Like living beings, they also need food for the growth of tree plants. In addition to water and air, tree plants also receive food as food. Trees plants take these substances from the ground.
The aqueous solutions of these substances reach the trees by capillary elevation where they are converted into other substances by various metabolic activities.
These other substances become part of tree plants. By continuously growing crops at one place, there is a shortage of those things in which the plants take food as food. In other words, by continuously growing the crop at one place, the fertility of the land there is reduced.
Some chemical substances made by artificial methods are added to the land to meet the shortage of the substances that the trees plant as food. These substances are called fertilizers, artificial manures or chemical manures.
Some of the major nitrogenous fertilizers are:
- Ammonium Sulphate: (NH4)2SO4
- Ammonium nitrate: NH4NO3
- Calcium Ammonium nitrate: Ca(NO3)2.NH4NO3
- Basic Calcium Nitrate (Nitrate of Lime): Ca(NO3)2.CaO
- Calcium Cyanamide: CaCN2
- Urea: NH2CONH2
Ammonium sulphate is made by the reaction of ammonia and sulfuric acid.
2NH3 + H2SO4 → (NH4)2SO4
To make ammonium sulphate in commercial quantities, the gypsum is finely ground and ground into water. Thus the NH3 obtained in the solution or suspension is saturated with NH3. After this, ammonium salfate is obtained by flowing CO2.
2NH3 + CO2 + H2O → (NH4)2CO3
CaSO4 + (NH4)2CO3 → (NH4)2SO4 + CaCO3
Calcium carbonate is obtained in precipitated form. It is filtered and separated and after concentrating the remaining solution, crystals of ammonium sulfate are obtained.
It is also made from ammonium liqueur in commercial quantities. Ammonium liqueur is obtained as a side product in the process of making coal gas from coal. In this, ammonia gas is obtained by heating water and caustic lime.
2NH4Cl + Ca(OH)2 → CaCl2 + 2NH3 + 2H2O
The ammonia gas thus obtained flows into an aqueous solution of sulfuric acid to obtain ammonium sulfate.
Ammonium sulfate is a white solid. It is soluble in water and contains 21.2% nitrogen and 24% ammonia.
Ammonium Nitrate (NH4NO3)
It is made by reaction of ammonia obtained by Haber method and nitric acid obtained by Ostward method.
It is a very useful fertilizer.
NH3 + NHO3 → NH4NO3
It is made by flowing nitrogen gas on a fine powder of calcium carbide heated at 1100°C.
CaC2 + N2 → CaCN2 + C
A mixture of calcium calcium cyanide and carbon is sold in the market as nitrolim. It is a good and cheap fertilizer. It is added while planting seeds in the ground. Under normal conditions, it reacts with water to form urea.
CaCN2 + 3H2O → Ca(OH)2 + NH2CONH2
Urea is made by reacting commercial quantities of ammonia and carbon dioxide at 125 – 150°C temperature and 200 atmospheric pressure.
2NH3 + CO2 → NH2CONH2 + H2O
It is a major fertilizer. It is a white colored crystalline solid. It is soluble in water. It contains 44% nitrogen.
Phosphorus is an essential ingredient of phosphatic fertilizers. In these, phosphorus is present as phosphate ion. Super phosphate of lime, phosphatic sintered and nitrophosphate are the major phosphatic fertilizers.
Super-Phosphate of Lime
Phosphorite and phosphate rock are the minerals of phosphorus. They mainly contain calcium phosphate. It is not available in water and cannot be used as fertilizer.
They are used to manufacture super phosphate of lime useful phosphatic fertilizer.
Appropriate amounts of sulfuric acid, containing about 70% concentration of fine powder of phosphorite or phosphate rock, are reacted to form the superphosphate of lime. By doing this, a mixture of more soluble calcium di-hydrogen sulfate and calcium sulfate is obtained.
Ca3(PO4)2 + 2H2SO4 → 2CaSO4 + Ca(H2PO4)2
Calcium di-hydrogen phosphate is also called calcium super phosphate or triple super phosphate. Adding appropriate amounts of water to a mixture of calcium di hydrogen phosphate and calcium sulfate. Calcium sulfate is converted into Gypsum(CaSO4.2H2O).
CaSO4 + 2H2O → CaSO4.2H2O
The mixture of calcium di hydrogen phosphate and gypsum thus obtained is called super phosphate of lime. This is a perfect phosphatic fertilizers.
The mixture of iron obtained in the form of slag in the metallurgy consists mainly of calcium phosphate and calcium silicate. This mixture is also used as a fertilizer.
Nitrophosphate is made from phosphorite or phosphate rock in the same way as super phosphate of lime. The difference is that instead of sulfuric acid, nitric acid is used to make nitrophosphate. It is a better fertilizer as it provides both nitrogen and phosphorus.
In order to increase soil fertility, the need of potassium element in addition to nitrogen and phosphorus is also important. The fertilizer or fertilizer mixture in which the presence of these three elements is ensured is called NPK fertilizer.
Potassium nitrate, potassium chloride and potassium sulfate are the major potash fertilizers.