Fertilisers And Pesticides


 
 
Concept Explanation
 

Fertilisers And Pesticides

Fertilisers And Pesticides: With repeated growing of crops, the agricultural land suffers loss of certain elements, largely nitrogen, phosphorus and potassium, which are known as primary nutrients. Other nutrient elements essential for plant growth but required in lesser amounts are calcium, magnesium and iron. Certain elements, called miero-nutrients, e.g. copper, manganese, cobalt, zinc and boron, are also essential for plant growth, but are needed only in very small quantities.

This deficiency of essential elements in the soil is made good by the addition of manures and fertilisers to the soil. Manure is a natural substance obtained by the decomposition of animal excreta or plant residues,  which supplies essential elements and humus to the soil and makes it more fertile. A chemical fertiliser is  a salt or some other chemical substance, containing the necessary plant nutrients.Some common fertilisers: Fertilisers having oly one primary nutrient (Le., N-Nitrogen, P-phosphorous or K-Potassium) are called single fertilisers. Examples are:

(1) Nitrogenous fertilisers such as ammonium sulphate, ammonium nitrate, sodium nitrate, urea;

(2) Phosphoric fertilisers such as super-phosphate; and

(3) Potassium fertiliser such as potassium chloríde.

Except urea (organic fertiliser), other fertilisers mentioned above are inorganic fertilisers.

Fertilisers having more than one primary nutrient are known are mixed fertilisers. Depending on the nature of nutrients, these may be classified as NK, NP, PK or NPK type. For example, potassium nitrate (KNO_3) is a mixed fertiliser of NK type; ammonium hydrogen phosphate, (NH_4)H_2PO_4, is of the NP type. Fertilisers of NPK type are known as complete fertilisers because they supply all the essential primary nutrients.

As compared to fertilisers, the manures are not very rich in the plant nutrients (i.e., N, P, K). But they do provide to the soil abundant organic matter such as humus. This helps to improve both the physical and chemical properties of the soil. The indiscriminate use of inorganic fertilisers leads to problem of soil pollution. Excessive and indiscriminate use of inorganic fertilisers is, therefore, avoided.

Control of Weeds and Pests - Pesticides: A weed is an unwanted plant that grows with a crop and consumes a lot of nutrients added to the soil for promotion of the growth of crops. The growth of weed reduces the crop yield, so it becomes necessary to control the growth of weed.

Pests are certain harmful plants as well as animals, such as rats (a rodent) or locusts (an insect) which cause tremendous damage to crops. They are controlled by using chemicals in different forms, such as dust, sprays, or as gas. Any chemical substance, organic or inorganic, which is used to destroy or inhibit the action of plant or animal pests, is known as pesticide. Pesticides include such chemicals as insecticides, herbicides, rodenticides, miticides, etc. Almost all pesticides are toxic to man to a greater or lesser degree. Some common pesticides are Dichloeo-Diphenyltrichloroethane (or simply DDT), Benzene Hexachloride (or simply BHC), gammexane, zinc phosphide, and methylparathion. Except zinc phosphide (inorganic pesticide), rest other pesticides mentioned above are organic pesticides

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