- Those fertilizers, which are sold in the market for their nitrogen content. They are classified into four classes on the basis of N present.
1. Nitrate (NO3-) containing nitrogenous fertilizers: Most of the field crops except rice in the early stage of plant growth take up in nitrate form. They are suitable for top and side dressing and on dry soils. In moist soils they leach rapidly e.g. Sodium nitrate (NaNO3) (16%N), Calcium nitrate [Ca (NO3)2 ] (15.5%N).
2. Ammonium (NH4+) containing nitrogenous fertilizers: Ammonia fertilizers are prerferred by the rice crop in the early stage. For other crops these fertilizers need to be nitrified to nitrate.
These are more resistant to loss by leaching e.g. Ammonium sulphate (NH4)2 SO4 (20%N), ammonium chloride (NH4Cl) (24-26%N, anhydrous ammonia (NH3) 82% N.
3. Both ammonium and nitrate containing fertilizers: These fertilizers contain both ammonium and nitrate These are acidic in nature. Leaching losses are less. e.g. Ammonium nitrate (NH4NO3) (33-34% N), Calcium ammonium nitrate (CAN) (20% N).
4. Amide fertilizers: These are organic form of N containing fertilizers, which are readily soluble in water and are easily decomposed in the soil where they are quickly changed into ammoniacal and thence to nitrate form e.g. Urea CO (NH2)2 (46%N), Calcium cyanamide (CaCN2) (21%N). These fertilizers are also known as organic fertilizers since they contain carbon atoms.