Any material which when added to the soil increases the quantity of soil elements is called a fertilizer.
Fertilizers are, thus, added to the soil to increase the crop yield.
Fertilizers may be of two types:
1. Natural Fertilizers
(i) Farm Yard Manure:
It consists of organic matter such as dung of cattle, dead leaves and twigs. It improves the texture of soil, provides food to the beneficial bacteria and increases the water-holding capacity of soil.
(ii) Green Manure:
These are the plants like sainji, maina and gwara (leguminous) the root-nodules of which contain beneficial bacteria which fix atmospheric nitrogen and add nitrates to the soil. These plants are grown in the soil which has become deficient in nitrogen compounds.
2. Artificial or Chemical Fertilizers :
These are chemical compounds which contain nitrogen, phosphorus and potassium and is used L a great extent in modern farming. The best known fertilizers are saltpeter and ammonium sulphate. Other artificial fertilizers used in agriculture are ammonium phosphate, calcium metaphosphate and potassium metaphosphate.
Root and its structure:
Root is defined as an organ of a plant which grows downwards into the soil, away from light and generally towards water. It is usually not green in colour and does not possess any node or internode.
A little behind the apex, the surface of a root bears root-hairs. The root-hairs are composed of single epidermal cells and are the chief organs of absorption of water from the soil. Root is represented in embryo within the seed by the radicle which on germination forms a primary root.
The primary root develops lateral branches called secondary roots which may bear branches of third order called tertiary roots.