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Question 1Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which soil order is dominated by kaolinite clay and iron/aluminium oxides, has low base saturation, and is typical of warm, humid tropical regions?

  1. Aridisol
  2. Gelisol
  3. Mollisol
  4. Oxisol Correct answer.

Explanation

Oxisols form under intense leaching in hot, humid climates, leaving kaolinite and sesquioxides with very low cation exchange capacity and low base saturation. Mollisols are dark, base-rich grassland soils, Aridisols are dry-region soils, and Gelisols are frozen soils with permafrost.

Question 2Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

In plant protection, which group of insecticides acts by blocking the insect nicotinic acetylcholine receptor and includes imidacloprid and thiamethoxam?

  1. Organophosphates
  2. Neonicotinoids Correct answer.
  3. Pyrethroids
  4. Insect growth regulators

Explanation

Neonicotinoids are systemic insecticides that bind insect nicotinic acetylcholine receptors, causing nervous overstimulation. Pyrethroids act on sodium channels, organophosphates inhibit acetylcholinesterase, and insect growth regulators disrupt moulting or development.

Question 3Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

A farmer wants to propagate a true-to-type mango cultivar that is difficult to root from cuttings. Which method is most appropriate?

  1. Stem cutting in plain water
  2. Veneer grafting on a seedling rootstock Correct answer.
  3. Air layering of mature branches
  4. Seed sowing from open-pollinated fruit

Explanation

Grafting onto a seedling rootstock propagates clonal mango true to type and combines scion quality with rootstock vigour. Seed sowing produces variable progeny, and mango is generally difficult to propagate by cuttings or simple layering.

Question 4Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which practice most directly reduces nitrate leaching loss from a sandy loam field after heavy rainfall?

  1. Flood irrigation after top-dressing
  2. Split nitrogen application timed to crop demand Correct answer.
  3. Applying all nitrogen as urea before sowing
  4. Deep ploughing immediately after fertilizer application

Explanation

Splitting nitrogen and applying it when the crop is actively taking up nutrients reduces the amount of mobile nitrate present during heavy rain. Single large pre-sowing doses and flood irrigation leave excess nitrate in the soil solution, which leaches readily through sandy loam.

Question 5Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

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

  1. The entire crop season, from sowing to harvest
  2. The early growth period during which weeds must be controlled to prevent yield loss Correct answer.
  3. Only the post-flowering stage when weeds set seed
  4. The period after harvest when stubble weeds emerge

Explanation

Most annual crops suffer the greatest yield loss when weeds compete during early establishment and vegetative growth, so this early window is the critical period for weed control. Later competition affects harvesting and seed return but has less effect on yield already determined.

Question 6Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which soil structure type is most favourable for arable crop production because it promotes both drainage and root penetration?

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

Explanation

Granular structure consists of small, rounded aggregates that create stable pore space for aeration, drainage, and root growth, making it ideal for arable soils. Platy structure is compact and layered, massive structure lacks aggregation, and single grain describes loose sand with poor water retention.

Question 7Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

A crop is showing interveinal chlorosis on older leaves while veins remain green, and the symptom appears first on lower leaves. Which nutrient deficiency is most likely?

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

Explanation

Magnesium is a mobile nutrient in the phloem, so deficiency symptoms appear first on older leaves as interveinal chlorosis because magnesium is redistributed to growing tissue. Iron, calcium, and boron are relatively immobile, so their deficiencies typically appear first on young leaves.

Question 8Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

In hybrid seed production of a self-pollinated crop, which mechanism is used to prevent self-pollination in the female parent?

  1. Photoperiod sensitivity
  2. Vernalization
  3. Cytoplasmic-genetic male sterility Correct answer.
  4. Apomixis

Explanation

Cytoplasmic-genetic male sterility renders the female parent pollen-sterile so that it must be pollinated by the male parent, ensuring hybrid seed. Apomixis produces clonal seed, while vernalization and photoperiod sensitivity influence flowering timing rather than preventing selfing.

Question 9Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

A field soil has a pH of 5.2 with high exchangeable aluminium. Which amendment is most appropriate to raise pH and reduce aluminium toxicity?

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

Explanation

Agricultural lime neutralizes soil acidity and precipitates exchangeable aluminium, raising pH and improving root growth. Gypsum supplies calcium without raising pH, while ammonium sulfate and elemental sulfur acidify soil further.

Question 10Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which plant protection measure is an example of cultural control for managing soil-borne pathogens?

  1. Crop rotation with a non-host species Correct answer.
  2. Foliar spraying with a systemic fungicide
  3. Releasing a parasitoid wasp
  4. Using a pheromone trap for monitoring

Explanation

Crop rotation with a non-host interrupts the pathogen's life cycle in soil by removing its host, which is a cultural control practice. Fungicide spraying is chemical control, parasitoid release is biological control, and pheromone trapping is a monitoring tool.

Question 11Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which irrigation method generally achieves the highest water-use efficiency for a widely spaced orchard crop on undulating land?

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

Explanation

Drip irrigation delivers water directly to the root zone with minimal evaporation and runoff, giving high water-use efficiency even on uneven terrain. Flooding and furrow methods lose water to deep percolation, evaporation, and runoff.

Question 12Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

The main purpose of treating seed with a fungicide such as carboxin before sowing is to:

  1. Protect germinating seed and seedlings from seed- and soil-borne fungal pathogens Correct answer.
  2. Supply nitrogen to the emerging seedling
  3. Improve seed vigour by hardening the seed coat
  4. Increase seed germination percentage by breaking dormancy

Explanation

Seed-treatment fungicides form a protective layer that suppresses seed-borne and soil-borne fungi attacking germinating seeds and young seedlings. They do not break dormancy, supply nutrients, or harden the seed coat.

Question 13Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which cropping system is described as growing two or more crops simultaneously in the same field with a definite row arrangement?

  1. Intercropping Correct answer.
  2. Relay cropping
  3. Sequential cropping
  4. Sole cropping

Explanation

Intercropping involves growing two or more crops together at the same time in a defined spatial arrangement. Sequential cropping grows crops one after another, relay cropping overlaps only part of the life cycles, and sole cropping involves a single crop.

Question 14Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

A soil test reports a cation exchange capacity of 25 cmol(+) per kg and high base saturation. What does this indicate about the soil?

  1. Very sandy soil with little nutrient retention
  2. Strongly acidic soil dominated by aluminium
  3. A soil with excessive soluble salts
  4. Good nutrient-holding capacity with adequate exchangeable bases Correct answer.

Explanation

A CEC of 25 cmol(+) per kg is moderately high, indicating good capacity to retain exchangeable cations, and high base saturation means those sites are occupied mainly by bases rather than aluminium. This points to a fertile, well-buffered soil.

Question 15Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which of the following is a key difference between a herbicide applied pre-emergence and one applied post-emergence?

  1. Pre-emergence herbicides are selective, while post-emergence herbicides are always non-selective
  2. Pre-emergence herbicides require a surfactant, while post-emergence herbicides never do
  3. Pre-emergence herbicides act on weed seeds and seedlings before crop and weed emergence, while post-emergence herbicides act on emerged weeds Correct answer.
  4. Pre-emergence herbicides are always systemic, while post-emergence herbicides are always contact

Explanation

The timing distinction is the defining feature: pre-emergence herbicides are applied to soil before weeds and crop emerge, whereas post-emergence herbicides are applied to foliage of emerged weeds. Selectivity and systemic versus contact action occur in both categories.

Question 16Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

In horticulture, which practice is used to induce flowering in pineapple by applying a growth regulator?

  1. Spraying ethephon to promote uniform flowering Correct answer.
  2. Spraying cytokinin to induce dormancy
  3. Treating with auxin to prevent fruit set
  4. Applying gibberellic acid to delay flowering

Explanation

Ethephon releases ethylene, which triggers uniform flowering and fruiting in pineapple, allowing synchronized harvest. Gibberellic acid, auxin, and cytokinin do not serve this flower-induction purpose in pineapple.

Question 17Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which type of soil water is most readily available to plants?

  1. Gravitational water draining freely through macropores
  2. Hygroscopic water held tightly by soil particles
  3. Water held in the saturated zone below the water table
  4. Capillary water held between field capacity and permanent wilting point Correct answer.

Explanation

Capillary water retained in micropores between field capacity and permanent wilting point is the fraction plants can absorb. Hygroscopic water is bound too tightly, gravitational water drains too quickly, and saturated zone water is generally below the root zone.

Question 18Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

A farmer observes white, cottony mycelium and sclerotia on the stem base of a crop near the soil line, with plants collapsing. Which disease is most consistent with these signs?

  1. Powdery mildew
  2. Downy mildew
  3. Sclerotinia stem rot Correct answer.
  4. Bacterial leaf blight

Explanation

Sclerotinia species produce white cottony mycelium and hard, dark sclerotia on stem bases, causing collapse of affected plants. Powdery mildew produces superficial white powder on leaves, bacterial blight causes water-soaked lesions, and downy mildew affects foliage with sporulation on leaf undersides.

Question 19Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which of the following best explains why legumes are included in crop rotations for soil fertility?

  1. Symbiotic rhizobia fix atmospheric nitrogen, adding nitrogen to the soil Correct answer.
  2. Legume residues have a very high C:N ratio that immobilizes nitrogen
  3. Legumes acidify the soil and release potassium
  4. Legume roots exude large amounts of phosphorus

Explanation

Legumes form symbioses with rhizobia that fix atmospheric nitrogen, which becomes available to the crop and subsequent crops through residue decomposition. They do not exude phosphorus, and legume residues are typically low in C:N ratio, favouring mineralization.

Question 20Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

In a seed germination test, 400 seeds were sown, 360 germinated, and 20 were dead. The remaining seeds were dormant. What is the germination percentage?

  1. 90% Correct answer.
  2. 80%
  3. 95%
  4. 85%

Explanation

Germination percentage is the number of normal seedlings divided by the total seeds tested, multiplied by 100. Here 360 divided by 400 equals 0.90, giving 90 percent; dormant seeds are not counted as germinated.

Question 21Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which phenomenon explains the loss of effectiveness of a herbicide such as atrazine after repeated use against the same weed population?

  1. Increased soil pH
  2. Selection of resistant weed biotypes Correct answer.
  3. Reduced herbicide adsorption to clay
  4. Enhanced crop canopy shading

Explanation

Repeated use of a single herbicide selects for individuals with resistant traits, which survive and reproduce, increasing the resistant proportion of the population. Soil pH, canopy shading, and adsorption affect herbicide behaviour but do not explain heritable resistance.

Question 22Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

In a soil profile, the horizon of maximum illuviation of clay, iron, and aluminium oxides in an Alfisol is designated as:

  1. A horizon
  2. O horizon
  3. Bt horizon Correct answer.
  4. C horizon

Explanation

The Bt horizon is a subsurface horizon showing accumulation of translocated silicate clay, often with iron and aluminium oxides. The A horizon is the surface mineral layer, the O horizon is organic litter, and the C horizon is relatively unweathered parent material.

Question 23Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

A grower applies 120 kg of urea (46% N) per hectare. How much actual nitrogen is applied?

  1. 55.2 kg N per hectare Correct answer.
  2. 46 kg N per hectare
  3. 120 kg N per hectare
  4. 27.6 kg N per hectare

Explanation

Actual nitrogen equals the fertilizer rate multiplied by its nitrogen percentage: 120 kg multiplied by 0.46 equals 55.2 kg N per hectare. The other values ignore the percentage or misapply it.

Question 24Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which of the following best describes the role of a pollenizer row in an orchard of a self-incompatible fruit crop?

  1. It provides shade to reduce sunburn on the main cultivar
  2. It supplies compatible pollen to the main cultivar to ensure fruit set Correct answer.
  3. It acts as a windbreak to reduce fruit drop
  4. It serves as a rootstock for grafting the main cultivar

Explanation

Self-incompatible fruit crops require cross-pollination, so a pollenizer cultivar with compatible pollen is planted to ensure adequate fruit set. Shade, rootstock, and windbreak functions are unrelated to pollenizer rows.

Question 25Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which integrated pest management principle is illustrated by using economic threshold levels to decide when to apply an insecticide?

  1. Spraying only after the entire crop has been destroyed
  2. Using the highest labelled dose at every spray
  3. Applying a calendar-based spray schedule regardless of pest density
  4. Treating only when pest numbers justify control to avoid unnecessary sprays Correct answer.

Explanation

Economic thresholds define the pest density at which control costs are justified by avoided crop loss, so sprays are applied only when necessary. This reduces pesticide use and selection pressure compared with calendar spraying or routine maximum doses.

Question 26Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which agronomic practice is defined as growing a short-duration crop between two main crops in the same field within one year?

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

Explanation

A catch crop is a quick-maturing crop sown between two main crops to use residual moisture and nutrients and to protect the soil. Relay cropping overlaps the life cycles of two crops, mixed cropping grows them together, and sequential cropping simply follows one crop with another.

Question 27Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

In horticulture, which propagation method produces clonal plants that are genetically identical to the parent and is achieved by burying a stem while still attached to the mother plant?

  1. Budding
  2. Stratification
  3. Layering Correct answer.
  4. Tonguing

Explanation

Layering induces roots on a stem while it is still attached to the parent plant, after which it is detached as an independent clonal plant. Budding is a grafting technique, tonguing is a cut used in grafting, and stratification is a seed pre-treatment.

Question 28Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which soil order is characterised by a thick, dark, humus-rich surface horizon formed under grassland vegetation?

  1. Oxisol
  2. Histosol
  3. Mollisol Correct answer.
  4. Andisol

Explanation

Mollisols have a dark, base-rich mollic epipedon built up under grassland and are among the most fertile agricultural soils. Oxisols are highly weathered tropical soils, Histosols are organic peat soils, and Andisols form from volcanic ash.

Question 29Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which insect order includes the majority of serious defoliating caterpillars such as armyworm and cutworm?

  1. Hemiptera
  2. Lepidoptera Correct answer.
  3. Coleoptera
  4. Thysanoptera

Explanation

Lepidoptera is the order of moths and butterflies, whose larvae are caterpillars and include armyworm and cutworm. Hemiptera are true bugs with piercing-sucking mouthparts, Coleoptera are beetles with chewing adults, and Thysanoptera are thrips.

Question 30Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which macronutrient is most directly involved in nodulation and nitrogen fixation by Rhizobium in legume roots?

  1. Chlorine
  2. Sulphur
  3. Phosphorus Correct answer.
  4. Calcium

Explanation

Phosphorus is required for root growth, ATP supply and nodule development, which strongly influences nodulation and nitrogen fixation. Calcium affects root hair infection, but the direct energy-linked role in nodule functioning is chiefly phosphorus.

Question 31Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which weed is a parasitic angiosperm that attaches to host roots and is a serious problem in sunflower and tomato?

  1. Striga
  2. Viscum
  3. Cuscuta
  4. Orobanche Correct answer.

Explanation

Orobanche (broomrape) is a root holoparasite that attaches to host roots and severely affects sunflower, tomato and tobacco. Cuscuta is a stem parasite, Striga mainly attacks cereals, and Viscum is a stem parasite of trees.

Question 32Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which irrigation scheduling approach uses pan evaporation data to estimate crop water use?

  1. Gravimetric method
  2. Pan evaporation method Correct answer.
  3. Tensiometer method
  4. Neutron probe method

Explanation

The pan evaporation method estimates crop evapotranspiration by multiplying pan evaporation by a crop coefficient. Tensiometers and neutron probes measure soil water status directly, and the gravimetric method measures soil moisture by oven drying.

Question 33Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which plant protection chemical group acts by inhibiting ergosterol biosynthesis in fungal cell membranes?

  1. Dithiocarbamates
  2. Triazoles Correct answer.
  3. Neonicotinoids
  4. Organophosphates

Explanation

Triazoles such as propiconazole and tebuconazole are sterol demethylation inhibitors that block ergosterol synthesis in fungal membranes. Dithiocarbamates are multi-site protectants, organophosphates are insecticides, and neonicotinoids are nicotinic insecticides.

Question 34Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

A soil sample weighs 50 g on an oven-dry basis and contains 10 g of water. What is the gravimetric water content?

  1. 10%
  2. 25%
  3. 20% Correct answer.
  4. 50%

Explanation

Gravimetric water content is mass of water divided by mass of oven-dry soil, multiplied by 100, giving 10/50 × 100 = 20%. Volumetric water content would require bulk density, which is not given.

Question 35Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which cropping practice most directly reduces soil erosion on a sloping field by maintaining continuous ground cover?

  1. Contour strip cropping with cover crops Correct answer.
  2. Clean cultivation between rows
  3. Deep summer ploughing
  4. Burning of crop residues

Explanation

Contour strip cropping with cover crops interrupts slope length and keeps soil covered, reducing raindrop impact and runoff. Clean cultivation, deep ploughing and residue burning all expose soil and increase erosion risk.

Question 36Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

A farmer wants to control broadleaf weeds in a grass crop without injuring the grass. Which herbicide group is most appropriate?

  1. Synthetic auxins such as 2,4-D Correct answer.
  2. Chloroacetamides such as metolachlor
  3. Dinitroanilines such as pendimethalin
  4. Thiocarbamates such as butachlor

Explanation

Synthetic auxins such as 2,4-D are selective for dicotyledonous weeds and are safe on established grasses at recommended doses. Pendimethalin, butachlor and metolachlor are mainly grass-active or broad-spectrum soil herbicides.

Question 37Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

A crop shows a purplish discolouration of older leaves and poor root development in a soil with high pH. Which nutrient deficiency is most likely?

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

Explanation

Phosphorus deficiency causes purplish or reddish older leaves and poor root growth, and is accentuated at high pH where P is fixed by calcium. Nitrogen deficiency causes general yellowing, potassium causes leaf-margin scorch, and magnesium causes interveinal chlorosis.

Question 38Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which of the following is the primary reason for practising crop rotation with cereals and pulses?

  1. Prevention of allelopathic effects in the field
  2. Uniform moisture use through the profile
  3. Elimination of the need for fertilizer
  4. Interruption of pest and disease cycles and improvement of soil nitrogen Correct answer.

Explanation

Rotating cereals with pulses breaks the host continuity of soil-borne pathogens and pests and adds biologically fixed nitrogen to the soil. It does not eliminate fertilizer needs or guarantee uniform moisture use, and allelopathy is a reason against continuous cropping of certain species.

Question 39Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

A seed lot has 98% purity and 85% germination. What is its pure live seed percentage?

  1. 98.0%
  2. 73.0%
  3. 83.3% Correct answer.
  4. 91.5%

Explanation

Pure live seed percentage is purity × germination ÷ 100, so 98 × 85 ÷ 100 = 83.3%. This value is used to adjust seeding rates to ensure the desired number of viable seeds.

Question 40Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which of the following best explains why systemic insecticides are effective against sap-sucking insects hidden in curled leaves?

  1. They attract natural enemies to the crop
  2. They are absorbed and translocated within plant tissues, reaching the feeding sites Correct answer.
  3. They sterilise the insects on contact with the leaf
  4. They form a protective film on the leaf surface

Explanation

Systemic insecticides move through the vascular system of the plant, so insects feeding in sheltered or curled tissues take up the toxic dose. Contact insecticides remain on the surface and depend on direct spray coverage.

Question 41Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

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

  1. Water-holding capacity Correct answer.
  2. Sand content
  3. Bulk density of the mineral fraction
  4. Particle density

Explanation

Organic matter increases aggregation and water retention in sandy soils, improving their low water-holding capacity. Particle density of the mineral fraction and the sand content itself are not changed by organic additions.

Question 42Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

In a nursery, which practice best prevents damping-off caused by Pythium in germinating seedlings?

  1. Applying lime to raise the medium pH above 8
  2. Using well-drained sterilised media and avoiding overwatering Correct answer.
  3. Sowing seed deeply to encourage rapid germination
  4. Maintaining a saturated medium to keep seedlings cool

Explanation

Pythium damping-off is favoured by high moisture and poor aeration, so sterilised, well-drained media and careful watering reduce disease pressure. High pH, deep sowing and saturated media all increase the risk of seedling mortality.

Question 43Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which agronomic measure is most effective for controlling Striga in sorghum on a heavily infested field?

  1. Deep ploughing after crop harvest only
  2. Flood irrigation during the growing season
  3. Continuous sorghum cropping with high nitrogen
  4. Rotation with a non-host trap crop and use of resistant varieties Correct answer.

Explanation

Striga control relies on reducing the soil seed bank through trap crops that stimulate suicidal germination and on growing resistant or tolerant varieties. Continuous sorghum maintains the parasite, and flood irrigation or post-harvest ploughing alone do not deplete the seed bank.

Question 44Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

A grower applies 200 kg of single superphosphate (16% P2O5) per hectare. How much P2O5 is applied?

  1. 200 kg
  2. 64 kg
  3. 16 kg
  4. 32 kg Correct answer.

Explanation

The quantity of nutrient is the product of fertilizer mass and nutrient percentage, so 200 × 0.16 = 32 kg P2O5 per hectare. This calculation is the basis for matching fertilizer grades to soil test recommendations.

Question 45Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which plant protection strategy best describes using a crop variety carrying the Bt gene against stem borer?

  1. Biological control by releasing Trichogramma
  2. Cultural control through crop rotation
  3. Chemical control with a systemic granular insecticide
  4. Host plant resistance through genetic transformation Correct answer.

Explanation

Bt crops express insecticidal proteins from Bacillus thuringiensis, making the plant itself resistant to the target pest. This is host plant resistance achieved through genetic transformation, distinct from biocontrol, chemical or cultural methods.

Question 46Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which soil horizon is the zone of maximum accumulation of illuviated clay and iron oxides in a well-drained Alfisol?

  1. C horizon
  2. R horizon
  3. A horizon
  4. Bt horizon Correct answer.

Explanation

The Bt horizon is an argillic subsurface horizon where clay, iron and aluminium oxides have accumulated by illuviation. The A horizon is the surface zone of organic accumulation, C is weathered parent material, and R is hard bedrock.

Question 47Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

A field experiment compares three nitrogen levels with four replications in a randomised block design. Which statement correctly describes the role of blocking?

  1. It removes field heterogeneity from the error term, improving precision Correct answer.
  2. It increases the number of treatments to be tested
  3. It eliminates the need for randomisation
  4. It guarantees a significant treatment effect

Explanation

Blocking groups plots of similar conditions so that field variation is accounted for separately from treatment effects, reducing experimental error and improving precision. Randomisation is still required, and blocking does not create additional treatments or guarantee significance.

Question 48Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which statement best explains why continuous rice monoculture under puddled conditions can reduce the availability of zinc over time?

  1. Continuous rice removes only iron, leaving zinc unavailable
  2. Flooding lowers pH and increases zinc solubility
  3. Flooding raises pH and promotes zinc precipitation as sulphides and carbonates Correct answer.
  4. Puddling increases exchangeable zinc in the soil solution

Explanation

Prolonged flooding shifts soil pH towards neutrality to alkalinity and creates reducing conditions in which zinc can precipitate as sulphides and carbonates, lowering its availability. Rice monoculture also exports zinc in grain, further depleting the available pool.

Question 49Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

In a hybrid seed production block, which factor most directly determines the required ratio of female to male rows?

  1. The seed rate of the female parent only
  2. The market price of the hybrid seed
  3. The number of herbicide sprays used
  4. Pollen output of the male parent and its synchrony with female receptivity Correct answer.

Explanation

The female-to-male row ratio is set so that pollen from the male parent is sufficient and available when female florets are receptive. Pollen production and flowering synchrony therefore determine the ratio, whereas seed rate, price and spraying do not.

Question 50Agriculture (Agronomy, Horticulture, Plant Protection, Soil Science)

Which mechanism best explains the development of resistance in a weed population after repeated use of a single herbicide mode of action?

  1. Induced mutation caused by the herbicide in every plant
  2. Selection of pre-existing resistant biotypes under repeated directional pressure Correct answer.
  3. Horizontal gene transfer from the crop to the weed during spraying
  4. Loss of herbicide potency through storage degradation

Explanation

Repeated use of one mode of action selects individuals that already carry resistance traits, allowing them to reproduce and dominate the population. Herbicides do not direct mutation in every plant, and resistance is not caused by storage degradation.