation on the earth’s surface.
The salts in the lower horizons are carried upwards towards the surface by capillary action.
This process occurs in areas with high temperatures and low rainfall such as the deserts.

           Fig 7.3 Salinisation process.

(f) Podzolisation
This process involves the decomposition of vegetative matter that results in the formation of humic acids. Minerals like calcium, iron, magnesium, aluminium, salts and bases and carbonates are dissolved from one horizon to another. This leads to the formation of acidic soils. This process
occurs in the cool temperatures.

      Fig 7.4 Soil that has undergone podzolisation.

(g) Calcification
The dissolved calcium carbonate is then carried downwards to horizon B where it is deposited.
This process occurs in dry climates. Calcium carbonate is dissolved in horizon A during the periods of rainfall or snowmelt.

      Fig 7.5 Soil that has undergone calcification.

Laterisation
This process occurs in warm humid climates. During the wet season, mineral salts in horizon A dissolve in rain water. The minerals that dissolve are mainly silica and the bases. The dissolved minerals percolate downwards to the lower layer. Insoluble minerals such as iron and aluminium
accumulate in the top layer. They form a crust of laterite. The top layer is reddish in colour.

(i) Humification
When plants and animals die, their remains decompose in the soil. This decomposition is aided by the micro-organisms that are found within the soils. The decomposed organic matter form humus. The humus mixes with the soils to form fertile layers of soil as shown in Figure 7.5.

                 Fig 7.6 Transformation of organic matter into humus.

Task 7.1
1. Define leaching.
2. Give the conditions that make it possible for leaching to occur.
3. Using specific examples, explain the effects of leaching in the soil.

Do this in groups of three.
Use the Internet, geography textbooks and journals.
1. Find out other soil formation processes.
2. Discuss the processes with the help of well labelled diagrams.

3. Make notes on your findings.
4. Present your findings in a class presentation for input from other class members.

Factors influencing soil formation

Soils are formed through the interaction of five major factors. These are parent rock, climate, topography (also referred to as relief) time and living organisms.

(a) Parent rock
This refers to the original material that forms the rock that weathers into soils.
The parent rock determines the chemical and physical characteristics of the soil. The nature of the parent rock influences the rate of weathering. Soft rocks are weathered faster thus enhancing the soil formation process. Hard rocks on the other hand are weathered slowly. This slows down the soil formation process.

The parent rock also determines the soil texture. Large grained rocks are weathered to produce coarse grained soils. Fine grained rocks produce fine grained soils. The type of minerals and colour of the parent rock are also transferred to soil during formation.

(b) Climate
The climate of an area determines the way in which weathering of the rocks takes place.
The main elements of weather that influence soil formation are temperature and rainfall.
Rainfall provides water. This water makes it possible for decay and disintegration of rocks that form soil.

(c) Topography or relief
The topography of an area influences the process of soil formation in many ways. The most important being the slope of land. Steep slopes encourage erosion. The areas of low relief or gentle slope experience deposition and have deep, well drained soils. The degree of slope also largely determines the fertility of soil.

(d) Time
Different types of soils require different durations of soil formation processes to reach maturity. A soil formation process that takes a long period of time forms mature soils. A process that takes a shorter period of time forms immature soils.

(e) Living organisms
When plants and animals die, they decay to form humus. Micro-organisms in the soil aid in plant and animal decomposition to form humus. These organisms include bacteria, fungi, vegetation and animals. Their major influence is the effect on the chemical and physical environment of the soils.
Roots of plants penetrate into the rocks facilitating weathering of the parent rocks.
This process forms soils. Human activities like ploughing and harrowing break up the rocks into small particles to form soil.

(f) Nature of vegetation
Natural vegetation reflects the combined effects of relief and climate. The formation and development of soil is very much influenced by the growth of vegetation.
The decayed leaf material adds much needed humus to soil thereby increasing its fertility. The densely forested areas contain some of the best soils. There is a close relationship between the vegetation types and soil types.

Figure 7.7 below shows a summary of the factors responsible for soil formation.

                                Fig 7.7 Factors that influence soil formation.

Do this in groups of three.
Use the Internet, geography textbooks and journals.
1. Find out other factors that influence soil formation.
2. Analyse the factors by way of group discussion.
3. Make notes on your findings.
4. Present your findings in a class presentation for input from other class members.

Task 7.2
1. Define the following terms.
(a) Parent rock
(b) Climate
(c) Topography
(d) Living organisms
2. Describe how each one of the factors in Question 1 influences soil formation.

Soil properties and constituents

Constituents of soil

Work in groups of five.
Under the guidance of your teacher, collect the following apparatus.
• A shovel
• A clear bottle or jar
• Water
• Soil
• Funnel

Carry out the experiment below.

Follow the steps below

1. Dig up soil from different parts of your school compound.
2. Carry the soil samples in paper bags and take them to the class.
3. Pour the water into the bottle until it is half full.
4. Add the soil into the bottle.
5. Stir the mixture and leave it to settle for 30 minutes.
6. Observe the mixture and record your findings.

Answer the questions below.
(a) Draw a diagram showing the appearance of the mixture in the bottle.
(b) As you stirred the soil in water, did you observe any bubbles? Explain why you think the bubbles formed.

(c) Explain the distribution of materials as the soil settled in the water.
(d) Give the reason why the water in the bottle changed its colour.

Soil is made up of the following components 

(a) Inorganic particles
(b) Organic matter
(c) Water (moisture)
(d) Air (gases)

(a) Inorganic components
These are particles that are obtained from the parent rock through weathering. These particles vary in shape and size.
They include the following.
(i) Rock particles such as sand, gravel, silt and clay.
(ii) Metallic and non metallic minerals such as calcium, iron and potassium. Inorganic matter provides important plant nutrients, determine soil aeration, soil texture and drainage. It also gives support to the plants. Inorganic matter makes up 45% of the soil.

(b) Organic matter
Organic matter in soil consists of small animals, bacteria, fungi, plants, animal waste and plants. Organic matter makes up 45% of the soil.
The breakdown of organic matter leads to the formation of humus. Humus is black or dark-brown in colour. It provides the soil with important benefits. They include the following.

(i) It enhances the soil’s ability to hold and store water.

(ii) It provides essential minerals to the soil.
(iii) It improves the soil structure.
(iv) It reduces eluviation of soluble minerals from the top soil.
(v) It helps in soil aeration.

(c) Soil water
Soil water (or moisture) makes up 25% of the soil. The water occupies the pore spaces in the soil.
Significance of soil water.
(i) It dissolves various substances for example salts that are derived from plant or animal remains forming solutions.
(ii) It helps plants to absorb minerals from the soil.
(iii) It washes away highly soluble minerals from the upper to the lower layers (leaching).
(iv) It brings soluble minerals from the lower to the upper horizons of soil through capillarity.

(d) Soil air
Air or gases make up 25% of the soil. The air occupies the pores in the soil. Importance of air in the soil.
(i) It facilitates plant growth by supplying oxygen to the root hairs.
(ii) Air supports micro-organisms which are found in the soil.
(iii) Air helps in the oxidation process. This process is responsible for breaking down rocks to form         soils.

Task 7.3
1. Name the components of soil.
2. Give three ways through which humus is important to soil.
3. Explain the significance of moisture in the soil.

Do this in groups of three.
Use the Internet, geography textbooks and journals.
1. Find out more information on the components of soil.
2. Analyse the importance of each of the components by way of discussion.
3. Make notes on your findings.
4. Present your findings in a class presentation for input from other class members.

Properties of soil

Work in groups of three.
Use the Internet, geography textbooks and journals.
1. Find out the properties of soil.
2. List and discuss each property in your group.
3. Present your findings in class.

Properties of soil refer to the physical and chemical characteristics of soil. Different types of soils have different properties.
The physical properties of soil include texture, structure, colour, depth, density, porosity, permeability and consistence.

(a) Soil texture
Soil texture refers to the proportions of the various soil aggregates that make up the soil. These soil aggregates include gravel, sand, silt and clay. The proportion of each of the aggregates is used to determine the type of soil. The soil texture is often defined as the roughness or the smoothness of the soil particles.

There are three classes of soil particles. These are sand, silt and clay. The proportions of the aggregates of sand, silt and clay in a soil add up to 100%. Soil texture is important due to the following reasons.
(i) It determines the amount of soil water available within the soil. Silt and clay soils have a high water holding capacity. Sandy soils have a low water holding capacity.
(ii) It determines the ease with which plant roots penetrate the soil.

(iii) It determines the soil’s ability to retain humus from being washed away.
(iv) It determines the aeration of the soil.

Work in pairs.
1. Collect samples of soil from the school garden or around the school.
2. Make the soils wet and rub each of the soils between your fingers.
3. Tell your partner what you feel when you rub each soil type between your fingers.
4. Record your findings in your notebooks.
5. Present your findings in class.

(b) Soil structure
The term soil structure refers to the physical arrangement of the soil aggregates.

               Fig 7.8 Summary of soil structures.

It is the arrangement of primary soil particles into compound structures referred to as aggregates. The soil aggregates cluster together into structural units called peds.
Between the peds are spaces which are occupied by water and air. Therefore, different aggregates are found in different soil horizons. They are also in different shapes. In most cases, soil structure is
commonly defined in terms of the shapes of the soil aggregates.

Types of soil structures
(i) Granular - composed of rounded particles.
(ii) Platy - composed of thin sheets of particles arranged in a horizontal manner.
(iii) Prismatic - composed of vertical prism-like particles.
(iv) Columnar - similar to prismatic but the particles are rounded at the top.
(v) Blocky - irregular angular particles that are arranged to form a block.

Work in pairs.
1. Under the guidance of your teacher, visit your school garden.
2. Dig holes using a hoe in different sections of the school garden.
3. Observe the soil layers in the different sections that you have dug.
4. Record your findings in your notebook.
5. Present your findings in class.

(c) Soil colour
This property of soil is easily identified through seeing. Soils have different colours.

Soil colour is influenced by the parent rock, organic matter , moisture content and minerals. Soils have a variety of colours.
They include red, yellow, black, grey, white and brown. A soil that is black or dark brown has high organic matter content. Soils that are reddish brown are well drained whereas grey soils are infertile.

For example, in well aerated soils, the presence of oxidised iron is responsible for the colours seen in the soils. The colours are brown, yellow, and red. When the iron is removed, the soil becomes
grey.

Work in pairs.
1. Under the guidance of your teacher, visit your school garden.
2. Observe the soil colour in different parts of the garden.
3. Record your findings in your notebook.
4. Present the findings in class.

(d) Depth

Work in pairs.
1. Under the guidance of your teacher, visit your school garden.
2. Using a hoe, dig holes in various areas of the school garden.
3. Observe the depth of each soil by looking at the depth of the dark soil rich in organic matter.
4. Use a tape measure to measure each soil depth.

5. Record the measurements in your notebooks.
6. Discuss your findings in class.

Soil depth indicates how thick the soil cover is. Soils are either shallow or deep. Shallow soils have the parent rock material lying close to the surface level. The parent rock material is found much
deeper in deep soils.

(e) Soil density
The density of soil is the mass per unit volume of soil particles. It is expressed in grams per cubic centimetres (g/cc). Most soils have a particle density of about 2.6 g/cc. The presence of organic matter decreases the density of soil. The presence of iron compounds increases the density of soil.

(f) Soil porosity

Work in groups of five.
1. Under the guidance of your teacher, collect samples of soil from different sections of your school garden.
2. Put the small amounts of about 150 ml of the soil samples in a clear container.
3. Using a marked cylinder, measure 100 ml of water and pour in each soil sample.
4. Do this slowly until the water is  slightly above each soil sample.
5. Record the amount of water that has been poured into each soil sample.

 6. Calculate the porosity of each soil sample using the formula provided below and report your findings in class.

Soil porosity refers to the number of pore spaces in the soil. The pore spaces relate to the portion of the soil space occupied by air and water. This is determined by the arrangement of the soil particles. Soils vary in porosity. Soils with large pores, for example sand are porous while clay is
non-porous. Soil porosity is expressed as a percentage. This percentage is of the total volume of a sample of soil.

(g) Soil permeability

Work in pairs.
1. Under the guidance of your teacher, go to your school garden.
2. Dig some holes in different parts of the garden.
3. Pour water to fill the holes.
4. Observe the reaction.
5. Write down your observations for class discussion

Soil permeability refers to the ease with which water or gases pass through soil.
Permeability is influenced by the size and texture of particles. Sandy soils are more permeable than clay soil.

Soil consistency

Work in groups of five to test for stickiness of wet soil.
1. Collect samples of different types of soil from different parts of your school garden.
2. Make the soil wet. Soil can also be collected after heavy rains.
3. Press a small amount of each soil sample between the thumb and forefinger.
4. Open the fingers slowly and tell your group members whether the soil is sticky, slightly sticky or non-sticky.
5. Record your findings and present them in class.

Soil consistency refers to the ease with which individual particles of soil can be crushed. This is done by the fingers or a cultivation tool. Soil consistency depends on the soil moisture content. The degree of soil consistency can be determined using moist, wet or dry soil.
The consistency of wet soils is determined by its stickiness and plasticity. Plasticity is the extent to which the soil can be moulded.

(i) Moist soils

Work in groups of five.
1. Collect samples of different types of soil from different parts of your school compound.
2. Make the soil moist. Ensure that it does not get wet.

3. Press a small amount of each soil sample between your forefinger and the thumb. You can squeeze the soil in your palm as shown in Figure 7.9.

   Fig. 7.9 How to press soil using fingers or the palm

4. Rate each soil sample as being loose, friable or firm.
5. Record your findings in your notebook.
6. Present your findings in class.

Moist soil consistency can be measured as loose, friable or firm. Loose soils do not hold together in a mass when moist. Friable soils are crushed easily under gentle pressure between the thumb and forefinger when moist. Firm soils can be crushed under moderate pressure between the thumb
and forefinger. However, the resistance is noticeable.

(ii) Wet soils

Testing for plasticity of wet soil
1. Take a sample of each wet soil that you have collected.
2. Roll it between the palms of your hands to form a ribbon.
3. Rate the soil as being non-plastic, slightly plastic, plastic or very plastic.
4. Record your findings and present them in class.

The soil is non-sticky if there is no soil that sticks to your fingers. It is slightly sticky when the soil sticks to your fingers slightly then comes off. It is sticky when the soil sticks to your forefinger and thumb.

     Fig. 7.10 Images illustrating stickiness of soil.

Soil is non-plastic when no ribbon is formed when it is rolled. The soil is slightly plastic when a ribbon is formed. It can also be broken easily and the soil returned to its original state. The soil is plastic when a ribbon is formed. It can also be broken down and then rolled back to its original form.

(iii) Dry soils
The consistency of dry soils is loose when the soil can be broken with little pressure. It is hard when the soil is broken with a lot of force.

Work in groups of five.
1. Collect different soil samples and airdry the soil.
2. Try to break each soil sample by pressing it between the thumb and forefinger. You can also break it in your palm.
3. Rate the soil as loose, soft or hard.
4. Record your findings and present them in class.

The chemical properties of soil include:
• Soil pH
• Salinity
• Nutrient status

(i) Soil pH
Soil pH is an indicator of the acidity or alkalinity of a soil. It is also known as soil reaction.
Soil pH refers to the concentration of hydrogen ions in the soil. Soil pH affects the availability of nutrients in the soil. Soil acidity is increased when the carbon dioxide reacts with water to form carbonic acid.
Alkalinity of the soil increases when too much lime is applied to the soil. The pH scale is used to determine the level of alkalinity or acidity of soil. The soil pH scale ranges from 0 to 14.

Table 7.1 Soil pH colour chart.

Less than pH 5	pH 5-6	pH7	pH8-10	Over pH9
Soil is very acidic(red)	Slightly acidic(pink)	Neutral(green)	Slightly alkaline(blue)	Alkaline (purple

Acidity of the soil increases as you move from pH 7 to 0. Alkalinity of the soil increases from pH 7 to 14. Most crops grow well at a pH of 6.5.

Work in groups of five.
Do the experiment given below. 

Materials
• Different soil samples
• Distilled or rain water
• Container with a lid
• Litmus paper
Procedure
1. Collect different soil samples from different locations in your school compound.
2. Mix two parts of a given sample of soil with one part of rain water.
3. Put them in a container with a lid.
4. Allow the mixture to settle.
5. Dip a litmus paper into the mixture and observe the colour change.
6. Repeat this procedure using soil samples from different areas of your school compound.
7. Record your observations and compare the colour produced with those on the soil pH colour chart.
8 Present your findings in class.

(j) Salinity

Work in groups of five. Do the experiment given below.

Materials

• Different soil samples
• Distilled or rain water
• Pestle and mortar
• Evaporating basins/tins
• Source of heat
• Weighing equipment

Procedure
1. Collect soil samples from different parts of your school compound.
2. Put the soil sample out to dry. Ensure that they are completely dry.
3. Crush the soil using the pestle and mortar. You can also use a stone to crush the soil until there are no soil aggregates left.
4. Add water to the soil and shake the container thoroughly for about 2 minutes.
5. Let the mixture settle for a minute. The ratio of soil to water should be 1:5.
6. Filter the water and pour it out into the evaporating tin. Heat the mixture until all the water evaporates.
7. Weigh the residue that is left in the tin. This is to determine the amount of salt available in the soil sample.
8. Repeat this procedure using different soil samples.
9. Present your findings in class.

Soil salinity refers to amount of salt present in soil. Salts occurs naturally within soils and water. Salination can be caused by natural processes such as mineral weathering or by gradual withdrawal of an ocean. It can also come about through artificial processes such as irrigation.

Salts in the soil also come from fertilisers, compost and manure. Introduction of water into the soil can reduce the amount of salt in the soil through leaching.

Nutrient status

Mr. Muhire, a farmer in Gashora village planted beans in one of his fields during the last planting seasons. However, the yield was very poor. He was advised by the agricultural office in his sector to use artificial and organic manure in the next season. When the planting season came, hedid that and his harvest greatly improved.

1. Explain what was missing in the soil that led to poor yield.
2. Why was he advised to use artificial and organic manure on the soil?
3. Why do you think the yield was good in his second harvest?
4. Use the advice he was given to help farmers in your home area to improve their yields.

The nutrient status of soil determines the level of fertility of the soil. Soils that have high levels of nutrients are very fertile whereas soils with low levels of nutrients are infertile. The nutrients that are found in the soil are referred to as minerals. These nutrients are divided into macro and micro
nutrients.

                                Fig 7.11 Nutrients found in the soil.

Do this in groups of five.
Use the Internet, geography textbooks and journals.
1. Find out other physical and chemical properties of soil.
2. Note down your findings in your notebooks

3. Observe the soils in your school compound. Find out if they possess the properties that you are
researching about.
4. Present your findings in class by way of discussion.

Soil structure

Do this in pairs.
Use the Internet, geography textbooks and journals.
1. Find out the meaning of soil structure.
2. What is the importance of soil structure?
3. Discuss and present your findings in class.

Soil structure describes the arrangement of the solid parts of a soil. It also describes the pore spaces located between them. The structure of a soil is determined by how individual soil granules bind together. Soil structure depends on what the soil developed from. The quality of soil structure
declines under most forms of cultivation and irrigation.

Different types of soil structure

Do this under the guidance of your teacher.
1. Go outside your classroom.
2. Dig holes in different parts of your school compound.
3. Observe the structure of the soils that you have dug up.
4. Record and discuss your findings in a class discussion.

Soil structure is classified by type (shape), class (size) of peds (soil aggregates) and grade (strength of cohesion) of the aggregates.
Shape, size and strength of aggregates determine pore structure and how easily air,water and roots move through soil.

(a) Granular structure
This is the most common structure in surface soil layers. It is present in soils with adequate organic matter. Granular structures offer the most pore spaces.

          Fig 7.12 Granular (high permeability).

(b) Columnar structure
Columnar structure is often found in soils with excessive sodium. This is because of the dispersing effects of sodium, which destroys the soil structure. Sodium seals the soil to air and water movement. It has moderate permeability.

     Fig 7.13 Columnar structure.

(c) Platy structure
Platy structure has the least amount of pore spaces. It is common in compacted soils. It
has low permeability.

            Fig 7.14 Platy structure

Soil profile and soil catena

Do this in pairs.
Use the Internet, geography textbooks and journals.
1. Find out the meaning of soil profile.
2. Name the horizons into which soil profile is categorised.
3. Record your findings and present them in class by way of discussion.

Major horizons

Work in groups of three.
Under the guidance of your teacher, visit a site near your school where the ground has been excavated to at least about 3 metres in depth.
1. Observe and note down the main characteristics of each layer and soil.
2. Name the horizon or layer that is important for plant growth.
3. Give reason(s) why the layer is important
4. Discuss your finding in class.

A soil horizon refers to the layer of soil which lies parallel to the land surface. Each horizon differs from the others in terms of colour, structure and mineral composition.
The horizons are identified by capital letters O, A, B, C and D.

1. Horizon O – This layer is also known as the superficial layer. It is the thin layer of dry, decaying and partially decomposed organic matter. It mainly consists of decomposing leaves and roots of plants.

2. Horizon A – This horizon is also known as the topsoil. This layer of soil is found beneath the superficial layer. It is a dark coloured horizon that is rich in humus. The layer has good aeration
and contains active living organisms.

3. Horizon B – This horizon is also referred to as the subsoil. It lies immediately below Horizon A. The soil particles are closely packed together. The soil in this layer is poorly aerated. It also has
fewer living organisms and is rich in clay deposits.

4. Horizon C – This is the zone of deposition. It forms the parent rock. It is also referred to as sub-stratum. It is the deepest and the thickest of all the layers.

5. Horizon D – This horizon resembles the C-horizon. It is made of the hard rock which is resistant to weathering.

Note
Not all of the five horizons may be present in every soil. This depends on the conditions under which the soil was formed.

Soil profile
This is the vertical arrangement of the soil in layers from the surface to the bedrock. The layers of soil are called horizons. Mature soil has four horizons. They are horizons A, B, C and D. Horizon A is composed of the top soil and horizon B the sub-soil.

Horizon C is composed of partially weathered rock and Horizon D the parent rock. The horizons have distinct structures, colours, textures, porosity and minerals.

Do this in groups of three.
1. Go to your school garden.
3. Dig small holes and observe the soil layers.
3. Record the different characteristics of the soil layers that you are able to see. Describe aspects such as texture, colour and particle sizes of the soil layers.
4. Discuss your observations in class under the guidance of your teacher.

Soil catena

Do this in pairs.
Use the Internet, geography textbooks and journals.
1. Find out the meaning of soil catena.
2. Name the factors responsible for soil catena.
3. Record your findings and present them in class for discussion.

Your teacher will take you to a sloppy area in the neighbourhood of your school.
1. Study the soils on the different heights of the slopes.
2. Name some of the factors that you think are responsible for the differences in soils.

3. Record your findings in your notebook.
4. Present your findings in class for discussion.

Soil catena refers to the sequence of different soil profiles that occur down a slope.
The soil down a hill slope is rarely uniform. Soil eroded from the top of the slope tends to accumulate near the bottom. Runoff water tends to infiltrate more in the flatter areas at the foot of the slope. This water encourages more plant growth there than on the steep part of the slope. Consequently, the factors forming the soil differ from top to bottom. Different soils thus develop. The steep slopes have thin soils while the valley bottoms have deep soils. Soil catena is therefore influenced by relief, drainage, leaching and transportation of soils during erosion.

                                             Fig 7.16 Soil catena.

Task 7.3
Use well-labelled diagrams to illustrate and explain:
(a) soil profile
(b) soil catena.

Types of soils

Do this in pairs.
1. Go outside your school and collect soils from different parts of the compound.
2. Observe the soil samples focusing on their appearance and characteristics.
3. Classify the soils into different types based on the knowledge that you have.
4. Present your findings in class.

There are four types of soils. Three are basic while the fourth one is a combination of the
three. They are:

           • Sand                • Clay
           • Silt                   • Loam soils

Sand is composed of small particles of weathered rock. Sand is fairly coarse and loose so water is able to drain through it easily. While this is good for drainage, it is not good for growing plants. This is because  sandy soil will not hold water or nutrients. Silt can be described as fine sand. It however
holds water better than sand.
Clay is very fine-grained soil. Its particles are even smaller than those of silt. This means that there is little space between the grains for air or water to circulate. Therefore, clay does not drain well.

Loam soil is a combination of sand, silt and clay. Loam will vary depending on how much of each component is present. It holds moisture and also allows for good drainage.

Do this in pairs.
Using the soil samples that you had collected;
1. Classify the soils according to their characteristics.
2. Present your findings in class by way of discussion

Effects of soils on human activities

Soils are important for the existence of plants, animals and humans. Most human activities are supported by soils. Some of the human activities that depend on soils include:

• Agriculture and food production
• Pottery
• Building and construction
• Mining
• Culture

Importance of soils

Work in pairs.
1. Observe the environment around your home or school.
2. Note the different uses of soil.
3. Discuss the uses of each type of soil that you identified in the activity above.

4. Record your findings in your notebook.
5. Present your findings for a class discussion.

Below are some of the ways in which soils are important:

1. Soil has vital nutrients which support the growth of plants.
2. Soil supports animal biodiversity, above and below ground.
3. Soil is important in providing an adequate water supply and maintaining quality vegetation.
4. The water absorption property of soil helps in reducing pollution from chemicals in pesticides.
5. Soil holds the key to the earth’s history. It contains and preserves artifacts of the planet’s past. For example dinosaur fossils were discovered in the earth.
6. Clay soils are commonly used in pottery, ceramics, bricks and other clay works.
7. Ordinary soil when mixed with water forms earth blocks that are used in building houses.
8. Murram soils are used in the construction of roads.

9. Some soils contain valuable minerals which are mined and sold to earn income.
10. Some soils contain minerals that are used by animals as salt lick.
11. Some soils are used to make medicine and beauty products. For example,
soils rich in clay can be used to make facial masks. Some other soils are used to make skin ointments.

Work in groups of four.
1. Observe your surroundings at home and in school.
2. Identify some of the human activities that take place around the area.
3. Identify the specific soil types that are used for the different activities.
4. Present your findings in class.

Relationship between soil types and human activities

Work in groups of three. Use the internet, geography textbooks and photographs;

1. Relate specific soil types to different human activities.
2. Discuss and present your findings in class.

The type of soil found in a region determines the human activities in that area. For example.
where there is a lot of sandy soils, there is extraction of the soil for building and construction.

• Clay soil supports.
– crop production of specific crops
– pottery and ceramics
– building and construction activities
– medicinal uses.
• Loam soil supports agricultural activities.
• Alluvial soil supports agricultural activities. It is also used in the manufacture of fertilisers.

Work in pairs.
Using the Internet, geography textbooks, journals and personal experience, answer the following questions.
1. How is soil related to agriculture and mining as human activities?
2. Which soil types support the activities?
3. Discuss and record your findings.
4. Present your findings in class.

Work in groups.
After finding out how soil relates to various human activities:
1. Suggest ways in which soil can be conserved.
2. Give reasons why you think it is important to conserve soil.
3. Why is agriculture an important activity?
4. Present your findings in a class discussion.

Did you know?
• Soil is a living system
• Soil hosts a quarter of the total planet’s biodiversity.
• There are more micro-organisms in a handful of soil than there are people on earth.
• Soil is a non-renewable resource.
• Soils help to combat and adapt to climate change.

Define soil.
1. Identify three soil formation processes.
2. Discuss the factors that influence soil formation.
3. (a) List the components of soil.
(b) Briefly describe any three properties of soil.
4. (a) Define soil profile.
(b) Draw a well-labelled diagram showing detailed sub-divisions of the horizons in a soil profile.
(c) Briefly describe the characteristics of each horizon.
5. (a) What is soil catena?
(b) State the conditions which influence soil catena.
(c) State the type and characteristics of soils on the following parts of a slope.
(i) upslope (ii) steep slope
(iii) lower slope.
6. Explain how the soils shown in the table below are used for different human activities.