Fertile soil contains minerals, organic matter and a number of microscopic forms of plant and animal life. The soil should also contain soluble minerals. If the soil is deficient in these minerals, fertilizers must be added to ensure healthy crops.
About 16 elements are needed for the healthy growth of a plant. Out of these, nitrogen, phosphorus and potassium are the major elements needed in large amounts. These elements are needed in their ionic forms by the plants for their growth and development. Most fertilizers contain soluble compounds of the three major elements. They are added to the soil because the nutrients in the soil get used up due to repeated cultivation. The crop yield also starts decreasing. Therefore, in order of revive the fertility of the soil, fertilizers are necessary.
Types of Fertilizers
There are mainly four nitrogenous fertilizers. The main raw material used in making nitrogenous fertilizers is ammonia gas. The common examples of nitrogenous fertilizers are
a. Urea [CO(NH2)],
b. Ammonium sulphate [(NH4)2SO4],
c. Ammonium nitrate (NH4NO3), and
d. Sodium nitrate (NaNO3).
Suitable fertilizers are added according to the need of the soil, for example, a field with leguminous plants such as pulses need not be given nitrogenous fertilizers.
Fertilizers containing phosphorus are called phosphatic fertilizers. Some of them are as follows.
a· Calcium hydrogen phosphate or superphosphate [Ca (H2PO4)2],
b· Ammonium hydrogen phosphate or ammophos [(NH4)H2PO4], and
c· Ammonium phosphate [(NH4)3PO4].
Deficiency of phosphorus in the soil causes stunted growth in plants and graying of leaves.
Some examples of potassium fertilizers are
a· Potassium nitrate (KNO3),
b· Potassium chloride (KCl) and
c· Potassium sulphate (K2SO4).
Deficiency of potassium causes the leaves to die out early.
Judicious use of fertilizers
The amount of fertilizers added to the soil varies from crop to crop. They should only be used when necessary. Excessive use of fertilizers degrades the quality of soil in the long run, for example, excessive use of nitrogenous fertilizers makes the soil and water rich in nitrates. Nitrogen-rich water is not good for drinking. Nitrates from the soil also flow into rivers and lakes with rainwater and enhance the growth of weeds and algae. This decreases the oxygen content of water leading to death of aquatic life. Excessive use of fertilizers can change the nature of the soil making it either too acidic or too alkaline.