Fertilizers are complex chemical compounds that are necessary for proper growth and development of plants. They are either added to the soil or applied on the leaves of the plants in the liquidated form. They can be broadly categorized into two types - organic and inorganic fertilizers. Organic fertilizers include - cow manure, green manure, organic compost, etc. The inorganic ones are chemical substances prepared specifically to suit a particular purpose. They are also known as chemical fertilizers, and are usually available in a powdered and granular appearance. Some of them are also manufactured in the form of liquid.
Fertilizers primarily supply three major nutrients to the soil. They are - Nitrogen (N), Phosphorus (P), and Potassium (K). Hence, they are commonly referred to as NPK fertilizers.
Fertilizers with Nitrogen Content
In each of these types, the nitrogen present in them combines with other elements in a definite manner.
On the application of this type, the nitrogen present in it gets converted into ammonia. It readily dissolves in water, and is capable of showing quick results. It is found in the form of granules or pellets, and is white in color. Due to its tendency to absorb moisture from the air, it is often coated with a thin layer of non-hygroscopic material. Normally, it is applied during sowing time. However, care should be taken that it does not make physical contact with the seeds.
Organic Fertilizers with Nitrogen Content
Blood meal, oil cakes and fish manure are some examples of this type. Nitrogen present in them needs to be converted into a usable form through bacterial action. It is a slow process, and hence is used along with some quick action fertilizers. The benefit of these examples are that they also contain some other elements, which are required by the plants. For instance, oil cakes have traces of phosphorus and potash, and also of organic matter in large amounts.
Fertilizers with Phosphorus Content
The main ingredient of the phosphorus fertilizers is either naturally occurring or artificially synthesized phosphates. Described below are two examples:
There are two kinds of this type of fertilizer - raw and steamed. Raw bone meal contains phosphorus and little nitrogen, and is insoluble in water. On the other hand, nitrogen is absent in steamed bone meal due to high pressure steaming. It is quite brittle, can be grounded to powder, and is good for those soils that are acidic in nature. It is applied to the soil either during sowing or few days before it.
In this type, phosphorus is present in the form of phosphoric acid. Based on the manufacturing process, superphosphate has three different grades - single, triple, and dicalcium. When added to soil, the acid changes to water soluble phosphate. This compound is suitable for all soil types, and is used during the time of sowing or transplantation.
Fertilizers with Potassium Content
The two most widely used variety of potassium fertilizers are - sulfate of potash and muriate of potash. Both of them are highly soluble in water, and are added before or during sowing. They are good for sandy soil, and are used for particular crops like chilies, potatoes, fruit trees, etc. These fertilizers should be applied only if the potassium content of the soil is inadequate.
The basic advantage of inorganic fertilizers as compared to organic ones is that they are far less bulky. As a result, it becomes easier for the plants to carry them from the soil to its different parts. On the other hand, the upside of organic fertilizers is that they do not mix up with groundwater and cause water pollution, nor do they adversely affect the growth of surrounding plants.