Soil - Class 7 Science Revision Notes

• Soil Fertility.
• Types of Fertilizers
  • Straight Fertilizer
  • Compound Fertilizer
• Advantages of using Manures and fertilizers.

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