⚖️ Complex Fertilizers

This lesson explains complex fertilizers, especially NPK complexes, their composition, and their manufacturing basis.

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Complex fertilizers

and NPK complexes

Complex fertilizers is defined as a material containing all three prirnary, nutrients ( N,P

and K) and it is also designated as complete complex fertilizers while a fertilizer material

containing one or two of the primary nutrient elements (N and P or P and K etc ) are

known as incomplete complex fertilizers. They are produced by a process of chemical

reaction. Most important complex fertilizers are Nitro phosphates & polyphosphate

based fertilizers etc

Nitro phosphates

It is a granular fertilizer containing stabilizer which prevents reversion of citrate soluble

phosphates to insoluble phosphate. Being granulated it maintains excellent physical

condition during storage and handling.Nitrophosphate contains nitrogen and phosphorus

in different proportions depending upon the process of manufacture. It also contains

easily soluble and readily available N03 N as well as NH4-N. Phosphorus is also present

as water soluble as well as citrate soluble forms. All nitrophosphates have less acidic

effect on soil compared to other fertilizers.

Ammonium Phosphate

Ammonium phosphate is an incomplete complex fertilizer and both monoammonium and

diammonium phosphates are manufactured by the combination of ammonia with H3PO4

and also by treating with rock phosphate with H2 SO 4and (NH4 )2SO4 as follows:

NH3+ H3PO4 = NH4H2PO4

(Mono-ammonium phosphate)

2 NH3+ H3PO4 = (NH4 ) 2 H2PO4

(Diammonium phosphate)

Ca3PO4) 2 + (NH4 )2SO4 + 2H2 SO 4 = 3 CaSO4 + 2NH4H2PO4

(Rock phosphate)

The resulting solution contains both nitrogen and phosphorus. The liquid is turned into a

granular product in the granulator. The granular product is dried and screened. Product

that is too small or too large is recycled to the granulator.

In India, different types of nitrophosphates are manufactured with different

chemical reactions and mixing process by different fertilizer company. They marketed

the complex fertilizers as their different grades and commercial names. Most important

grades of nitrophosphate is 20: 20 : 0 and it means that nitrophosphate contains 20

percent nitrogen. 20 per cent phosphorus and no potassium. Besides these there are

various other commercially produced complex fertilizers suphala of different grades e.g.

15: 15 : 15: 20: 20 : 20 etc.

Polyphosphate based fertilizers

Ammonium polyphosphate. potassium polyphosphate. zincated poly phosphates

etc. are the most popular complex fertilizers that have been recently developed.

Ammonium polyphosphate

It is a complex fertilizer.Although it contains Nand P but it contains chiefly

phosphorus because polyphosphate is a compound derived from the condensation of

two or more phosphoric acids.

Ammonium polyphosphates may be granular and liquid. Different grades of

polyphosphates are marketed like 15-62-0; 12-53-0, 15-60-0; etc. as solid or granular

and 10-54-0, 11-37-0 as liquid. In addition to these there are Sulphated and Zincated

ammonium polyphosphates which are also available in the market to supply secondary

and micronutrient to the plant along with nitrogen and phosphorus. So the

polyphosphate based different micronutrient fertilizers which acts as slow-release

micronutrient are going to be developed recently.

Zincated polyphosphates can also be manufactured with the rock-phosphate

containing Zn and polyphosphates and that is also soluble in water and available to

plants.

A potassium polyphosphate solution of grade 0-26-26 was produced and this

was made by reacting superphosphoric acid and potassium hydroxide and contained a

mixture of ortho- pyro-and higher polyphosphates. Solid potassium polyphosphates of

grades 0-42-42 to 0-47-47 are also available

When polyphosphatic fertilizers are applied to soils, these are hydrolysed step

by step either chemically or biologically to form orthosphosphate.

Diammonium phosphate (DAP) (chemical formula (NH4)2HPO4 )

It is one of a series of water-soluble ammonium phosphate salts which can be

produced when ammonia reacts with phosphoric acid. DAP is used as a fertilizer and a

fire retardant. When applied as plant food, it temporarily increases the soil pH (more

basic), but over a long term the treated ground becomes more acidic than before upon

nitrification of the ammonium. It is incompatible with alkaline chemicals because its

ammonium ion is more likely to convert to ammonia in a high-pH environment.

Product containing diammonium phosphate as essential ingredient with small

amount of mono ammonium phosphate

Total nitrogen: x (18-21)%

P2O5 soluble in neutral ammonium citrate and water: y (45-53)%

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Summary Cheat Sheet

Topic	Key exam point
Main meaning	Fertilizers containing two or more nutrients produced by chemical reaction
Common examples	DAP and NPK complexes
Major groups in lesson	Nitrophosphates, ammonium phosphates, and polyphosphate-based fertilizers
DAP status	Important NP complex fertilizer
Nitrophosphate logic	Prepared using nitric acid route and phosphate sources
Advantage over mixed fertilizers	More uniform nutrient distribution in each granule
Agronomic value	Convenient application of multiple nutrients together
Manufacturing distinction	Complex fertilizers are chemically integrated products, not simple blends
Exam point	Ammonium polyphosphate belongs under polyphosphate-based fertilizer category
Trap	Do not classify physically mixed grades as complex fertilizers

References

3 sources • [1] [2] [3]

[1]

Indian Council of Agricultural Research (ICAR)

Official

[2]

Principles of Soil Science and Agricultural Chemistry — Standard BSc Agriculture Textbook

Book

[3]

Department of Agriculture & Farmers Welfare

Website