Fertilizers are those chemicals which improve the fertility of the soil and increase crop productivity. Chemical fertilizers played an important role in ‘Green Revolution’ in multiplying crop productivity to several times. Large scale use of chemical fertilizers has resulted into several evil effects such as the loss of soil fertility, environmental pollution, and persistence of fertilizer residues in the produce. Due to this the concentration is focussed on the use of biofertilizers to improve the agricultural productivity.
The fertilizers are of three types namely—1. Organic fertilizers, 2. Inorganic fertilizers and 3. Biofertilizers.
Organic fertilizers : Farm-yard manure, compost, green manure and vermicompost are some organic fertilizers. The use of farm-yard manure is a very old practice. The role of farm-yard manure in improving the fertility of the soil and enhancing the crop yield has been well known to the farmers.
Decomposition of animals excreta plant residues, domestic wastes etc. result in the production of compost. Compost is useful to increase the fertility of the soil and increases crop yield.
The employment of green parts of the plants directly into the soil has been an old practice. There are two methods in the application of green manure to agricultural fields. In one method nitrogen fixing plants are raised in fields like rice fields and when these plants attain certain height, the field is flooded with water and thoroughly ploughed. After this, rice transplantation is made. In another method branches from trees are cut and directly put into the soil.
The role of earthworms in protecting the soil fertility and in improving the physical features of the soil is well-known. With the help of earthworms, organic wastes can be converted into highly beneficial manure. The practice of earthworm rearing is referred to as ‘vermicompost’. Vermicompost contains 18% carbon, 2-3% nitrogen, 1-2% phosphorus and 1.5% potassium.
Inorganic fertilizers : It is well-known that the use of nitrogen, phosphorus and potassium fertilizers has been very useful to enhance the yield of agricultural crops. Important forms of these fertilizers are given below :
(A) Nitrogen fertilizers
(i) Urea (NH2.CO.NH2) : Urea is organic form of nitrogen fertilizer. It has the nitrogen content of 46%.
(ii) Ammonium sulphate [(NH4)2 SO4] : This contains 21% nitrogen (as ammonia) and 24% sulphur (as sulphate).
(iii) Calcium ammonium nitrate: This contains 26% nitrogen in the form of nitrate and ammonia in equal proportions.
(B) Phosphorus fertilizers : The quality of phosphate fertilizers is expressed as a percentage of phosphorus pentoxide (P2O5) equivalent.
(i) Superphosphate : Most commonly used phosphorus fertilizer in India has 16 to 20 as P2O5.
(ii) Rock phosphate : 25 to 35 as available P2O5 percent. Effectiveness depends on the degree of fineness and soil.
(iii) Bone-meal : 17 to 30 as available P2O5 percent. It is available in two forms, raw bone-meal and steamed bone-meal.
(iv) DAP (Diammonium phosphate) : In this, 40% phosphorus and 18% nitrogen are present.
(C) Potassium Fertilizer : The quality of potassium fertilizer is expressed as a percentage of potassium oxide (K2O) equivalent.
(i) Potassium Chloride : It contains 50 to 60% K2O, the whole of which is readily available. It is the most commonly used potassic fertilizer.
(ii) Sulphate of potash : It contains 49 to 52% K2O. It dissolves readily in water and becomes available to the crop almost immediately.
The use of micronutrients has been increased to enhance crop productivity. Several formulations containing one or more combinations of microelements are now available in the market.
Biofertilizers : Biofertilizers provide the nutrient input for plant growth which is of biological origin. Biofertilizers comprise of a variety of living micro-organisms. Nitrogen fixation by Rhizobium in the root nodules of legumes is well-known. Employment of legume crops in mixed cropping and crop rotation for soil enriching has been in practice for several centuries.
(A) Rhizobium inoculants : Rhizobium inoculants are being used on large scale to enhance the productivity of legume crops. Rhizobium inoculants have now become industrial products in several countries.
(B) Cyanobacteria : In Japan blue green algae are used in rice fields for increasing the yield. In India also the use of blue green algae is being encouraged. Farmers can develop cyanobacterial inoculants in their fields by following simple procedures. These inculants develop as dense mats. These mats are to be cut into small blocks and can be introduced into rice fields. A quantity of 10 kilograms per hectare gives better yield.
(C) Azospirillum : In maize, sorghum, wheat, barley and finger millet, Azospirillum lives as an endosymbiont in cortical cells and protoxylem vessels. Besides the ability to fix atmospheric nitrogen, Azospirillum also secretes certain growth promoting substances.
(d) Azolla : Azolla is a water fern. In leaves, the blue green algae Ababaena azolla lives as an endosysmbiont and fixed nitrogen. The importance of Azolla as biofertilizer was first shown in Vietnam in 1957. Azolla adds 30-40 kg. of nitrogen per hectare. By using Azolla as biofertilizer the yield can be increased.
(E) VAM : Vesicular arbuscular mycorrhizae (VAM) are endogenous mycorrhizae. VAM fungi increase the phosphate absorption by the roots. Researches revealed the yield of potato, wheat, maize, soyabean and red gram can be increased by the employment of VAM fungi.
Importance of biofertilizers : Biofertilizers have many advantages such as—
(i) By the use of biofertilizers, the effects of chemical fertilizers can be reduced.
(ii) There is no environmental pollution problem in the use of biofertilizers.
(iii) Biofertilizers are not costly and are available at cheap rates.
(iv) Biofertilizer production requires no energy input in the form of fossil fuels.
(v) Crop produce will not contain any toxins.
(vi) The production cost of biofertilizes is cheapper than chemical fertilizers.
Pesticides
Man is using the pesticides since the evolution and development of agriculture. This word has derived from Latin word pestis which means the destructive agent or plague. Thus it means the factors (living) which causes economic loss, destruction or injury to agricultural or other household articles.
The pests affect the reproductive potentiality of the products over which they feed.
The chemicals that can kill these pests are known as pesticides. These are generally oily or waxy substances. These may be in the form of dust, granules, pallets, emulsified concentrates, aerosols, soluble powders, wettable powders.
Uses of pesticides
The insects which destroy the agricultural crops are killed by the use of insecticides. So crop yield has increased many fold.
The insects which are the carrier of disease of many human and household animals are also killed by the use of insecticides.
Certain fungus causing diseases to the crops or certain store grains or food products are also killed by the use of fungicides (pesticides).
Hazards of pesticides
Pesticides kill the insects and other pests. Because these pests also make food chain in the ecosystem and if any component of food chain is disturbed or eliminated, the ecosystem is disturbed.
The pesticides after killing the pest, their excess amount causes toxicity to other non-pest useful organisms.
The pesticides are mostly soluble in water. When they come in water streams, they cause water pollution of different nature.
Pesticides are also harmful to the man. Regular exposure in gaseous form or smoke form or in fumigation form can cause different lungs and body disorders.
The pesticides are making pest resistant to these killers such as houseflies are now resistant to the DDT. The DDT was very effective in the beginning.
Types of Pesticides
According to their chemical nature, they are classified as :
Organochlorines : Slow decomposing chlorinated organic compounds are very effective. These compounds are lipophilic and show much affinity for the fatty tissue of animals. e.g. D.D.T., B.H.C., aldrin, endosulphan etc. D.D.T. is the most famous chemical in the world and is the oldest synthetic pesticide. B.H.C. is used in the public health programmes. Aldrin is applied to foundations of buildings to prevent termite. DDT and BHC are not highly toxic, whereas aldrin, dieldrin and endrin are highly poisonous chemicals. These chemicals have been banned in western countries.
In 1971, the brown pelican bird had completely vanished from Louisiana–once nicknamed the Pelican state–and only eight of this species were left in Anacapa island near California. In 1972, the U.S.A. banned the use of D.D.T. and in 1983, over 3,000 pelicans had come to breed in Anacapa island. Thus the brown pelican has been removed from the list of endangered species.
Organophosphates : They effect the nervous system. They are organic esterns of phosphoric, thiophosphoric and other phosphoric acids. e.g. malathion, parathion, fenitrothion etc. Malathion is one of the two active ingredients in Flit. It is also used in anti-malaria programmes.
Carbanates : They are organic esters of the hypothetical carbanic acid. They are having structural resemblance with acetylcholine and, therefore, they have a high affinity for the enzyme acetylcholine esterase, e.g. carbaryl, carbofuran, aldicarb propoxur etc. Carbufuran is sold as Furadon, propoxur as Baygon and aldicarb as Temik.
Pyrethoids : They are synthetic derivatives of pyrethrin. Pyrethrin is obtained from a plant botanically called Chrysanthemum cinerari-folium. These compounds are the fastest growing groups of chemicals today. They are very quick acting, broad spectrum insecticides. They are highly toxic and quite expensive.
Triazines : These are the herbicides derived from urea. They are used for controlling weeds in tea, tobacco and cotton. e.g. simazine, atrazine etc.
Biopesticides
Animals or plants used willfully to destroy pests are called biopesticides. These a—
Bioherbicides : Pesticides destroying herbs are called bioherbicides. Generally they are selective feeder. e.g. cochineal insect cactoblastis cactorum eats only cactus of Opuntia variety. The first bioherbicide was developed in 1981. It is a mycoherbicide based on the fungus Phytophthora palmivora. It controls the growth of milk weed vines in citurs orchards.|
Bioinsecticides : Insect killing other insects, e.g. praying mantis eats aphids.
Fungicides : Most common fungicide used in our country is Bordeaux. It is used on large scale.
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