6th June 2020



DATE: 2nd June 2020


SUBJECT: Agricultural Science.

TOPIC: Composition and properties of soil.

REFERENCES: Comprehensive Agricultural science (Lantern BK 2) pages 6 & 7

Learning Objectives: At the end of this lesson, the pupils should be able to:

  1. Define soil and state the functions.
  2. Explain soil texture and soil structure.
  3. List the soil types and explain their properties.
  4. State the components of the soil.
  5. List the types of soil structure.
  6. Explain the causes and remedy of soil acidity.

Brief Explanation: Agriculture is practised on land which is a resource of man. The land is used for cultivation of crops and rearing of animals and for other things like building of houses and construction of roads etc.

Soil, is that portion of land that supports the growth of crops and provides plants nutrients.


Soil can be defined as the medium on which plants grow or the uppermost layer of the earth’s crust on which plants grow.

Functions of soil

  1. Provision of water, air and nutrients for the plants.
  2. Provision of environment for the elaboration of root system and anchorage.

Types of soil are: sandy soil, clayey soil, loamy soil and silt

  1. Sandy soil: The particles are coarse, gritty to touch, large enough to be seen. They are loose and have large air spaces. They are well drained and nutrients leach out of it easily.
  2. Clayey soil: Clay particles are fine and very tiny. They are sticky when moistened with water and could be moulded into shapes. Clay soil holds water and excludes air. It is poorly drained and water logged.
  1. Loamy soil: Loamy soil has roughly equal propositions of sand, silt and clay. It is gumy to touch, has good air spaces and drainage. It is rich in nutrients.
  2. Silt: They are smooth, powdery and large surface area. They are slightly sticky.

Composition of soil

The physical composition of the soil can be derived from four sources.

  1. Lithosphere (rocks), (inorganic or mineral matter).
  2. Atmosphere (air).
  3. Hydrosphere (water).
  4. Biosphere (living organisms).

Physical properties of soil

  1. Soil texture: This is the relative proportion of sand, silt and clay in a soil sample.
  2. Soil structure: This is the arrangement of soil particles into various aggregate sizes.
  3. Soil temperature: Soil temperature is simply the measurement of the warmth in the soil.
  4. Soil PH: This is the measure of the degree of acidity and alkalinity of a soil.

Causes of soil acidity – The causes of soil acidity are listed below:

  1. Crop removal.
  2. Prolonged use of certain inorganic fertilizers.
  3. Leaching as a result of two much rainfalls.
  4. Water logging in a soil.

Remedy or control of soil acidity

Soil acidity is usually corrected by liming. Liming materials includes:

(i) Calcium Carbonate

(ii) Calcium Hydroxide

(iii) Wood ash

(iv) Magnesium oxide

Types of soil structure

  1. Platy structure (plate-like-structure).
  2. Blocky structure (block-like).
  3. Prismatic
  4. Single grained structure.


  1. Define soil.
  2. State two functions of soil.
  3. Copy and complete this table

Soil type                     properties

1. Sandy soil              i.


2. clayey soil              i


3. loamy soil              i