SOIL FERTILITY I ( ORGANIC MANURE )

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
• 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 micro­organism 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:

Procedure

• 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.