The use of fertilisers (chemical) has increased the productivity of agriculture crops in short term. These chemical fertilisers are expensive, pollutant and are lost in surface run-off. To combat the ill effects of synthetic agriculture chemicals, Bio fertilisers have been introduced. Moreover, Indian soils are usually poor in organic matters as well as Nitrogen.
Biofertilizers are of biological origin. They are organisms which can bring about soil nutrient enrichment. The sources of bio-fertilizers are Bacteria-Rhizobium, Azospirillum (i) Fungi-Mycorrhiza (ii) Fern-Azolla.
The Biofertilisers works in association and are given below:
Legume Rhizobium Symbiosis: Rhizobium produces roof nodules in Leguminosaeplants and fixes atmospheric nitrogen. Phosphorous is also required at optimal levels for better nitrogen fixation.
Azolla-Anabaena Symbiosis: Azolla is a fern growing in water. Anabaena, Blue-Green Algae (BGA), lives in cavities of Azolla leaves. Anabaena fixes atmospheric Nitrogen and excretes in leaf cavity of Azolla. This leaf is excellent biofertiliser for rice.
Loose association of Nitrogen fixing bacteria: Azospirillum, a Nitrogen fixing bacteria is present in maize.
Free living bacteria: Azotobacter and Baccillus polymyxa fix atmospheric notrogen. These are useful in crops like cereals, millets, maize, vegetable, cotton, rice etc.
Cynobacteria: Cynobacteria are those bluegreen algae which fixes atmospheric nitrogen. Anabaena, Nostoc, and Aulosira derive the energy needed for nitrogen fixation through photosynthesis.
Mycorrhiza: Mycorrhiza is a symbiotic association of certain fungi with the roots of certain seed-bearing plants, e.g. orchids. The improtance of mycorrhiza are given below: Enhance water and nutrient uptake (i) resulting in greater plant vigour, growth and yield. (ii) important in phosphate nutrition in plants.
Recent Development: Cynobacteria not only fixes 'nitrogen' but also excretes Vitamin B12, ascorbic acid and auxins, which may improve the growth of plant. They also possess the properties of solubilising the bond phosphate of soil.
Biopesticide: Pest may be defined as any organism that is perceived to damage the economics and physical well being of humans. Pesticides and chemicals that kill pests are called pesticides.
Pesticides:
* 1. Fungicide kills fungi,
2.Herbicide kills weeds,
3. Insecticide killls insects,
4. Nematicide kills nematode,
5. Rodenticide kills rodents
* The chemical pesticides are of the following groups:
Organochlorines, Organophosphates, Carbamates, Pyrethroids, Triazines These chemicals are resistant, non-biodegradable, expensive and bioaccumulate / bioconcentrate in food chain.
* Biological Pest Control / Biopesticides (Pesticides of Biological origin) are best way to overcome these problems.
Biological control of weeds and Bio herbicides:
Biological control of weeds involves utilization of insects that would feed selectively on a weed or use of certain microorganisms, which will produce diseases in weeds and eliminate them e.g. Cacti can be checked by Cochineal insects, Phytophthora plamivors controls the growth of milk weed.
Bioinsecticides: (Pathogens, parasites and predators ) A number of destructive insects can be reduced by other insects, disease, parasite or predators, e.g. aphids can be controlled by the use of beetles.
Sterilisation Strategy: By sterilisation of male insects, by irradiation to check population of insects.
Insect hormones: Pheromones are the principal means of communication between insects, e.g. attracting males, controlling the mating behaviour of the insects through the use of pheromones which can reduce the population size of the concerned insect pest.
Natural insecticides: The Chinese were the first to discover the insecticidal properties of Rotenones present in the roots of Derris elliptica, Cincerin from Pyretrin, Azadirachtin from Neem. Bacillus thuringiensis (BT) produces protein toxin namely Thurioside which in insecticide.
IPM ( Integrated Pest Management ): Scientists have now accepted that a more ecologically fitting way of dealing with pest is IPM. IPM uses following techniques: Biological Control, Mechanical Control, Careful use of pesticides, Use of Resistant Varieties, Mixed cropping and crop rotation and Chemical Management.
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