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BGCSE Field Crop Production 1256 study materials
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BGCSE Field Crop Production 1256 practice questions

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Question 1Crop Biology, Growth and Development

Which part of a seed is the main storage tissue that supplies food to the embryo during germination in a cereal grain such as maize?

  1. Plumule
  2. Endosperm Correct answer.
  3. Radicle
  4. Seed coat

Explanation

The endosperm is the starchy storage tissue that nourishes the embryo as it germinates. In cereals it forms the largest part of the grain, which is why maize and wheat seeds store most of their food there. The plumule and radicle are embryonic organs, not storage tissue.

Question 2Crop Biology, Growth and Development

Which process describes the uptake of water by a dry seed at the start of germination?

  1. Photosynthesis
  2. Imbibition Correct answer.
  3. Respiration
  4. Transpiration

Explanation

Imbibition is the absorption of water by dry seed tissues, causing them to swell and triggering enzyme activity. It is the first visible event in germination and occurs before the radicle emerges. Transpiration and photosynthesis are processes of established plants, not dry seeds.

Question 3Crop Biology, Growth and Development

A farmer plants maize seed and the seedlings emerge with a single cotyledon remaining below ground. To which group does maize belong?

  1. Monocotyledon Correct answer.
  2. Gymnosperm
  3. Pteridophyte
  4. Dicotyledon

Explanation

Monocotyledons have one cotyledon, and in maize this remains below ground while the shoot emerges. Grasses such as maize, sorghum and wheat are all monocotyledons. Dicotyledons have two cotyledons and gymnosperms and pteridophytes are not flowering crop plants of this type.

Question 4Crop Biology, Growth and Development

Which environmental factor is most directly responsible for triggering the germination of most crop seeds?

  1. Soil colour
  2. Day length
  3. Adequate moisture Correct answer.
  4. Wind speed

Explanation

Most crop seeds require adequate moisture, suitable temperature and oxygen to germinate, and moisture is the factor that initiates imbibition. Soil colour, wind and day length do not control the germination of typical field crops. Day length influences flowering in some plants rather than germination.

Question 5Crop Biology, Growth and Development

In a root, which zone is responsible for the greatest increase in length as the root grows?

  1. Meristematic zone
  2. Zone of maturation
  3. Zone of elongation Correct answer.
  4. Root cap

Explanation

Cells produced by the meristematic zone behind the root cap enlarge in the zone of elongation, and this expansion pushes the root tip downward. The root cap protects the tip while the maturation zone develops root hairs for absorption. Length increase is therefore due mainly to cell elongation.

Question 6Crop Biology, Growth and Development

Which structure on a leaf allows gaseous exchange during photosynthesis?

  1. Vein
  2. Cuticle
  3. Xylem
  4. Stomata Correct answer.

Explanation

Stomata are pores, mainly on the leaf surface, that open to let carbon dioxide in and oxygen and water vapour out. The cuticle limits water loss but also restricts gas movement. Xylem and veins conduct water and food rather than exchange gases.

Question 7Crop Biology, Growth and Development

Which of these is the correct sequence of growth stages in a cereal crop such as maize?

  1. Emergence, tasselling, flowering, grain filling Correct answer.
  2. Tasselling, grain filling, emergence, flowering
  3. Flowering, emergence, grain filling, tasselling
  4. Grain filling, emergence, flowering, tasselling

Explanation

A cereal first emerges from the soil, then produces its male tassel, then flowers and fertilises, and finally fills grain. The stages follow this order because reproduction must occur before grain can develop. Any sequence placing grain filling before flowering is impossible.

Question 8Crop Biology, Growth and Development

A crop plant shows yellowing between the veins of older leaves while the veins remain green. Which nutrient deficiency is most likely?

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

Explanation

Magnesium is a central atom in chlorophyll and is mobile in the plant, so deficiency appears as interveinal yellowing of older leaves. Nitrogen deficiency also affects older leaves but usually causes general yellowing rather than a distinct interveinal pattern. Phosphorus and potassium deficiencies show different symptoms such as purpling or leaf-margin scorch.

Question 9Crop Biology, Growth and Development

Which type of root system is characteristic of a maize plant?

  1. Aerial prop roots only
  2. Adventitious tubers
  3. Tap root system
  4. Fibrous root system Correct answer.

Explanation

Maize, like other monocotyledons, produces a fibrous root system made of many similar slender roots arising from the stem base. Dicotyledons typically develop a single main tap root with side branches. Fibrous roots spread widely and increase anchorage and absorption near the soil surface.

Question 10Crop Biology, Growth and Development

Why does a farmer usually plant seed at a recommended depth rather than very deep in the soil?

  1. Deep planting may exhaust seed reserves before the shoot reaches the surface Correct answer.
  2. Deep planting exposes seed to light
  3. Deep planting prevents water uptake
  4. Deep planting increases soil oxygen

Explanation

A seed relies on stored food until the shoot emerges and begins photosynthesis. If planted too deep, the shoot may use up its reserves before reaching the surface, reducing emergence. Recommended planting depth balances moisture supply with the ability of the shoot to emerge.

Question 11Crop Biology, Growth and Development

Which statement best explains why a legume such as groundnut can improve soil fertility?

  1. Its roots absorb excess nitrogen from the air directly
  2. Its leaves produce nitrogen during photosynthesis
  3. Nodule bacteria fix atmospheric nitrogen into forms the plant can use Correct answer.
  4. Its deep roots bring nitrogen up from the subsoil

Explanation

Legumes form nodules containing rhizobia bacteria that convert atmospheric nitrogen into ammonia the plant can use. When residues decompose, this fixed nitrogen becomes available to following crops. Plants cannot absorb nitrogen gas directly, and photosynthesis does not produce nitrogen.

Question 12Crop Biology, Growth and Development

A plant breeder selects plants that flower at the same time so that cross-pollination occurs readily. Which aspect of crop biology is being exploited?

  1. Vegetative propagation
  2. Flowering synchrony Correct answer.
  3. Seed dormancy
  4. Root competition

Explanation

When plants flower at the same time, pollen release and stigma receptivity coincide, which favours cross-pollination and seed set. This synchrony is important in breeding and in seed production fields. Vegetative propagation and root competition do not depend on simultaneous flowering.

Question 13Crop Biology, Growth and Development

Which change in a plant indicates that it has reached physiological maturity?

  1. Leaves become larger and greener
  2. Grain moisture content falls and the grain hardens Correct answer.
  3. Roots grow more rapidly
  4. New tillers begin to form

Explanation

Physiological maturity is reached when grain has accumulated its maximum dry matter and begins to lose moisture and harden. At this stage further growth of the grain stops. Active leaf growth, root growth or new tillering indicate a plant that is still developing.

Question 14Crop Biology, Growth and Development

Which plant hormone is chiefly responsible for the elongation of cells that causes a seedling stem to bend towards light?

  1. Ethylene
  2. Auxin Correct answer.
  3. Abscisic acid
  4. Cytokinin

Explanation

Auxin redistributes to the shaded side of a stem, where higher concentration promotes cell elongation, causing the stem to bend towards light. This response is called phototropism. Abscisic acid, ethylene and cytokinin have different roles such as dormancy, ripening and cell division.

Question 15Crop Biology, Growth and Development

A farmer notices that maize plants near the edge of a field are shorter than those in the middle. Which explanation is most reasonable?

  1. The edge plants are genetically different
  2. The edge plants compete more with weeds and suffer more wind damage Correct answer.
  3. The edge plants receive too much water
  4. The edge plants have more nutrients

Explanation

Edge plants often face greater weed competition and more wind and drying stress, which can reduce growth. Field margins may also be poorer in soil and moisture. Differences in genetics or excess water are less consistent explanations for a general edge effect.

Question 16Crop Biology, Growth and Development

Which practice would most directly reduce the risk of poor germination caused by soil crusting after sowing?

  1. Sowing deeper than usual
  2. Breaking the crust with light tillage after sowing Correct answer.
  3. Increasing seed rate greatly
  4. Applying more nitrogen fertiliser at sowing

Explanation

Soil crusting forms a hard layer that seedlings cannot easily push through, so breaking the crust with light tillage after sowing helps emergence. Sowing deeper or increasing seed rate does not remove the physical barrier. Fertiliser at sowing does not soften a crust.

Question 17Crop Biology, Growth and Development

Which feature distinguishes a monocotyledonous leaf from a dicotyledonous leaf?

  1. Monocot leaves have net venation
  2. Monocot leaves have parallel venation Correct answer.
  3. Monocot leaves always lack stomata
  4. Monocot leaves have two cotyledons

Explanation

Monocotyledonous leaves typically show parallel venation, with veins running lengthwise and rarely branching. Dicotyledonous leaves usually show net or reticulate venation. Leaf venation is therefore a useful field characteristic for separating the two groups.

Question 18Crop Biology, Growth and Development

A crop is described as having a determinate growth habit. What does this mean?

  1. It produces only roots and no shoots
  2. It grows indefinitely and keeps producing new leaves
  3. It requires no water after establishment
  4. The main stem ends in a flower or inflorescence and growth stops Correct answer.

Explanation

In determinate plants the terminal bud becomes a flower or inflorescence, so the main axis stops growing after flowering. Indeterminate plants continue producing new vegetative growth while flowering. This distinction affects management, harvesting and yield patterns.

Question 19Crop Biology, Growth and Development

A farmer wants to save seed from a crop but must avoid seed that will not germinate because of a hard seed coat. Which treatment is most appropriate?

  1. Sowing seed much deeper
  2. Scarifying the seed coat before sowing Correct answer.
  3. Storing seed in a sealed wet bag
  4. Soaking seed in cold water only

Explanation

A hard, impermeable seed coat prevents water uptake and is a form of physical dormancy. Scarifying, by nicking or abrading the coat, lets water enter and allows germination. Cold water soaking alone may not penetrate an impermeable coat, and wet storage or deep sowing do not overcome the barrier.

Question 20Crop Biology, Growth and Development

Two plots are planted with the same maize variety on the same day. Plot A receives full sunlight while Plot B is shaded. Which result is most likely and why?

  1. Both plots will yield equally because the variety is the same
  2. Plot B will flower earlier because shade speeds development
  3. Plot B will grow taller because shade increases photosynthesis
  4. Plot A will accumulate more dry matter because light limits photosynthesis Correct answer.

Explanation

Photosynthesis depends on light, so shading reduces the carbohydrate produced and therefore dry matter accumulation. The same variety may respond to shade by elongating, but this does not increase yield. Yield differences between the plots are therefore expected.

Question 21Crop Biology, Growth and Development

A crop shows stunted growth, purple-tinged older leaves and poor root development. Which nutrient is most likely deficient?

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

Explanation

Phosphorus is needed for energy transfer and root development, and deficiency commonly causes stunted plants with dark green or purplish older leaves. Calcium and sulphur deficiencies tend to affect new growth, and manganese deficiency usually causes interveinal chlorosis. The symptoms described therefore point to phosphorus.

Question 22Crop Biology, Growth and Development

Why is it important that a cereal crop completes flowering before the onset of a prolonged dry spell?

  1. Dry weather improves grain filling
  2. Water stress at flowering can reduce pollination and grain set Correct answer.
  3. Dry weather increases tillering
  4. Flowering requires no water

Explanation

Flowering and early grain set are very sensitive to water stress, which can disrupt pollination and reduce the number of grains set. A dry spell at this stage therefore lowers yield more than at some other stages. Adequate moisture during flowering supports good grain set.

Question 23Crop Biology, Growth and Development

A researcher observes that a crop planted at a low density produces more branches per plant but the total yield per hectare is lower than at a moderate density. Which explanation best fits this result?

  1. Moderate density reduces photosynthesis per plant
  2. Low density increases competition for light
  3. Low density allows individual plants to branch but too few plants occupy the area Correct answer.
  4. Plant density has no effect on total yield

Explanation

At low density each plant has more space and branches more, but the small number of plants limits total yield per hectare. At moderate density the greater number of plants compensates for less branching, giving a higher total yield. Competition and photosynthesis per plant are not the main explanation here.

Question 24Crop Biology, Growth and Development

Which combination of conditions would most likely cause poor germination of freshly harvested maize seed even when moisture and temperature are adequate?

  1. Seed that has been graded by size
  2. Seed that has been stored dry
  3. Seed that has not completed after-ripening Correct answer.
  4. Seed that has been treated with fungicide

Explanation

Freshly harvested seed may still be dormant and need a period of after-ripening before it can germinate well. Dry storage, size grading and fungicide treatment do not prevent germination. Adequate moisture and temperature alone cannot overcome this internal dormancy.

Question 25Soils, Soil Fertility and Plant Nutrition

Which soil particle size fraction holds the greatest amount of plant-available water and nutrients in a typical agricultural soil?

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

Explanation

Clay particles are extremely small and carry negative surface charges, giving them a very large surface area per unit mass. This lets them adsorb water films and exchangeable nutrient cations such as calcium, potassium and magnesium. Sand and gravel are far coarser, so they drain quickly and retain little water or nutrients.

Question 26Soils, Soil Fertility and Plant Nutrition

A farmer wants to raise soil pH from strongly acid toward neutral on a field. Which material should be applied?

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

Explanation

Agricultural lime, mainly calcium carbonate, neutralises soil acidity by reacting with hydrogen ions in the soil solution. Gypsum supplies calcium and sulphur but does not raise pH appreciably. Ammonium sulphate and elemental sulphur both acidify soil through oxidation and nitrification reactions.

Question 27Soils, Soil Fertility and Plant Nutrition

Which three plant nutrients are classified as primary macronutrients in standard fertiliser recommendations?

  1. Nitrogen, phosphorus, potassium Correct answer.
  2. Calcium, magnesium, sulphur
  3. Carbon, hydrogen, oxygen
  4. Iron, manganese, zinc

Explanation

The primary macronutrients are nitrogen, phosphorus and potassium because crops remove them in the largest quantities and they most often limit yield. They are the three numbers shown on a fertiliser grade label. Calcium, magnesium and sulphur are secondary macronutrients, while iron, manganese and zinc are micronutrients.

Question 28Soils, Soil Fertility and Plant Nutrition

What is the main reason legume crops such as cowpea improve soil nitrogen status in a rotation?

  1. Their roots excrete large amounts of nitrate
  2. Their residues have a very wide carbon to nitrogen ratio
  3. Rhizobia in root nodules fix atmospheric nitrogen Correct answer.
  4. They absorb nitrogen from subsoil and store it in leaves

Explanation

Legumes form a symbiosis with rhizobia bacteria that live in root nodules and reduce atmospheric nitrogen gas to ammonia. Some of this fixed nitrogen remains in roots and residues and becomes available to the following crop. This biological fixation reduces reliance on purchased nitrogen fertiliser.

Question 29Soils, Soil Fertility and Plant Nutrition

Which soil structure type is generally most favourable for root growth and drainage in a field crop soil?

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

Explanation

Granular structure consists of small, rounded aggregates that create a network of pores for air, water and roots. It is typical of well-managed topsoil with adequate organic matter. Massive and platy structures restrict water movement and root penetration, while single grain sand drains too fast and holds little water.

Question 30Soils, Soil Fertility and Plant Nutrition

A soil test reports a cation exchange capacity of 4 cmol per kg. What does this indicate about the soil?

  1. It has very high organic matter content
  2. It has a low capacity to hold nutrient cations Correct answer.
  3. It is dominated by expanding clay minerals
  4. It is strongly alkaline

Explanation

Cation exchange capacity measures the number of negatively charged sites that hold exchangeable cations. A value of about 4 cmol per kg is low and typical of sandy soils, meaning nutrients leach readily and frequent small applications are needed. High values are associated with fine clays and organic matter.

Question 31Soils, Soil Fertility and Plant Nutrition

Which practice most directly reduces soil erosion by water on a sloping cultivated field?

  1. Increasing slope length
  2. Ploughing up and down the slope
  3. Planting along the contour Correct answer.
  4. Removing all crop residues

Explanation

Planting and cultivating along the contour creates small ridges and furrows that slow runoff and trap soil. This reduces the velocity and erosive power of water moving downhill. Ploughing up and down the slope concentrates runoff into channels and accelerates rill erosion.

Question 32Soils, Soil Fertility and Plant Nutrition

A crop shows pale yellowing of older leaves first, with slow growth and poor tillering. Which nutrient deficiency is most likely?

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

Explanation

Nitrogen is mobile within the plant, so when supply is short the plant moves nitrogen from older leaves to new growth. This causes uniform pale yellowing of the oldest leaves first, along with stunted growth and reduced tillering. Calcium, boron and iron are largely immobile and show symptoms on young tissue.

Question 33Soils, Soil Fertility and Plant Nutrition

A farmer applies 200 kg of a 20:10:10 compound fertiliser to one hectare. How much nitrogen is applied?

  1. 20 kg
  2. 200 kg
  3. 40 kg Correct answer.
  4. 10 kg

Explanation

The first figure in a fertiliser grade is the percentage of nitrogen by mass. Twenty percent of 200 kg is 200 multiplied by 0.20, which equals 40 kg of nitrogen. The remaining figures give 20 kg of phosphate and 20 kg of potash.

Question 34Soils, Soil Fertility and Plant Nutrition

Why is phosphorus fertiliser usually placed in a band near the seed rather than broadcast over the whole field?

  1. Phosphorus moves very little in soil, so placement improves root access Correct answer.
  2. Banding prevents phosphorus from fixing nitrogen
  3. Phosphorus is toxic to seedlings at any distance
  4. Phosphorus is highly mobile and would leach away if broadcast

Explanation

Phosphate ions react with soil minerals and are largely immobile, moving only a few centimetres from where they are applied. Banding places the nutrient close to developing roots so the crop can absorb it efficiently. Broadcasting spreads the same amount over a much larger soil volume, where much of it remains out of reach.

Question 35Soils, Soil Fertility and Plant Nutrition

A field has been continuously cropped for years with no organic matter returns. Which change in soil properties is most likely?

  1. Decline in organic matter and reduced aggregate stability Correct answer.
  2. Increase in cation exchange capacity
  3. Increase in water-holding capacity
  4. Increase in earthworm populations

Explanation

Continuous removal of crop residues without manure or compost inputs depletes soil organic carbon. Organic matter is the main binding agent for aggregates, so its loss reduces aggregate stability and makes the soil more prone to crusting and erosion. It also lowers cation exchange capacity and water-holding capacity.

Question 36Soils, Soil Fertility and Plant Nutrition

Which process converts ammonium nitrogen to nitrate in a warm, moist, well-aerated soil?

  1. Denitrification
  2. Nitrification Correct answer.
  3. Ammonification
  4. Nitrogen fixation

Explanation

Nitrification is a two-step microbial oxidation in which ammonium is first converted to nitrite and then to nitrate. It requires oxygen and proceeds rapidly in warm, moist, well-aerated soils. Nitrate produced this way is highly mobile and easily leached.

Question 37Soils, Soil Fertility and Plant Nutrition

A farmer notices white salt crusts on the soil surface of an irrigated field and poor germination. Which problem is most likely?

  1. Soil acidity
  2. Salinity build-up from irrigation water Correct answer.
  3. Nitrogen deficiency
  4. Phosphorus fixation

Explanation

Irrigation water carries dissolved salts that remain in the soil when water evaporates from the surface. Over time these salts accumulate and form visible white crusts, and high salt concentrations reduce water uptake and hinder germination. Leaching with good drainage and better water management are the usual remedies.

Question 38Soils, Soil Fertility and Plant Nutrition

Which soil condition most strongly favours denitrification losses from a fertilised field?

  1. Dry, well-aerated sandy soil
  2. Waterlogged, poorly aerated soil Correct answer.
  3. Freshly limed surface soil
  4. Neutral pH with high calcium

Explanation

Denitrification is carried out by bacteria that use nitrate as an oxygen source when free oxygen is scarce. In waterlogged soils air spaces fill with water, creating the anaerobic conditions these bacteria need. The nitrate is reduced to nitrogen gases that escape to the atmosphere, wasting applied nitrogen.

Question 39Soils, Soil Fertility and Plant Nutrition

What is the main benefit of including a deep-rooted green manure crop in a rotation?

  1. It eliminates the need for any mineral fertiliser
  2. It sterilises the soil against all pathogens
  3. It recycles nutrients from deeper layers and adds organic matter Correct answer.
  4. It raises soil pH to neutral immediately

Explanation

Deep-rooted green manure crops take up nutrients that have moved below the rooting zone of shallow crops and return them to the surface when incorporated. The incorporated biomass also adds organic matter that improves structure and biological activity. Nutrient recycling is gradual and does not remove the need for balanced fertilisation.

Question 40Soils, Soil Fertility and Plant Nutrition

Which statement best explains why a sandy soil needs more frequent, smaller fertiliser applications than a clay soil?

  1. Sandy soil has low cation exchange capacity and leaches nutrients readily Correct answer.
  2. Sandy soil has higher organic matter than clay
  3. Sandy soil fixes more phosphorus
  4. Sandy soil holds more water for longer

Explanation

Sandy soils contain little clay and organic matter, so their cation exchange capacity is low and they retain few nutrients. Water moves through them quickly, carrying mobile nutrients such as nitrate below the root zone. Split applications supply nutrients as the crop needs them and reduce losses.

Question 41Soils, Soil Fertility and Plant Nutrition

Which symptom pattern indicates an iron deficiency rather than a nitrogen deficiency?

  1. Purple colouration of lower leaves
  2. Uniform yellowing of the oldest leaves
  3. Interveinal yellowing of the youngest leaves Correct answer.
  4. Brown necrotic spots on mature leaves

Explanation

Iron is immobile in the plant, so deficiency appears first on the youngest leaves, where the tissue between veins turns yellow while veins stay green. Nitrogen is mobile and causes uniform yellowing that starts on older leaves. This difference in symptom location helps distinguish the two problems.

Question 42Soils, Soil Fertility and Plant Nutrition

A farmer has a soil test showing adequate phosphorus but very acid pH of 4.5. Why might phosphorus still be poorly available to the crop?

  1. Acid soils contain too much free lime
  2. Strongly acid conditions cause phosphorus to bind with iron and aluminium Correct answer.
  3. Phosphorus is only available above pH 8
  4. Low pH converts phosphorus to nitrate

Explanation

In strongly acid soils, soluble phosphate reacts with iron and aluminium compounds to form insoluble complexes that roots cannot absorb. Liming to a suitable pH range of about 6 to 6.5 reduces this fixation and improves phosphorus availability. This is why correcting acidity can improve crop response to phosphorus already in the soil.

Question 43Soils, Soil Fertility and Plant Nutrition

Which soil management practice best conserves moisture for a rainfed crop in a semi-arid region?

  1. Maintaining a mulch of crop residues on the surface Correct answer.
  2. Bare fallow with frequent tillage
  3. Compacting the surface with heavy machinery
  4. Removing all plant cover between rows

Explanation

A surface mulch of crop residues reduces evaporation, shades the soil and lowers surface temperature. It also intercepts raindrop impact and improves infiltration, so more water enters the profile for the crop. Frequent tillage of bare soil does the opposite by exposing moist soil and accelerating evaporation.

Question 44Soils, Soil Fertility and Plant Nutrition

A crop rotation includes cereals followed by a legume. Which sequence of nitrogen availability is most likely within the legume season?

  1. Nitrogen supply increases as nodules fix nitrogen during active growth Correct answer.
  2. Nitrogen fixation supplies no nitrogen until the following season
  3. Nitrogen supply falls to zero because legumes take up all soil nitrogen
  4. Nitrogen is fixed only after the legume dies

Explanation

Nitrogen fixation begins once nodules form and the plant is actively growing, so the legume can meet much of its own nitrogen demand during the season. When roots and residues decompose after harvest, remaining fixed nitrogen becomes available to the next crop. The benefit therefore builds during growth and is released mainly afterwards.

Question 45Soils, Soil Fertility and Plant Nutrition

Two fields receive the same amount of ammonium nitrate. Field A is a well-drained loam and Field B is waterlogged clay. Which outcome is most likely within a week?

  1. Field B loses more nitrogen as gas through denitrification Correct answer.
  2. Field A loses more nitrogen as gas through denitrification
  3. Field B converts all nitrate to ammonium
  4. Both fields retain identical nitrogen levels

Explanation

Ammonium nitrate supplies nitrate, which denitrifying bacteria reduce to nitrogen gas when oxygen is lacking. Waterlogged clay in Field B creates the anaerobic conditions needed for this process, so gaseous loss is greater there. Well-drained loam in Field A remains aerated and retains most of the nitrate.

Question 46Soils, Soil Fertility and Plant Nutrition

A soil analysis shows pH 5.2, low calcium and high exchangeable aluminium. Which recommendation is most appropriate?

  1. Apply lime and monitor pH before the next crop Correct answer.
  2. Apply muriate of potash to displace aluminium
  3. Apply gypsum only to add sulphur
  4. Apply ammonium sulphate to increase acidity

Explanation

At pH 5.2, exchangeable aluminium becomes soluble and can damage root tips, limiting water and nutrient uptake. Lime raises pH and precipitates aluminium as insoluble hydroxide while adding calcium. The pH should be monitored because over-liming can reduce micronutrient availability.

Question 47Soils, Soil Fertility and Plant Nutrition

Why does adding fresh, high-carbon residue such as mature cereal straw temporarily reduce nitrogen available to a young crop?

  1. Straw raises pH and locks up nitrogen
  2. Straw increases denitrification by aerating the soil
  3. Microbes immobilise nitrate while decomposing the low-nitrogen residue Correct answer.
  4. Straw chemically destroys nitrate in the soil

Explanation

Residues with a wide carbon to nitrogen ratio give decomposing microbes abundant carbon but little nitrogen. The microbes therefore take up nitrate and ammonium from the soil solution, temporarily immobilising nitrogen that the crop would otherwise use. The nitrogen is released later as the microbial population turns over.

Question 48Soils, Soil Fertility and Plant Nutrition

A farmer wants to compare two soils for nutrient-holding ability. Soil X has 30 percent clay and 1 percent organic matter; Soil Y has 15 percent clay and 4 percent organic matter. Which conclusion is most defensible?

  1. Soil X must hold more cations because it has more clay
  2. Both soils have equal exchange capacity because clay and organic matter balance
  3. Soil Y may hold more cations because organic matter contributes strongly to exchange capacity Correct answer.
  4. Soil Y has lower exchange capacity because it has less clay

Explanation

Organic matter has a very high exchange capacity per unit mass, often several times that of clay minerals. A fourfold difference in organic matter can therefore offset a moderate difference in clay content, so Soil Y may hold more cations. The comparison shows why organic matter management matters as much as texture.

Question 49Land Preparation and Crop Establishment

Which primary tillage implement is best suited to breaking up compacted subsoil before planting a deep-rooted crop?

  1. Roller
  2. Disc harrow
  3. Rotary tiller
  4. Chisel plough Correct answer.

Explanation

A chisel plough has heavy rigid tines that penetrate below the normal plough layer and shatter compacted subsoil without inverting it, which improves root penetration and drainage. Disc harrows, rotary tillers and rollers work mainly at or near the surface and cannot relieve deep compaction.

Question 50Land Preparation and Crop Establishment

What is the main purpose of secondary tillage after primary ploughing?

  1. To drain excess water from the field
  2. To invert the soil profile completely
  3. To produce a fine, level seedbed Correct answer.
  4. To bury crop residues at depth

Explanation

Secondary tillage breaks down clods, levels the surface and creates a fine tilth so that seed can be placed at uniform depth with good soil contact. Inversion and deep burial of residues belong to primary tillage, and drainage is achieved by land-forming works rather than by harrowing.