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RBSE Sec Voc Agriculture study materials
RBSE Sec Voc Agriculture study resources

RBSE Sec Voc Agriculture practice questions

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Question 1Agronomy and Crop Production

Which soil property is improved most directly by adding well-decomposed farmyard manure to a sandy field over several seasons?

  1. Water-holding capacity and cation exchange capacity Correct answer.
  2. Soil pH reduction to strongly acidic levels
  3. Bulk density increase and pore space reduction
  4. Electrical conductivity rise to saline levels

Explanation

Organic manure adds humus, which increases the soil's ability to retain moisture and to hold exchangeable nutrient cations on colloidal surfaces. It also improves aggregation and structure rather than compacting the soil. Raising salinity or driving pH strongly acidic are not the intended outcomes of manure application.

Question 2Agronomy and Crop Production

A farmer wants to sow a pulse crop to restore nitrogen in a cereal-based rotation. Which process supplies this nitrogen?

  1. Biological nitrogen fixation by rhizobia in root nodules Correct answer.
  2. Nitrification of ammonium by Nitrosomonas
  3. Denitrification of nitrate under waterlogged conditions
  4. Mineralisation of soil organic matter by fungi

Explanation

Legumes form symbiotic associations with rhizobia, which reduce atmospheric nitrogen to ammonia inside root nodules and make it available to the plant. When residues decompose, part of this fixed nitrogen enters the soil for the following crop. The other listed processes either release existing soil nitrogen or remove it as gas.

Question 3Agronomy and Crop Production

Which irrigation scheduling approach best matches water supply to crop demand in a canal command area with limited supply?

  1. Irrigating only after visible wilting has persisted for several days
  2. Irrigating at fixed calendar intervals regardless of weather
  3. Irrigating when cumulative pan evaporation reaches a set fraction of the crop coefficient times reference evapotranspiration Correct answer.
  4. Flooding the field continuously to keep the soil saturated

Explanation

Scheduling based on reference evapotranspiration adjusted by the crop coefficient and a permitted depletion fraction tracks actual crop water use. It avoids both under-irrigation and waste. Fixed calendars ignore weather, continuous flooding wastes water and damages roots, and waiting for prolonged wilting causes yield loss.

Question 4Agronomy and Crop Production

A seed lot of wheat has 90 percent germination and 95 percent purity. What is its pure live seed percentage?

  1. 90.0 percent
  2. 92.5 percent
  3. 85.5 percent Correct answer.
  4. 95.0 percent

Explanation

Pure live seed percentage is the product of percentage purity and percentage germination divided by 100. Here 0.95 multiplied by 0.90 equals 0.855, or 85.5 percent. This figure is used to adjust seeding rates so that the desired number of viable seeds is planted.

Question 5Agronomy and Crop Production

Which practice most effectively reduces soil erosion on a sloping field with row crops?

  1. Leaving the field bare and fallow through the rainy season
  2. Ploughing up and down the slope each season
  3. Burning crop residues after harvest
  4. Growing crops in contour strips alternated with close-growing cover Correct answer.

Explanation

Contour strip cropping places close-growing vegetation in bands that slow runoff and trap soil moving downslope. Alternating these bands with row crops breaks the length of erodible slope. Ploughing up and down the slope, bare fallow and residue burning all accelerate erosion.

Question 6Agronomy and Crop Production

Which crop is a kharif season crop in most of the Indian subcontinent?

  1. Wheat
  2. Paddy rice Correct answer.
  3. Chickpea
  4. Mustard

Explanation

Kharif crops are sown with the onset of the monsoon and harvested in autumn, and paddy rice is a typical example. Wheat, mustard and chickpea are rabi crops grown in the cooler post-monsoon season. Matching a crop to its season is fundamental to planning a cropping calendar.

Question 7Agronomy and Crop Production

A farmer wants to increase cropping intensity from 100 to 200 percent on the same land. Which combination achieves this?

  1. Growing two crops in sequence within the same year Correct answer.
  2. Leaving the land fallow for half the year
  3. Growing a single crop with a lower seed rate
  4. Growing one long-duration crop occupying the field for the full year

Explanation

Cropping intensity expresses the number of crops grown on the same land in a year as a percentage of the standard single-crop area. Two successive crops on the same field give 200 percent. One long-duration crop or fallow periods keep the value near 100 percent or below.

Question 8Agronomy and Crop Production

Which herbicide timing is appropriate for a pre-emergence application in a direct-seeded rice field?

  1. After the crop has formed a full canopy
  2. At the panicle initiation stage
  3. Immediately after sowing before weeds and crop emerge Correct answer.
  4. After the field has been drained for harvest

Explanation

Pre-emergence herbicides form a soil-surface barrier that kills germinating weed seeds, so they must be applied soon after sowing before weeds and crop seedlings appear. Applying them later misses the susceptible weed stage. Canopy-stage or harvest-time applications serve other purposes and cannot control early weeds.

Question 9Agronomy and Crop Production

Which type of insecticide acts by disrupting the insect moulting process and is therefore relatively selective against caterpillars?

  1. Pyrethroid contact insecticides
  2. Organophosphate nerve poisons
  3. Inorganic sulphur dusts
  4. Insect growth regulators that mimic juvenile hormone Correct answer.

Explanation

Insect growth regulators that mimic juvenile hormone prevent larvae from developing into viable adults, so they act specifically on moulting stages. This gives selectivity toward caterpillars while sparing many beneficials. Nerve poisons and broad-spectrum contact insecticides act on the nervous system and kill a wide range of insects.

Question 10Agronomy and Crop Production

Which practice is the most reliable way to break seed dormancy in freshly harvested paddy seeds?

  1. Sowing them immediately after threshing
  2. Coating the seeds with fungicide
  3. Dry heat treatment or a period of after-ripening storage Correct answer.
  4. Soaking the seeds in cold water for one hour

Explanation

Freshly harvested paddy often shows post-harvest dormancy that is broken by dry heat or a period of dry storage known as after-ripening. These treatments reduce the dormancy block so that germination becomes uniform. Short soaking, immediate sowing or fungicidal coating does not remove physiological dormancy.

Question 11Agronomy and Crop Production

Which element is most commonly deficient in alkaline, calcareous soils and causes interveinal chlorosis in young leaves?

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

Explanation

Iron availability falls sharply as soil pH and lime content rise, so iron deficiency is common in calcareous soils. Because iron is immobile in the plant, chlorosis appears first on young leaves between the veins. Potassium, magnesium and nitrogen deficiencies show different patterns and are less tied to high pH.

Question 12Agronomy and Crop Production

Which method of sowing places seed and fertiliser at the same depth but in separate bands to avoid seedling injury?

  1. Broadcasting seed and fertiliser together
  2. Drilling fertiliser directly with the seed in the same furrow
  3. Top-dressing fertiliser on the surface after emergence
  4. Placing fertiliser in a band below and to the side of the seed row Correct answer.

Explanation

Placing fertiliser in a band below and to the side of the seed, often called side-band placement, separates the salt-rich fertiliser from the germinating seed. This avoids salt injury and improves nutrient uptake by the developing roots. Mixing fertiliser with seed in the same furrow raises the risk of seedling damage.

Question 13Agronomy and Crop Production

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

  1. The colour of the seed coat
  2. The depth of ploughing done before sowing
  3. The stage-specific crop coefficient and local evaporative demand Correct answer.
  4. The number of tillers removed at thinning

Explanation

Crop water requirement during a critical stage is estimated from reference evapotranspiration multiplied by the crop coefficient for that stage. Local evaporative demand drives the reference value. Seed coat colour, thinning and ploughing depth do not directly set the crop's water use.

Question 14Agronomy and Crop Production

Which cropping system is an example of mixed cropping?

  1. Rotating a legume after three years of cereals
  2. Growing a sole crop of cotton for the whole year
  3. Growing paddy followed by wheat on the same field
  4. Growing maize and cowpea together in the same field in the same season Correct answer.

Explanation

Mixed cropping means growing two or more crops simultaneously in the same field without a definite row arrangement. Maize with cowpea in the same season fits this definition. Sequential cropping, sole cropping and rotation involve different time arrangements of crops.

Question 15Agronomy and Crop Production

Which soil structure condition is most favourable for root growth and aeration in a field crop?

  1. Massive, cloddy structure with few pores
  2. Platy structure compacted by repeated shallow tillage
  3. Granular structure with stable aggregates and good pore space Correct answer.
  4. Single-grain sandy structure with no aggregation

Explanation

Granular structure with stable aggregates provides a balance of macro- and micropores that supports root penetration, aeration and drainage. Massive, single-grain and platy structures restrict root growth or hold too little water. Good structure is maintained by organic matter and appropriate tillage.

Question 16Agronomy and Crop Production

A crop shows pale yellow lower leaves, stunted growth and poor tillering despite adequate moisture. Which nutrient deficiency is most likely?

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

Explanation

Nitrogen is mobile in the plant, so deficiency first appears as general yellowing of older, lower leaves with stunted growth and reduced tillering. Calcium and boron are immobile and affect growing points, while iron chlorosis appears on young leaves. The described pattern therefore points to nitrogen.

Question 17Agronomy and Crop Production

Which agronomic practice best helps a crop tolerate a short dry spell without yield loss?

  1. Applying a high dose of nitrogen just before the dry spell
  2. Applying a pre-sowing irrigation and conserving moisture with mulch Correct answer.
  3. Increasing plant density to cover the soil
  4. Removing all crop residues from the field

Explanation

Pre-sowing irrigation charges the soil profile, and mulching reduces evaporation from the surface, so the crop has more stored water to draw on during a dry spell. Higher plant density increases competition for limited water, and heavy nitrogen before drought can worsen stress. Residue removal increases evaporation.

Question 18Agronomy and Crop Production

Which statement about the role of a legume in an intercropping system with a cereal is correct?

  1. The legume reduces soil organic matter because it is harvested
  2. The legume competes less for nitrogen because it can fix atmospheric nitrogen Correct answer.
  3. The legume eliminates the need for any phosphorus fertiliser
  4. The legume always outcompetes the cereal for light and water

Explanation

A legume in intercrop with a cereal can meet part of its nitrogen need through symbiotic fixation, which reduces competition for soil nitrogen and can leave residual nitrogen for the cereal. It does not automatically dominate for light and water, and it does not remove the need for phosphorus. Legume residues generally add to rather than deplete organic matter.

Question 19Agronomy and Crop Production

Which measure is most appropriate for managing a field with a soil pH of 4.8 for a cereal crop?

  1. Flooding the field with saline water
  2. Applying agricultural lime and incorporating it before sowing Correct answer.
  3. Applying gypsum to the surface
  4. Applying elemental sulphur

Explanation

A pH of 4.8 is strongly acidic for most cereals, and agricultural lime raises pH by neutralising acidity. Lime should be incorporated into the plough layer before sowing so it can react with the soil. Gypsum addresses sodicity, elemental sulphur acidifies further, and saline water worsens the problem.

Question 20Agronomy and Crop Production

Which factor most limits the effectiveness of a contact herbicide applied to a dense weed canopy?

  1. Poor spray coverage of lower leaves shielded by the canopy Correct answer.
  2. The herbicide's soil residual activity
  3. The herbicide's systemic movement through the phloem
  4. The herbicide's selectivity to the crop

Explanation

Contact herbicides kill only the plant tissue they touch, so dense canopies shield lower leaves and allow weeds to survive and regrow. Good coverage and spray volume are therefore critical. Systemic movement, soil residual activity and crop selectivity are separate properties that do not explain the coverage limitation.

Question 21Agronomy and Crop Production

Which practice is recommended for safe storage of a harvested cereal grain lot at farm level?

  1. Storing at moisture content above 16 percent to save drying cost
  2. Sealing damp grain in airtight bags immediately after threshing
  3. Drying grain to safe moisture and storing in clean, aerated bins Correct answer.
  4. Mixing fresh and old grain in the same bin

Explanation

Grain must be dried to a safe moisture level and stored in clean, aerated structures to prevent mould growth and insect infestation. Mixing lots or sealing damp grain creates hotspots and spoilage. Safe storage protects both quality and germination.

Question 22Agronomy and Crop Production

Which crop geometry is most suitable for a widely spaced crop such as maize grown for grain?

  1. Rows spaced 10 centimetres apart with very dense plants
  2. Rows spaced about 60 to 75 centimetres with plants 20 to 25 centimetres apart Correct answer.
  3. Random dibbling at very low plant density
  4. Broadcasting seed without rows

Explanation

Maize needs adequate space per plant for light interception and cob development while maintaining a plant population that supports yield. Rows of roughly 60 to 75 centimetres with plants 20 to 25 centimetres apart provide this balance. Broadcast or extremely dense or sparse arrangements reduce yield.

Question 23Agronomy and Crop Production

Which statement correctly describes the difference between certified seed and truthfully labelled seed?

  1. Certified seed is tested for genetic purity and germination under a certification agency, while truthfully labelled seed carries a label declaring its quality without certification Correct answer.
  2. Truthfully labelled seed is always of higher genetic purity than certified seed
  3. Truthfully labelled seed cannot be sold in any market
  4. Certified seed needs no germination testing before sale

Explanation

Certified seed has passed field and laboratory checks by a certification agency for genetic purity and quality. Truthfully labelled seed is sold with a label stating its known quality but without formal certification. Both are legitimate categories, but only certified seed carries the agency guarantee.

Question 24Agronomy and Crop Production

Which cultural practice most directly reduces the build-up of soil-borne pathogens in a continuous cereal field?

  1. Increasing the nitrogen dose every year
  2. Irrigating more frequently to wash the soil
  3. Rotating with a non-host crop for one or more seasons Correct answer.
  4. Growing the same cereal variety every year

Explanation

Many soil-borne pathogens survive in residues and soil and depend on a susceptible host. Rotating to a non-host crop breaks this cycle and reduces inoculum. Continuous cropping of the same host, extra nitrogen or frequent irrigation do not remove the pathogen and may worsen the problem.

Question 25Agronomy and Crop Production

A field shows a patchy crop stand with stunted plants and poor nodulation in a legume. Which soil condition is the most likely cause?

  1. Neutral pH with adequate phosphorus and calcium
  2. Strongly acidic pH with low available phosphorus and molybdenum Correct answer.
  3. Well-drained loam with adequate moisture
  4. High organic matter with good aggregation

Explanation

Legume nodulation and nitrogen fixation are sensitive to acidity, and low phosphorus and molybdenum availability further limit rhizobial activity. The result is poor nodulation and stunted plants. Neutral pH with adequate nutrients, good organic matter and well-drained loam are favourable conditions.

Question 26Agronomy and Crop Production

Which agronomic term describes the sequence of crops grown on the same field over a year along with the associated management practices?

  1. Cropping pattern Correct answer.
  2. Cropping scheme
  3. Crop rotation
  4. Land equivalent ratio

Explanation

A cropping pattern is the yearly sequence and spatial arrangement of crops and fallow on a given area, together with the management practices used. Crop rotation is only the temporal succession of crops, and land equivalent ratio measures intercropping advantage rather than the whole farm plan.

Question 27Agronomy and Crop Production

A grower wants to sow a small-seeded fodder legume into a standing, well-established crop without destroying the existing stand. Which sowing method is most appropriate?

  1. Broadcasting the seed over the standing crop Correct answer.
  2. Drilling with a seed-cum-fertiliser drill
  3. Transplanting raised seedlings
  4. Sowing in furrows opened with a country plough

Explanation

Broadcasting scatters seed uniformly over the existing crop and causes minimal disturbance to the established stand, which suits small seeds and over-sowing situations. Furrow opening, drilling and transplanting all require soil disturbance or removal of the standing crop, which defeats the purpose.

Question 28Agronomy and Crop Production

Which irrigation scheduling approach bases the next irrigation on the amount of water actually lost from the field since the previous irrigation?

  1. Critical stage approach
  2. Soil moisture depletion approach Correct answer.
  3. Irrigation water to cumulative pan evaporation ratio
  4. Fixed calendar interval approach

Explanation

The soil moisture depletion approach irrigates when the available soil water in the root zone falls to a defined depletion level, so scheduling follows actual water loss. The IW/CPE ratio uses pan evaporation as an index, the critical stage approach ties irrigation to growth stages, and a calendar interval ignores field water status.

Question 29Agronomy and Crop Production

Which soil-water condition is described as the water content at which gravity drainage has essentially ceased and the soil is at field capacity?

  1. Water held at tensions between about 0.1 and 0.33 bar after free drainage Correct answer.
  2. Water content at permanent wilting point
  3. Water content at the hygroscopic coefficient
  4. Water content at saturation with all pores filled

Explanation

Field capacity is the water retained after excess water has drained under gravity, corresponding to a matric suction of roughly 0.1 to 0.33 bar in most mineral soils. Saturation, permanent wilting point and hygroscopic coefficient represent wetter or much drier reference states.

Question 30Agronomy and Crop Production

A grower notices that a cereal crop in a sandy loam field shows nitrogen deficiency symptoms only in irrigation furrows where ponding occurs. Which process best explains this pattern?

  1. Fixation of ammonium by clay minerals
  2. Leaching of nitrate below the root zone
  3. Volatilisation of ammonia from the soil surface
  4. Denitrification in temporarily saturated soil Correct answer.

Explanation

In saturated, poorly aerated soil, nitrate is used as an electron acceptor by anaerobic bacteria and is lost as nitrogen gas through denitrification. This produces patchy nitrogen deficiency where water ponds, whereas leaching, volatilisation and fixation do not explain a pattern tied to waterlogged furrows.

Question 31Agronomy and Crop Production

Which weed characteristic makes a species most difficult to control with selective herbicides in a field crop?

  1. A shallow root system
  2. Germination over an extended period from a persistent seed bank Correct answer.
  3. Emergence in a single flush after the first rain
  4. Broad, horizontal leaves

Explanation

Weeds that germinate in repeated flushes from a long-lived seed bank escape a single herbicide application and keep reinfesting the crop. A single emergence flush, shallow roots and broad leaves are not by themselves barriers to selective chemical control.

Question 32Agronomy and Crop Production

Which statement correctly describes the role of a trap crop in insect pest management?

  1. It is a preferred host planted to attract pests away from the main crop Correct answer.
  2. It is a non-host crop planted to shade the main crop
  3. It is a crop that is harvested and sold to compensate for pest damage
  4. It is a crop that repels pests through root exudates

Explanation

A trap crop is a preferred host that draws pests away from the main crop, after which the pests are destroyed on the trap crop. It is not a marketable compensation crop, a repellent through root exudates, or a shade provider.

Question 33Agronomy and Crop Production

Which practice best reduces the risk of aflatoxin contamination in groundnut after harvest?

  1. Storing pods in damp, ventilated sheds
  2. Drying pods rapidly to safe moisture and storing them cool and dry Correct answer.
  3. Delaying harvest until the crop is over-mature
  4. Piling pods in heaps to allow sweating

Explanation

Aspergillus flavus and aflatoxin production are favoured by high moisture and warm storage, so rapid drying to safe moisture followed by cool, dry storage is the key control. Damp storage, sweating heaps and delayed harvest of over-mature pods all increase infection risk.

Question 34Agronomy and Crop Production

A field has a clay content of 45 percent, a bulk density of 1.6 grams per cubic centimetre and poor infiltration. Which management measure most directly improves its physical condition for a following cereal crop?

  1. Applying additional nitrogen fertiliser
  2. Adding organic matter and growing a deep-rooted green manure Correct answer.
  3. Compacting the surface to reduce evaporation
  4. Increasing the frequency of shallow tillage passes

Explanation

Organic matter improves aggregation, lowers bulk density and increases porosity and infiltration in heavy clay soils, and a deep-rooted green manure adds organic matter and creates root channels. Repeated shallow tillage, extra nitrogen and deliberate compaction do not correct the structural problem.

Question 35Agronomy and Crop Production

Which crop is grown mainly as a rabi season crop in northern India?

  1. Pigeon pea
  2. Cotton
  3. Wheat Correct answer.
  4. Pearl millet

Explanation

Wheat is a classic rabi crop, sown in winter and harvested in spring in northern India. Pearl millet, cotton and pigeon pea are predominantly kharif or warm-season crops in this region.

Question 36Agronomy and Crop Production

Which statement best explains why a cereal–legume rotation often raises the yield of the following cereal compared with continuous cereal?

  1. The legume increases soil pH strongly
  2. The legume leaves residual nitrogen and breaks pest and disease cycles Correct answer.
  3. The legume removes excess potassium
  4. The legume raises soil bulk density

Explanation

A legume in the rotation contributes biologically fixed nitrogen to the following crop and interrupts the build-up of cereal-specific pathogens and pests. It does not raise bulk density, remove potassium, or strongly raise pH, so the rotation benefit comes from nitrogen and break-crop effects.

Question 37Agronomy and Crop Production

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

  1. The weight of 1000 seeds
  2. The percentage of pure seed by weight
  3. The percentage of seedlings that develop into normal seedlings under controlled conditions Correct answer.
  4. The percentage of seed that floats in water

Explanation

The germination test reports the proportion of seeds that produce normal seedlings under specified moisture, temperature and light conditions. Purity, float tests and thousand-grain weight measure different attributes and do not establish germination capacity.

Question 38Agronomy and Crop Production

A farmer applies 120 kilograms of urea to one hectare. Urea contains 46 percent nitrogen. Approximately how much nitrogen is applied?

  1. 46 kilograms
  2. 55 kilograms Correct answer.
  3. 26 kilograms
  4. 120 kilograms

Explanation

Nitrogen applied equals the fertiliser quantity multiplied by its nitrogen fraction, that is 120 times 0.46, which gives about 55 kilograms of nitrogen. The other values confuse the product weight, the percentage figure, or an incorrect fraction with the actual nitrogen content.

Question 39Agronomy and Crop Production

In a crop water balance, which term accounts for water lost as vapour through plant stomata together with evaporation from the soil surface?

  1. Transpiration
  2. Percolation
  3. Evapotranspiration Correct answer.
  4. Runoff

Explanation

Evapotranspiration is the combined loss of water as transpiration through plant stomata and evaporation from the soil surface. Transpiration is only the plant component, while percolation and runoff are downward and surface water movements rather than vapour losses.

Question 40Agronomy and Crop Production

A field trial compares a cereal–legume intercrop with sole crops. The intercrop yields 4.0 tonnes of cereal and 1.5 tonnes of legume per hectare, while sole cereal yields 5.0 tonnes and sole legume yields 3.0 tonnes. What is the land equivalent ratio?

  1. 1.10
  2. 0.90
  3. 0.50
  4. 1.30 Correct answer.

Explanation

The land equivalent ratio is the sum of the intercrop yields each divided by their sole crop yields, that is 4.0 divided by 5.0 plus 1.5 divided by 3.0, which equals 0.80 plus 0.50, or 1.30. A value above one indicates a yield advantage for intercropping over sole cropping.

Question 41Soil Science and Soil Fertility Management

Which soil particle size fraction has the greatest capacity to hold plant-available water and nutrients due to its high surface area?

  1. Sand
  2. Clay Correct answer.
  3. Coarse silt
  4. Gravel

Explanation

Clay particles are the smallest soil separates and carry a very large specific surface area with net negative charge, giving them the highest capacity among separates to adsorb water and nutrient cations. Sand and gravel have large pores and low surface area, so they drain quickly and retain little.

Question 42Soil Science and Soil Fertility Management

A soil test reports a pH of 5.2. Which management practice is most directly justified by this reading for a cereal crop?

  1. Flooding the field to leach bicarbonate out of the profile
  2. Applying elemental sulfur to acidify the soil further
  3. Applying agricultural lime to raise pH toward the crop's optimum Correct answer.
  4. Applying gypsum to lower the sodium adsorption ratio

Explanation

A pH of 5.2 is strongly acidic and can reduce availability of phosphorus and molybdenum while increasing aluminum activity. Finely ground agricultural lime (calcium carbonate) neutralizes acidity and raises pH toward the range preferred by most cereals.

Question 43Soil Science and Soil Fertility Management

Which organism group is chiefly responsible for converting ammonium to nitrate in aerobic soils?

  1. Nitrifying bacteria Correct answer.
  2. Rhizobia in root nodules
  3. Actinomycetes decomposing lignin
  4. Mycorrhizal fungi

Explanation

Nitrification is a two-step aerobic process carried out by specialized chemoautotrophic bacteria, first oxidizing ammonium to nitrite and then nitrite to nitrate. Rhizobia fix atmospheric nitrogen rather than nitrifying, and fungi and actinomycetes are primarily decomposers.

Question 44Soil Science and Soil Fertility Management

In a soil profile description, the layer that is richest in accumulated organic matter and is the primary zone of root activity is designated as which horizon?

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

Explanation

The A horizon is the surface mineral horizon where organic matter accumulates and biological activity is greatest, making it the main rooting and tillage zone. The B horizon is a subsoil zone of accumulation, the C horizon is weathered parent material, and the R horizon is consolidated bedrock.

Question 45Soil Science and Soil Fertility Management

Which soil structure type is generally most favorable for root penetration and water infiltration in agricultural topsoil?

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

Explanation

Granular structure consists of small, rounded aggregates that create a well-aerated pore network, promoting infiltration, drainage, and root growth. Platy, columnar, and massive structures restrict water movement and root penetration.

Question 46Soil Science and Soil Fertility Management

Which essential plant nutrient is taken up primarily as the molybdate anion and becomes less available as soil pH decreases?

  1. Boron
  2. Calcium
  3. Potassium
  4. Molybdenum Correct answer.

Explanation

Molybdenum is absorbed mainly as molybdate, and its availability declines sharply in acidic soils, which is why liming often corrects molybdenum deficiency. Potassium and calcium are taken up as cations and behave differently with pH, while boron is taken up as boric acid.

Question 47Soil Science and Soil Fertility Management

Which practice most directly reduces nitrogen loss through ammonia volatilization after a surface application of urea to a dry, high-pH soil?

  1. Applying urea just before heavy rainfall
  2. Leaving the urea on the surface and delaying irrigation
  3. Applying urea together with lime
  4. Incorporating the urea into the soil promptly Correct answer.

Explanation

Ammonia volatilization occurs when urea hydrolyzes at the surface and ammonium converts to ammonia gas, a process favored by high pH and drying. Mixing urea into the soil places the ammonium where it can be adsorbed and taken up before loss occurs.

Question 48Soil Science and Soil Fertility Management

A soil has a cation exchange capacity of 25 cmol(+) per kg and 60 percent base saturation. What is the approximate quantity of exchangeable base cations held per kg of soil?

  1. 40 cmol(+)
  2. 10 cmol(+)
  3. 15 cmol(+) Correct answer.
  4. 25 cmol(+)

Explanation

Base saturation is the proportion of the cation exchange capacity occupied by basic cations. Multiplying 25 cmol(+) per kg by 0.60 gives 15 cmol(+) per kg of exchangeable bases, with the remaining 10 cmol(+) occupied by acidic cations.

Question 49Soil Science and Soil Fertility Management

Why does banding phosphorus fertilizer near the seed row usually improve phosphorus use efficiency compared with broadcasting?

  1. Phosphorus leaches rapidly, so banding prevents groundwater contamination
  2. Phosphorus is relatively immobile in soil, so placement close to roots increases contact with the root zone Correct answer.
  3. Banding converts phosphorus into a gaseous form that plants absorb through leaves
  4. Banding raises soil pH sharply around the seed, releasing fixed phosphorus

Explanation

Phosphate ions move very little in soil because they are adsorbed and precipitated, so roots must grow to the phosphorus. Concentrating phosphorus in a band near the root zone increases the chance of interception and reduces fixation by spreading soil contact.

Question 50Soil Science and Soil Fertility Management

A farmer continuously grows a cereal and observes declining yields despite adequate nitrogen. Which rotation change best addresses declining soil organic matter and disease buildup?

  1. Applying more nitrogen fertilizer to the cereal
  2. Introducing a legume into the rotation Correct answer.
  3. Burning crop residues after each harvest
  4. Increasing cereal plant density

Explanation

A legume in the rotation adds biologically fixed nitrogen and returns more diverse residues, improving soil organic matter and breaking cereal disease and pest cycles. Adding nitrogen alone does not restore organic matter or interrupt pathogen carryover.