Soil is the thin, outer layer of the earth which supports the growth of plants. It is also referred to as the outer layer or the upper most layer of the earth’s crust on which plants grow and from where they derive their nutrients. Soil is defined as the topmost layer of the earth crust on which plants grow.

Soil is made up of mineral inorganic particles (sand, soil and clay) and organic matter (humus) derive form decomposed remains of plants and animals. It is also made up of air, water and living organisms (earth worms, bacteria, fungi).

Soil as we know being the layer of the earth is made up of a mixture of minerals, air and water (formed from the underlying rocks and plants and animal material by various physical, chemical and biological processes.


The soil is made up of five components:

  1. Mineral matter/inorganic matter
  2. Organic matter
  3. Air
  4. Water
  5. Living organisms
  6. ORGANIC MATTER: this is made up of remains of decayed plant and animals that form humus soil and provides essential nutrients for the plants.
  7. INORGANIC MATTER: these mineral matter represents small rock fragments of the soil. The inorganic matter from the bulk of about 45% of the total volume of the soil. The mineral matter consists of gravels, stones, sand, salt and clay.


  1. It forms the solid part of the soil which brings about the firmness of plants
  2. It acts or stands as the habitat/homes of animals
  • It is the source of plant nutrients
  1. It moderates the soil temperature
  2. It holds water for both plant and animal activities.


  1. Organic matter are rich soil nutrient
  2. It is an habit for micro-organism
  • It prevents leading in soil
  1. It controls soil erosion and evaporation
  2. It regulates soil temperature
  3. It improves the structure of the soil
  • It encourages water holding capacity of the soil
  1. SOIL WATER: this is the water in the soil which is obtained either from rain or irrigation activities. This water represents, 25% of the total volume of water in the soil and usually found in the soil within the pore spaces when there is too much water in the soil. It makes the soil to be water logged.


  1. It serves as agent of weathering
  2. It helps in dissolving plant nutrients
  1. The presence of water is soil encourages tillage of the soil
  2. Water in the soil is needed for germination of seed
  3. It protects plants from injurious high temperature
  4. SOIL AIR: it can be referred to as the gases present in the soil pore spaces found between the soils particles.


  1. Soil air is required carbon and nitrogen cycles
  2. Soil organisms required oxygen or respiration
  • Soil air is needed for germination of seed
  1. It also encourages weathering processes in the rock
  2. LIVING ORGANISMS: these can be referred to as micro-organisms, plants and animals that assist in the formation of soil. They range from microscopic organisms to bigger organisms. Plants and animals which inhabit the soil either through borrowing or through the root of plants gaining entrance into rocks assist greatly in breaking down the rocks into pieces which lead to the formation of soil.


  1. They help to decompose organic matter
  2. The microorganisms provide acidic materials which help to break down rocks
  • Living organisms improve the structure of the soil
  1. Microorganisms like bacteria help to fix nutrient into the soil
  2. These living organisms assist percolation of water
  3. Pests and parasite causes diseases of the crops and these are part of living organisms that aid the formation of soil.

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