GENERAL KNOWLEDGE सामान्य ज्ञान : CHEMISTRY: FERTILIZERS AND PESTICIDES

About fertilizers

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Synthetic fertilizers

Synthetic fertilizers are manufactured using the Haber-Bosch process to produce ammonia, which is then used to manufacture other nitrogen fertilizers
Urea is the most commonly used fertilizer. It has the highest nitrogen content
Synthetic fertilizers do not replace trace minerals in the soil (eg Zinc, copper, magnesium etc)
Production of synthetic fertilizers is highly energy intensive. The production of synthetic ammonia currently accounts for 5% of global natural gas consumption
Excess and unregulated use of synthetic fertilizers can cause Fertilizer Burn, in which plant tissues die due to excess nitrogenous salts

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Biofertilizers

Include naturally occurring minerals such as manure, worm castings, compost, etc.
Primary sources of biofertilizers are
- Bacteria: Rhibozium, Azopirillum
- Fungi: Mycorrhiza
- Fern: Azolla
Cover crops can also be used to enrich soil between plantings of the main crop. Cover crops work through the principle of nitrogen fixation: i.e. convert atmospheric nitrogen into a plant-accessible form
Minerals such as limestone, rock phosphate and sulphate of potash can also be used
Biofertilizers release their nutrients much slowly compared to synthetic fertilizers and thereby prevent Fertilizer Burn
In addition to improving crop yields, biofertilizers also improve the health and long-term productivity of soil

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Environmental effects of fertilizer use

Oxygen depletion: Nitrogen compounds in fertilizer run-off are primarily responsible for serious oxygen depletion in oceans and lakes. This lack of dissolved oxygen causes serious damage to aquatic life in lakes and along coastal areas. Also leads to discolouration of water (green, yellow, red, brown)
Soil acidification: Nitrogen containing synthetic fertilizers cause soil acidification
Heavy metal accumulation: Synthetic fertilizers, especially those based on phosphates, can contain significant amounts of cadmium, uranium, zinc, lead and radioactive polonium, all of which can be stored in plant tissues, and later enter the food chain in the form of produce
Greenhouse gases: Due to the large scale use of fertilizers, nitrous oxide has now become the third most important greenhouse gas (after carbon dioxide and methane).

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Overview

A pesticide is a substance that is used to kill pests
Pests can include insects, molluscs, birds, weeds etc
In addition to preventing crop losses due to pests, pesticides can kill disease-spreading mosquitoes, allergy inducing bees or wasps, and also to control algae levels in lakes
Due to its negative effects on birds, DDT has been banned as a pesticide for agricultural use under the 2001 Stockholm Convention. However, it is still used in developing countries for malaria prevention and other vector control

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Commonly used pesticides

Pesticide	Used to control	Example
Algaecide	Algae	Copper sulphate, barley straw
Avicide	Birds	Strychnine, DRC1339, parathion (in diesel oil)
Bactericides	Bacteria	Chlorine, iodine, oxygen, alchohol, phenol
Fungicide	Fungi, oomycete (water molds)	Sulphur, neem oil, tea tree oil, rosemary oil, milk
Herbicide	Weeds	Dichlorophenoxyacetic acid (2,4D), atrazine, glyphosate
Insecticide	Insects	Organochlorine, organophosphates, carbamates, pyrethroids
Miticide	Mites	Methoprene, permethrin, dicofol
Molluscicides	Molluscs (slugs and snails)	Metal salts (iron phosphate, aluminium sulphate), metaldehyde
Nematicide	Nematodes (worms)	Nematophagus fungi, neem cake
Rodenticide	Rodents	Anticoagulants, metal phosphides, hypercalcemia

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Environmental effects of pesticides

Over 98% of insecticides and 95% of herbicides reach a destination other than their target species
Pesticides contaminate land and water when they run-off from fields, when discarded, sprayed etc
Air pollution: pesticide drift occurs when pesticides suspended in the air get carried away to other areas. Pesticides also react with other chemicals to produce ozone, accounting for about 6% of total ozone production
Water pollution: run-off and eroding soil lead to pesticide pollution of water. This affects water solubility, and also the pesticides enter the food chain through water. Some pesticides are toxic to fish, kill off zooplankton (the main food source for fish). Harmful to amphibians such as tadpoles and frogs
Soil contamination: nitrogen fixation is affected by pesticides in soil. Pesticides also kill bees and are responsible for pollinator decline, leading to decreased crop yields. Widespread use of pesticides eliminates animals’ food sources causing them to change food habits or starve. Pesticide poisoning also travels up the food chain

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Pest resistance and rebound

Pests may evolve to become resistant to pesticides
Managed through pesticide rotation
Mixture of pesticides may also be used
Certain pests sometimes themselves act as pesticides in the sense that they control other pests. In this case pesticides that target one pest species may lead to a secondary pest outbreak due to the other species
Also, sometimes use of pesticides may affect natural enemies of the pest more than the pest itself. In this case, the pesticide may lead to temporary decrease in pest populations, but in the long-term the pest population may increase due to the absence of its natural enemies (especially for mosquitoes). This is called pest rebound.

THANKS

JOHAR

GENERAL KNOWLEDGE सामान्य ज्ञान