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Maharashtra HSC Agricultural Science & Technology study materials
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Maharashtra HSC Agricultural Science & Technology practice questions

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Question 1Plant Science and Crop Production

Which practice is the most appropriate primary treatment for improving the water-holding capacity of a sandy soil in a Maharashtra field before kharif sowing?

  1. Spraying a contact herbicide to reduce surface evaporation
  2. Applying well-decomposed farmyard manure and incorporating it into the topsoil Correct answer.
  3. Flooding the field repeatedly to settle the fine particles
  4. Applying gypsum at 2.5 t/ha before ploughing

Explanation

Sandy soils have low water-holding capacity because of large pore spaces and low organic matter. Incorporating well-decomposed organic manure improves aggregation and moisture retention. Gypsum is a reclamation amendment for sodic soils, not for improving sandy soil texture.

Question 2Plant Science and Crop Production

In the classification of crops by life cycle, which crop is a true annual completed within one season?

  1. Pigeon pea
  2. Sugarcane
  3. Banana
  4. Jowar Correct answer.

Explanation

Jowar (sorghum) completes its life cycle from seed to seed within a single season and is treated as an annual crop. Pigeon pea is grown as a long-duration annual-to-semi-perennial crop, while sugarcane and banana are perennial crops retained through ratoon or sucker cycles.

Question 3Plant Science and Crop Production

A farmer wants to raise a legume in the rabi season on residual soil moisture with minimal irrigation. Which crop fits this requirement best?

  1. Green gram
  2. Bengal gram Correct answer.
  3. Soybean
  4. Groundnut

Explanation

Bengal gram (chickpea) is the classic rabi pulse grown largely on stored soil moisture after the monsoon. Green gram and soybean are predominantly kharif crops, and groundnut is mainly a kharif or summer crop in Maharashtra.

Question 4Plant Science and Crop Production

Which seed-quality parameter is measured by the standard germination test in a seed testing laboratory?

  1. The percentage of seedlings that develop into normal seedlings under specified conditions Correct answer.
  2. The moisture content of the seed lot
  3. The percentage of pure seed in the sample
  4. The weight of one thousand seeds

Explanation

The germination test places seeds under prescribed moisture, temperature and light conditions and counts the normal seedlings produced. Purity analysis, moisture determination and thousand-grain weight are separate tests in seed quality evaluation.

Question 5Plant Science and Crop Production

Which plant nutrient is the central atom of the chlorophyll molecule?

  1. Magnesium Correct answer.
  2. Manganese
  3. Iron
  4. Calcium

Explanation

Magnesium occupies the central position of the porphyrin ring in chlorophyll, so deficiency causes interveinal chlorosis. Iron and manganese are involved in chlorophyll synthesis but are not structural components of the molecule.

Question 6Plant Science and Crop Production

Which type of inflorescence is characteristic of the wheat plant?

  1. Raceme
  2. Panicle
  3. Spike Correct answer.
  4. Umbel

Explanation

Wheat bears a spike, in which sessile spikelets are arranged directly on the rachis. Rice carries a panicle, while mustard bears a raceme and umbelliferous crops bear umbels.

Question 7Plant Science and Crop Production

Which irrigation method is most suitable for a closely spaced row crop such as onion on a light-textured soil?

  1. Border strip flooding
  2. Basin flooding
  3. Furrow irrigation
  4. Drip irrigation Correct answer.

Explanation

Drip irrigation delivers water directly to the root zone with high application efficiency and suits closely spaced crops on light soils. Flooding methods waste water and can cause uneven wetting, while furrows are awkward for dense, shallow-rooted crops.

Question 8Plant Science and Crop Production

Which of the following is a kharif cereal commonly grown in the rainfed areas of Maharashtra?

  1. Mustard
  2. Barley
  3. Wheat
  4. Bajra Correct answer.

Explanation

Bajra (pearl millet) is a kharif cereal well adapted to rainfed conditions and light soils. Wheat and barley are rabi cereals, and mustard is a rabi oilseed, so they do not fit a kharif rainfed cereal description.

Question 9Plant Science and Crop Production

A soil test reports a pH of 8.9 with an exchangeable sodium percentage of 22. Which reclamation measure is most appropriate?

  1. Applying powdered elemental sulphur with thorough mixing
  2. Growing a crop without any amendment to save cost
  3. Applying lime to raise the calcium status
  4. Applying gypsum followed by leaching with good-quality water Correct answer.

Explanation

High pH together with a high exchangeable sodium percentage identifies a sodic soil. Gypsum supplies soluble calcium that replaces sodium on the exchange complex, and the displaced sodium is then removed by leaching. Elemental sulphur is slower acting and is more suited to calcareous soils where gypsum is less effective.

Question 10Plant Science and Crop Production

In a crop rotation, which sequence best exploits the nitrogen contribution of a preceding legume to a cereal?

  1. Legume followed by cereal in the next season Correct answer.
  2. Cereal followed by cereal in the same year
  3. Fallow followed by fallow
  4. Cereal followed by legume followed by bare fallow

Explanation

A legume in the preceding season adds biologically fixed nitrogen and improves soil structure, which benefits the following cereal. Continuous cereals deplete nitrogen, and bare fallow wastes the growing period without adding nitrogen.

Question 11Plant Science and Crop Production

A grower wants to control weeds in a standing crop of soybean without disturbing the crop canopy. Which approach is most consistent with integrated weed management?

  1. Broadcast sowing of a competitive cereal
  2. Removing the crop rows to expose weeds
  3. Deep ploughing after crop emergence
  4. Post-emergence selective herbicide supported by intercultivation Correct answer.

Explanation

Integrated weed management combines a selective chemical measure with mechanical or cultural methods. A post-emergence selective herbicide that spares soybean, supported by intercultivation, controls weeds without harming the crop. Deep ploughing after emergence would damage the crop root system.

Question 12Plant Science and Crop Production

Which factor most directly determines the water requirement of a crop during its critical growth stage?

  1. The crop coefficient at that stage combined with reference evapotranspiration Correct answer.
  2. The number of seeds per pod
  3. The length of the peduncle
  4. The colour of the seed coat

Explanation

Crop water requirement is estimated as reference evapotranspiration multiplied by the crop coefficient for that growth stage. Critical stages such as flowering and grain filling have high coefficients and are most sensitive to moisture stress. Seed and morphological characters do not determine water demand.

Question 13Plant Science and Crop Production

Which practice best reduces post-harvest losses of freshly harvested paddy during the monsoon?

  1. Mixing fresh and old grain in the same storage bin
  2. Storing the grain in open gunny bags on a damp floor
  3. Drying the grain to safe moisture before bagging in a dry store Correct answer.
  4. Heaping wet paddy in large covered piles for several days

Explanation

Freshly harvested paddy carries high moisture and heats rapidly if heaped, encouraging mould and discoloration. Drying to safe moisture and storing in a dry, ventilated place prevents spoilage. Mixing lots and damp floors promote moisture migration and insect build-up.

Question 14Plant Science and Crop Production

Which soil microorganism is chiefly responsible for the symbiotic fixation of atmospheric nitrogen in the root nodules of pulses?

  1. Rhizobium Correct answer.
  2. Azotobacter
  3. Azospirillum
  4. Mycorrhiza

Explanation

Rhizobium forms nodules on the roots of leguminous crops and fixes atmospheric nitrogen in symbiosis with the host. Azotobacter and Azospirillum are free-living or associative fixers, and mycorrhiza assists mainly with phosphorus uptake.

Question 15Plant Science and Crop Production

A cotton field shows plants with leaves turning reddish and shedding squares heavily, and the soil test reports low potassium. Which corrective action is most appropriate?

  1. Soil application of muriate of potash followed by irrigation Correct answer.
  2. Application of lime to raise the pH
  3. Foliar spray of urea to correct the potassium shortage
  4. Increasing the seed rate in the next sowing

Explanation

Reddening of leaves with premature square shedding in cotton is a recognised symptom of potassium deficiency. Muriate of potash applied to the soil and watered in supplies potassium, which is taken up in large amounts by cotton. Urea supplies nitrogen and would not correct the deficiency.

Question 16Plant Science and Crop Production

Which of the following describes the correct way to take a representative soil sample from a field for fertility testing?

  1. Collect several random cores from the plough layer, mix them and quarter to a composite sample Correct answer.
  2. Collect soil from the surface crust only, avoiding the root zone
  3. Collect one sample from the field corner and mix it with water
  4. Collect a single sample from the lowest spot in the field

Explanation

A representative sample is built from several random cores taken across the field at plough-layer depth and mixed into a composite. Quartering reduces the bulk while retaining representativeness. Single or edge samples misrepresent field fertility.

Question 17Plant Science and Crop Production

Which practice is the most effective cultural control for the stem borer complex in paddy?

  1. Burning the harvested grain
  2. Increasing the nitrogen dose to raise plant vigour
  3. Removing and destroying stubble after harvest to break the pest cycle Correct answer.
  4. Flooding the field immediately after harvest

Explanation

Stem borer larvae survive in the stubble and straw after harvest, so clipping and destroying stubble breaks the carry-over cycle. Excess nitrogen makes plants more succulent and attractive to borers, and flooding after harvest is not a standard borer control.

Question 18Plant Science and Crop Production

Which plant growth regulator is used to induce uniform ripening in a standing crop of banana or to hasten fruit ripening after harvest?

  1. Ethephon Correct answer.
  2. Benzyl adenine
  3. Gibberellic acid
  4. Indole-3-butyric acid

Explanation

Ethephon releases ethylene on application and is used to advance and synchronise ripening. Gibberellic acid mainly promotes elongation, indole-3-butyric acid promotes rooting of cuttings, and benzyl adenine is a cytokinin used for cell division effects.

Question 19Plant Science and Crop Production

Which agronomic practice best conserves soil moisture in a rainfed kharif field during a dry spell?

  1. Frequent shallow ploughing after every shower to break the surface crust
  2. Removing all crop residues from the field after harvest
  3. Maintaining a soil mulch through intercultivation and a crop residue cover Correct answer.
  4. Increasing the plant population to shade the soil

Explanation

A soil mulch created by intercultivation, combined with crop residue cover, reduces evaporation from the surface and conserves stored moisture. Residue removal exposes the soil, and raising plant population increases transpiration without adding water.

Question 20Plant Science and Crop Production

Which statement correctly distinguishes hybrid seed from ordinary varietal seed in a cross-pollinated crop?

  1. Hybrid seed can be saved indefinitely without loss of vigour
  2. Hybrid seed must be produced from two genetically distinct parents and is normally re-sown each season Correct answer.
  3. Hybrid seed is always produced by self-pollination within a single line
  4. Hybrid seed has no requirement for controlled pollination

Explanation

Hybrid seed is produced by crossing two distinct parental lines under controlled pollination, and its advantage is expressed in the first generation. Saving seed from the hybrid crop leads to segregation and loss of vigour, so fresh hybrid seed is used each season.

Question 21Plant Science and Crop Production

A grower applies 120 kg N, 60 kg P2O5 and 40 kg K2O per hectare to a cereal. If urea, single superphosphate and muriate of potash are used, which calculation correctly gives the quantity of urea needed?

  1. About 60 kg of urea per hectare
  2. 120 kg of urea per hectare
  3. About 46 kg of urea per hectare
  4. About 261 kg of urea per hectare Correct answer.

Explanation

Urea contains 46 per cent nitrogen, so the quantity required is the nitrogen dose divided by 0.46. Dividing 120 by 0.46 gives approximately 261 kg of urea per hectare. Using the nitrogen dose directly or halving it would under-supply nitrogen.

Question 22Plant Science and Crop Production

In a field trial, a new variety out-yields the local check by 18 per cent, but its seed has a higher moisture content at harvest and germinates poorly after six months of ordinary storage. Which conclusion is most defensible?

  1. The variety should be rejected outright because of the storage problem
  2. The yield advantage is irrelevant because storage is a problem
  3. The germination problem proves the yield data are wrong
  4. The variety is promising but seed must be dried to safe moisture and stored properly before release is recommended Correct answer.

Explanation

A yield advantage is a genuine merit, but poor storage behaviour affects seed viability and must be managed by proper drying and storage. The sensible conclusion is conditional release with a defined seed-handling protocol, not outright rejection or dismissal of the yield data.

Question 23Plant Science and Crop Production

A farmer intercrops pigeon pea with sorghum in 6:2 rows. Which statement best explains the agronomic advantage of this system under rainfed conditions?

  1. Both crops compete for the same soil layer and the system always yields less than sole cropping
  2. The cereal provides support and the legume adds nitrogen, while the two crops use different canopy layers Correct answer.
  3. The legume suppresses the cereal completely, so the cereal yield is nil
  4. Intercropping eliminates the need for any weed control

Explanation

In a cereal-legume intercrop the tall cereal and the legume exploit different canopy and rooting layers, and the legume contributes fixed nitrogen. The system aims at higher total productivity and stability under rainfed conditions rather than mutual elimination.

Question 24Plant Science and Crop Production

A soil shows poor infiltration, surface crusting and a high sodium adsorption ratio in the irrigation water. Which combination of management steps is most logical?

  1. Apply gypsum, improve drainage and leach with good-quality water before sowing a tolerant crop Correct answer.
  2. Sow a sensitive crop immediately without any amendment
  3. Apply more of the same high-sodium water to flush the salts downward
  4. Apply lime and reduce irrigation frequency

Explanation

High sodium relative to calcium disperses clay, causing crusting and poor infiltration. Applying gypsum supplies calcium to flocculate the soil, and adequate drainage plus leaching removes the excess sodium. Adding more sodic water or lime would worsen the problem.

Question 25Plant Science and Crop Production

Two plots receive the same total irrigation water, but plot A is irrigated by drip and plot B by flood. Which outcome is most consistent with the physics of the two methods?

  1. Plot B shows higher application efficiency because more water is applied
  2. Both plots show identical efficiency because the water volume is the same
  3. Plot A loses more water to deep percolation because of point placement
  4. Plot A shows higher application efficiency and less deep percolation than plot B Correct answer.

Explanation

Drip delivers water slowly to the root zone, so evaporation, runoff and deep percolation losses are lower than with flood irrigation. Equal total volume does not mean equal efficiency, because the distribution and losses differ between methods.

Question 26Plant Science and Crop Production

In the classification of crops by life cycle and growing habit, which crop is grown as an annual for its seed and completes its life cycle within a single kharif season?

  1. Sugarcane
  2. Pigeon pea Correct answer.
  3. Banana
  4. Castor

Explanation

Pigeon pea (tur) is raised from seed and completes germination, flowering, pod formation and maturity within one kharif season, so it is treated as an annual field crop. Sugarcane, castor and banana are long-duration or perennial crops that are ratooned or maintained over more than one season in Maharashtra.

Question 27Plant Science and Crop Production

A seed lot of soybean has a germination percentage of 80 per cent and a purity of 98 per cent. What is its germination-adjusted seed rate if the recommended rate for pure viable seed is 75 kg per hectare?

  1. 92 kg/ha
  2. 60 kg/ha
  3. 96 kg/ha Correct answer.
  4. 75 kg/ha

Explanation

The seed lot's usable value is the product of purity and germination, i.e. 0.98 x 0.80 = 0.784. Dividing the recommended rate by this value gives 75 / 0.784 = about 96 kg per hectare, so the grower must sow more seed to obtain the same plant population.

Question 28Plant Science and Crop Production

Which practice is the most appropriate way to break seed dormancy in freshly harvested groundnut kernels before sowing the next season?

  1. Soaking the kernels in water for 24 hours before sowing
  2. Storing the kernels dry for the required rest period before sowing Correct answer.
  3. Storing the kernels in moist jute bags at high humidity
  4. Treating the kernels with a systemic fungicide before sowing

Explanation

Freshly harvested groundnut kernels show a period of after-ripening, and dormancy is naturally broken by dry storage for a few weeks to months. Dry storage allows the embryo to complete maturation, after which the kernels germinate readily without any chemical or moisture treatment.

Question 29Plant Science and Crop Production

A farmer wants to raise seedlings of a vegetable crop in a low tunnel during winter. Which combination of conditions inside the structure best favours healthy seedling growth without excessive elongation?

  1. High temperature with low light intensity and dense sowing
  2. Moderate temperature with adequate light and thin, uniform sowing Correct answer.
  3. High humidity with no ventilation and heavy nitrogen application
  4. Low temperature with continuous shading and frequent overhead irrigation

Explanation

Seedlings become thin and etiolated when temperature is high relative to light or when sowing is dense, because plants compete for light and shade each other. Moderate temperature, good light transmission and uniform thin sowing keep internodes short and produce stocky, transplantable seedlings.

Question 30Plant Science and Crop Production

A grower in the assured-rainfall zone of Maharashtra plans a sequence over three years on the same field. Which rotation best improves soil fertility and reduces the build-up of a cereal-specific pathogen while remaining agronomically sound?

  1. Continuous cereal-cereal-cereal with the same variety each year
  2. Cereal-cereal-legume with the legume always sown in the same month
  3. Cereal-legume-cereal with a different non-host crop in the third year Correct answer.
  4. Continuous legume-legume-legume without any cereal in the sequence

Explanation

Inserting a legume adds biologically fixed nitrogen and breaks the cereal disease cycle, while a different non-host crop in the third year further interrupts pathogen survival. Continuous cropping of the same host, or an unchanging sequence, allows soil-borne pathogens and pests to multiply.

Question 31Soil Science and Soil Fertility Management

In the context of Maharashtra agriculture, which soil order is most characteristic of the black cotton soils (regur) of the Deccan trap region?

  1. Gelisols
  2. Vertisols Correct answer.
  3. Spodosols
  4. Oxisols

Explanation

Black cotton soils derived from Deccan basalt are dominated by smectite clays, giving high shrink-swell behaviour, and are classified as Vertisols. Oxisols are highly weathered tropical soils, Gelisols are permanently frozen soils, and Spodosols show a spodic horizon with accumulated iron and organic matter.

Question 32Soil Science and Soil Fertility Management

The cation exchange capacity of a soil is most directly determined by which soil property?

  1. Amount and type of clay and organic matter Correct answer.
  2. Bulk density of the plough layer
  3. Depth of the water table
  4. Total sand percentage

Explanation

CEC arises from negative charge on clay mineral surfaces and humus functional groups, so both the quantity and the type of clay and organic matter govern it. Smectite and organic matter contribute far more exchange sites than kaolinite or sand. Sand percentage, bulk density and water-table depth do not supply exchange sites.

Question 33Soil Science and Soil Fertility Management

A soil test reports a pH of 5.2 for a field in the Konkan region. Which amendment is most appropriate to raise the pH to the target range for most field crops?

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

Explanation

Acidic soils are corrected by applying lime, which neutralises hydrogen and aluminium ions and raises pH. Elemental sulphur and ammonium sulphate are acidifying materials, and gypsum supplies calcium without neutralising acidity, so none of them raises pH.

Question 34Soil Science and Soil Fertility Management

Which essential plant nutrient is taken up by plants mainly as the anions nitrate and ammonium?

  1. Phosphorus
  2. Nitrogen Correct answer.
  3. Potassium
  4. Zinc

Explanation

Nitrogen is absorbed chiefly as nitrate (NO3-) and ammonium (NH4+) ions, and legumes additionally obtain it through symbiotic fixation. Phosphorus is taken up as phosphate ions, potassium as the K+ cation, and zinc as the Zn2+ cation.

Question 35Soil Science and Soil Fertility Management

Which practice best conserves soil moisture in a rainfed kharif field during a dry spell?

  1. Mulching the soil surface with crop residue Correct answer.
  2. Deep ploughing to expose subsoil
  3. Increasing irrigation frequency to daily light sprinklings
  4. Burning standing stubble

Explanation

A surface mulch reduces evaporation, moderates soil temperature and protects the surface from crusting, thereby conserving stored moisture. Exposing subsoil and burning residue increase evaporative loss, and daily light sprinklings wet only the surface and promote evaporation losses.

Question 36Soil Science and Soil Fertility Management

Which organism group is chiefly responsible for converting ammonium to nitrate in well-aerated soils?

  1. Mycorrhizal fungi
  2. Cyanobacteria
  3. Rhizobium bacteria
  4. Nitrifying bacteria Correct answer.

Explanation

Nitrification is a two-step aerobic process carried out by specialised chemoautotrophic bacteria, first oxidising ammonium to nitrite and then nitrite to nitrate. Rhizobium fixes nitrogen inside legume nodules, mycorrhizal fungi aid nutrient and water uptake, and cyanobacteria fix nitrogen mainly in flooded or moist surfaces.

Question 37Soil Science and Soil Fertility Management

A soil analysis gives available nitrogen 180 kg/ha, available phosphorus 12 kg/ha and available potassium 240 kg/ha. Using the usual soil-test rating classes, how should the phosphorus status be interpreted?

  1. Excessive, so phosphorus should be withheld for two seasons
  2. Low, so a phosphorus dose above the normal recommendation is justified Correct answer.
  3. High, so no phosphorus is needed
  4. Medium, so only maintenance phosphorus is needed

Explanation

Available phosphorus of about 12 kg/ha falls in the low category, generally below roughly 15 to 20 kg/ha of available P2O5 depending on the rating chart used. Low status justifies a higher phosphorus dose than the normal recommendation to build up the soil. High or excessive ratings correspond to much larger test values.

Question 38Soil Science and Soil Fertility Management

Which soil structure type is most favourable for root growth and aeration in a cultivated field?

  1. Massive structure
  2. Single-grain structure
  3. Platy structure
  4. Granular (crumb) structure Correct answer.

Explanation

Granular or crumb aggregates create a network of pores that allows air, water and roots to move freely, which is ideal for crop growth. Single-grain sandy soils drain too fast, massive clays restrict root penetration and aeration, and platy structure impedes vertical water movement.

Question 39Soil Science and Soil Fertility Management

In a long-term experiment, continuous application of ammonium sulphate without lime caused a decline in soil pH. What is the best explanation?

  1. Sulphate ions are converted to bicarbonate, raising alkalinity
  2. Sulphur is volatilised as gas, leaving no residue
  3. Nitrification of ammonium releases hydrogen ions, acidifying the soil Correct answer.
  4. Ammonium is leached unchanged, leaving the soil neutral

Explanation

When ammonium is nitrified, hydrogen ions are released into the soil solution, and the accompanying sulphate can be leached with base cations, leaving the soil more acidic. This acidification is a recognised consequence of long-term use of ammonium-based fertilisers. Sulphate does not raise alkalinity, ammonium does not leach unchanged, and sulphur is not lost as a gas from this fertiliser.

Question 40Soil Science and Soil Fertility Management

The main purpose of adding organic manure such as FYM to a sandy loam soil is to improve which combination of properties?

  1. Depth of the solum and bedrock type
  2. Water-holding capacity and cation exchange capacity Correct answer.
  3. Bulk density and particle density
  4. Soil colour and thermal conductivity only

Explanation

Organic manure adds humus that increases both the water-holding capacity and the cation exchange capacity of a sandy soil, while also improving aggregation. Bulk density may fall slightly, but particle density is essentially unchanged. Colour and thermal conductivity are minor side effects, and solum depth is not altered by manuring.

Question 41Soil Science and Soil Fertility Management

A farmer applies 100 kg of urea (46 per cent N) to one hectare. How much nitrogen is actually applied?

  1. 64 kg N
  2. 46 kg N Correct answer.
  3. 23 kg N
  4. 100 kg N

Explanation

Urea contains 46 per cent nitrogen, so 100 kg of urea supplies 100 × 0.46 = 46 kg of nitrogen. The remaining mass is mainly the carbon, oxygen and hydrogen framework of the urea molecule. Multiplying the whole fertiliser mass or using other percentages gives incorrect nitrogen figures.

Question 42Soil Science and Soil Fertility Management

Which soil-water term describes the water held so tightly by soil particles that plants cannot absorb it?

  1. Permanent wilting point Correct answer.
  2. Field capacity
  3. Saturation
  4. Gravitational water

Explanation

At permanent wilting point the remaining water is held by matric forces too strong for plant roots to overcome, so plants wilt and do not recover. Field capacity is the water retained after free drainage, saturation is when all pores are filled, and gravitational water drains away under gravity.

Question 43Soil Science and Soil Fertility Management

Which of the following is a micronutrient essential for plant growth?

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

Explanation

Boron is required in very small amounts and is classified as a micronutrient, taking part in cell wall formation and reproductive development. Calcium, magnesium and sulphur are required in larger quantities and are classified as secondary macronutrients.

Question 44Soil Science and Soil Fertility Management

Waterlogging in a heavy black soil during the monsoon causes yellowing of crops. Which sequence best explains this?

  1. Waterlogging increases the exchangeable sodium percentage, causing chlorosis
  2. Water entry increases oxygen diffusion, boosting nitrogen uptake
  3. Waterlogging raises soil pH sharply, causing iron toxicity
  4. Pore spaces fill with water, oxygen is depleted, denitrification losses occur and root function declines Correct answer.

Explanation

When pores fill with water, gas exchange with the atmosphere is blocked, oxygen is consumed by microbes and roots, and anaerobic conditions develop. Under these conditions nitrate is denitrified to gaseous nitrogen and roots lose function, producing nitrogen-deficiency yellowing. Waterlogging does not increase oxygen diffusion, and the other explanations misstate the mechanism.

Question 45Soil Science and Soil Fertility Management

Reclamation of a sodic soil (high exchangeable sodium) typically requires which combination of treatments?

  1. Gypsum application followed by leaching with good-quality water and drainage Correct answer.
  2. Deep tillage alone without any amendment
  3. Application of ammonium sulphate with no drainage provision
  4. Addition of lime without leaching

Explanation

Sodic soils carry a high exchangeable sodium percentage and often show poor structure and high pH. Gypsum supplies calcium that replaces sodium on the exchange complex, and the displaced sodium must then be leached out with adequate drainage. Lime does not supply soluble calcium effectively at high pH, tillage alone does not remove sodium, and ammonium sulphate is acidifying rather than a sodium-replacing amendment.

Question 46Soil Science and Soil Fertility Management

A soil has a bulk density of 1.5 g/cm3 and a particle density of 2.5 g/cm3. What is its approximate porosity?

  1. 25 per cent
  2. 60 per cent
  3. 15 per cent
  4. 40 per cent Correct answer.

Explanation

Porosity equals one minus the ratio of bulk density to particle density, so 1 minus (1.5/2.5) = 1 minus 0.6 = 0.4, or 40 per cent. The pore space is the fraction of the soil volume not occupied by solid particles. The other figures do not follow from this ratio.

Question 47Soil Science and Soil Fertility Management

Which statement correctly distinguishes soil fertility from soil productivity?

  1. Fertility refers only to the physical condition of the soil, whereas productivity refers only to nutrient content
  2. Fertility and productivity are identical and cannot be distinguished
  3. Fertility is the ability to supply nutrients, whereas productivity is the capacity to yield a crop under a given management system Correct answer.
  4. Fertility is measured only by pH, whereas productivity is measured only by organic carbon

Explanation

Soil fertility is the inherent ability of a soil to supply essential nutrients in available forms and adequate amounts. Soil productivity is broader: it is the capacity of a soil to produce a specified crop under defined management, and it depends on fertility together with physical, biological, climatic and management factors. The other options narrow or conflate these concepts incorrectly.

Question 48Soil Science and Soil Fertility Management

A field shows poor crop response even though soil tests indicate adequate phosphorus. Which factor most plausibly limits phosphorus availability to the crop?

  1. High soil pH causing phosphorus fixation as calcium phosphates Correct answer.
  2. Absence of nitrogen-fixing bacteria in the soil
  3. Very low soil temperature throughout the year
  4. Low cation exchange capacity of the soil

Explanation

In calcareous or alkaline soils, soluble phosphate reacts with calcium to form less soluble calcium phosphates, reducing availability even when total or test phosphorus appears adequate. Temperature, nitrogen-fixing bacteria and CEC do not primarily control phosphorus solubility in this way. This fixation explains a poor crop response despite an adequate soil test.

Question 49Soil Science and Soil Fertility Management

In a rice-wheat rotation, which nutrient management principle best explains the need to apply nitrogen in split doses to rice?

  1. Split application eliminates the need for phosphorus and potassium
  2. Split application matches nitrogen supply to crop demand and reduces losses through leaching and volatilisation Correct answer.
  3. Split application increases the total nitrogen content of the fertiliser
  4. Split application converts nitrate permanently into organic nitrogen

Explanation

Rice takes up nitrogen steadily over the season, and a single large dose is vulnerable to ammonia volatilisation from flooded soils, denitrification and leaching. Splitting the dose synchronises supply with crop demand and reduces these losses, improving recovery efficiency. Splitting does not change fertiliser composition, permanently immobilise nitrate, or replace other nutrients.

Question 50Soil Science and Soil Fertility Management

Two soils have the same clay percentage, but one is dominated by smectite and the other by kaolinite. Which difference in behaviour is expected?

  1. The smectite soil shows greater swelling, higher CEC and stronger water retention than the kaolinite soil Correct answer.
  2. Both soils behave identically because clay percentage is the same
  3. The kaolinite soil retains more water because its crystals are larger
  4. The kaolinite soil shows greater swelling and higher CEC than the smectite soil

Explanation

Smectite has a 2:1 expanding lattice with high surface area and high negative charge, giving strong swelling, high CEC and high water retention. Kaolinite has a 1:1 non-expanding lattice with low surface area and low CEC. Clay percentage alone therefore does not determine these behaviours; mineralogy matters greatly.