Q35. Which two elements are primarily added to soil by green manure?
[RRB JE CBT 1 (20 February 2026, Shift 1)]
(A) Phosphorus and calcium
(B) Potassium and magnesium
(C) Nitrogen and phosphorus
(D) Nitrogen and potassium
Answer: (C) Nitrogen and phosphorus
Explanation: Green manuring means growing a crop, often a legume, and incorporating it into the soil while green. It adds nitrogen-rich biomass and organic matter, improves soil microbial activity, and supports phosphorus cycling. The examination’s intended pair is nitrogen and phosphorus.
Q34. What is a key difference between chemical fertilisers and manures in terms of nutrient release to plants?
[RRB JE CBT 1 (20 February 2026, Shift 1)]
(A) Manures have higher and less variable nutrient concentrations.
(B) Conventional chemical fertilisers release nutrients gradually.
(C) Chemical fertilisers enhance biological activity.
(D) Manures release nutrients gradually.
Answer: (D) Manures release nutrients gradually.
Explanation: Most nutrients in manure are tied up in organic substances and become available as microorganisms decompose them. Conventional soluble chemical fertilisers generally provide nutrients more rapidly. Manure also improves soil structure and biological activity, although its nutrient composition is less predictable.
Q33. Why is using compost or vermi-compost preferable to excessive use of fertilizers for increasing soil fertility?
[RRB JE CBT 1 (19 February 2026, Shift 1)]
(A) It eliminates bacterial and viral plant diseases.
(B) It supplies only micro-nutrients and avoids macronutrients.
(C) It recycles biological waste and avoids environmental harm.
(D) It replaces the need for irrigation and weeding.
Answer: (C) It recycles biological waste and avoids environmental harm.
Explanation: Compost and vermicompost recycle decomposed organic waste into useful soil amendments. They contribute organic matter, improve soil structure and water retention, and supply nutrients gradually. Using them appropriately can reduce reliance on excess chemical fertilisers and the associated runoff and pollution risks.
Q32. Which chemical fertiliser is most widely used in agriculture as a concentrated source of nitrogen for crops?
[Delhi Police Head Constable AWO/TPO 2025 (16 January 2026, Shift 1)]
(A) Urea, CO(NH₂)₂
(B) Gypsum, CaSO₄·2H₂O
(C) Limestone, CaCO₃
(D) Potassium chloride, KCl
Answer: (A) Urea, CO(NH₂)₂
Explanation: Urea contains approximately 46% nitrogen by mass, making it a concentrated and widely used nitrogenous fertiliser. Soil enzymes convert urea into ammonium-containing forms. Gypsum supplies calcium and sulphur, limestone treats acidic soils, and potassium chloride primarily supplies potassium.
Q31. Consider the following statements and select the correct option.
Statement A: Plants require specific soil pH for proper growth.
Statement B: Farmers use pH values to decide the type of fertiliser to add.
[RRB Group D (29 December 2025, Shift 3)]
(A) Both statements A and B are correct.
(B) Statement A is correct but B is incorrect.
(C) Statement A is incorrect but B is correct.
(D) Both statements A and B are incorrect.
Answer: (A) Both statements A and B are correct.
Explanation: Soil pH controls the availability of many plant nutrients and influences microbial activity. Different crops tolerate different pH ranges. Farmers use soil tests, including pH measurements, when choosing suitable fertilisers or amendments and determining whether lime or other corrections are needed.
Q30. Manure prepared with the help of earthworms is called:
[UPPSC LT Grade Assistant Teacher, Hindi (6 December 2025, Shift 2)]
(A) Compost
(B) Vermicompost
(C) Green manure
(D) Farm yard manure
Answer: (B) Vermicompost
Explanation: Vermicompost is obtained when earthworms process biodegradable plant and animal residues. Their castings contain stabilised organic matter, useful nutrients and microorganisms. Ordinary composting does not specifically require earthworms; green manure uses incorporated growing plants, while farmyard manure comes mainly from livestock wastes.
Q29. Which of the following raw materials for the fertiliser industry is entirely imported as India does not have any reserves?
[DSSSB TGT Natural Science (6 September 2025, Shift 2)]
(A) Sulphur (S)
(B) Nitrogen (N)
(C) Potash (K)
(D) Phosphate (P)
Answer: (C) Potash (K)
Explanation: The paper identifies potash as the imported fertiliser raw material. India has historically relied heavily on imported potassic fertilisers because commercially exploitable domestic supplies are limited. Potassium is important for water regulation, enzyme function and crop quality; muriate of potash is a common source.
Q28. Which one of the following is classified as a complex fertilizer?
[UPSSSC Agriculture Technical Assistant Mains (13 July 2025)]
(A) Single Super Phosphate (SSP)
(B) Urea
(C) Muriate of Potash
(D) Di-Ammonium Phosphate (DAP)
(E) None of the above
Answer: (D) Di-Ammonium Phosphate (DAP)
Explanation: Diammonium phosphate supplies two primary plant nutrients: nitrogen and phosphorus. Its commercial grade is commonly expressed as 18-46-0, meaning 18% nitrogen and 46% available phosphate as P₂O₅. Urea and muriate of potash chiefly supply one primary nutrient each.
Q27. Chemical fertilisers were used intensively during the Green Revolution. What was the result of their overuse?
[RRB NTPC Graduate CBT-I (19 June 2025, Shift 3)]
(A) Crop diversification
(B) Soil salinity
(C) Higher pest resistance
(D) Flooding
Answer: (B) Soil salinity
Explanation: Repeated, poorly balanced fertiliser use, particularly alongside intensive irrigation, can contribute to salt accumulation and deteriorating soil quality. High salinity makes water uptake difficult for plants. Proper nutrient management, drainage, testing and irrigation practices help prevent such long-term damage.
Q26. The Paramparagat Krishi Vikas Yojana (PKVY) launched in 2015–16 by the Central Government is aimed to:
[UPSC CDS-I General Knowledge (13 April 2025)]
(A) Make agriculture more modern and globally competitive.
(B) Provide improved access to irrigation and enhanced water efficiency.
(C) Support promotion of organic farming in the country.
(D) Reduce dependence of agriculture on monsoon.
Answer: (C) Support promotion of organic farming in the country.
Explanation: PKVY supports organic cultivation through farmer clusters, capacity building, certification and use of natural inputs. The scheme encourages compost, green manure and biofertilisers as alternatives to excessive synthetic inputs. Its primary purpose is organic farming, not irrigation expansion or monsoon management.
Q25. The Fertilizer Corporation of India has established coal-based chemical fertilizer plant in which of the following districts of Chhattisgarh?
[CGPSC Preliminary GS Paper I (9 February 2025)]
(A) Raigarh
(B) Korba
(C) Raipur
(D) Durg
Answer: (B) Korba
Explanation: The examination identifies Korba, a Chhattisgarh district known for major coal deposits. Coal can be gasified to obtain synthesis gas used in producing ammonia, which is a feedstock for urea. This connects the availability of coal with nitrogenous fertiliser manufacture.
Q24. In which of the following industry is rock-phosphate utilized?
[MPPSC Assistant Professor GS Paper II, 2022 cycle (17 November 2024)]
(A) Cement Industry
(B) Iron-steel Industry
(C) Fertilizer Industry
(D) Cotton textile Industry
Answer: (C) Fertilizer Industry
Explanation: Phosphate rock is the principal mineral feedstock for manufacturing phosphatic fertilisers. Treatment with acids converts comparatively insoluble mineral phosphates into forms suitable for crops. Important products include single superphosphate and phosphoric acid-derived fertilisers such as diammonium phosphate.
Q23. Consider the following fertilizers:
(a) Urea,
(b) Ammonium nitrate,
(c) Triple superphosphate,
(d) Potassium sulphate.
Which of the above are nitrogenous fertilizers?
[KEA Village Administrative Officer GK Paper I (27 October 2024)]
(A) (a) and (c) only
(B) (a), (b) and (c) only
(C) (a) and (b) only
(D) (b), (c) and (d) only
Answer: (C) (a) and (b) only
Explanation: Urea and ammonium nitrate both contain nitrogen and are classified as nitrogenous fertilisers. Triple superphosphate chiefly supplies phosphorus, while potassium sulphate supplies potassium and sulphur. Fertilisers are commonly classified as nitrogenous, phosphatic or potassic according to their principal nutrient.
Q22. Which inorganic compound is known to undergo solid state reaction to form urea?
[SSC MTS (18 October 2024, Shift 1)]
(A) Ammonium cyanate
(B) Ammonium phosphate
(C) Ammonium acetate
(D) Ammonium nitrate
Answer: (A) Ammonium cyanate
Explanation: Friedrich Wöhler famously prepared urea by rearranging ammonium cyanate in 1828. The reaction demonstrated that an organic compound could be synthesised from inorganic starting materials. Urea subsequently became one of agriculture’s most widely used concentrated nitrogen fertilisers.
Q21. Microbes like Rhizobium, Nitrosomonas and Nitrobacter are used for:
[SSC CGL Tier I (12 September 2024, Shift 1)]
(A) Nitrogen cycling
(B) Carbon cycling
(C) Water cycling
(D) Sulphur cycling
Answer: (A) Nitrogen cycling
Explanation: Rhizobium helps fix atmospheric nitrogen in legume root nodules. Nitrosomonas oxidises ammonium to nitrite, and Nitrobacter converts nitrite to nitrate. Together these microbes participate in the nitrogen cycle, which is fundamental to natural soil fertility and plant nutrition.
Q20. The aquatic plant commonly used as bio fertilizer in the water-logged rice field is —
[UPPSC PCS Prelims GS Paper I, Set C (14 May 2023)]
(A) Wolfia
(B) Azolla
(C) Trapa
(D) Lemna
Answer: (B) Azolla
Explanation: Azolla is a floating aquatic fern associated with the nitrogen-fixing cyanobacterium Anabaena azollae. In paddy fields this symbiosis adds biologically fixed nitrogen to the farming system. Azolla can be grown and incorporated into soil as a green biofertiliser.
Q19. ________ is used to manufacture fertilizers, synthetic fibers, plastics, adhesives, paints, and dyes.
[SSC GD Constable, 2022 cycle (30 January 2023, Shift 3)]
(A) Nitric acid
(B) Soda ash
(C) Alkalis
(D) Sulphuric acid
Answer: (D) Sulphuric acid
Explanation: Sulphuric acid is a major industrial chemical used to process phosphate rock and manufacture phosphate fertilisers. It also serves numerous chemical industries, so industrial consumption is often viewed as an indicator of development. Soda ash and alkalis have different principal manufacturing applications.
Q18. Which of the following statements regarding fertilizers is FALSE?
[RRB Group D (25 August 2022, Shift 3)]
(A) Must be properly stored
(B) Leaches out with rains or irrigation water
(C) Never contaminate air and water
(D) Nutrient amounts calculated in advance can be applied
Answer: (C) Never contaminate air and water
Explanation: Fertilisers can pollute air and water when applied excessively or mishandled. Rainwater runoff and leaching move nutrients into streams and groundwater, encouraging eutrophication. Some fertiliser nitrogen is also lost as ammonia or nitrous oxide. Storage and carefully calculated application reduce these effects.
Q17. Which of the following statements is correct?
I. Converting plant and animal waste including that from kitchen into manure is called composting.
II. The method of making compost from kitchen garbage using redworms is called vermicomposting.
[SSC MTS (14 July 2022, Shift 3)]
(A) Only I is correct.
(B) Neither I nor II is correct.
(C) Both I and II are correct.
(D) Only II is correct.
Answer: (C) Both I and II are correct.
Explanation: Composting converts biodegradable organic wastes into manure through microbial decomposition. Vermicomposting specifically uses earthworms, such as redworms, to break down waste into nutrient-rich castings. Both processes recycle refuse, support soil structure and provide natural sources of plant nutrients.
Q16. The systematic name of which compound is nitrogen trihydride that is widely used in many industrial processes, and as a fertiliser and refrigerant?
[SSC CHSL, 2021 cycle (3 June 2022, Shift 2)]
(A) Potash
(B) Urea
(C) Phosphine
(D) Ammonia
Answer: (D) Ammonia
Explanation: Ammonia has formula NH₃ and is sometimes called nitrogen trihydride. It can be applied directly as a nitrogen fertiliser or converted into urea and ammonium salts. Industrial ammonia is chiefly synthesised from nitrogen and hydrogen by the Haber–Bosch process.
Q15. Which one of the following statements about fertilizers is not correct?
[UPSC NDA-I General Ability Test (10 April 2022)]
(A) Urea is a phosphorus-containing fertilizer.
(B) Application of fertilizer to the soil increases fertility of the soil.
(C) Urea can be prepared by action of ammonia and carbon dioxide under high pressure and at high temperature.
(D) Urea contains more nitrogen than other fertilizers.
Answer: (A) Urea is a phosphorus-containing fertilizer.
Explanation: Urea, CO(NH₂)₂, contains carbon, hydrogen, nitrogen and oxygen but no phosphorus. It is manufactured commercially from ammonia and carbon dioxide under elevated pressure and temperature. Its high nitrogen fraction, about 46%, makes it an important concentrated nitrogenous fertiliser.
Q14. Which of the following bacteria is associated with the formation of root nodules of leguminous plants?
[RRB NTPC CBT-I (24 July 2021, Shift 2)]
(A) Clostridium
(B) Escherichia
(C) Rhizobium
(D) Salmonella
Answer: (C) Rhizobium
Explanation: Rhizobium bacteria form a symbiotic association with legumes such as peas and beans. They inhabit root nodules and convert atmospheric nitrogen into plant-usable compounds. This natural nitrogen fixation improves soil fertility and helps decrease the requirement for external nitrogen fertilisers.
Q13. What do the letters NPK on a fertilizer pack indicate?
[RRB NTPC CBT-I (4 March 2021, Shift 2)]
(A) Nitric acid, Phosphorus, Potassium
(B) Nitrogen, Phosphoric acid, Potassium
(C) Nitrogen, Potassium, Phosphors
(D) Nitrogen, Phosphorus, Potassium
Answer: (D) Nitrogen, Phosphorus, Potassium
Explanation: N, P and K denote nitrogen, phosphorus and potassium, the three primary fertiliser nutrients. Nitrogen supports leafy growth, phosphorus assists roots and energy transfer, and potassium regulates water balance and enzymes. Fertiliser grades express their concentrations using the N–P₂O₅–K₂O convention.
Q12. Artificial fertilizers were first created during the _______ century.
[RRB NTPC CBT-I (9 January 2021, Shift 1)]
(A) 19th
(B) 16th
(C) 18th
(D) 17th
Answer: (A) 19th
Explanation: The nineteenth century saw major advances in agricultural chemistry, including manufactured superphosphate fertilisers. Early industrial fertiliser production predated the twentieth-century Haber–Bosch ammonia process. These innovations helped agriculture move beyond exclusive reliance on manure and naturally occurring nutrient deposits.
Q11. With reference to chemical fertilizers in India, consider the following statements:
1. At present, the retail price of chemical fertilizers is market-driven and not administered by the Government.
2. Ammonia, which is an input of urea, is produced from natural gas.
3. Sulphur, which is a raw material for phosphoric acid fertilizer, is a by-product of oil refineries.
Which of the statements given above is/are correct?
[UPSC CSE Prelims GS Paper I (2020)]
(A) 1 only
(B) 2 and 3 only
(C) 2 only
(D) 1, 2 and 3
Answer: (B) 2 and 3 only
Explanation: Urea pricing in India is administered rather than fully market-driven, so statement 1 is incorrect. Natural gas provides hydrogen for ammonia synthesis, and sulphur recovered from petroleum refining is used to make sulphuric acid for phosphatic fertiliser production. Thus, statements 2 and 3 hold.
Q10. Which one is a fertilizer?
[WBCS Prelims (2020)]
(A) N₂
(B) O₂
(C) P₄
(D) NaNO₃
Answer: (D) NaNO₃
Explanation: Sodium nitrate, NaNO₃, also called Chile saltpetre, is a nitrate-based nitrogen fertiliser. Plants readily absorb nitrogen in nitrate form. Molecular nitrogen in air is not directly usable by most plants, while oxygen and elemental phosphorus are not conventional fertilisers.
Q9. Which of the following is not a raw-material for fertilizer industry?
[MPPSC State Service GS (2020)]
(A) Naphtha
(B) Gypsum
(C) Sulphur
(D) Caustic soda
Answer: (D) Caustic soda
Explanation: Naphtha can provide feedstock for ammonia manufacture, sulphur is used to make sulphuric acid for phosphate processing, and gypsum has agricultural amendment uses. Caustic soda is principally used in soap, paper, aluminium and other industries, rather than as a standard fertiliser raw material.
Q8. How much amount of urea will be required for supplying 1 kg of nitrogen?
[UPPSC BEO (16 August 2020)]
(A) 2.0 kg
(B) 2.2 kg
(C) 2.5 kg
(D) 2.7 kg
Answer: (B) 2.2 kg
Explanation: Commercial urea contains about 46% nitrogen by mass. To supply one kilogram of nitrogen, divide 1 by 0.46, giving approximately 2.17 kilograms. Rounded to one decimal place, the required quantity is 2.2 kilograms of urea.
Q7. Which of the following fertilizers has more nitrogen content?
[WBCS Prelims (2019)]
(A) Urea
(B) Ammonium nitrate
(C) Potassium nitrate
(D) Ammonium phosphate
Answer: (A) Urea
Explanation: Urea has approximately 46% nitrogen by mass, higher than the nitrogen fractions of the other listed fertilisers. Its chemical formula is CO(NH₂)₂. High nitrogen concentration makes it economical to transport and apply, although efficient use requires appropriate management.
Q6. Grey revolution is related to ______.
[RRB Group D (28 September 2018, Shift 2)]
(A) Leather
(B) Silk
(C) Fish
(D) Fertilizers
Answer: (D) Fertilizers
Explanation: The term Grey Revolution is conventionally associated in competitive-exam terminology with increased fertiliser production. Other colour-coded revolutions denote different sectors, such as the White Revolution for milk and the Blue Revolution for fisheries. Such terms are general-knowledge associations rather than formal chemical classifications.
Q5. Why does the Government of India promote the use of ‘Neem-coated Urea’ in agriculture?
[UPSC CSE Prelims GS Paper I (2016)]
(A) Release of neem oil in the soil increases nitrogen fixation by soil microorganisms.
(B) Neem coating slows down the rate of dissolution of urea in the soil.
(C) Nitrous oxide, which is a greenhouse gas, is not at all released into atmosphere by crop fields.
(D) It is a combination of a weedicide and a fertilizer for particular crops.
Answer: (B) Neem coating slows down the rate of dissolution of urea in the soil.
Explanation: Neem coating slows nitrogen release and inhibits processes that rapidly convert urea nitrogen into easily lost forms. This can improve nitrogen-use efficiency and limit diversion of subsidised urea. It does not eliminate nitrous oxide emissions or turn urea into a weedicide.
Q4. The bio-fertilizer used as a supplementary food for the cattle, especially for milking bovines is:
[RPSC RAS Prelims (2016)]
(A) Azotobacter
(B) Azospirillum
(C) Rhizobium
(D) Azolla
Answer: (D) Azolla
Explanation: Azolla is a small floating aquatic fern used both as a biofertiliser and, after suitable preparation, as protein-rich supplementary animal feed. Its association with nitrogen-fixing cyanobacteria supports paddy cultivation. The other options are nitrogen-fixing bacteria, not comparable aquatic feed plants.
Q3. Directions: The following items consist of two statements, Statement I and Statement II. You are to examine these two statements carefully and select the answers to these items using the code given below:
Statement I: Growth of plants is smooth with a complete fertilizer.
Statement II: A complete fertilizer always contains N, P, K.
[UPSC NDA General Ability Test (19 April 2015)]
(A) Both the statements are individually true and Statement II is the correct explanation of Statement I.
(B) Both the statements are individually true but Statement II is not the correct explanation of Statement I.
(C) Statement I is true but Statement II is false.
(D) Statement I is false but Statement II is true.
Answer: (B) Both the statements are individually true but Statement II is not the correct explanation of Statement I.
Explanation: A complete fertiliser supplies all three primary nutrients: nitrogen, phosphorus and potassium. Both statements were treated as true by the paper’s answer key, but the second was not accepted as a sufficient explanation of the first. Crop growth also depends on other nutrients and conditions.
Q2. Consider the following organisms: 1. Agaricus, 2. Nostoc, 3. Spirogyra. Which of the above is/are used as biofertilizer/biofertilizers?
[UPSC CSE Prelims GS Paper I (2013)]
(A) 1 and 2
(B) 2 only
(C) 2 and 3
(D) 3 only
Answer: (B) 2 only
Explanation: Nostoc is a cyanobacterium capable of fixing atmospheric nitrogen and can enrich soils as a biofertiliser. Agaricus is a mushroom genus, and Spirogyra is a filamentous green alga not normally used as a nitrogen-fixing biofertiliser. Therefore only the second organism qualifies.
Q1. Which of the following is/are used as biofertilizers? 1. Azolla, 2. Blue-green algae, 3. Alfalfa. Choose the correct answer using the codes given below.
[UPPSC PCS Prelims (2002)]
(A) 2 only
(B) 1 and 2
(C) 1 and 3
(D) 1, 2 and 3
Answer: (B) 1 and 2
Explanation: Azolla hosts nitrogen-fixing cyanobacteria, and certain blue-green algae also fix atmospheric nitrogen and enrich cultivated soils. Alfalfa is itself a nitrogen-fixing leguminous crop, generally regarded here as fodder or green manure rather than a microbial biofertiliser. Hence the first two qualify.