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Tamil Nadu HSE Second Year Agricultural Science study materials
Tamil Nadu HSE Second Year Agricultural Science study resources

Tamil Nadu HSE Second Year Agricultural Science practice questions

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Question 1Principles of Agronomy and Crop Production

Which crop is classified as a kharif season crop in Tamil Nadu agriculture?

  1. Bengal gram
  2. Linseed
  3. Maize Correct answer.
  4. Black gram

Explanation

Kharif crops are sown with the onset of the south-west monsoon and harvested in autumn. Maize is a typical kharif crop in Tamil Nadu, while black gram, Bengal gram and linseed are generally grown in the rabi season.

Question 2Principles of Agronomy and Crop Production

In the classification of tillage operations, ploughing to a depth of about 20-30 cm to break the hardpan is termed:

  1. Intercultivation
  2. Levelling
  3. Secondary tillage
  4. Primary tillage Correct answer.

Explanation

Primary tillage opens up the soil and is done by implements such as the mouldboard plough or disc plough to a depth of 20-30 cm. Secondary tillage follows to prepare a fine seedbed, while intercultivation is done after crop establishment.

Question 3Principles of Agronomy and Crop Production

The recommended seed rate of rice for transplanted lowland cultivation is approximately:

  1. 25-30 kg/ha
  2. 10-15 kg/ha
  3. 50-60 kg/ha Correct answer.
  4. 100-120 kg/ha

Explanation

Transplanted rice requires a dense nursery and about 50-60 kg of seed per hectare to raise enough seedlings. Direct sown and dry nursery systems use lower seed rates, while very high rates are wasteful and cause lodging.

Question 4Principles of Agronomy and Crop Production

Which of the following is a leguminous green manure crop commonly grown in Tamil Nadu before rice?

  1. Cumbu
  2. Sorghum
  3. Sunhemp Correct answer.
  4. Castor

Explanation

Sunhemp (Crotalaria juncea) is a fast-growing legume that fixes atmospheric nitrogen and is ploughed in as green manure before rice. Sorghum, cumbu and castor are non-leguminous crops grown for grain or oil and do not serve as nitrogen-fixing green manure.

Question 5Principles of Agronomy and Crop Production

A farmer wants to reduce soil erosion on a sloping field by ploughing and planting across the slope rather than up and down it. This practice is called:

  1. Terracing
  2. Mulching
  3. Strip cropping
  4. Contour farming Correct answer.

Explanation

Contour farming aligns tillage and crop rows along the contour so that each ridge slows runoff and traps soil. Strip cropping uses alternating crop bands, terracing cuts stepped platforms, and mulching covers the surface with residue.

Question 6Principles of Agronomy and Crop Production

Which plant nutrient is described as a primary macronutrient that promotes root development and early maturity in cereals?

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

Explanation

Phosphorus supports root proliferation, tillering and early maturity, and is applied largely as basal fertilizer. Nitrogen mainly drives vegetative growth, potassium regulates water and enzyme function, and zinc is a micronutrient.

Question 7Principles of Agronomy and Crop Production

The critical period of crop-weed competition in most field crops is best described as:

  1. The flowering and grain filling stage
  2. The entire crop growth period
  3. The early vegetative stage up to about one-third of crop duration Correct answer.
  4. The maturity stage

Explanation

Weeds must be suppressed during the early vegetative stage, when the crop canopy has not closed and competition is most severe. Once the crop canopy covers the ground, later weed growth causes relatively less yield loss.

Question 8Principles of Agronomy and Crop Production

Which irrigation method is most water-use efficient for a widely spaced orchard crop on a sandy soil?

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

Explanation

Drip irrigation delivers water directly to the root zone with minimal evaporation and percolation losses, which suits widely spaced trees and sandy soils. Flood and basin methods wet the whole surface and lose much water.

Question 9Principles of Agronomy and Crop Production

In a crop rotation, including a pulse such as cowpea after a cereal mainly benefits the following crop by:

  1. Eliminating the need for potassium
  2. Increasing soil nitrogen through symbiotic fixation Correct answer.
  3. Reducing soil organic matter
  4. Increasing soil pH sharply

Explanation

Pulses form nodules with Rhizobium bacteria that fix atmospheric nitrogen, part of which remains in the soil for the succeeding crop. They also break pest cycles and improve soil structure, but they do not replace potassium or raise pH sharply.

Question 10Principles of Agronomy and Crop Production

A farmer applies 100 kg of urea to one hectare. Approximately how much nitrogen does this supply?

  1. 60 kg N
  2. 46 kg N Correct answer.
  3. 20 kg N
  4. 100 kg N

Explanation

Urea contains about 46 per cent nitrogen, so 100 kg of urea supplies roughly 46 kg of nitrogen. The remainder is mainly carbon, oxygen and hydrogen lost as carbon dioxide and water.

Question 11Principles of Agronomy and Crop Production

The main purpose of puddling in lowland rice cultivation is to:

  1. Reduce water percolation and control weeds Correct answer.
  2. Improve drainage of the field
  3. Increase soil aeration for roots
  4. Increase soil temperature

Explanation

Puddling destroys soil structure and creates a compact layer that reduces water percolation losses and helps suppress weeds. It actually reduces aeration, so rice varieties adapted to anaerobic conditions are used.

Question 12Principles of Agronomy and Crop Production

Which cropping system is an example of multiple cropping that includes both a cereal and a pulse within the same year?

  1. Cotton - cotton
  2. Rice - black gram Correct answer.
  3. Sugarcane monoculture
  4. Rice - rice

Explanation

Multiple cropping involves growing more than one crop in a year, and rice followed by black gram combines a cereal with a pulse, adding nitrogen and diversity. Rice-rice and cotton-cotton are sequential monocultures, and sugarcane is a long-duration monocrop.

Question 13Principles of Agronomy and Crop Production

The optimum time to take up intercultivation and weeding in transplanted rice is generally:

  1. About 20-25 days after transplanting Correct answer.
  2. At panicle initiation
  3. Immediately after transplanting
  4. At harvest

Explanation

The first weeding and intercultivation should be done about 20-25 days after transplanting, when weeds are young and the crop is established but the canopy has not yet closed. Later operations are less effective and risk root damage.

Question 14Principles of Agronomy and Crop Production

Which of the following best explains why a legume is grown in a mixed cropping system with a cereal such as sorghum?

  1. The combined crop requires no fertilizer or water
  2. The legume fixes nitrogen and provides additional returns per unit area Correct answer.
  3. The cereal suppresses the legume entirely
  4. The legume shades out the cereal completely

Explanation

Mixed cropping with a cereal and a legume uses different canopy layers and root zones, and the legume adds nitrogen to the system while providing extra income. Neither crop suppresses the other completely, and inputs are still required.

Question 15Principles of Agronomy and Crop Production

A soil test recommends 120 kg N, 60 kg P2O5 and 40 kg K2O per hectare for a maize crop. Which fertilizer schedule applies all the phosphorus as basal dressing?

  1. Apply full N as basal and P at tasselling
  2. Apply all fertilizers at flowering
  3. Apply no fertilizer at sowing
  4. Apply full P and K as basal, and N in split doses Correct answer.

Explanation

Phosphorus and potassium are usually applied as basal dressing at sowing, while nitrogen is split across growth stages to reduce losses. Applying all fertilizers at flowering or omitting basal application would deprive the crop during establishment.

Question 16Principles of Agronomy and Crop Production

The main advantage of raised bed planting over flat planting in a heavy clay soil with poor drainage is:

  1. Increased soil compaction
  2. Higher water requirement
  3. Better drainage and reduced waterlogging of the root zone Correct answer.
  4. Complete elimination of weeds

Explanation

Raised beds lift the root zone above the waterlogged layer, improving aeration and drainage in heavy soils. They do not remove weeds entirely, and they reduce rather than increase water requirement.

Question 17Principles of Agronomy and Crop Production

Which of the following is the correct sequence of operations in the cultivation of a transplanted crop?

  1. Land preparation - transplanting - nursery raising - harvesting - intercultivation
  2. Nursery raising - harvesting - transplanting - land preparation - intercultivation
  3. Nursery raising - land preparation - transplanting - intercultivation - harvesting Correct answer.
  4. Land preparation - harvesting - nursery raising - transplanting - intercultivation

Explanation

The logical sequence begins with raising seedlings in a nursery while the main field is prepared, followed by transplanting, intercultivation and finally harvesting. Harvesting cannot precede transplanting, and nursery raising must precede transplanting.

Question 18Principles of Agronomy and Crop Production

The term 'land equivalent ratio' in intercropping is used to:

  1. Measure the depth of ploughing
  2. Measure the relative yield advantage of intercropping over sole cropping Correct answer.
  3. Calculate the seed rate of a crop
  4. Estimate the water requirement of a crop

Explanation

Land equivalent ratio compares the land area needed in sole cropping with the area needed in intercropping to produce the same yield. A value greater than one indicates a yield advantage for the intercrop system.

Question 19Principles of Agronomy and Crop Production

A farmer notices that continuous rice-rice cropping has led to declining yields and increased pest incidence. Which practice is most appropriate to address this problem?

  1. Flooding the field continuously
  2. Introducing a pulse or oilseed in rotation with rice Correct answer.
  3. Applying more pesticide without changing the cropping pattern
  4. Increasing nitrogen fertilizer alone

Explanation

Diversifying the rotation with a pulse or oilseed breaks pest and disease cycles and improves soil fertility, addressing the causes of declining yield. Merely increasing fertilizer or pesticide does not correct the underlying rotation problem.

Question 20Principles of Agronomy and Crop Production

The depth of sowing a small-seeded crop such as ragi should generally be:

  1. Very deep, about 10 cm
  2. At the soil surface without covering
  3. About 15 cm
  4. Shallow, about 2-3 cm Correct answer.

Explanation

Small seeds have limited food reserves and must be sown shallow, about 2-3 cm, so that the young seedling can reach the surface. Deep sowing exhausts the reserves before emergence and reduces germination.

Question 21Principles of Agronomy and Crop Production

Which of the following best describes the concept of 'duty of water' in irrigation?

  1. The volume of water required to produce a unit weight of crop produce
  2. The interval between two irrigations
  3. The number of hectares that can be irrigated by a unit discharge of water Correct answer.
  4. The depth of water applied in a single irrigation

Explanation

Duty of water expresses the area of land that can be irrigated by a unit flow of water, usually as hectares per cubic metre per second. It is inversely related to the water requirement of the crop.

Question 22Principles of Agronomy and Crop Production

A crop has a consumptive use of 600 mm over a 120-day season. The average daily water use rate is approximately:

  1. 10 mm/day
  2. 12 mm/day
  3. 5 mm/day Correct answer.
  4. 2 mm/day

Explanation

Dividing the seasonal consumptive use of 600 mm by the 120-day season gives an average of 5 mm per day. This value guides irrigation scheduling and the design of the water delivery system.

Question 23Principles of Agronomy and Crop Production

In the context of integrated nutrient management, the primary reason for combining organic manures with chemical fertilizers is to:

  1. Replace all chemical fertilizers completely
  2. Increase soil salinity
  3. Sustain soil organic matter while meeting crop nutrient demand Correct answer.
  4. Reduce the crop duration

Explanation

Integrated nutrient management combines organic sources with inorganic fertilizers to supply nutrients in balanced amounts while maintaining soil organic matter and biological activity. Organic manures alone usually cannot meet the full nutrient demand of high-yielding crops.

Question 24Principles of Agronomy and Crop Production

Which statement correctly describes the relationship between the soil moisture tension and the availability of water to plants?

  1. Water is most readily available near field capacity and becomes less available as tension rises toward wilting point Correct answer.
  2. Water availability is independent of soil moisture tension
  3. Water is more readily available at higher tension
  4. Water is unavailable at field capacity

Explanation

At field capacity the moisture tension is low and water is easily absorbed by roots. As the soil dries, tension increases and the plant must exert more force to extract water until the permanent wilting point is reached.

Question 25Principles of Agronomy and Crop Production

A farmer wants to control weeds in a direct-seeded rice field while avoiding crop injury. Which approach is most consistent with the principles of integrated weed management?

  1. Flooding the field continuously throughout the season
  2. Combining pre-emergence herbicide with timely hand weeding and proper crop stand Correct answer.
  3. Delaying sowing to allow weeds to emerge first
  4. Repeated application of a single herbicide at higher doses

Explanation

Integrated weed management combines cultural, mechanical and chemical methods, such as a pre-emergence herbicide with hand weeding and a competitive crop stand, to control weeds while minimizing selection pressure and crop injury. Repeating one herbicide at high doses encourages resistance.

Question 26Principles of Agronomy and Crop Production

In agronomic terminology, the 'germination percentage' of a seed lot is calculated as the number of normal seedlings produced divided by the total number of seeds sown, expressed as a percentage. If 400 seeds are placed for germination and 360 normal seedlings emerge, what is the germination percentage of that seed lot?

  1. 80 per cent
  2. 90 per cent Correct answer.
  3. 72 per cent
  4. 96 per cent

Explanation

Germination percentage is the ratio of normal seedlings to the total seeds tested, multiplied by 100. Here 360 divided by 400 equals 0.90, which gives 90 per cent. Only normal, healthy seedlings are counted; abnormal or dead seeds are excluded from the numerator.

Question 27Principles of Agronomy and Crop Production

A crop is grown on a sandy loam soil where the available soil moisture at field capacity is 18 per cent by weight and at permanent wilting point is 8 per cent by weight. The root-zone soil mass per hectare is 2.0 million kg. What is the available water capacity of this root zone per hectare?

  1. 100,000 kg
  2. 360,000 kg
  3. 200,000 kg Correct answer.
  4. 180,000 kg

Explanation

Available water capacity equals the difference between field capacity and wilting point percentages applied to the root-zone soil mass. The difference is 18 minus 8, that is 10 per cent, and 10 per cent of 2.0 million kg is 200,000 kg of available water. This stored water is what the crop can draw before wilting becomes permanent.

Question 28Principles of Agronomy and Crop Production

A farmer grows a cereal and a pulse together in the same field and season, and the land equivalent ratio of the mixture works out to 1.25. Which interpretation of this value is agronomically sound?

  1. The mixture gives the same yield as sole cropping but with 25 per cent less fertilizer.
  2. The mixture yields 25 per cent less than the better sole crop grown alone.
  3. The mixture gives 25 per cent more yield than the same land under sole cropping. Correct answer.
  4. The mixture needs 25 per cent more land than sole cropping to give the same total yield.

Explanation

A land equivalent ratio compares the land needed under sole cropping with the land needed in the intercrop to produce the same yield. A value of 1.25 means sole cropping would need 1.25 hectares to match one hectare of the mixture, so the intercrop gives a 25 per cent yield advantage. Values above 1.0 indicate a biological advantage from the combination.

Question 29Soil Science and Soil Fertility Management

In soil science, the term 'soil texture' refers to which property of the fine earth fraction?

  1. The volume of pore space occupied by air
  2. The colour of the surface soil horizon
  3. The arrangement of soil particles into aggregates
  4. The relative proportion of sand, silt and clay particles Correct answer.

Explanation

Soil texture is defined by the relative proportions of the three primary particle-size separates, namely sand, silt and clay, in the mineral fraction below 2 mm. It is a fixed characteristic of a soil and is read from a textural triangle once particle percentages are known. Structure, porosity and colour are separate properties that change with management.

Question 30Soil Science and Soil Fertility Management

According to the international particle-size classification, particles with an equivalent diameter between 0.002 mm and 0.02 mm are grouped as:

  1. Clay
  2. Fine sand
  3. Silt Correct answer.
  4. Gravel

Explanation

In the international (Atterberg) system, silt is the separate with particles between 0.002 mm and 0.02 mm, while clay is below 0.002 mm. Sand ranges from 0.02 mm up to 2 mm and gravel is coarser than 2 mm. Particle size determines the separate name regardless of mineral composition.

Question 31Soil Science and Soil Fertility Management

A soil sample contains 55 per cent sand, 25 per cent silt and 20 per cent clay. Using the textural triangle, this soil is classified as:

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

Explanation

A soil with sand dominant and moderate silt plus about 20 per cent clay plots in the sandy loam class of the textural triangle. Sandy loam requires roughly 43 to 85 per cent sand and less than 20 per cent clay with limited silt. The high sand fraction rules out loam and silt loam, and the clay content is too low for a clay loam class.

Question 32Soil Science and Soil Fertility Management

Which soil separate contributes most to the cation exchange capacity and nutrient retention of a soil?

  1. Coarse sand
  2. Fine sand
  3. Clay Correct answer.
  4. Silt

Explanation

Clay particles carry net negative surface charge and have very high specific surface area, so they hold exchangeable cations and dominate the cation exchange capacity of the fine earth. Sand and silt have small surfaces and little charge. This is why clay-rich soils retain nutrients better but are harder to work.

Question 33Soil Science and Soil Fertility Management

The single most important factor controlling the formation of soil from parent material over long periods is:

  1. Soil colour
  2. Land slope direction
  3. Climate Correct answer.
  4. Biological nitrogen fixation

Explanation

In the classic five-factor model of soil formation, climate governs the amount of water passing through the profile and the rate of weathering and organic matter accumulation, making it the dominant factor at a regional scale. Parent material, relief, organisms and time modify the result. Climate therefore explains broad soil belts better than any other single factor.

Question 34Soil Science and Soil Fertility Management

A soil profile showing a dark surface A horizon, a lighter eluvial E horizon, a zone of illuvial accumulation and underlying weathered material is best described by which sequence?

  1. A, E, B, C Correct answer.
  2. A, B, E, C
  3. O, C, B, A
  4. C, A, B, E

Explanation

Master horizons are named in order of depth from the surface downward. The organic-rich A horizon is followed by the eluvial E horizon, then the illuvial B horizon, and finally the comparatively unweathered C horizon. Any sequence that places C above B or reverses A and E contradicts the definition of horizonation.

Question 35Soil Science and Soil Fertility Management

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

  1. Milligrams of soil per litre of water
  2. Per cent by weight of calcium carbonate
  3. Centimoles of charge per kilogram of soil Correct answer.
  4. Kilograms of soil per cubic metre

Explanation

Cation exchange capacity measures the quantity of exchangeable positive charge held per unit mass of soil and is reported in centimoles of charge per kilogram, formerly milliequivalents per 100 g. It reflects the number of negatively charged sites available to retain nutrient cations. Bulk density and lime content are unrelated quantities.

Question 36Soil Science and Soil Fertility Management

A soil has a pH of 5.2 and high exchangeable aluminium. Which management practice most directly corrects this acidity for a sensitive crop?

  1. Adding urea to increase the nitrogen supply
  2. Incorporating fresh farmyard manure without any lime
  3. Applying gypsum to supply calcium without changing pH
  4. Applying agricultural lime at a rate based on a buffer-pH test Correct answer.

Explanation

Acidic soils are corrected by applying calcium or magnesium carbonate, which neutralises hydrogen and aluminium ions on the exchange complex and raises pH. The rate should be set from a buffer-pH or lime requirement test rather than a fixed dose. Gypsum supplies calcium but does not neutralise acidity, and urea acidifies soil further.

Question 37Soil Science and Soil Fertility Management

Reclamation of a sodic soil is normally achieved by:

  1. Applying ammonium sulphate and withholding irrigation
  2. Deep ploughing alone without any amendment
  3. Flooding with saline water to displace sodium
  4. Applying gypsum and leaching the displaced sodium below the root zone Correct answer.

Explanation

Sodic soils carry excess exchangeable sodium, so reclamation requires a calcium source such as gypsum to displace sodium from exchange sites, followed by leaching to carry the sodium salts away. Drainage must be adequate for leaching to work. Saline water or ammonium sulphate would worsen the problem.

Question 38Soil Science and Soil Fertility Management

Which essential plant nutrient is taken up mainly as the anion H2PO4- and is known for being relatively immobile in most soils?

  1. Magnesium
  2. Phosphorus Correct answer.
  3. Calcium
  4. Potassium

Explanation

Phosphorus is absorbed by roots mainly as the dihydrogen phosphate anion and is strongly fixed by iron, aluminium and calcium compounds in soil. Because of this fixation and its low mobility, placement near the root zone matters more than for mobile nutrients. Potassium, calcium and magnesium are taken up as cations.

Question 39Soil Science and Soil Fertility Management

A farmer applies 100 kg of urea (46 per cent nitrogen) to one hectare. The quantity of nitrogen actually applied is approximately:

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

Explanation

The nitrogen content of urea is about 46 per cent, so 100 kg of urea supplies roughly 46 kg of nitrogen. The remaining mass is mainly carbon, oxygen and hydrogen that are lost as carbon dioxide and water. Multiplying the product mass by its nutrient percentage is the standard way to compute nutrient doses.

Question 40Soil Science and Soil Fertility Management

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

  1. Pseudomonas and Clostridium
  2. Nitrosomonas and Nitrobacter Correct answer.
  3. Azotobacter and Beijerinckia
  4. Rhizobium and Bradyrhizobium

Explanation

Nitrification is a two-step aerobic process in which Nitrosomonas-type bacteria oxidise ammonium to nitrite and Nitrobacter-type bacteria oxidise nitrite to nitrate. It requires oxygen and a near-neutral pH, and it is inhibited in waterlogged soil. The other listed genera are involved in nitrogen fixation or denitrification.

Question 41Soil Science and Soil Fertility Management

In a flooded paddy field, applied urea is most likely to be lost by which pathway if it is broadcast into standing water?

  1. Volatilisation of ammonia from the floodwater Correct answer.
  2. Leaching of nitrate through the subsoil
  3. Fixation of ammonium by iron oxides
  4. Immobilisation into clay lattices

Explanation

When urea is broadcast into floodwater, hydrolysis raises the pH and ammonium accumulates in the water, favouring ammonia volatilisation to the atmosphere. Denitrification can also occur, but volatilisation is the immediate loss from floodwater. Leaching of nitrate is unlikely because the reduced zone favours ammonium.

Question 42Soil Science and Soil Fertility Management

Which practice is an example of biological nitrogen fixation being used directly in field agriculture?

  1. Spraying a micronutrient mixture on the foliage
  2. Applying ammonium chloride as a top dressing
  3. Incorporating wheat straw into the soil
  4. Growing a legume crop inoculated with an appropriate Rhizobium strain Correct answer.

Explanation

Legumes form symbiotic associations with host-specific rhizobia, and inoculation ensures effective nodulation and nitrogen fixation from the atmosphere. This adds nitrogen to the system without synthetic fertiliser. Applying ammonium chloride is industrial nitrogen, while straw incorporation and foliar sprays do not fix atmospheric nitrogen.

Question 43Soil Science and Soil Fertility Management

Organic matter improves the physical condition of a sandy soil mainly because it:

  1. Raises the bulk density of the surface layer
  2. Increases aggregation and water-holding capacity Correct answer.
  3. Reduces the cation exchange capacity
  4. Increases the proportion of gravel-sized particles

Explanation

Decomposing organic matter binds sand grains into aggregates, improving structure, and its high surface area and water retention increase the water-holding capacity of coarse soils. It also raises cation exchange capacity rather than lowering it. It does not create gravel-sized mineral particles.

Question 44Soil Science and Soil Fertility Management

The carbon to nitrogen ratio of a crop residue is about 80:1. When this residue is incorporated, the likely short-term effect is:

  1. Immediate release of large amounts of nitrate
  2. Complete loss of soil phosphorus by volatilisation
  3. Temporary immobilisation of available soil nitrogen Correct answer.
  4. A rapid rise in soil pH to alkaline levels

Explanation

Residues with a wide carbon to nitrogen ratio force microbes to draw on soil nitrate and ammonium to build their own biomass, causing temporary immobilisation. Net mineralisation begins only after the ratio narrows. This is why high-carbon residues are often supplemented with nitrogen fertiliser.

Question 45Soil Science and Soil Fertility Management

Which soil structure type is typically found in the surface layer of a well-managed grassland soil?

  1. Columnar
  2. Single grain
  3. Granular Correct answer.
  4. Platy

Explanation

Dense grass roots and organic matter promote the formation of small, rounded granular aggregates in the surface horizon, which gives good porosity and tilth. Platy structure is often associated with compaction or alluvial layers, columnar structure with sodic subsoils, and single grain with loose sand.

Question 46Soil Science and Soil Fertility Management

Water held in soil at tensions between field capacity and permanent wilting point is described as:

  1. Available water Correct answer.
  2. Gravitational water
  3. Hygroscopic water
  4. Capillary rise from the water table

Explanation

Available water is the portion of soil moisture held between field capacity and the permanent wilting point, because plants can extract it against the suction of the roots. Water above field capacity drains as gravitational water, and water below the wilting point is tightly bound and unavailable. Capillary rise is a movement process, not a moisture category.

Question 47Soil Science and Soil Fertility Management

A field has a bulk density of 1.5 g per cubic centimetre and a particle density of 2.5 g per cubic centimetre. The approximate porosity is:

  1. 40 per cent Correct answer.
  2. 10 per cent
  3. 25 per cent
  4. 60 per cent

Explanation

Porosity is computed as one minus the ratio of bulk density to particle density, so 1 minus 1.5 divided by 2.5 equals 0.40, or 40 per cent. This value represents the total pore space available for air and water. The calculation assumes a uniform particle density of about 2.5 for most mineral soils.

Question 48Soil Science and Soil Fertility Management

Which soil-water conservation measure is best suited to a sloping cultivated field to reduce runoff and soil loss?

  1. Contour bunding Correct answer.
  2. Removing all crop residues after harvest
  3. Levelling the field to a uniform flat surface
  4. Increasing the slope length without any obstruction

Explanation

Contour bunds follow the contour and intercept runoff, giving water time to infiltrate and reducing the velocity of flow down the slope. They are a standard dryland conservation practice on moderate slopes. Removing residues or lengthening the unobstructed slope would accelerate erosion.

Question 49Soil Science and Soil Fertility Management

A fertiliser recommendation is stated as 120 kg nitrogen, 60 kg phosphorus pentoxide and 40 kg potassium oxide per hectare. Which fertiliser combination supplies these nutrients most directly?

  1. Urea, single superphosphate and muriate of potash Correct answer.
  2. Urea, gypsum and lime
  3. Ammonium sulphate, rock phosphate and gypsum
  4. Farmyard manure, lime and zinc sulphate

Explanation

Urea is the standard nitrogen source, single superphosphate supplies phosphorus pentoxide, and muriate of potash supplies potassium oxide, so this combination matches the three nutrients in the recommendation. The other mixtures either lack a potassium source or supply nutrients that were not recommended. Matching straight fertilisers to the recommendation avoids unnecessary nutrients.

Question 50Soil Science and Soil Fertility Management

Which essential nutrient deficiency typically produces interveinal chlorosis in the younger leaves of a crop?

  1. Magnesium
  2. Nitrogen
  3. Iron Correct answer.
  4. Molybdenum

Explanation

Iron is largely immobile in the plant, so deficiency appears first in young leaves as interveinal chlorosis while veins remain green. Magnesium and nitrogen are mobile, so their deficiency symptoms appear first on older leaves. Recognising mobility helps distinguish the cause of chlorosis in the field.