Fertilizers are the substances, which are added to the soil to make up and provide the elements necessary for the growth of plants. These may include naturally occurring inorganic or organic substances or such substances prepared synthetically.
Classification of Fertilizers
According to crop-to-crop need of Nitrogen, Phosphorus and Potassium the fertilizers can be classified as under.
1- Direct fertilizers
These fertilizers are directly assimilated by the plants and contain nutrient elements in the form of mineral salts .For Sample super phosphates, nitrates and ammonium compounds.
2- Indirect fertilizers
These fertilizers are used to improve the mechanical, chemical and biological properties of the soil. For example dolomite, limestone are used to reduce the soil acidities and gypsum used to improve the properties of the soil with a high salt content.
3 –Complete fertilizers
These fertilizers supply all the the essential elements namely N,P and K to the soil, in combine form. These are also known as mixed fertilizers or NPK fertilizers. For example guano, it is prepared artificially.
4- Incomplete fertilizers
These fertilizers contain only one or two elements needed for the growth of plants. For examples Ammonium Phosphate, Potassium Nitrate etc.
These fertilizers are classified as:-
(a) Natural organic fertilizer
such as plant matter, farmyard manures, animal matter etc.
(b) Artificial organic fertilizer
Examples are waste materials from animals excretion, Meat obtained from slaughterhouses, urea etc.
(c) Natural Inorganic fertilizers
Example being Chile saltpeter, rock phosphates, potassium salts etc.
(d) Artificial inorganic fertilizers
Examples are Ca(NO3)2, (NH4)2SO4, NHNO3, NH4Cl, Calcium Cyanamid, Super phosphates etc.
6 –Micro fertilizers
These contain the elements, Boron, Maganes, Zinc and Copper needed in very small amounts to stimulate the plant growth.