Introduction.

Soil fertility refers to the stock of nutrients in a soil. A soil with plenty of nutrients required for proper plant growth is said to be fertile while that lacking some of the nutrients required for normal plant growth is said to be infertile.

Under certain conditions the soil can lose its fertility and therefore its ability to sustain plant growth. Some of these include poor farming methods like monocropping, overcultivation and also loss of top soil in the process of soil erosion.

Hence the need for soil conservation to ensure sustenance of plant and animal life depends on soil. In this chapter you will learn the features of a fertile soil, understand the causes of reduced soil fertility and describe methods of soil conservation.

You will be able to understand the importance of micro organisms in the nitrogen and other cycles that keep soil fertile. You will be also be able to outline the processes involved in the nitrogen cycle.

2.1Features of Fertile Soil

From Chapter one, you discussed the types of soil and some features of a fertile soil. Soil is considered fertile if it is productive, that is, if it can support healthy growth of desirable plants, such as garden plants, landscape plants or crops.

Activity 2.1 Identifying the features of fertile soil

Key question

Identifying the features of fertile soil What are the features of fertile soil?

What you need

Notebooks and pens

Biology textbook/computer with internet

What to do

1. In a pair, using textbooks/computer connected to internet, research about features of fertile soil.
2. .Present your findings to the rest of the class.
3. Compare your findings with the findings of other students.

Soil Erosion

Soil erosion is the detachment and movement of soil material. The process may be natural or accelerated by human activity.

Depending on the local landscape and weather conditions, erosion may be very slow or very rapid. Soil erosion can be damaging because top soil, which is rich in organic matter, high fertility and soil life, is relocated elsewhere “on-site” where it builds up over the time or is carried “off-site” where it fills in drainage channels. See Figure 2.1.

Soil erosion may be a slow process that continues relatively unnoticed, or it may occur at an alarming rate causing serious loss of top soil.

The loss of soil from farmland may be reflected in reduced crop production potential, lower surface water quality, and damaged drainage networks.

In this chapter, you will investigate the process of soil erosion, the factors that lead to soil erosion, and its impact in the community.

Process of soil erosion

Figure 2.1 Types of soil erosion

Figure 2.2 Soil erosion

Activity 2.2 Demonstrating thye process of soil erosion

Key questIon

What is the process of soil erosion?

What you need

A pile of dirt/ dry soil

Water

Aluminum baking pans /big tray

Empty 2 litre bottles with caps

Large blocks

A chart with a picture of land showing process of soil erosion

Textbooks/computer with internet connection

Notebooks and pens

What to do

1. Working in groups of 3 to 4, study Figure 2.2 showing the process of soil erosion, explain the process of soil erosion.
2. Collect the provided aluminum baking pan/ big tray and fill it with soil.
3. Put large blocks or other means to raise one end of the pan so that it has a slope.
4. Use the bottles with perforated caps to pour 2 litres of water onto the sloped surface mimicking rain, and observe the results.

5. Sketch the soil conditions before, during and after the activity in your notebook.

6. What events in nature might cause soil to be moved from one place to another?

7. Using textbook/computer with internet connection, research more about soil erosion process.

8. Present your findings to the whole class.

2.3 Factors leading to soil erosion

Activity 2.3 Identifying causes of soil erosion and the impact it has on communities

Key question: What are the causes of soil erosion and how does it impact on communities?

What you need

Pictures of the factors that lead to soil erosion.

Textbook/computer with internet connection

Notebooks/pen

What to do

1 In a small group, study the pictures provided and group them under natural and human-induced factors.

2 Research on other factors that cause soil erosion.

3 Discuss how each factor leads to soil erosion.

4 Using textbooks/computer with internet connection, research on how soil erosion creates an impact in the community.

5 Present what you have discussed to the rest of the class.

There are many underlying factors responsible for soil erosion, some induced by nature and others by human beings. The main factors that lead to soil erosion include the destruction of natural protective cover such as:

indiscriminate

cutting of trees,

overgrazing of the vegetative cover and

forest fires.

2.4 Types of soil erosion

Key question: Identifying types of soil erosion

What are the types of soil erosion?

What you need

Pictures of different types of water and wind soil erosion

Textbook/computer with internet connection

Notebooks/pens

What to do

1 Working in pairs, use textbooks/internet and research how each type of soil erosion is formed.

2 Match the types of soil erosion (sheet, rill, gully and wind erosion) with pictures shown in Figure 2.4.

3 What impact does each type of soil erosion create in your community?

4 Present your work to the rest of the class.

n this chapter, you will understand the types of soil erosion and the impact they create in the community.

2.5 Causes of reduced soil fertility

Causes of reduced soil fertility In this study you will understand the causes of loss essential plant nutrients.

Activity 2.5 Identifying causes of reduced soil fertility

Key question

What are the causes of reduced soil fertility?

What you need •

Pictures/photography of the actions /features that cause reduced soil fertility

Textbooks/computer with internet connection

Notebooks/pens

Figure 2.5 Factors that cause reduced fertility

What to do

1. In a small group study the picture provided and discuss how each can lead to reduced fertility f soil
2. Research and discuss other causes of reduced soil fertility.
3. Present what you have discussed to the rest of the class.

2.6 Methods of soil conservation

Soil conservation is the protection of soil from erosion and other types of deterioration, so as to maintain soil fertility and productivity.

Soil loss and loss of fertility can be traced back to a number of causes of soil erosion as discussed earlier. Soil conservation protects the soil from being washed away and loss of minerals from the soils.

In activity 2.6, you will understand the methods of preventing loss of soil fertility which will enable you to develop concern for the environment and promote its conservation.

Activity 2.6 Identifying the methods used to prevent loss of soil fertility

Key question

What are the methods of soil conservation?

What you need:

Pictures/photography of the methods of soil conservation

Text books/computer with internet connection

Notebooks/pens

Figure 2.6 Methods of soil conservation

What to do

1 In a small group, study the pictures/photographs provided and discuss which methods are practiced by farmers in hilly areas and those in semi-arid areas.

2 Using textbook or computer with internet connection, research on how each method maintains soil fertility.

3 Record your findings.

4 Present what you have discussed to the rest of the class.

Key question

How is soil fertility maintained in Kigezi?

What you need:

A picture of hill with one of methods of soil conservation used to control soil erosion

Text book/computer with internet connection

A projector

Notebooks/pens

Figure 2.7 : One of the methods of soil conservation in Kigezi area

What to do

1. Working in pairs , study a picture on the chart or the one projected on the screen from a Kigezi area and identify the method of soil conservation indicated in this picture.

2. Using textbook / Google , research and write a report on the other different methods of soil conservation that are commonly used in such hilly areas.

3. Present your work to the rest of the class.

2.7 Soil organisms that carry out decomposition

When living organisms die, they decay and release nutrients to the soil to be used again by plants. Organisms that break down organic materials such as remains of dead organisms are called decomposers.

Decomposers include bacteria and fungi. These organisms play a critical role in maintaining soil health and fertility.

The knowledge gained in this study will help you to know the importance of decomposers and how dead organisms can be properly disposed.

Activity 2.8 Finding out the importance of decomposers

key question

Why are decomposers important?

What you need

Pictures of decaying piece of wood and animal

Textbook,

computer with internet connection

Notebooks and pens

what to do

1 In a pair, study the pictures of decaying wood and animal as shown above and explain why they are breaking apart and diminishing in size.

2 Using a textbook/Google, research and write a report on the importance of soil organisms called decomposers.

3 Share your report with the rest of the class.

2.8 Nitrogen cycle

Nitrogen is one of the primary nutrients critical for the survival of all living organisms. Although nitrogen is very abundant in the atmosphere, it is largely inaccessible in gaseous form to most organisms.

Through the cycle, atmospheric nitrogen is converted to a form which plants can incorporate into new proteins. In this chapter you will explore how nitrogen moves among animals, plants, bacteria, the atmosphere and soil, and you will learn how the cycle affects all living things.

Let’s look at some activities to help you understand the nitrogen cycle and its importance.

Activity 2.9 Role playing to demonstrate the nitrogen cycle

Key question

How is the nitrogen cycle made complete?

What you need

Diagram of nitrogen cycle

Sets of cards with vocabulary words associated with nitrogen cycle written on them

Notebooks/pens

Figure 2.9 Nitrogen cycle

What to do

1 Working in a group of 3 to 4 people, study the provided diagram of the nitrogen cycle and discuss the processes and important terms associated with the cycle.

2 You are to act a simple play in which members take on roles of components of the cycle.

3 Let a representative from each group pick a task card from the teacher and discuss how you are going to carry out the activity.

The actors in the nitrogen cycle will be represented by the following groups:

Group 1 – Decomposers

Group 2 – Nitrates

Group 3 – Nitrogen fixing bacteria

Group 4 – Denitrifying bacteria

Group 5 – Green plants

Group 6 – Animals

Group 7 – Nitrogen gas.

5 The processes in the nitrogen cycle will be represented by the following:

A nitrogen fixation B denitrification

C decomposition D ammonification

6 In your role-play, figure out where you are coming from, where you are going and how you will act out your role.

7 Why is the nitrogen cycle important to all living things?

8 What are the main processes that are involved in the nitrogen cycle? What happens during each process?

9 Present your findings to the rest of the class and compare them with other groups.

All living things require proteins because they are bodybuilding foods and form the enzymes that catalyse reactions in their bodies. One element required for the formation c protein is nitrogen.

Plants have the ability to make their own proteins provided they get nitrogen. However most plants cannot use free nitrogen from the air even though it is the most abundant gas.

They use nitrates instead. Animals obtain their nitrogen in form of proteins from plants and other animals they feed on. When plants and animals die their bodies are decomposed by bacteria and fungi in the soil to form humus and break it down further to release nitrates.

The nitrates are then taken up by plants to make proteins. Therefore as a remarkable fact of nature, the materials in soil and of living organisms are never used up but rather are constantly used and reused again by different living things.

This passing round of nitrogen from dead animal and plants to the soil and back again to plants and animals is called the nitrogen cycle.

2.9 Micro-organisms in root nodules of legumes

There are microbes in the nodules on the roots of leguminous plants. These microbes usually depend on the plant to grow – because they have a symbiotic relationship with the plant.

This is a relationship in which both the micro organisms and plants benefit. The main microbes that will grow here are bacteria called rhizobium.

These are able to fix nitrogen from the air and make it available to plants. A group of plants known as leguminous plants play a special role in the nitrogen cycle in addition to the role played by a plants. Peas, beans and groundnuts belong to this group Certain bacteria live in the roots of leguminous plants

These bacteria have the ability to make amino acids from the nitrogen in the air. Hence we call them nitrogen fixing bacteria.

These amino acids are used to make proteins by both the leguminous plant and the bacteria. Thus in addition to nitrates from the soil.

The nitrogen fixing bacteria provide a further supply of useful nitrogen. Soil micro organisms include bacteria and fungi. They are important in the process of decomposing of organic matter and in nitrogen cycle for nitrification, denitrification and nitrogen fixation.

In the next Activity 2.10 you are going to investigate the presence of micro organisms in soil and then find information about microorganisms in root nodules of legumes.

Figure 2.10 Illustration of root nodules

Activity 2.10 Investigating the presence of soil micro-organisms

Key question

How do you investigate the presence of soil micro-organisms?

What you need

Two test tubes Soil samples

Two muslin bags

Two cork

Cotton thread

Lime water

Crucible

what you need

1 Work in pairs, get provided soil samples and heat strongly one portion on the crucible and leave the other portion unheated.

2 Cool the heated portion. Now pack both the heated and unheated soil samples in separate muslin bags.

3 Pour an equal amount of lime water in the two test tubes A and B. Suspend the muslin bag containing fresh moist soil in one test tube A, using a piece of thread.

4 Suspend the other muslin bag containing heated soil sample in the second test tube B.

5 Leave the experiment for some three days and observe any changes in the colour of lime water.

6 Which lime water changes colour? Explain why.

7 Which lime water didn’t change the colour? Explain why.

8 Using a textbook/Google, research and write a report on the importance of micro-organisms in the soil including those that live in the roots of leguminous plants.

9 Present your work to the rest of the class.

GROUP PROJECT

2.10 Formation of compost in a compost bin

Compost is organic matter that has been decomposed in a process called composting. It is broken by microorganisms called decomposers. Composting biodegrades organic waste , that is , food waste , manure , leaves , grass trimmings , paper , wood , feathers , crop residue etc. , and turns it into a valuable organic fertilizer . The resulting nutrients are returned to the soil to support plant growth.

The effectiveness of the composting process is dependent upon the environmental conditions present within the composting system, that is, oxygen, temperature, moisture, material disturbance, organic matter and the size and activity of microbial populations.

 Learning about and taking part in compost production at school, will enable you to acquire skills such as team building, communication and organization that are needed to make good compost in schools and also in the community.

Activity 2.11 making compost

 Key question

 How do you make compost?

What you need.

• Manufactured compost bin
• Green materials (grass trimming, fruit and vegetable peelings, leaves, manure from cattle and poultry)
• Brown materials ( dried leaves , dried grass trimming , hedge cuttings , shredded paper , newspaper , empty toilet and kitchen rolls , cereal boxes , egg boxes , )
• Garden hoe
• Shovel / spade
• Compost thermometer
• Biology textbook
• Computer connected to the internet

What to do

1. Using the materials provided and by research, designs an investigation into the formation of compost in a compost bin.
2. Locate an area in the school compound where you are to carry out the investigation.
3. From your observation, which materials decompose quickly? Explain your answer.
4. Which materials take long to decompose? Explain your answer. Keep visiting the compost bin on a weekly basis for 2 to 3 months until the compost is formed.
5. Why is it important to mix brown materials with green materials?
6. Why some materials are inappropriate to compost?

Activity 2.12 investigating how temperature affects rate of formation of compost

Key question

 How does temperature affect rate of formation of compost?

 What you need

• Water
• Fresh soil
• Fridge
• Jars
• Trash items as used in Activity 2.11

What to do

1. Working in small groups, repeat the experiment in Activity 2.11 by using fresh soil only. Use two jars.
2. Kept one jar in the fridge and leave one at room temperature.
3. Is there any difference between the trash items in the jars at room temperature and jar in the fridge? Give explanation for your answer.
4. Summaries what happened over time to each piece of trash item in the two jars.
5. Discuss the importance of temperature in the process of decomposition.
6. What do you think will happen to the rate of decomposition if the jar at room temperature was put in an environment that is slightly warmer than room temperature?
7. Share your findings with rest of the class.

 Chapter summary

In this chapter, you have learnt that:

• Fertile soil has features like: good soil drainage, large population of microorganism, sufficient nutrients, adequate minerals, and enough organic matter, sufficient soil depth, and good water retention.
• Soil erosion is a form of soil degradation where the upper layer of the soil is displaced.
• Types of soil erosion like; sheet soil erosion, rill, wind, and gully soil erosion.
• The factors leading to soil erosion include; monocroping, overgrazing, faulty cultivation, deforestation, and steep slopes.
• The causes of reduced soil fertility; leaching of soil, monocropping, soil erosion, over cultivation.
• The methods of soil conservation include; terracing, contours, crop rotation, and afforestation.
• Atmospheric nitrogen is converted to a form which plants can incorporate into new proteins through nitrogen cycle.
• Processes involved in nitrogen cycle include nitrogen fixing, decomposition, ammonification, nitrification, and denitrification.
• Decomposers are living organisms that break down organic materials such as remains of dead organisms. Decomposers include bacteria and fungi. These organisms play a critical role in maintaining soil health and fertility.
• Making of compost.