Artificial Or Chemical Or Inorganic Fertilizers
These can be classified as:
1) Straight fertilizers: These are those which supply only one primary plant nutrient, viz. N, P or K. Depending upon the nutrient present in the fertilizer, these are classified as:
a) Nitrogenous fertilizers: These are those which contain and supply only the nitrogen. Or are those fertilizers that are sold for their ‘N’ content and manufactured on a commercial scale.
These are classified into 4 groups on the basis of the chemical form in which ‘N’ is combined with other elements in a fertilizer (Chemical form of ‘N’).
i) Nitrate form (NO3): Sodium nitrate (Chilean nitrate), Calcium nitrate, Potassium nitrate and Nitrate of Soda Potash.
ii) Ammonical form (NO3): Ammonium sulphate, Ammonium Chloride and Anhydrous ammonia.
iii) Nitrate & ammoniacal form: Ammonium Nitrate, Calcium Ammonium Nitrate & Ammonium sulphate nitrate.
iv) Amide form (Cn2 or NH2): Calcium cynamide, Urea and Sulphur coated urea.
b) Phosphatic fertilizers: These are those which contain and supply only the ‘P’. P content in fertilizers is expressed in oxidized form, phosphorus pent oxide (P2O5) while its content in soil and plant is expressed in elemental form as ‘P’. The conversion factors for elemental to oxidized form and vice versa are 2.29 and 0.43, respectively.
These can be divided into 3 groups based on their availability to crop and solubility.
i) Containing water soluble phosphoric acid: Fertilizers are available in the form of mono calcium phosphate or ammonium phosphate. E.g.: single super phosphate, double super phosphate and triple super phosphate.
ii) Containing citric acid soluble phosphoric acid: These fertilizers contain citrate soluble phosphoric acid or dicalcium phosphate. E.g.: Basic slag, Di-calcium phosphate.
iii) Containing phosphoric acid not soluble in water or citric acid: E.g.: Rock phosphate, raw bone meal, steamed bone meal.
c) Potassic fertilizers: These are those which contain and supply only the ‘K’. Potassium in the fertilizer is expressed as K2O (Potassium oxide). The conversion factor to express in elemental factor (K) is 0.83 and oxide form is 1.2.
These are grouped in two as:
a. Chloride form: – E.g. Muriate of potash or pot. Chloride.
b. Non chloride form: – E.g. Potassium Sulphate, Potassium Magnesium sulphate, Potassium nitrate.
2) Complex or Compound fertilizers: These are those which contain two or three primary plant nutrients of which two primary nutrients are in chemical combination. E.g.: Diammonium phosphate, Nitro phosphates, Ammonium phosphate, Potassium nitrate, Ammonium Sulphate phosphate, Ammonium Nitrate phosphate, Ammonium Potassium phosphate.
a. Fertilizer mixtures/Mixed fertilizers: These are physical mixtures of straight fertilizers containing two or three primary plant nutrients.
These are made by thoroughly mixing the ingredients either mechanically or manually. Fertilizer grade refers to the guaranteed minimum percentage of N, P2O5 and K2O contained in fertilizer materials. E.g.: 20:20:0, 28:28:0, 18:18:10, 14:25:14, 17:17:17, 14:28:14 and 18:8:9, etc.
b. Micro nutrient fertilizers: These are the nutrients which supply the nutrients required in smaller quantities. These are the chemicals which supply the elements required by the plant in very small quantity. E.g.: Copper Sulphate, Zinc Sulphate, Borax, Sodium Borate, Manganese Sulphate, Sodium Molybdate, Ammonium Molybdate, Ferrous Sulphate, etc.
c. Soil amendments: These are those which improve the soil by correcting its acidic or saline, or alkaline conditions and neutralizing the injurious effects that may result from improper use of fertilizer. E.g.: Lime, Gypsum, Sulphur, and Molasses. These are the substances that influence the plant growth favourably by producing the soil one or more of the following beneficial effects:
1. Changing the soil reactions i.e. making the soil less acidic (Lime) or less alkaline (Gypsum).
2. Changing the plant nutrients in the soil from unavailable forms.
4. Improving the physical condition of soil (Molasses).
5. Correcting the effects of injurious substance.
d. Bio-fertilizers/Microbial innoculents: It may be defined as preparation containing live or latent cells of the efficient strains of N fixing, phosphate solubilizing or cellulytic micro organisms.
These are used for application to seed, soil or decomposing areas to increase the no. of such certain microbial process to make the nutrients in available form to plants such as Rhizobium, Azotobacter, Azospirillum, Blue-green algae and Azolla.