Which species of earthworm is most widely used in vermicomposting?

The correct answer is C, natural manures and pesticides are used. Organic farming is defined by the inputs it refuses. In place of factory made fertilisers it uses farmyard manure, compost, vermicompost, green manure and biofertilisers such as Rhizobium and Azotobacter. In place of synthetic insecticides it uses biopesticides such as neem extract and Bacillus thuringiensis, along with natural enemies of the pest. Option A is the opposite of the definition, since the use of chemical fertilisers disqualifies a farm from organic certification. Option B is wrong because certification standards under the National Programme for Organic Production specifically exclude genetically modified seed and planting material. Option D is wrong because organic farming in India is practised in cereals, pulses, oilseeds, spices, tea and fruit, and no rule limits it to cotton; organic cotton is simply one of the better known export lines.

The correct answer is B, Rhizobium. Rhizobium is a symbiotic bacterium that enters the roots of pulses, groundnut, soybean and other legumes and multiplies inside swellings called root nodules. Inside the nodule the enzyme nitrogenase converts atmospheric nitrogen into ammonia, which the plant uses, while the plant supplies the bacterium with sugars. This is why a legume is placed after a cereal in crop rotation. Option A, Azotobacter, also fixes nitrogen but lives freely in the soil and is recommended for wheat, maize, cotton and vegetables, not inside nodules. Option C, Azospirillum, is an associative fixer that lives close to the roots of sugarcane, sorghum and millets without forming nodules. Option D, Trichoderma, is a fungus used as a biofungicide against soil borne diseases such as root rot and wilt; it does not fix nitrogen at all.

The correct answer is C, Biomagnification. A pesticide such as DDT dissolves in fat, is not broken down and is not excreted, so the amount in a predator's body is the sum of what all its prey carried. Concentration therefore rises step by step from water to plankton to small fish to large fish to fish eating birds, which may hold several thousand times the level in the water. Option A, eutrophication, is the enrichment of a water body with nitrate and phosphate that causes algal blooms and oxygen loss, a nutrient problem rather than a food chain problem. Option B, bioremediation, is the useful process of employing microbes or plants to clean a polluted soil or water body. Option D, biofortification, is the breeding of crops richer in iron, zinc or vitamin A, as in the iron rich pearl millet varieties released in India.

The correct answer is C, Sikkim. Sikkim began phasing chemical fertilisers out in 2003, converted its entire cultivated area to certified organic practice and was declared a fully organic state. For this work it received the Future Policy Gold Award of the Food and Agriculture Organization in 2018, the first state anywhere to be honoured in that way. Option A, Kerala, has a strong organic policy and is remembered in this chapter for the endosulfan tragedy in Kasaragod district, but it has not converted all its farmland. Option B, Uttarakhand, has a large certified organic area and an organic commodity board, yet it came later and only in parts. Option D, Himachal Pradesh, promotes natural farming through a state scheme and has declared the goal of becoming organic, which is not the same as having achieved it. Examiners often pair Sikkim with the year 2016 and with the Gold Award.

The correct answer is D, Organochlorine. Dichloro diphenyl trichloroethane is built on a chlorinated hydrocarbon skeleton, which makes it fat soluble, chemically stable and extremely slow to break down in soil and water. Those same properties made it a cheap malaria control spray and also made it the first pesticide shown to biomagnify, which is why it stands on the Stockholm Convention list of persistent organic pollutants. BHC, aldrin and endosulfan are its companions in this class. Option A, organophosphate, covers malathion and parathion, which degrade in days but inhibit acetylcholinesterase sharply. Option B, carbamate, covers carbaryl and carbofuran, which act on the same enzyme reversibly. Option C, pyrethroid, covers cypermethrin and permethrin, laboratory versions of pyrethrin obtained from chrysanthemum flowers; they are far less persistent than DDT.