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This article throws light upon the two important complex fertilizers used in soil. The complex fertilizers are: 1. Nitro-Phosphates 2. Polyphosphate Based Fertilizers.
Complex Fertilizer # 1. Nitro-Phosphates:
It is a granulated fertilizer containing stabilizer which prevents reversion of citrate soluble phosphate. Being granulated it maintains excellent physical condition during storage and handling. Nitro-phosphate contains nitrogen and phosphorus in different proportions depending upon the process of manufacture.
It also contains easily soluble and readily available NO3— N as well as NH4—N. Phosphorus is also present as water soluble as well as citrate soluble forms. All nitro-phosphates have less acidic effect on soil compared to other fertilizers.
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Ammonium phosphate is an incomplete complex fertilizer and both mono-ammonium and di-ammonium phosphates are manufactured by the combination of ammonia with H3PO4, and also by treating with rock phosphate with H2SO4 and (NH4)2SO4 as follows:
In India, different types of nitro-phosphates are manufactured with different chemical reactions and mixing process by different fertilizer companies. They are marketed the complex fertilizers by their different grades and commercial names.
Most important grades of nitrophosphateare 20: 20: 0 and it means that nitrphosphate contains 20 per cent nitrogen, 20 percent phosphorus and no potassium. Besides these there are various other commercially produced complex fertilizers sulphala of different grades e.g. 15: 15: 15, 20: 20: 20 and 10: 26: 26 etc.
Complex Fertilizer # 2. Polyphosphate Based Fertilizers:
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Ammonium polyphosphate, potassium polyphosphate, zincated polyphosphates etc. are the most popular complex fertilizers that have been recently developed.
Ammonium polyphosphate is a complex fertilizer. Although it contains N and P but it contains chiefly phosphorus because polyphosphate is a compound derived from the condensation of two or more phosphoric acids.
Polyphposphoric acid contains more than one phosphorus atom. Pyrophosphoric acid is the simplest member of polyphosphoric acid series. So with the further condensation of phosphoric acid with the pyrophosphoric acid and so on, long chain polyphosphoric acids are formed.
In this way with the increasing number of phosphoric acid and ammonia, polyphosphatic fertilizers are formed.
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 micro-nutrient to the plant along with nitrogen and phosphorus. So the polyphosphate based different micronutrient fertilizers which act as slow-release micro-nutrient fertilizers 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 super phosphoric 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 soil, these are hydrolysed step-by-step either chemically or biologically to form orthophosphate.
Once the formation of orthophosphates takes place from the hydrolysis of polyphosphates, then the reaction mechanism is almost similar to that of superphosphate when applied to the soil.
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