Any natural or manufactured material, which contains at least 5% of one or more of the three primary nutrients(N, P2O5, K2O) can be called fertilizer. Industrially manufactured fertilizers are called mineral fertilizer.
There are organic fertilizers and inorganic fertilizers. The organic fertilizers are made of enriched organic matter of plants and animals and inorganic nitrogenous fertilizers are synthesized chemically. The production of inorganic nitrogen fertilizer has increased rapidly in the past few decades.
Diagram of fertilizer production route is shown below.
Fertilizer is defined as any substance containing one or more recognized plant nutrients which is used for its plant nutrient content and which is designed for use or claimed to have value in promoting plant growth.
A fertilizer material is a fertilizer which either
"Fertilizers prepared by processing a combination of materials of biological origin, unprocessed mineral materials like lime, rock phosphate etc and organic wastes from industrial processing units homogenized by microbial decomposition are called organic fertilizers."
- Contains important quantities of no more than one of the primary plant nutrients: nitrogen(N), phosphorus(P) and potassium(K) or
- Has 85% or more of its plant nutrient content present in the form of a single chemical compound or
- Is derived from a plant or animal residue or by-product or natural material deposit which has been processed in such a way that its content of plant nutrients has not been materially changed except by purification and concentration.
Organic fertilizers should contain sufficient amount of plant nutrients to be valued as fertilizers. They may not be immediately available to the plants, but they enhance the fertility of the soil.
Organic fertilizers are referred to commonly as organic manures, although processes carried out on organic fertilizers make them more standardized, which is not the same case with manures.
The advantages of organic fertilizers include the slow release of available water-insoluble nitrogen and phosphate. The slow-release minimizes the leaching of nutrients. Organic fertilizers contain no soluble salts and can be applied in large quantities without damaging the crops. There are some situations when organic fertilizers can even be better than inorganic fertilizer in supplying nitrogen and phosphorus to crops.
Organic fertilizers enriched with inorganic minerals or fertilizers are called organic mineral fertilizers. Organic mineral fertilizers are mixtures of inorganic fertilizers (N, P, K) with peat, composted bark, lignite dust or dried slurry. These are classified as
- Fertilizers capable of improving soil condition, having stable organic compounds and a slow effect on the nitrogen supply (bio-genic composts, garden composts).
- Fertilizers with short-term effects on nutrient supply especially of nitrogen, having a high content of mineral nitrogen and readily available organic nitrogen compounds.
All commercial nitrogen fertilizers are produced from ammonia. The later is obtained by combination of atmospheric nitrogen with hydrogen in the ratio 1:3 at high temperatures (400 - 500o
C) and pressure (500 -1000 atmospheres) using the Haber process
in the presence of a catalyst. The hydrogen is obtained by hydrolyzing water, burning coke or distilling coal, petroleum or natural gas.
Classification of Nitrogen Fertilizers
- Nitrate fertilizer - In these fertilizers, nitrogen is present in the form of nitrates. Examples are sodium nitrate and calcium nitrate. Nitrate fertilizers are made from natural salt deposits or by the oxidation of ammonia.
- Ammonia fertilizers - here nitrogen is present in an ammonium ion form, such as in ammonium sulphate, ammonium chloride, ammonium phosphate, anhydrous ammonia and ammonia solution.These fertilizer are not easily lost by leaching and leave acidic residual effects in the soil.
- Nitrate and ammonium fertilizers - Nitrogen is present in these fertilizers in both the nitrate and ammonium forms, such as in ammonium nitrate, calcium ammonium nitrate and ammonium nitrate sulfate. Fertilizers of this group are readily soluble in water and suitable for a variety of soils and crops. They leave an acidic residual effect in the soil.
- Amide fertilizers - In these fertilizers, nitrogen is present in an amide form, such as in urea and calcium cyan amide. These fertilizers are soluble in water and readily converted into ammonia cal nitrogen by micro organisms.