Introduction to SOIL FERTILITY (ORGANIC MANURES): Soil fertility is the ability of the soil to provide crops with the required nutrients in their proper proportions.

Characteristics of a Fertile Soil

  • Good depth – Good soils give roots greater volume to obtain plant nutrients and provide strong anchorage.
  • Good aeration – for the respiration of plant roots and use by soil organisms.
  • Enough water holding capacity – ensures the provision of adequate water for plant growth.
  • Proper drainage – ensures the provision of adequate air for plant growth.
  • Correct soil pH – different crops have different soil pH requirements.
  • Adequate nutrients supply – it should supply the required nutrients in the correct amounts and a form available to plants.
  • Free from the excessive infestation of soil-borne pests and diseases.

ALSO READ Organic manures: Natural products applied by farmers to enhance suitable crop production.

How soil loses fertility

  1. Leaching – vertical movement of dissolved minerals from the top to the lower horizons of the soil profile.
  2. Soil erosion – The removal and carrying away of the top fertile soil from one place to another.
  • Monocropping – This is the practice of growing one type of crop on a piece of land over a long time.
  • Continuous cropping – crops take away a lot of nutrients from the soil which are never returned.
  • Growing crops continuously without giving the soil time to rest makes the soil infertile.
  • Change in soil pH – changes in soil pH affect the activity of soil microorganisms as well as the availability of soil nutrients.

Maintenance of Soil Fertility

  • Soil fertility is maintained through the following methods:
  • Control of Soil Erosion ;
  • Terracing,
  • Contour cultivation,
  • Strip cropping,
  • Cut off drains
  • Planting cover crops.
  • Crop Rotation ;
  • The practice of growing different crops on the same field in different seasons in an orderly sequence.
  • Control of Soil pH :
  • Application of liming materials such as limestone, quicklime, magnesium
  • Burning of vegetation – burning of vegetation cover destroys organic matter. It also exposes the soil to the agents of soil erosion.
  • Accumulation of salts – soils with a lot of salts are said to be saline. The state of having too much salt in the soil is referred to as soil salinity.
  • Salts accumulation causes water deficiency in plants. It may also lead to a change in soil pH

Carbonate and slaked lime if the soil is acidic.

  • Application of acidic fertilizers if the soil is alkaline.
  • Application of manures.
  • Proper drainage;

Done through:

  • Breaking hardpan.
  • Construction of water channels.
  • Growing crops on cambered bed
  • Pumping out water from the soil.
  • Weed control:
  • Use of herbicides.
  • Slashing
  • Uprooting.
  • Mulching
  • Use of proper farming practices such as early planting, correct spacing, and cover crops.
  • Intercropping –
  • Farming practice where different crop species are grown together in the field.
  • Minimum Tillage;
  • Use of herbicides.
  • The uprooting of weeds.
  • Slashing weeds
  • Mulching
  • Strip cultivation.
  • Use of Inorganic Fertilizer;
  • Chemical compounds manufactured to apply specific plant nutrients for example

Calcium ammonium nitrate (CAN).

  • Use of Manure;
  • Well decomposed manures release nutrients into the soil and increase its water holding capacity.

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.
  • Releases a wide range of nutrients into the soil hence Improves soil fertility.
  • 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 color.

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 Used For Soil Fertility.

  • Green manure.
  • Farmyard manure.
  • Compost manure

Green Manure

Made from green plants which are grown to incorporate 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 the 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)

This 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 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 the shed to decompose.
  • After some time, the materials decompose and FYM is formed.
  • It can then be used in the farm

Factors to consider in selecting a site for making compost manure:

  • A well-drained place.
  • The 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)


  • Select a sheltered place with a shade and near the field.
  • Dig a pit with a dimension of 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 microorganisms for the decomposition of organic remains.

Note: Some water should be sprinkled on the materials to initiate the decomposition process and regulate temperatures.

Four heaps method:


  1. 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.
  • 3 – 4 weeks after, the material should be 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.
  •  Production of a lot of manure 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

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








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