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MHT-CET : Biology Entrance Exam

MHT - CET : Biology - Fertilizes Pesticides and Biological Methods of Pest Control Page 1

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  • The substance, which when added to the soil, increases the fertility of soil, is called fertiliser.
  • There are two main types of fertilisers:


Chemical or synthetic
Biological or organic
- obtained from plants and animals.




Classification of Fertilisers


  • Chemical Fertiliser: Contains NPK, i.e. nitrogen, phosphorus, potassium. E.g. Urea, superphosphate, etc.
  • Farmyard Manure: Dung of cattle or other animals, plant residues.
  • Green Manure: Entire plant is used as fertiliser. E.g. Cowpea, sunn-hemp, cluster bean, etc.
  • Compost: Green plants and animal waste are decomposed under layers of soil for several weeks and is then used.






  • Biofertilisers: Some organisms like bacteria, cyanobacteria and fungi that are present in the soil or inside the roots of plants, and which increase the fertility of the soil are called biofertilisers.
  • Rhizobium: It is a type of bacterium present in the root nodules of leguminous plants and is capable of nitrogen fixation. Rhizobium cultures can now be grown in laboratories and are used for inoculation of seeds of legume plants.
  • Cyanobacteria: Nitrogen fixation is carried out by cyanobacteria like Nostoc, Anabaena. Nitrogen fixation is possible because of a special cell in cyanobacteria called heterocyst. Anabaena is present in the air spaces in leaves of an aquatic fern -  Azolla. Cyanobacteria are mainly used as biofertilisers in paddy (rice) fields.
  • Free Living Soil Bacteria: Clostridium, Chlorobium, Azotobacter and Azomonas are some of the bacteria found in the soil that are capable of fixing nitrogen, thus, helping to increase the fertility of the soil.
  • Mycorrhiza: An association between fungal hyphae with the roots of higher plants like angiosperms and gymnosperms is called mycorrhiza.
  • Ectomycorrhiza: Here, the fungal hyphae form a covering only on the surface of root. This helps the absorptive area of the root. E.g. Pinus, oak, eucalyptus.
  • Endomycorrhiza: Here, the fungal hyphae penetrate the roots and form a branching called arbuscules or swollen structures called vesicles to form VAM, i.e. vesicular - arbuscular - mycorrhiza.






  • Any animal or insect that harms a plant, animal or human being is called a pest.
  • Pest Control: The method used to reduce or kill the population of pests and pathogens is called pest control.
  • Pest control can be physical, chemical or biological.
  • Pesticides: These are chemicals used to control or kill the pests.
  • Depending Upon The Organisms, Pesticides Can be Classified as: Insecticides, bactericides, herbicides (weedicides), fungicides, rodenticides, etc.
  • Insecticides Can be Used as:


Contact poison: D.D.T., Malathion
Stomach poison: Zinc phosphide
Fumigants: Ethylene dibromide (EDB), aluminium phosphide

  • Benefits of Pesticides:



Due to control of pests, the crop yield increases.
Insects which spread diseases are killed. E.g. Malaria, plague, filariasis are vector-borne diseases.
Protection of furniture, garments, books, etc. from various pests.

  • Hazards of Pesticides:





Since pesticides are general poisons, they kill useful insects like honey bees, butterflies, etc.
Resistance to pesticide is acquired in successive generations by pests, and thus, the effect of pesticides on the pests gradually reduces.
Balance of the ecosystem is disturbed due to killing of organisms from the wells, rivers, etc.
Biomagnification: The increase in concentration of pesticides at each trophic level of the food chain is called biomagnification, which kills the animals.

  • Due to the hazards of pesticides we can also think of alternative methods such as mechanical control of pests or cultural methods of pest control.
  • Mechanical Control: Uprooting infected plants, soil heat treatment, keeping the field flooded with water.
  • Cultural Methods: Crop rotation, mixed cropping.




Biological Control of Weeds


  • Biological Control of Weeds: Weeds are the unwanted plants that grow along with the crop plants. They can be controlled by using herbicides but this method is harmful.
  • In biological control of weeds, certain insects are used which feed only on the weeds. Sometimes, certain fungi or bacteria are used, which infect the weeds and kill them.
  • In India, a weed, prickly pear (opuntia), is controlled by cochineal insect.






  • Bioinsecticides: Use of bioinsecticides is an alternative method for controlling insect pests without damaging the environment.
  • Insects can be controlled with the help of some predators. E.g. fluted scale insects of citrus trees are controlled by lady bird beetles.
  • Male insects are sterilised using gamma rays. These insects are used to control the population of insect pests.
  • Insect Hormones: Pheromones are the chemicals secreted by insects to attract the opposite sex. If traps are set using pheromones, the insects will be attracted and will be trapped. The insects can also be controlled by spraying juvenile hormones which carry out abnormal metamorphosis.
  • Certain natural compounds such azadirachtin, which is extracted from neem, repels insects. This is an example of natural insecticide.
  • Bacteria, Bacillus thuringinesis is used in microbial control of insects.




Integrated Pest Management (IPM)


  • Integrated Pest Management (IPM): This mainly depends on greater application of biological control methods and lesser use of chemical pesticides.
  • IPM involves different cultural methods such as crop rotation, good sanitation, early or late planting, etc.
  • IPM suggests the use of disease-resistant varieties.
  • IPM also involves natural enemies, parasites or natural herbicides for natural control of pests or weeds.
  • As use of chemical pesticides is minimum in IPM, it is possible to control pests and diseases without damaging the environment.



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