Introduction 

• 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. 

• Good water holding capacity - ensures provision of adequate water for plant growth. 

• Proper drainage - ensures 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 in a form available to plants. 

• Free from excessive infestation of soil borne pests and diseases. 

How soil loses fertility 

• Leaching: vertical movement of dissolved minerals from the top to the lower horizons of the soil profile. 

• 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 a 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. 

• 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. State of having too much salt in the soil is referred to as soil salinity. 

• Salts accumulation cause water deficiency in plants. It may also lead to change in soil pH. 

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 ;

- 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 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 hard pan. 

- 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 crops species are grown together in the field. 

• Minimum Tillage; 

- Use of herbicides. 

- 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. 

• 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.