Pesticides

The chemical substances that are used for the control of insects, herbs, fungi, rodents, etc. are called pesticides.

Insecticides: 

They are the chemicals used to kill insects.
Examples:

Weedicides or Herbicides: 

The chemicals which are used to kill weeds(herbs) are called weedicides.

Examples: 

1) 2,4-D [2,4-dichlorophenoxy acetic acid]

-Effective in controlling broad-leaved plants

2) 2,4,5-T [2,4,5-trichlorophenoxyacetic acid]

-Effective in killing woody plants

Fungicides: 

The chemicals which are used to destroy or stop the growth of fungi are called fungicides.

Examples: Copper sulphate, Aluminium phosphide(ALP), Bordeaux mixture (mixture of CuSO4 and lime), etc.

Rodenticides: 

Those chemicals which are used to kill rodents (rats, squirrels, etc…) are called rodenticides. Example: Sodium monochloroacetate[ClCH2COONa], Zinc phosphide [Zn3P2], etc.

Fertilizers

Materials added to the soil to provide necessary nutrients for better growth and development of plants or for increasing productivity are called fertilizers.

Types of Fertilizers:

Organic fertilizer [Manure]: 

The fertilizer obtained from decomposition of animal excreta and plant remaining is called organic fertilizer. Examples: green manure, compost manure. Green manure is prepared by ploughing green plants directly on field and compost manure is prepared by decomposition of animal dung and plants remaining in a pit.

Chemical fertilizers:

Artificially prepared chemical compounds used to improve soil fertility are called chemical fertilizers. They are of three main parts:

a. Nitrogenous fertilizer:

Those fertilizers which supply nitrogen to the soil and plants are called nitrogenous fertilizers. 

Examples: Ammonium sulphate [(NH4)2SO4], Ammonium nitrate [NH4NO3], Urea [NH2-CO-NH2] etc.

Function of nitrogen:

• It helps in formation of chlorophyll and protein.


• It helps in rapid growth and development of plants.

b. Phosphatic fertilizers:

Those fertilizers which supply phosphorus to the soil and plants are called phosphorus fertilizers. 

Examples: Ammonium phosphate, calcium superphosphate, triple super phosphate etc. 

Function of phosphorus:

• It helps in cell division and ripening of fruits.


• It increases the resistance against diseases.

c. Potassium fertilizer:

Those fertilizers which supply potassium to the soil and plants are called potassic fertilizers.

Examples: Potassium chloride, Potassium sulphate, Potassium nitrate, Potassium carbonate etc. 

Function of potassium:

• They help in tuber formation in plants.


• They help in photosynthesis.

Types of fertilizers, on the basis of number of primary nutrients:

a. Simple Fertilizers: They are the fertilizers containing only one primary nutrient. Examples: Urea, KCl, (NH4)2SO4 etc.

b. Mixed Fertilizers: They are the fertilizers containing more than one type of primary nutrients Examples: (NH4)2PO4 , KNO3 etc.

c. NPK Fertilizers

Fertilizers as pollutants

Fertilizers are water soluble. Nitrates enter into different water resources which increase biological oxygen demand (BOD) of water. Nitrate ions change into nitrite ions inside the body, especially in young children. It reduces the oxygen carrying capacity of haemoglobin due to which babies suffer from “blue baby syndrome”. Sometimes it can also cause stomach cancer and resist body growth. Maximum concentration of NO3- in drinking water as recommended by WHO is 10 ppm.

In addition to this, fertilizers cause excessive growth of aquatic plants covering the water surface which in turn reduces sunlight and oxygen supply for aquatic lives.