ISC 12> UNIT 4> APPLICATIONS OF BIOLOGY> 3. BIO-FERTILIZERS AND PESTICIDES
Biofertiliser:
Green manure; reasons for preference of biofertiliser to chemical fertiliser. Brief idea of different types of manures and role of bacteria in improving the soil fertility. Pesticides: Advantages and disadvantages of pesticides; biological methods of pest control. Integrated Pest Management (IPM) - a general idea of the concept; Bioinsecticides e.g. Bacillus thuringiensis, Bioherbicides e.g. Cochineal insect.
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FERTILIZERS
Constant use of land leads to loss of its fertility and thus the fertility needs to be replenished. The deficiency of any one or more nutrients in the soil may impair the growth and development of plants. Macroelements like nitrogen, phosphorous and potassium are required in larger quantities. These are referred to as the NPK fertilizers. CHEMICAL fertilizers like nitrogen, and phosphorous are applied to the land so that it regains its fertility. |
Materials of biological origin commonly used to maintain and improve soil fertility are called bio-fertilizers. These are categorized as- Manures and Bio-fertilizers
MANURES
Manures are organic wastes that after partial decay are added to the soil to increase crop productivity. Manures supply all essential elements required by the crop plants. They Improve physical condition of soil. They also add to water holding capacity of soil. KINDS OF MANURE GREEN MANURE Quick growing leguminous crops are grown and ploughed when they are about one foot in height. This supplies the soil with organic as well as inorganic components to the soil. It also provides a protective action against erosion and leaching. Crops like cluster beans (Cyamopsis tetragonoloba), horse gram (Macrotyloma uniforma), lentil or masur (Lens esculenta) etc., are grown as green manure crops. FARMYARD MANURE It is obtained by partial decay of animal dung, farm refuse and crop residues. Manure consists of colloidal particles that help to imbibe water and loosen the soil, increase its aeration and permit easy penetration of roots in the soil. It enriches the soil with many organic substances and releases mineral element in the soil. Residue of gobar gas plant is a kind of farmyard manure. COMPOST MANURE It consists of rotten vegetables, animal refuse, groundnut husk and other substances. It is prepared by dumping these substances in heaps with sprinkling of chemical fertilizers like ammonium sulphate, superphosphate etc. It takes about 4-6 months to form compost manure. |
BIOFERTILIZERS
Microorganisms that enrich the soil in nutrients by their biological activity are bio-fertilizers. Main sources are- bacteria, cyanobacteria and fungi.
Microorganisms that enrich the soil in nutrients by their biological activity are bio-fertilizers. Main sources are- bacteria, cyanobacteria and fungi.
BACTERIA AS BIOFERTILIZERS
Bacteria that improve soil fertility may be symbiotic, non symbiotic (free living) or occurring in loose association with roots of higher plants. They enrich the soil by fixing free nitrogen into nitrogen compounds and thus reduce the dependence on the use of chemical fertilizers. SYMBIOTIC NITROGEN FIXING BACTERIA Rhizobium is a symbiotic bacteria living in association with leguminous plants. It forms root nodules in the legume plants and fixes atmospheric nitrogen. They fix atmospheric nitrogen in the presence of a pigment leghemoglobin. After harvesting the crop, the roots of legume crops are allowed to decay in the soil. This enriches the soil with nitrogen compounds. Thus the succeeding crop requires less nitrogenous fertilizers. The legume crops are thus used in crop rotation and green manuring. Frankia is a nitrogen fixing bacteria living in symbiotic association with non leguminous plants. The non leguminous plants are Casuarina, Myrica, Rubus and Alnus. FREE LIVING OR NON SYMBIOTIC BACTERIA Azotobacter fixes free nitrogen of the air. This is utilised by crops like cereals, millets, fruits etc. LOOSE ASSOCIATION OF NITROGEN FIXING BACTERIA Azospirillum has been isolated from the roots of grasses, rice and maize. Simple seed inoculation with this bacterium increases the dry weight of cereals. It gives high yield when mixed with chemical fertilizers. SYMBIOTIC CYANOBACTERIUM Cyanobacterium can fix nitrogen hence act as bio-fertilizers. Azolla is a floating fern, leaves show cavities in which Anabaena is found. They convert free nitrogen and exude nitrogenous compounds into cavities of the leaves. These leaves are excellent bio-fertilizers. |
FUNGI AS BIOFERTILIZERS
MYCORRHIZA
Symbiotic relationship between fungal hyphae and roots of higher plants is known as mycorrhiza.
The fungi obtain food from the plant and gives mineral elements in return. Mycorrhizal association converts a marginal land into a fertile land and reduces dependency on irrigation and fertilizers. According to their relationship they are classified as ectomicorrhiza and endomicorrhiza |
ECTOMICORRIZA
Fungal hyphae form a dense sheath external to the root. They are found on the roots of forest trees like Pine, Oak etc. They absorb Nitrogen, Phosphorous potassium and calcium, they also convert complex organic molecules into simpler available forms. |
ENDOMYCORRHIZA
Endomycorrhiza in association with cortex cells of roots. Some penetrate the roots and form vesicles and arbuscules in the cortex. This type of fungi are called vescicular-arbuscular micorrhizal (VAM) fungi. Eg. Acaulospora, glomus, gigaspora etc. |
BIOFERTILIZERS: SIGNIFICANCE
LOW COST
NO POLLUTION
REDUCE DEPENDENCE ON CHEMICAL FERTILIZERS
HOWEVER, BIOFERTILIZERS ARE NOT POPULAR AS THEY DO NOT SHOW QUICK RESULTS
LOW COST
NO POLLUTION
REDUCE DEPENDENCE ON CHEMICAL FERTILIZERS
HOWEVER, BIOFERTILIZERS ARE NOT POPULAR AS THEY DO NOT SHOW QUICK RESULTS
ADVANTAGES AND DISADVANTAGES
Advantage-
It is used to increase the yield.
It is also used to control vector borne diseases.
Disadvantages-
It is injurious to man and animals.
It causes destruction of ecosystem
Pesticides also destroy other organisms along with the target organisms.
The pests that survive become pest resistant and further breed pest resistant progeny.
It causes pollution.
Pesticides like organophosphates are stable compounds and cannot be broken down easily. Thus they tend to get accumulated in the body of the animals. This increase in the pesticides in the body of the organisms is called bio-magnification.
Advantage-
It is used to increase the yield.
It is also used to control vector borne diseases.
Disadvantages-
It is injurious to man and animals.
It causes destruction of ecosystem
Pesticides also destroy other organisms along with the target organisms.
The pests that survive become pest resistant and further breed pest resistant progeny.
It causes pollution.
Pesticides like organophosphates are stable compounds and cannot be broken down easily. Thus they tend to get accumulated in the body of the animals. This increase in the pesticides in the body of the organisms is called bio-magnification.
BIOLOGICAL METHOD OF PEST CONTROL
BIOHERBICIDES
Weeds are undesirable plants that grow along with the crops and compete with them for food, space and water.
The modern technique of biological control of weeds, that involve the use of insects and microorganisms to feed on these weeds, and not on the crops, are called bioherbicides.
The insects used as bioherbicides are first tested with regard to their specificity on a particular weed.
Examples of weed control by bio herbicides.
1) The first effective bioherbicide was a mycoherbicide phytophthora plamivora, which controls the growth of milk weed units in citrus orchards.
2) Growth of cacti in India was checked by the introduction of the natural herbivore cochineal insect cactoblastis cactorum.
3) Attempts to control water hyacinth in India were made by the application of Alternaria eichhorniae.
4) Plant breeders have developed transgenic tomato and tobacco plants by genetic engineering by introducing the genes for herbicidal resistance into crop plants so that the new plants became herbicidal resistant. The herbicide kills the weeds selectively and the transgenic crop plants remain healthy.
The modern technique of biological control of weeds, that involve the use of insects and microorganisms to feed on these weeds, and not on the crops, are called bioherbicides.
The insects used as bioherbicides are first tested with regard to their specificity on a particular weed.
Examples of weed control by bio herbicides.
1) The first effective bioherbicide was a mycoherbicide phytophthora plamivora, which controls the growth of milk weed units in citrus orchards.
2) Growth of cacti in India was checked by the introduction of the natural herbivore cochineal insect cactoblastis cactorum.
3) Attempts to control water hyacinth in India were made by the application of Alternaria eichhorniae.
4) Plant breeders have developed transgenic tomato and tobacco plants by genetic engineering by introducing the genes for herbicidal resistance into crop plants so that the new plants became herbicidal resistant. The herbicide kills the weeds selectively and the transgenic crop plants remain healthy.
Cochineal insect-
Cactoblastis cactorum was first introduced to Australia in 1925 from Argentina, where it was successfully utilized as a biological control agent for Opuntia cacti. Due to this success, it was subsequently introduced into other countries. A primarily sessile parasite, this insect lives on cacti from the genus Opuntia, feeding on plant moisture and nutrients. The insect produces carminic acid that deters predation by other insects. |
BIO-INSECTICIDES
Bio-insecticides are organic formulations recommended for the management of insects that feed on crops. They are different from chemical pesticides in several ways. They contain live bacteria that produce toxins which cause stomach poison in the insects and kill them.
Bacillus thuringiensis (or Bt) is a Gram-positive, soil-dwelling bacterium, commonly used as a pesticide. B. thuringiensis also occurs naturally in the gut of caterpillars of various types of moths and butterflies, as well as on the dark surface of plants.
Bt has to be eaten to cause mortality. The Bt toxin dissolve in the high pH insect gut and become active. The toxins then attack the gut cells of the insect, punching holes in the lining. The Bt spores spills out of the gut and germinate in the insect causing death within a couple days. Even though the toxin does not kill the insect immediately, treated plant parts will not be damaged because the insect stops feeding within hours. Bt spores do not spread to other insects or cause disease outbreaks on their own. |
HOW Bt WORKS.....
1. Insect eats Bt crystals and spores.
2. The toxin binds to specific receptors in the gut and the insects stops eating.
3. The crystals cause the gut wall to break down, allowing spores and normal gut bacteria to enter the body.
4. The insect dies as spores and gut bacteria proliferate in the body.
Bt action is very specific. Different strains of Bt are specific to different receptors in insect gut wall. Bt toxicity depends on recognizing receptors, damage to the gut by the toxin occurs upon binding to a receptor. Each insect species possesses different types of receptors that will match only certain toxin proteins, like a lock to a key.
2. The toxin binds to specific receptors in the gut and the insects stops eating.
3. The crystals cause the gut wall to break down, allowing spores and normal gut bacteria to enter the body.
4. The insect dies as spores and gut bacteria proliferate in the body.
Bt action is very specific. Different strains of Bt are specific to different receptors in insect gut wall. Bt toxicity depends on recognizing receptors, damage to the gut by the toxin occurs upon binding to a receptor. Each insect species possesses different types of receptors that will match only certain toxin proteins, like a lock to a key.
Further reference - pathogens, parasites and predators in pest control
http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74140.html
http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74140.html
INTEGRATED PEST MANAGEMENT (IPM)
It is the selection, integration and implementation of pest control based on economic, ecological and sociological consequences.
IPM is an “economically justified and sustainable system of protection of crops that leads to the maximum agricultural productivity with the least possible negative impacts on the natural environment”.
The concept of Integrated Pest Management was developed by Dr. Ray Smith (1919 – 1999). He was an American Entomologist and educator, around 1950. The Integrated Pest Management Programme (IPM) is now a worldwide programme which lays emphasis on the application of Bio-pesticides, and Bio-agents with rarest and unavoidable application of safe chemical pesticides.
It involves following principles-
IPM is an “economically justified and sustainable system of protection of crops that leads to the maximum agricultural productivity with the least possible negative impacts on the natural environment”.
The concept of Integrated Pest Management was developed by Dr. Ray Smith (1919 – 1999). He was an American Entomologist and educator, around 1950. The Integrated Pest Management Programme (IPM) is now a worldwide programme which lays emphasis on the application of Bio-pesticides, and Bio-agents with rarest and unavoidable application of safe chemical pesticides.
It involves following principles-
- Cultural control- like crop rotation.
- Mechanical control- like catching and killing the insects and rodents.
- Genetic practise- Selection of comparatively pest resistant/tolerant varieties with reasonable yield levels
- Chemical control- Use of chemical pesticides is the last resort when all other methods fail to keep the pest population below economic loss. Use of pesticides should be need based, judicious, based on pest surveillance and economic threshold level
- Use of resistant varieties- like disease resistant wheat, rice etc.
- Biological control- like use of parasites and predators to control pests.
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