According to the World Bank’s population projections, the world’s population will increase from 6 billion people in 1999 to 7 billion in 2020. All these people will have to be housed, dressed, and above all, fed. Up to 90 percent of this necessary increase in food production will have to come from fields already under cultivation.

Fertilizers will continue to play a decisive role in increased food production. It is estimated that, globally, roughly 40% of the world’s dietary protein supply in the mid-1990 originated in synthetic nitrogen.

Therefore, in order to obtain high yields, fertilizers are needed to supply the crops with the nutrients the soil is lacking. With fertilizers, crop yields can often be doubled or even tripled.

In this article, fertilizers and their types, importance of each fertilizer in crop nutrition, deficiency symptom of each fertiliser, methods of calculating fertiliser rates, methods of fertiliser application and determining fertiliser needs are treated.

Plant Nutrients: their Roles in Plant Growth and their Sources

For proper plant growth, a regular supply of plant nutrients especially the essential ones, is necessary. Plants absorb a large number of elements from the soil, air and water during their growth period, but not all of these are essential.

Only 16 elements have been found to be essential for all plants and four others have been found to be essential for some plants.

Essential Elements for Plant Growth

For element to be so classified, it has to fulfill the following criteria:

A deficiency of the element makes it impossible for the plant to complete the vegetative or reproductive stage of its life cycle

The deficiency symptom of the element in question can be prevented or corrected only by supplying that element

The element must have a direct influence on the plant, and must be directly involved in the nutrition of the plant, quite apart from its possible effect in correcting some microbiological or chemical condition in the soil or culture medium.

Essential elements like carbon, hydrogen, oxygen, nitrogen, phosphorus and sulphur are the elements of which proteins and hence protoplasm are composed.

The other ten elements which are essential for plants are potassium, calcium, magnesium, iron, manganese, molybdenum, copper, boron, zinc, and chlorine.

The four elements which are essential only for some and not for all plants are sodium, cobalt, vanadium and silicon.

Sources of Nutrients

The following elements are derived:

From air; carbon (C) as CO₂ (carbon dioxide).

From the water: hydrogen (H) and oxygen (O) as H₂O (water).

From the soil, fertilizer and animal manure: nitrogen (N) a considerable amount of nitrogen is also fixed by leguminous plants through root nodule bacteria.

Macro and Micro nutrients

Macronutrients are needed by the plants in large amount, and large quantities have to be applied if the soil is deficient in one or more of them.

Within the group of macronutrients, which are needed for plant growth in large amounts, the primary nutrient such as nitrogen, phosphorus and potassium.

Calcium, magnesium and sulphur are sometimes called secondary nutrients due to their secondary importance in plant nutrition.

In contrast with macronutrients, micronutrients or trace elements are required in only minute amounts for correct plant growth and have to be added in very small quantities when they cannot be provided by the soil.

In conclusion, fertilizers are applied to crops to supply the nutrients that are not present in sufficient quantities in the soil. The purpose of an adequate fertilization programme is to supply, year after year, the amount of nutrients that will result in sustained maximum net returns.

This means that fertilisers are to be used in the most efficient way. To achieve maximum benefit from fertilisers, it is most essential to apply them at the right time and in the right place.

Various types of fertilizers, the methods of their application, deficiency symptoms, and methods of calculating fertilizer needs have been discussed in this article.

The role of fertilizer in sustainable crop production cannot be overemphasized. This article examines the types of organic fertilizer and chemical fertilizers, the role of each essential and non-essential elements in crop nutrition, method of determining fertilizer needs of crop, methods of fertilizer application, symptoms of deficiency of various types of fertilizers, method of calculating fertilizer needs of crops, principles of effective utilization of fertilizers were discussed. Also, soil reaction as it relates soil pH and its correction were treated in this article.