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Maharashtra HSC Crop Science (Vocational) study materials
Maharashtra HSC Crop Science (Vocational) study resources

Maharashtra HSC Crop Science (Vocational) practice questions

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Question 1Introduction to Crop Science and Crop Classification

In crop science, the term 'agronomy' is best defined as the branch that deals with which of the following?

  1. Field crops grown on a large scale and their soil and water management Correct answer.
  2. Only the breeding of new varieties under laboratory conditions
  3. Only fruit trees and plantation crops grown for cash income
  4. Only the processing and marketing of harvested produce

Explanation

Agronomy is the branch of crop science concerned with field crops and the management of soil, water and cultivation practices for them. Horticulture, by contrast, deals with garden, fruit and plantation crops. Processing and marketing belong to post-harvest and agricultural economics, not agronomy.

Question 2Introduction to Crop Science and Crop Classification

A crop that completes its life cycle within a single growing season and must be sown again each year is classified as which type?

  1. Biennial
  2. Annual Correct answer.
  3. Ephemeral
  4. Perennial

Explanation

Annual crops germinate, grow, flower, set seed and die within one season, so they must be resown each year; examples include rice, wheat and maize. Biennials need two seasons and perennials live for several years. 'Ephemeral' is not a standard class in crop classification.

Question 3Introduction to Crop Science and Crop Classification

Which of the following pairs correctly matches a crop with the family to which it belongs?

  1. Groundnut - Poaceae
  2. Wheat - Solanaceae
  3. Rice - Fabaceae
  4. Chickpea - Fabaceae Correct answer.

Explanation

Chickpea (Cicer arietinum) is a legume and belongs to the family Fabaceae. Rice and wheat are grasses of the family Poaceae, while groundnut belongs to Fabaceae and not Poaceae. Matching crops to families is a basic step in botanical classification.

Question 4Introduction to Crop Science and Crop Classification

Crops grown primarily for their edible seeds rich in protein and used as pulses, such as pigeon pea and lentil, are grouped under which category?

  1. Fibre crops
  2. Oilseeds
  3. Cereals
  4. Pulses Correct answer.

Explanation

Pulses are the dried edible seeds of leguminous crops and are valued mainly for their protein content. Cereals are grasses grown for starch-rich grains, oilseeds for oil extraction, and fibre crops for lint or stem fibre. Pigeon pea and lentil are therefore pulses.

Question 5Introduction to Crop Science and Crop Classification

The practice of growing two or more crops simultaneously in the same field in a definite row arrangement is known as which of the following?

  1. Sole cropping
  2. Sequence cropping
  3. Shifting cultivation
  4. Intercropping Correct answer.

Explanation

Intercropping is the growing of two or more crops together in the same field in a definite row proportion during the same season. Sole cropping involves one crop alone, and sequence cropping involves crops one after another. Shifting cultivation is a land-use system, not a spatial arrangement of crops.

Question 6Introduction to Crop Science and Crop Classification

Which of the following is the correct scientific name for the crop commonly known as rice?

  1. Sorghum bicolor
  2. Oryza sativa Correct answer.
  3. Zea mays
  4. Triticum aestivum

Explanation

Rice is Oryza sativa, a member of the grass family Poaceae. Triticum aestivum is wheat, Zea mays is maize and Sorghum bicolor is sorghum. Binomial names follow the genus-species convention, with the genus capitalised.

Question 7Introduction to Crop Science and Crop Classification

A crop is described as 'kharif' in Maharashtra. Which criterion is used to place a crop in this group?

  1. The crop is harvested only after three growing seasons
  2. The crop is sown in winter and harvested in spring
  3. The crop is sown with the onset of the monsoon and harvested in autumn Correct answer.
  4. The crop requires irrigation throughout the year

Explanation

Kharif crops are sown with the arrival of the south-west monsoon around June-July and harvested in autumn, for example rice, cotton and soybean. Rabi crops are sown in winter and harvested in spring. The kharif-rabi grouping is based on the season of sowing and harvest.

Question 8Introduction to Crop Science and Crop Classification

A farmer wants a classification that tells him how a crop is used after harvest. Which system of classification should he use?

  1. Economic classification based on the end use of the produce Correct answer.
  2. Botanical classification based on the plant family
  3. Classification based on the life cycle of the crop
  4. Classification based on the mode of pollination

Explanation

Economic classification groups crops by the purpose of the harvested produce, such as cereals, pulses, oilseeds, fibres, sugar crops and fodder. Botanical, life-cycle and pollination-based systems describe the plant itself rather than its end use. A farmer planning utilisation would therefore choose economic classification.

Question 9Introduction to Crop Science and Crop Classification

Which of the following crops is a legume that can enrich soil nitrogen through symbiosis with Rhizobium bacteria?

  1. Soybean Correct answer.
  2. Sugarcane
  3. Cotton
  4. Wheat

Explanation

Soybean is a legume of the family Fabaceae and forms root nodules with Rhizobium bacteria, which fix atmospheric nitrogen. Cotton, sugarcane and wheat are non-legumes and do not form this symbiotic association. This is why legumes are favoured in rotations and intercropping.

Question 10Introduction to Crop Science and Crop Classification

In a cropping scheme, a short-duration pulse is grown between the harvest of kharif rice and the sowing of a rabi crop. This practice is best described as which of the following?

  1. Relay cropping
  2. Catch cropping Correct answer.
  3. Mixed cropping
  4. Monocropping

Explanation

Catch cropping uses a short-duration crop to fill the unutilised period between two main crops so that land and moisture are not wasted. Mixed cropping grows two or more crops together without a definite row pattern, and relay cropping overlaps the sowing of the next crop before the previous one is harvested. Monocropping is repeated growing of one crop.

Question 11Introduction to Crop Science and Crop Classification

Which of the following statements about the classification of crops as cereals is correct?

  1. All cereals belong to the family Fabaceae
  2. Cereals are always perennial crops
  3. Cereals are grown mainly for their oil-rich seeds
  4. Cereals are grasses grown for their starchy grains Correct answer.

Explanation

Cereals are members of the grass family Poaceae cultivated for their starchy grains, which form a staple food for most people. Examples include rice, wheat, maize and sorghum. They are not oil crops, not Fabaceae, and most are annual.

Question 12Introduction to Crop Science and Crop Classification

A crop scientist notes that a particular crop has a C4 photosynthetic pathway. Which advantage would this confer in a hot, dry environment?

  1. Complete inability to use atmospheric carbon dioxide
  2. Higher water-use efficiency and reduced photorespiration Correct answer.
  3. Greater dependence on cool, humid conditions
  4. Obligate parasitism on other crop plants

Explanation

C4 plants concentrate carbon dioxide in bundle-sheath cells, which suppresses photorespiration and improves water-use efficiency under high temperature and light. Crops such as maize, sorghum and sugarcane are C4. The pathway does not prevent carbon dioxide use or imply parasitism.

Question 13Introduction to Crop Science and Crop Classification

Which of the following correctly distinguishes a 'cash crop' from a 'food crop'?

  1. Cash crops are always grown on smaller areas than food crops
  2. Food crops are always perennial while cash crops are annual
  3. Cash crops cannot be processed before sale
  4. Cash crops are grown mainly for sale and income rather than home consumption Correct answer.

Explanation

Cash crops such as cotton, sugarcane and oilseeds are cultivated primarily for sale and income, while food crops are grown chiefly to feed the farm family and local population. The distinction is based on the purpose of production, not on area, life span or processing.

Question 14Introduction to Crop Science and Crop Classification

Which of the following crops is best described as a ' fibre crop' grown for its lint?

  1. Sunflower
  2. Cotton Correct answer.
  3. Sugarcane
  4. Jute

Explanation

Cotton is grown for the lint borne on its seeds, which is spun into textile fibre. Jute is also a fibre crop but its fibre comes from the stem bast rather than seed lint. Sunflower is an oilseed and sugarcane a sugar crop.

Question 15Introduction to Crop Science and Crop Classification

Which crop is a 'plantation crop' in the Indian context?

  1. Lentil
  2. Rubber Correct answer.
  3. Wheat
  4. Pearl millet

Explanation

Plantation crops are perennial crops grown on estates and usually processed on or near the estate; rubber, tea, coffee and coconut are examples. Wheat and pearl millet are annual cereals, and lentil is a pulse. Rubber therefore fits the plantation category.

Question 16Introduction to Crop Science and Crop Classification

A crop that requires a period of low temperature to induce flowering is described as having which requirement?

  1. Vernalisation Correct answer.
  2. Apomixis
  3. Dormancy
  4. Photoperiodism

Explanation

Vernalisation is the induction of flowering by exposure to low temperature, seen in crops such as wheat and some brassicas. Photoperiodism is the response to day length, dormancy is a resting state, and apomixis is asexual seed formation. These are distinct physiological concepts.

Question 17Introduction to Crop Science and Crop Classification

Two crops, A and B, are grown together in alternate rows. Crop A is a tall cereal and crop B is a short legume. Which statement best explains the advantage of this arrangement?

  1. The legume fixes nitrogen that may benefit the cereal, and the two crops use light and space differently Correct answer.
  2. The cereal shades the legume completely so that weeds cannot grow
  3. The arrangement eliminates the need for any soil moisture
  4. Both crops compete for exactly the same resources, so yields always rise

Explanation

In such an intercrop, the legume can add nitrogen through symbiosis while the two crops exploit different canopy heights and rooting depths, improving resource use. Complete shading would harm the legume, and competition for identical resources would reduce rather than raise yields. Water is still required.

Question 18Introduction to Crop Science and Crop Classification

Which of the following pairs of crops is correctly classified as belonging to the same economic group?

  1. Cotton and sugarcane - fibre crops
  2. Tea and wheat - plantation crops
  3. Groundnut and mustard - oilseeds Correct answer.
  4. Rice and chickpea - cereals

Explanation

Groundnut and mustard are both grown for their oil-rich seeds and belong to the oilseed group. Rice is a cereal but chickpea is a pulse, cotton is a fibre crop while sugarcane is a sugar crop, and tea is a plantation crop whereas wheat is a cereal.

Question 19Introduction to Crop Science and Crop Classification

A crop is described as 'drought escaping' rather than 'drought tolerant'. Which characteristic best fits this description?

  1. It completes its life cycle before the soil moisture is exhausted Correct answer.
  2. It closes stomata permanently during the entire season
  3. It accumulates osmolytes to survive severe internal water deficit
  4. It maintains high tissue water potential through deep roots under prolonged drought

Explanation

Drought escape means the crop finishes its critical growth stages before drought becomes severe, often through early maturity and short duration. Drought tolerance involves maintaining function under internal water deficit through deep roots or osmotic adjustment. Permanent stomatal closure would be harmful, not adaptive.

Question 20Introduction to Crop Science and Crop Classification

Which of the following best explains why crops are classified by their root system into tap-rooted and fibrous-rooted groups?

  1. It indicates the crop's photoperiodic response
  2. It shows whether the crop is annual or perennial
  3. It determines the crop's market price
  4. It indicates whether the crop belongs to the dicotyledons or monocotyledons Correct answer.

Explanation

Dicotyledonous crops generally develop a tap root system, whereas monocotyledonous crops such as grasses have fibrous roots. Root type is therefore a useful indicator of the broader botanical group. Life cycle, market price and photoperiodic response are unrelated to root morphology.

Question 21Soil Science and Soil Fertility Management

In the standard classification of soil separates, which particle size range corresponds to clay?

  1. Less than 0.002 mm in diameter Correct answer.
  2. 0.002 to 0.05 mm in diameter
  3. Greater than 2.0 mm in diameter
  4. 0.05 to 2.0 mm in diameter

Explanation

Clay is the finest soil separate, defined as particles smaller than 0.002 mm. Silt occupies the 0.002 to 0.05 mm range and sand the 0.05 to 2.0 mm range. Because clay particles are so small, they carry the greatest surface area per unit mass and dominate a soil's adsorption behaviour.

Question 22Soil Science and Soil Fertility Management

A soil sample has 55% sand, 20% silt and 25% clay. Using the soil textural triangle, this soil falls in which textural class?

  1. Loam
  2. Sandy clay loam
  3. Silt loam
  4. Sandy loam Correct answer.

Explanation

A soil with 55% sand, 20% silt and 25% clay plots in the sandy loam class, because sandy loam spans roughly 43 to 85% sand with limited clay and silt. The dominant sand fraction pulls the texture toward the sandy side rather than toward loam or silt loam.

Question 23Soil Science and Soil Fertility Management

Which soil structure type is best described as having rounded, granular aggregates with high porosity and is typically promoted by organic matter in the surface horizon?

  1. Columnar
  2. Granular Correct answer.
  3. Blocky
  4. Platy

Explanation

Granular structure consists of small, rounded aggregates that create high porosity and good aeration, and it is strongly associated with organic-matter-rich surface horizons. Platy, columnar and blocky structures have flatter or more angular shapes that restrict water and air movement.

Question 24Soil Science and Soil Fertility Management

The cation exchange capacity of a soil is expressed in which unit?

  1. Decisiemens per metre
  2. Megapascals
  3. Centimoles of charge per kilogram Correct answer.
  4. Milligrams per litre

Explanation

Cation exchange capacity measures the number of negative charges available to hold exchangeable cations and is expressed as centimoles of charge per kilogram, formerly written as milliequivalents per 100 g. It is a measure of charge concentration in the solid phase, not of solution concentration or salinity.

Question 25Soil Science and Soil Fertility Management

Among the common soil colloids, which one generally contributes the highest cation exchange capacity per unit mass?

  1. Organic humus Correct answer.
  2. Quartz sand
  3. Iron oxide
  4. Kaolinite

Explanation

Humus carries a very high density of pH-dependent negative charges, giving it the greatest cation exchange capacity per unit mass among common soil colloids. Kaolinite has low CEC, while quartz sand and iron oxides contribute almost none.

Question 26Soil Science and Soil Fertility Management

A farmer applies gypsum to a sodic soil. Which process does this amendment primarily promote?

  1. Reduction of exchangeable calcium in the soil
  2. Replacement of exchangeable sodium by calcium Correct answer.
  3. Increase in soil pH to alkaline levels
  4. Formation of platy structure in the subsoil

Explanation

Gypsum supplies calcium ions that displace exchangeable sodium on the clay complex, and the released sodium is leached away with drainage water. This reclamation improves aggregate stability and permeability in sodic soils.

Question 27Soil Science and Soil Fertility Management

The soil reaction at which most crop nutrients are optimally available and microbial activity is generally highest is approximately:

  1. pH 4.0
  2. pH 9.0
  3. pH 6.5 Correct answer.
  4. pH 5.0

Explanation

Around pH 6.5 most essential nutrients remain soluble and available while toxic concentrations of aluminium and manganese are minimised. Microbial decomposition and nutrient cycling also proceed efficiently in this near-neutral range.

Question 28Soil Science and Soil Fertility Management

Which material is most commonly recommended to raise the pH of an acidic agricultural soil?

  1. Agricultural lime (calcium carbonate) Correct answer.
  2. Aluminium sulphate
  3. Elemental sulphur
  4. Ammonium sulphate

Explanation

Calcium carbonate neutralises soil acidity by reacting with hydrogen ions and raising the pH, and it is the standard liming material. Acidifying amendments such as sulphur and ammonium sulphate lower pH instead.

Question 29Soil Science and Soil Fertility Management

Which essential plant nutrient is classified as a primary macronutrient along with nitrogen and potassium?

  1. Boron
  2. Calcium
  3. Zinc
  4. Phosphorus Correct answer.

Explanation

The primary macronutrients are nitrogen, phosphorus and potassium, required in the largest quantities by crops. Calcium is a secondary macronutrient, while zinc and boron are micronutrients.

Question 30Soil Science and Soil Fertility Management

A legume crop such as soybean is grown mainly because it can obtain nitrogen through symbiosis. Which organism carries out this symbiotic fixation in root nodules?

  1. Rhizobium bacteria Correct answer.
  2. Mycorrhizal fungi
  3. Azotobacter bacteria
  4. Nitrosomonas bacteria

Explanation

Rhizobium bacteria invade legume roots and form nodules in which atmospheric nitrogen is reduced to ammonia for the plant. Azotobacter fixes nitrogen freely in soil without nodules, Nitrosomonas oxidises ammonia, and mycorrhizal fungi aid phosphorus uptake rather than nitrogen fixation.

Question 31Soil Science and Soil Fertility Management

A grower wants to apply 60 kg of nitrogen per hectare using urea, which contains 46% nitrogen. How much urea is required per hectare?

  1. 130.4 kg Correct answer.
  2. 46.0 kg
  3. 60.0 kg
  4. 27.6 kg

Explanation

The quantity of fertiliser needed is the nutrient dose divided by the fraction of nutrient in the product: 60 divided by 0.46 equals about 130.4 kg of urea per hectare. This calculation ensures the correct nutrient dose is delivered without over- or under-application.

Question 32Soil Science and Soil Fertility Management

The fertiliser grade 10-26-26 printed on a bag indicates which composition?

  1. Percentage of nitrogen, phosphorus and potassium in elemental form
  2. Ratio of nitrogen to phosphorus to potassium in the applied solution
  3. Kilograms of nitrogen, phosphorus and potassium per bag
  4. Percentage of nitrogen, phosphorus as P2O5 and potassium as K2O Correct answer.

Explanation

Fertiliser grades express the percentage of nitrogen, available phosphorus expressed as phosphorus pentoxide (P2O5) and potassium expressed as potassium oxide (K2O). The phosphorus and potassium figures are oxide forms, not elemental contents, which is why conversion factors are used.

Question 33Soil Science and Soil Fertility Management

Which soil water form is most readily available to plants?

  1. Capillary water Correct answer.
  2. Gravitational water
  3. Hygroscopic water
  4. Water held below permanent wilting point

Explanation

Capillary water is held in the fine pores by surface tension at tensions between field capacity and the permanent wilting point, making it the main available supply for roots. Hygroscopic water is tightly bound and unavailable, gravitational water drains too quickly, and water below wilting point cannot be absorbed.

Question 34Soil Science and Soil Fertility Management

The permanent wilting point of a soil represents the water content at which:

  1. Plants can no longer extract water and remain wilted even in a humid atmosphere Correct answer.
  2. The soil is saturated and all pores are filled with water
  3. Water drains freely under gravity after rainfall
  4. The soil reaches its maximum water-holding capacity

Explanation

Permanent wilting point is the water content at which plants wilt and cannot recover even when placed in a saturated atmosphere. It marks the lower limit of available water, held at very high tension around the soil particles.

Question 35Soil Science and Soil Fertility Management

Which soil organism is most closely associated with the decomposition of organic matter and the formation of humus in arable soils?

  1. Nematodes
  2. Earthworms
  3. Termites
  4. Bacteria and fungi Correct answer.

Explanation

Bacteria and fungi are the principal decomposers that break down plant residues and synthesise humus through the microbial biomass cycle. Earthworms and other fauna fragment residues and mix soil but rely on microbes for the actual chemical decomposition.

Question 36Soil Science and Soil Fertility Management

Which practice is most effective for conserving soil moisture in a rainfed field during a dry spell?

  1. Removing all crop residue after harvest
  2. Applying irrigation at permanent wilting point
  3. Mulching the soil surface with crop residue Correct answer.
  4. Frequent deep ploughing to expose the soil surface

Explanation

A surface mulch of crop residue reduces evaporation, moderates soil temperature and protects the surface from crusting, thereby conserving moisture. Exposing or bare soil increases evaporative loss, and irrigation at permanent wilting point is too late to prevent stress.

Question 37Soil Science and Soil Fertility Management

A soil test reports 280 kg/ha of available nitrogen, and the recommended dose is 120 kg/ha. What is the fertiliser nitrogen requirement per hectare?

  1. 120 kg/ha, matching the recommended dose
  2. Zero, because the soil already has more nitrogen than the recommended dose Correct answer.
  3. 160 kg/ha, the difference between soil test and dose
  4. 400 kg/ha, the sum of soil test and dose

Explanation

When soil test values already meet or exceed the recommended dose, no additional fertiliser nitrogen is needed. Applying more would waste money and risk nitrogen loss to the environment through leaching and volatilisation.

Question 38Soil Science and Soil Fertility Management

Which form of nitrogen is most susceptible to loss through denitrification under waterlogged conditions?

  1. Ammonium held on clay
  2. Urea in dry soil
  3. Nitrate Correct answer.
  4. Organic nitrogen in humus

Explanation

Under anaerobic, waterlogged conditions, denitrifying bacteria reduce nitrate to nitrogen gas and nitrous oxide, which escape to the atmosphere. Ammonium is held on exchange sites and is not the substrate for denitrification, and organic nitrogen is not directly lost this way.

Question 39Soil Science and Soil Fertility Management

Leaching of nitrate below the root zone is most likely under which combination of conditions?

  1. Light irrigation on a clay soil with high CEC
  2. Foliar spraying on a silt loam
  3. Dry weather on a loam soil with moderate organic matter
  4. Heavy rainfall on a sandy soil with low CEC Correct answer.

Explanation

Nitrate is an anion and is not held by negatively charged exchange sites, so it moves freely with drainage water. Sandy soils with low CEC and heavy rainfall create rapid downward movement that carries nitrate below the root zone.

Question 40Soil Science and Soil Fertility Management

A soil has a pH of 5.2, high exchangeable aluminium and low base saturation. Which limitation is most likely to affect crop growth?

  1. Sodium toxicity and boron deficiency
  2. Molybdenum deficiency and aluminium toxicity Correct answer.
  3. Potassium toxicity and calcium excess
  4. Phosphorus toxicity and manganese deficiency

Explanation

Strongly acidic soils with high exchangeable aluminium restrict root growth through aluminium toxicity and also reduce the availability of molybdenum, which becomes less soluble at low pH. Liming to raise pH near neutral alleviates both problems.

Question 41Soil Science and Soil Fertility Management

Which statement correctly describes the relationship between soil organic matter and cation exchange capacity?

  1. Organic matter has no effect on CEC because it lacks charge
  2. Increasing organic matter lowers CEC by diluting clay minerals
  3. Increasing organic matter raises CEC and improves nutrient retention Correct answer.
  4. Organic matter affects CEC only in sandy soils

Explanation

Organic matter carries numerous negative charges, particularly at pH values above neutral, so building organic matter increases CEC and improves the soil's ability to retain cations such as calcium, magnesium and potassium. This is one reason organic amendments improve fertility on low-CEC soils.

Question 42Soil Science and Soil Fertility Management

In a long-term experiment, continuous application of ammonium sulphate without liming caused a decline in soil pH. Which explanation best accounts for this?

  1. Sulphate ions neutralise soil acidity
  2. Ammonium is leached away without any reaction
  3. Ammonium oxidation releases hydrogen ions, acidifying the soil Correct answer.
  4. Sulphate is converted to calcium carbonate

Explanation

Nitrifying bacteria oxidise ammonium to nitrate and release hydrogen ions in the process, which lowers pH over time. Ammonium-based fertilisers are therefore acidifying, and continuous use requires periodic liming to maintain a favourable pH.

Question 43Soil Science and Soil Fertility Management

Which soil physical property is most directly improved by adding organic matter to a compacted clay soil?

  1. Particle density rises sharply
  2. Bulk density decreases and aggregate stability increases Correct answer.
  3. Bulk density increases and porosity decreases
  4. Water-holding capacity falls to zero

Explanation

Organic matter binds clay particles into stable aggregates, increasing porosity and lowering bulk density, which improves root penetration and water movement. This is a key reason organic amendments are used to rehabilitate compacted soils.

Question 44Soil Science and Soil Fertility Management

Which recommendation is most appropriate for correcting a zinc deficiency in a standing crop of wheat?

  1. Apply ammonium sulphate to the soil
  2. Spray the foliage with zinc sulphate solution Correct answer.
  3. Increase irrigation frequency
  4. Apply gypsum to the soil

Explanation

Foliar spraying with zinc sulphate solution delivers zinc directly to the leaves and corrects deficiency quickly in a standing crop. Soil application of zinc is also used, but gypsum, ammonium sulphate and irrigation do not supply zinc.

Question 45Plant Nutrition, Manures and Fertilizers

Which nutrient is absorbed by plants mainly as the divalent cation Mg2+ and forms the central atom of the chlorophyll molecule?

  1. Sulphur
  2. Boron
  3. Calcium
  4. Magnesium Correct answer.

Explanation

Magnesium is taken up as Mg2+ and occupies the centre of the porphyrin ring of every chlorophyll molecule, so a deficiency quickly produces interveinal chlorosis in older leaves. The other three elements have different structural roles and are not part of chlorophyll.

Question 46Plant Nutrition, Manures and Fertilizers

A farmer applies a fertilizer labelled 10:26:26. What does the figure 26 in the middle position represent?

  1. Percentage of potassium expressed as K2O
  2. Percentage of phosphorus expressed as P2O5 Correct answer.
  3. Percentage of sulphur expressed as SO3
  4. Percentage of nitrogen expressed as N

Explanation

Fertilizer grades follow the N-P2O5-K2O convention, so the middle value is available phosphorus expressed as phosphorus pentoxide. The third figure would be potash as K2O. This oxide convention allows different P and K sources to be compared on the same basis.

Question 47Plant Nutrition, Manures and Fertilizers

Which material is classed as an oilcake organic manure rather than a chemical fertilizer?

  1. Muriate of potash
  2. Neem cake Correct answer.
  3. Single superphosphate
  4. Urea

Explanation

Neem cake is the residue left after oil extraction from neem seed and is used as an organic manure that also supplies nitrogen and has some nematicidal action. Urea, muriate of potash and single superphosphate are manufactured inorganic fertilizers.

Question 48Plant Nutrition, Manures and Fertilizers

In the classification of essential elements, which group contains only the macronutrients?

  1. Copper, boron, molybdenum
  2. Chlorine, sodium, silicon
  3. Nitrogen, phosphorus, potassium Correct answer.
  4. Iron, manganese, zinc

Explanation

Macronutrients are required in relatively large amounts and include nitrogen, phosphorus, potassium, calcium, magnesium and sulphur. The other lists contain micronutrients or beneficial elements needed only in trace quantities.

Question 49Plant Nutrition, Manures and Fertilizers

Which process converts ammonium nitrogen to nitrate in well-aerated soil?

  1. Denitrification by Pseudomonas
  2. Nitrification by Nitrosomonas and Nitrobacter Correct answer.
  3. Nitrogen fixation by Rhizobium
  4. Ammonification by decay fungi

Explanation

Nitrification is a two-step aerobic process in which Nitrosomonas oxidises ammonium to nitrite and Nitrobacter then oxidises nitrite to nitrate. It requires adequate aeration, moisture and a near-neutral pH, and it is the reason ammonium fertilizers eventually feed the crop as nitrate.

Question 50Plant Nutrition, Manures and Fertilizers

A soil test shows a pH of 5.2 in a field where a legume crop is planned. Which amendment is most appropriate to raise the pH before sowing?

  1. Ammonium sulphate
  2. Gypsum
  3. Agricultural lime Correct answer.
  4. Elemental sulphur

Explanation

Agricultural lime, mainly calcium carbonate, neutralises soil acidity and raises pH towards the near-neutral range legumes prefer for nodulation. Gypsum supplies calcium and sulphur without a strong liming effect, while sulphur and ammonium sulphate acidify the soil further.