Soil Fertility I : Organic Manures - Form 1 Agriculture Note

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Organic Manures

- Manures are derived from plants and animal remains.

- They supply organic matter to the soil which after decomposition releases plant nutrients.

- The end product of this decomposition is known as humus.

- It influences soil chemical properties and soil temperature.

- Manures supply a wide range of essential plant nutrients. 

Importance of Organic Matter in the Soil

  • Increases the soil water holding capacity of the soil.
  • Improves soil fertility by releasing a wide range of nutrients into the soil.
  • Provides food and shelter for soil micro-organisms.
  • Improves the soil structure.
  • Buffers soil pH/moderates soil pH.
  • Reduces the toxicity of plant poisons in the soil.
  • Moderates soil temperature by its dark colour.

Limitations in the Use of Manure

  • They are bulky - low nutritive value per unit volume.
  • Laborious in application and transport.
  • They spread diseases, pests and weeds.
  • Loss of nutrients if poorly stored.
  • If not fully decomposed crops may not benefit from them.

Types of Organic Manures

  • Green manure.
  • Farm yard manure.
  • Compost manure

Green Manure

- Made from green plants which are grown for the purpose of incorporating into the soil.

Characteristics of plants used for preparation for green manure:

  • Have fast growth rates.
  • Have high nitrogen content.
  • Capable of rotting quickly.
  • Capable of growing in poor conditions.

Preparation of Green Manure

  • Plant the green manure crop in the field.
  • Allow the crop to grow up to flowering stage.
  • Incorporate it into the soil through ploughing.
  • Allow the crop to decompose for two weeks.
  • Prepare the field for planting the major crop.

Reasons why Green Manure is not Commonly Used/Limitations:

  • Most of the plants used as green manure are food crops.
  • Green manure crops may use most of the soil moisture.
  • Most of the nutrients are used up by soil micro-organisms in the process of decomposing the green manure.
  • Planting of the major crop is delayed.

Farm Yard Manure (FYM)

- Is a mixture of animal waste and crop residues used as beddings in animal houses.

Factors that Determine the Quality of FYM

  • The types of the animals used.
  • Types of food eaten
  • Types of litter used.
  • Method of storage.
  • Age of farmyard manure.
  • Age of the animals used.

Preparation of FYM

  • Provide beddings in the houses of farm animals.
  • Animals deposit their droppings and urine on the beddings.
  • Animals mix them through trampling.
  • The beddings together with dung are removed and heaped under shed to decompose.
  • After sometime, the materials decompose and FYM is formed.
  • It can then be used in the farm

Compost Manure

- Is manure prepared from heaped (composted) organic materials.

Factors To Consider In Selecting Site For Making Compost Manure:

  • A well drained place.
  • Direction of the prevailing wind.
  • Size of the farm.
  • Accessibility.

Preparation of Compost Manure

Two methods:

  • Four heaps method
  • Indore Method (Pit Method)
Indore Method (Pit Method)

Procedure ;

  • Select a sheltered place with a shade and near the field.
  • Dig a pit with the dimension 1.2m x 1.2m x 1.2m.
  • Place the materials in the following order:
    • Hedge cuttings or maize stalks to a depth of 30cm as a foundation
    • A layer of grass, green weeds or leaves and kitchen wastes to 30cm.
    • A well rotten manure/poultry droppings.
    • Wood ash and phosphatic fertilizers.
    • A layer of topsoil to introduce micro¬organism for the decomposition of organic remains.
    • Note: Some water should be sprinkled to the materials to initiate the decomposition process and regulate temperatures.
Four heaps method:


  • Clear the site.
  • Level the site
  • Four posts 2m high are fixed 1.2m apart from four corners of the heap.
  • Fix wood planks on the sides.
  • Materials are placed in two heaps as in the pit method,
  • The two heaps make up heap 1.
  • After 3-4 weeks, the decomposed material from heap 1 is transferred to heap II.
  • After another 3 - 4 weeks the material is transferred to heap III.
  • After 3-4 weeks it is ready for use in the farm.

Indicators of well decomposed manure

  • Absence of bad odour.
  • Materials are lighter.
  • Manure is brown in colour.

Advantages of Compost Manure

  • One does not have to own livestock in order to prepare it.
  • A lot of manure can be produced within a short time.
  • A variety of materials can be used in its preparation.
  • Uses locally available materials thus cheaper than the artificial fertilizers.
  • Improves the soil structure.

Limitations of Compost Manure

  • It releases nutrients slowly into the soil.
  • Large quantities of compost manure are required to supply enough plant nutrients.
  • Its preparation is labour intensive.
  • It may induce soil-borne pests and diseases.

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