FERTILIZER

 

FERTILIZERS

Fertilizers or inorganic manures are sources of crop nutrients which can be added to the soil to supplement its natural fertility. Fertilizers are chemical substances, generally in the form of powders, granules, pellets or crystals, which can be added to the soil when soil tests show that some important minerals are lacking.

They are usually solids, but may be dissolved and applied as liquids.

Fertilizers are much more concentrated than organic manures but most of their constituents are generally more soluble and are therefore of less lasting values.

Kinds of Fertilizers

Two kinds of fertilizers can be identified according to whether they contain either one or more of any of the three major nutrients, namely:

• Nitrogen (N)
• Phosphorus (P)
• Potassium (K)

When they contain only one of three major nutrients,they are referred to as single, simple or straight fertilizer

Fertilizers are divided into two classes:

1. Single fertilizers – fertilizers that contain only one of the major nutrients.
2. Compound or mixed fertilizers – fertilizers that contain a combination of nitrogen, phosphorus and potassium (NPK). When only two major nutrients are mixed, we have a 2-in-1 fertilizer.

Types of fertilizers

The following inorganic fertilizers are commonly used in West Africa and Nigeria in particular:

• Urea — NPK 15:15:15
• NPK 18:48:0 (D.A.P.)
• NPK 15:15:15
  
  
  
• Ammonium sulphate (AS)
• NPK 12:12:17 + 2MgO
• NPK 20:20:20
• NPK 20:10:10
• Single super phosphate (SSP)

Examples of nitrogenous fertilizers

Nitrogenous fertilizers are particularly used for crops that require plenty of nitrogen. Most nitrogenous fertilizers will dissolve fairly rapidly and become available to plants.

Examples include:

(a) Ammonium nitrate
(b) Ammonium sulphate
(c) Urea

(d) Sodium nitrate
(e) Potassium nitrate

Examples of phosphate fertilizers

They are formed when mineral phosphate is combined with sulphuric acid:

(a) Single superphosphate (SSP)
(b) Triple superphosphate (TSP)

Example of potassium fertilizers

(a) Potassium nitrate
(b) Potassium sulphate

Fertilizer application

Chemical fertilizers are generally applied to the soil before planting or during crop development at intervals of 14–21 days. The time interval depends on the type of soil and the requirements of the plant.

Instructions

Chemical fertilizers need to be used as soon as they are bought because they easily deteriorate during storage. They should be kept in plastic bags and in a dry place. They should not be mixed until just before using them, otherwise they may chemically react with one another or give off gases. They should not be spread during the dry season, but only when needed for immediate crop growth. The fertilizer may be applied to the soil either in a general fashion or in a more specific way.

Fertilizers applied to the soil in different ways

(a) Broadcasting: This involves scattering the fertilizer evenly on the surface of the soil before cultivation. It could also be mixed thoroughly with the soil by being ploughed into it. Broadcasting could be done before ploughing and planting. The fertilizer should not come in contact with the plant roots because it may burn them.

Advantages:

1. It is the easiest way of spreading fertilizers.

Disadvantages:

1. It is the most wasteful method.
2. Much of the fertilizer will never get used by the plants because it has been distributed so thinly and widely.
3. The fertilizer may be washed away from the soil.

Fertilizer Application Methods

(b) Top dressing:

Here fertilizer is applied around the base of a well-established plant in order to give it a boost at a certain point in its development. This may be done just prior to flowering or allowed to touch the leaves or stem since this could cause scorching Very young plants should never be given top dressing. Another way is by spreading fertilizer on the surface of the soil on which crops are already growing. Soluble fertilizers like muriate of potash are good examples for this method.

(c) Ring method:
The fertilizer is applied in a ring form or in a circle about fifteen centimetres away from the plant. This avoids wastage and makes it easier for the roots to absorb the fertilizer nutrients quickly. It is a very slow process as one plant is applied at a time.

(d) Row application:
Adopted mainly for crops that are planted in rows or straight lines. The fertilizer is applied in a row or straight line a few centimetres away from the plant. It places the nutrient within the immediate reach of the root hairs of the crops. It is very suitable but can only be used on small gardens because of high labour requirements. Drilling machine can be used in applying fertilizer in this way. Mechanization of this method is not yet very much achieved because of lack of adequate machinery to handle it.

(e) Band placement:
Fertilizers are applied in bands or a band made by the side of a plant. This placement of fertilizer is very suitable for individual plants.

Important minerals to plants and symptoms of deficiencies

Mineral	Form taken into plant	Symptoms of deficiency
Nitrogen	Nitrate (NO₃⁻), ammonium (NH₄⁺)	Stunted growth, yellowing of leaves
Phosphorus	Phosphoric acid (H₃PO₄)	Poor growth, leaves dull green or red
Potassium	K	Yellow edges to leaves, early death
Calcium	Ca	Stunted root and stem
Iron	Fe	Yellowing of leaves
Magnesium	Mg	Yellowing of leaves
Sulphur	SO₄	Yellowing of leaves

Important minerals for animal growth

Mineral	Required for
Calcium	Healthy bones, teeth, clotting of blood
Phosphorus	Healthy bones, teeth
Sodium	Healthy blood
Potassium	Healthy blood
Chlorine	Healthy blood
Magnesium	Formation of bones and teeth
Iron	Formation of healthy blood
Copper	Formation of healthy blood
Cobalt	Formation of healthy blood
Iodine	Working of thyroid gland in the neck
Manganese	Involved in reproduction