Wednesday, 15 September 2021 11:43

Soil - Class 7 Science Revision Notes

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Soil Fertility.

This is the ability of the soil to produce high yields for a long time.

Fertilizer: These are organic or inorganic substances that are added to soil that have lost their fertility.

They are grouped into natural fertilizers and artificial fertilizers.

Green Manure:They are made from green plants,these plants should be:

  • Leafy.
  • Able to grow fast.
  • Able to decay quickly
  • Contain a high amount of nitrogen.

Farmyard manure: They are made from animals wastes such as urine,dung, poultry droppings and animal bedding.
Compost manure: This is a mixture of decayed plants,animal waste,leaves and vegetable peelings

How to encourage fast decomposition of compost heap:

  • Keeping the heap moist.
  • Adding a layer of decayed materials rich in bacteria.
  • Adding a layer of topsoil to introduce decomposers.
  • Covering the heap duriing the wet season.
  • Turning the heap occasionally,at leastafter 3-4weeks to allow circulation of air.
    NB:Farmyard manure introduces bacteria.

Mulches: These are plant materials such as plant leaves and dry grass which are used as soil cover.



Types of Fertilizers (Inorganic manure)

They are classified into two:

  • Straight fertilizer
  • Compound fertilizer.

Straight Fertilizers:

They contain only one macronutrient.

Examples of nitrogenous fertilizer.

  • Calcium Ammonium Nitrate.
  • Ammonium Sulphate Nitrate.
  • Urea

Examples of Phosphatic fertilizers.

  • Single super phosphate.
  • Double super phosphate

Examples of potassic fertilizers.

  • Muriate of potash.
  • Sulphate of potash.

Compound Fertilizers:

They provide two or more of the macronutrients to a plant.

Examples of compound fertilizers.

  • Diammonium Phosphate(DAP)
  • Nitrogen, Phosphorus,Potassium(NPK)


Advantages of using Manures and fertilizers.

  • Results in high growth rate of crops.
  • Leads to high crop yields which are of high quality.
  • Leads to growth of crops that are deep green in colour.
  • Encourage the vegetative growth.
  • Leads to quick ripening of fruits.
  • Provides the necessary nutrients for growth and development of crops.
  • Increase the size of seeds,grain and fruits.
  • Strengths the plantstems that support the plant.
  • Improves soil fertility.


Disadvantages of Using Manures and Fertilizers.

  • Some are expensive to prepare eg Green manure.
  • Some pollutes the environment if not use by plants immediately eg Inorganic manure.
  • Some fertilizers are corrosive.
  • Some manures and fertilizers scorch the plant if applied in great quantities.

Activity 2: State other advantages and disadvantages of using manures.and fertilizers


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