I85PREP
⌘ K
NSSCAS Agricultural Science 8222 study materials
NSSCAS Agricultural Science 8222 study resources

NSSCAS Agricultural Science 8222 practice questions

One question at a time. Build your NSSCAS Agricultural Science 8222 understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Agricultural principles, systems and the Namibian context

In Namibian communal farming areas, which soil management practice most directly reduces wind erosion on sandy soils during the dry season?

  1. Burning crop residues after harvest
  2. Removing all trees and shrubs from the field margins
  3. Maintaining a crop or mulch cover on the soil surface Correct answer.
  4. Deep ploughing to expose fresh subsoil

Explanation

Wind erosion lifts loose, dry sand particles when the surface is bare and exposed to strong winds. Keeping a cover of growing crops, dry mulch or stubble shields the soil surface, slows wind speed at ground level and anchors particles. Practices that expose or destroy this cover accelerate the loss of topsoil and organic matter.

Question 2Agricultural principles, systems and the Namibian context

A Namibian farmer wants to compare the water-holding capacity of two soil samples. Which soil property should be measured directly to indicate how much water each soil can retain?

  1. Soil colour
  2. Bulk density of the subsoil only
  3. pH of the surface layer
  4. Field capacity or water retention at a given suction Correct answer.

Explanation

Water-holding capacity is defined by how much water a soil retains after free drainage, which is measured as field capacity or as water content held at a specified matric suction. This property depends on texture, structure and organic matter content. Colour, subsoil bulk density and pH influence other characteristics but do not directly quantify retention.

Question 3Agricultural principles, systems and the Namibian context

Which group of organisms is primarily responsible for converting atmospheric nitrogen into forms usable by leguminous crops in Namibian soils?

  1. Earthworms in the topsoil
  2. Free-living nitrifying bacteria
  3. Mycorrhizal fungi
  4. Rhizobia bacteria in root nodules Correct answer.

Explanation

Biological nitrogen fixation in legumes is carried out by rhizobia bacteria that form nodules on the roots. These bacteria reduce atmospheric nitrogen to ammonia that the plant can use. Mycorrhizal fungi assist with phosphorus uptake, nitrifying bacteria convert ammonium to nitrate, and earthworms improve soil structure.

Question 4Agricultural principles, systems and the Namibian context

In a Namibian livestock enterprise, which practice best reduces heat stress in cattle during the hot summer months?

  1. Concentrating animals in a small unshaded kraal
  2. Grazing animals only during the hottest part of the day
  3. Providing shade and ensuring access to cool drinking water Correct answer.
  4. Restricting water intake to reduce sweating

Explanation

Cattle dissipate excess body heat through shade, air movement, evaporation and drinking water. Providing shade and cool water lowers body temperature and maintains feed intake and growth. Confinement without shade or restricted water worsens heat stress and can reduce production and fertility.

Question 5Agricultural principles, systems and the Namibian context

Which characteristic distinguishes a ruminant digestive system from that of a monogastric animal such as a pig?

  1. A single-compartment stomach with no microbial fermentation
  2. A multi-compartment stomach where microbial fermentation precedes gastric digestion Correct answer.
  3. Absence of a caecum and large intestine
  4. Reliance on gastric acid alone for fibre digestion

Explanation

Ruminants have a multi-compartment stomach (rumen, reticulum, omasum, abomasum) in which microbes ferment fibrous feed before it reaches the acid-secreting abomasum. This allows them to use roughage that monogastrics cannot digest efficiently. Pigs have a simple stomach and rely largely on enzymatic digestion.

Question 6Agricultural principles, systems and the Namibian context

Which factor most strongly determines the length of the growing season for rain-fed crops in the northern communal areas of Namibia?

  1. The number of cattle grazing the field
  2. The price of maize at harvest
  3. The timing and duration of the rainy season Correct answer.
  4. The depth of the water table

Explanation

Rain-fed crop production depends on rainfall, so the length of the growing season is set mainly by when the rains start and how long they persist. Soil water stored from rain supports crop growth until it is exhausted. Water-table depth, market prices and grazing animals affect management but not the seasonal rainfall window.

Question 7Agricultural principles, systems and the Namibian context

A farmer in the Kavango region wants to reduce soil nutrient depletion between maize crops. Which rotation is most appropriate for restoring nitrogen in the soil?

  1. Maize grown every season with no other crop
  2. Maize rotated with a legume such as cowpea or groundnut Correct answer.
  3. Maize rotated with another cereal such as sorghum
  4. Continuous maize followed by bare fallow

Explanation

Legumes such as cowpea and groundnut form symbiotic associations with rhizobia that fix atmospheric nitrogen, adding nitrogen to the soil when residues are incorporated. Rotating maize with a legume therefore helps restore fertility. Continuous cereals or bare fallow deplete nutrients without adding nitrogen.

Question 8Agricultural principles, systems and the Namibian context

A soil sample from a Namibian field has a pH of 4.8 and high exchangeable aluminium. Which corrective measure is most appropriate?

  1. Flooding the field with saline water
  2. Adding elemental sulphur
  3. Applying gypsum to increase salinity
  4. Applying agricultural lime to raise pH and reduce aluminium toxicity Correct answer.

Explanation

Acidic soils with high exchangeable aluminium restrict root growth and nutrient availability. Agricultural lime (calcium carbonate) neutralises acidity, raises pH and precipitates toxic aluminium. Elemental sulphur and saline water would lower pH further or add salts, worsening the problem.

Question 9Agricultural principles, systems and the Namibian context

A Namibian farmer observes that irrigation water applied to a sandy soil drains rapidly below the root zone. Which management practice would most improve water-use efficiency?

  1. Increasing the slope of the field
  2. Removing organic matter from the topsoil
  3. Applying smaller amounts of water more frequently and adding organic matter Correct answer.
  4. Applying large volumes of water at long intervals

Explanation

Sandy soils have large pores and low water-holding capacity, so water moves quickly past the roots. Frequent light irrigations match crop demand, while organic matter improves structure and retention. Large infrequent applications and removal of organic matter increase deep percolation losses.

Question 10Agricultural principles, systems and the Namibian context

In a communal cattle herd, which practice is the most effective way to control internal parasites such as roundworms?

  1. Ignoring parasites because cattle in dry areas are never affected
  2. Treating only animals that appear healthy
  3. Strategic deworming based on faecal egg counts and body condition Correct answer.
  4. Deworming all animals every week throughout the year

Explanation

Strategic deworming uses faecal egg counts and body condition to time treatment when parasite burdens are high, reducing production losses and slowing the development of anthelmintic resistance. Weekly treatment is wasteful and promotes resistance, while ignoring or misdirecting treatment allows infection to spread.

Question 11Agricultural principles, systems and the Namibian context

A farmer wants to select breeding cows for a herd in a semi-arid area of Namibia. Which selection criterion best supports long-term productivity under limited rainfall?

  1. Earliest possible age at first calving regardless of body condition
  2. Largest body size regardless of feed requirements
  3. Adaptation to local conditions combined with fertility and mothering ability Correct answer.
  4. Highest milk yield under intensive feeding

Explanation

In semi-arid environments, animals must cope with variable rainfall and limited forage, so adaptation, fertility and mothering ability determine how many calves are weaned per cow over her lifetime. Selecting only for high milk yield or large size under intensive conditions increases feed requirements that cannot be met. Extremely early calving without adequate body condition harms cow and calf.

Question 12Agricultural principles, systems and the Namibian context

Which irrigation method is generally most suitable for a small-scale vegetable plot on uneven ground with limited water supply?

  1. Flood irrigation of the whole plot
  2. Furrow irrigation across the slope
  3. Drip irrigation with emitters placed near each plant Correct answer.
  4. Sprinkler irrigation during the hottest part of the day

Explanation

Drip irrigation delivers water directly to the root zone, reducing evaporation and runoff and allowing uniform application even on uneven ground. This conserves a limited water supply. Flood and furrow methods waste water and are uneven on sloping land, while midday sprinkling loses water to evaporation.

Question 13Agricultural principles, systems and the Namibian context

A farmer notices that maize plants in a field show yellowing of older leaves, stunted growth and poor grain filling, despite adequate rainfall. Which nutrient deficiency is most likely?

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

Explanation

Nitrogen is mobile within the plant, so deficiency appears first as yellowing of older leaves as nitrogen is moved to new growth. It also reduces vegetative growth and grain filling. Calcium, iron and boron are less mobile and their deficiencies typically appear on younger tissue.

Question 14Agricultural principles, systems and the Namibian context

Which integrated pest management approach best reduces damage from stalk borers in maize while limiting reliance on chemical pesticides?

  1. Removing all crop residues and natural vegetation from around the field
  2. Spraying the most toxic pesticide available every week
  3. Combining resistant varieties, crop rotation, timely planting and scouting Correct answer.
  4. Planting only one highly susceptible variety

Explanation

Integrated pest management combines several compatible tactics to keep pest populations below economic thresholds. Resistant varieties, rotation, timely planting and scouting reduce stalk borer pressure while preserving natural enemies. Frequent broad-spectrum spraying or susceptible monoculture increases cost, resistance and pest build-up.

Question 15Agricultural principles, systems and the Namibian context

A Namibian farmer stores maize grain in bags in a poorly ventilated shed and finds weevils and mould after several weeks. Which combination of measures best protects the stored grain?

  1. Mixing fresh moist grain with old grain to reduce losses
  2. Storing grain at high moisture in sealed bags
  3. Drying grain to a safe moisture level and storing it in a clean, dry, well-ventilated place Correct answer.
  4. Storing grain directly on a damp floor

Explanation

Insect and mould development in stored grain depends strongly on moisture and temperature. Drying grain to a safe moisture content, cleaning the store and maintaining dry, ventilated conditions limits both weevils and fungal growth. High moisture, damp floors and mixing old and new grain all encourage deterioration.

Question 16Agricultural principles, systems and the Namibian context

Which grazing management system is most appropriate for maintaining veld condition in a semi-arid communal area with variable rainfall?

  1. Increasing stocking rate every year regardless of rainfall
  2. Rotational grazing with planned rest periods to allow recovery Correct answer.
  3. Continuous grazing with no rest period
  4. Grazing only the most palatable species until they disappear

Explanation

Rotational grazing with planned rest allows palatable grasses to recover, set seed and maintain root reserves, which is important where rainfall is variable. Continuous grazing and selective overgrazing deplete desirable species, while rising stocking rates increase pressure on already variable forage.

Question 17Agricultural principles, systems and the Namibian context

A farmer in a semi-arid area wants to improve soil fertility on a field that has been cropped for many years. Which practice provides the most sustainable long-term improvement?

  1. Burning all crop residues before planting
  2. Leaving the field bare during the off-season
  3. Combining compost or manure with crop residues and appropriate rotations Correct answer.
  4. Applying only inorganic nitrogen fertiliser each season

Explanation

Organic amendments such as compost and manure, together with residue retention and rotations, build soil organic matter, improve structure and supply nutrients slowly. This supports sustained fertility. Sole reliance on inorganic nitrogen, residue burning and bare fallow deplete organic matter and degrade soil over time.

Question 18Agricultural principles, systems and the Namibian context

In a Namibian mixed farm, which factor most directly limits the efficiency of converting feed into animal products by livestock?

  1. The colour of the animals' coats
  2. The number of farm workers employed
  3. The shape of the grazing camp
  4. The quality and digestibility of the available forage Correct answer.

Explanation

Feed conversion efficiency depends on how much of the ingested feed can be digested and absorbed. Forage quality and digestibility, especially crude protein and fibre content, therefore determine how much energy and nutrients are available for growth, milk and reproduction. Coat colour, labour numbers and camp shape do not directly affect digestion.

Question 19Agricultural principles, systems and the Namibian context

A farmer applies a nitrogen fertiliser to a maize field just before heavy rain and finds poor crop response. Which explanation best accounts for the poor response?

  1. The fertiliser increased soil pH and locked up phosphorus
  2. The fertiliser was fully absorbed by the crop before the rain
  3. The rain washed nitrate below the root zone through leaching Correct answer.
  4. Nitrogen became unavailable because it was converted to protein in the soil

Explanation

Nitrate is highly mobile in soil water, so heavy rain shortly after application can move it below the rooting depth before the crop can absorb it. This leaching reduces the nitrogen available to the maize. The other explanations misdescribe how nitrogen behaves in the soil.

Question 20Agricultural principles, systems and the Namibian context

A farmer wants to adopt conservation agriculture on a sandy field in northern Namibia. Which set of practices best matches the principles of conservation agriculture?

  1. Burning residues, deep ripping and planting a single crop
  2. Continuous deep ploughing, residue removal and monocropping
  3. Flood irrigation, bare fallow and frequent tillage
  4. Minimum soil disturbance, permanent soil cover and crop diversification Correct answer.

Explanation

Conservation agriculture is built on three linked principles: minimum mechanical soil disturbance, permanent soil cover with crop residues or living plants, and diversification through rotations or intercropping. Together these protect soil, conserve moisture and improve structure. Deep tillage, residue removal and monocropping contradict these principles.

Question 21Soil science, soil management and conservation

A soil sample from a field in the Zambezi floodplain has a pH of 4.8 and shows aluminium toxicity symptoms in maize seedlings. Which liming material would raise pH most rapidly while also supplying magnesium?

  1. Calcitic limestone (calcium carbonate)
  2. Dolomitic limestone (calcium magnesium carbonate) Correct answer.
  3. Gypsum (calcium sulfate)
  4. Elemental sulfur

Explanation

Dolomitic limestone contains both calcium carbonate and magnesium carbonate, so it neutralises acidity while supplying magnesium to a deficient acid soil. Calcitic limestone raises pH but adds no magnesium, gypsum does not neutralise acidity, and elemental sulfur acidifies soil further.

Question 22Soil science, soil management and conservation

Which soil texture class typically holds the greatest plant-available water per unit depth of soil?

  1. Sandy loam
  2. Coarse sand
  3. Silt loam Correct answer.
  4. Gravelly loam

Explanation

Silt loam combines moderate clay content, which retains water, with silt particles that create good pore structure, giving high available water capacity. Sands drain too freely to store much water, and gravelly loam has less fine material and lower total porosity.

Question 23Soil science, soil management and conservation

A farmer continuously grows maize on a sloping field without any soil cover between seasons. Which process is the most direct cause of declining topsoil depth on this field?

  1. Sheet and rill erosion by raindrop impact and runoff Correct answer.
  2. Leaching of soluble salts below the root zone
  3. Salinisation from capillary rise of groundwater
  4. Compaction caused by farm machinery traffic

Explanation

Bare soil on a slope is exposed to raindrop impact, which detaches particles, and to runoff, which carries them downslope as sheet and rill erosion, physically removing topsoil. Leaching, compaction and salinisation alter soil condition but do not directly strip away surface soil layers.

Question 24Soil science, soil management and conservation

In a laboratory determination of soil bulk density, a core of known volume is oven-dried at 105 degrees Celsius to constant mass. Which additional measurement is required to calculate total porosity?

  1. Electrical conductivity of the saturation extract
  2. Cation exchange capacity
  3. Particle density of the soil solids Correct answer.
  4. Organic carbon content

Explanation

Total porosity is calculated from bulk density and particle density using the relationship porosity equals one minus bulk density divided by particle density. Particle density is normally assumed near 2.65 grams per cubic centimetre but must be known or assumed to complete the calculation.

Question 25Soil science, soil management and conservation

Which practice best conserves soil moisture in a rainfed maize field during a dry spell in a semi-arid region?

  1. Applying irrigation water in a single large flood
  2. Maintaining a mulch cover of crop residues on the surface Correct answer.
  3. Removing all weeds and leaving the soil bare
  4. Deep ploughing to expose fresh subsoil

Explanation

A surface mulch reduces evaporation, moderates soil temperature and protects the surface from crusting, so more stored water remains available to the crop. Bare soil loses water rapidly by evaporation, and deep ploughing exposes moist soil to drying.

Question 26Soil science, soil management and conservation

A soil test reports a cation exchange capacity of 4 cmol(+) per kg and a sandy texture. What does this value most strongly indicate about the soil's management?

  1. It has a low nutrient-holding capacity and requires frequent, split fertiliser applications. Correct answer.
  2. It has a high capacity to retain applied nutrients and needs little fertiliser.
  3. It has excessive clay and requires deep ripping.
  4. It is strongly sodic and requires gypsum amendment.

Explanation

A cation exchange capacity of about 4 cmol(+) per kg is low and typical of sandy soils with little clay and organic matter, so applied cations leach readily. Management should therefore use smaller, more frequent applications and build organic matter to improve retention.

Question 27Soil science, soil management and conservation

Which soil structure type is most favourable for root penetration and water movement in a cultivated topsoil?

  1. Platy structure with thin horizontal plates
  2. Massive structure with no visible aggregates
  3. Granular structure with rounded aggregates Correct answer.
  4. Single grain structure with loose sand

Explanation

Granular structure consists of small, rounded, porous aggregates that create interconnected pore space for air, water and roots. Massive and platy structures restrict movement, and single grain sands have poor aggregation and low water retention.

Question 28Soil science, soil management and conservation

A farmer applies fresh, uncomposted cattle manure to a vegetable bed two weeks before transplanting. Which risk is most directly associated with this practice?

  1. Nitrogen immobilisation caused by a high carbon to nitrogen ratio
  2. Ammonia burn and pathogen contamination from unstable organic material Correct answer.
  3. Loss of cation exchange capacity through leaching
  4. Immediate phosphorus fixation by iron oxides

Explanation

Fresh manure is still undergoing decomposition and may release ammonia and heat near roots while carrying pathogens such as Salmonella and E. coli. Composting stabilises the material and reduces these risks before field application.

Question 29Soil science, soil management and conservation

Which sequence correctly describes the transformation of nitrogen in a well-aerated, moist agricultural soil receiving ammonium-based fertiliser?

  1. Nitrate to ammonium by ammonifying bacteria
  2. Nitrate to ammonium to nitrite by denitrifying bacteria
  3. Ammonium to nitrite to nitrate by nitrifying bacteria Correct answer.
  4. Ammonium to nitrogen gas to nitrate by nitrogen-fixing bacteria

Explanation

Nitrification is a two-step aerobic process in which Nitrosomonas-type bacteria oxidise ammonium to nitrite and Nitrobacter-type bacteria oxidise nitrite to nitrate. It requires oxygen and warm, moist, near-neutral conditions.

Question 30Soil science, soil management and conservation

A soil has an exchangeable sodium percentage of 18 percent, a pH of 9.6 and poor infiltration. Which amendment is most appropriate?

  1. Lime (calcium carbonate)
  2. Ammonium sulfate fertiliser
  3. Sulfuric acid applied as a drench
  4. Gypsum (calcium sulfate) Correct answer.

Explanation

These properties indicate a sodic soil, where excess sodium disperses clay and destroys structure. Gypsum supplies calcium that displaces sodium from the exchange complex, and the sodium can then be leached with good-quality water.

Question 31Soil science, soil management and conservation

Which factor most directly increases the rate of organic matter decomposition in a tropical agricultural soil?

  1. Strong adsorption of organic matter onto clay surfaces
  2. Frequent waterlogging and anaerobic conditions
  3. Low soil pH below 4.5
  4. High temperature combined with adequate moisture and aeration Correct answer.

Explanation

Microbial decomposition is fastest when soils are warm, moist and well aerated, conditions common in the tropics, so organic matter turns over quickly. Anaerobic, acidic or strongly adsorbing conditions slow decomposition.

Question 32Soil science, soil management and conservation

A farmer wants to reduce soil erosion on a steep cultivated hillside. Which combination of measures is most effective?

  1. Removing all vegetation from waterways to speed drainage
  2. Contour ridges combined with vegetative strips and residue retention Correct answer.
  3. Planting row crops up and down the slope with clean weeding
  4. Increasing tillage depth to loosen the surface

Explanation

Contour ridges shorten slope length and slow runoff, vegetative strips trap sediment, and residues protect the surface from raindrop impact. Together these reduce both detachment and transport of soil particles.

Question 33Soil science, soil management and conservation

Which statement correctly describes the effect of soil compaction on plant growth?

  1. It increases available water by squeezing pores smaller.
  2. It reduces total pore space and increases mechanical resistance to root growth. Correct answer.
  3. It raises infiltration rate by destroying aggregates.
  4. It increases macropore space and improves aeration.

Explanation

Compaction presses soil particles closer together, reducing pore space and raising bulk density. Roots then meet greater mechanical resistance and less air-filled porosity, which restricts growth.

Question 34Soil science, soil management and conservation

A soil analysis shows 2.1 percent organic carbon, a pH of 5.4 and a clay content of 35 percent. Which interpretation is most defensible?

  1. The soil is sodic and needs gypsum.
  2. The soil is highly saline and needs leaching.
  3. The soil is water-repellent and needs wetting agents.
  4. The soil is moderately acidic with reasonable organic matter and requires liming for sensitive crops. Correct answer.

Explanation

A pH of 5.4 is moderately acidic and may limit sensitive crops and reduce phosphorus availability, so liming is warranted. Organic carbon above 2 percent and 35 percent clay indicate reasonable fertility and buffering capacity.

Question 35Soil science, soil management and conservation

Which soil water category is measured as the water retained at field capacity minus the water retained at permanent wilting point?

  1. Available water capacity Correct answer.
  2. Hygroscopic water
  3. Saturation percentage
  4. Gravitational water

Explanation

Available water capacity is the difference between water held at field capacity, about minus 33 kPa, and at permanent wilting point, about minus 1500 kPa. It represents the water plants can extract from the soil.

Question 36Soil science, soil management and conservation

A farmer notices white salt crusts on the surface of an irrigated field in a dry area. Which management approach is most appropriate?

  1. Incorporate fresh manure heavily to dilute the salts
  2. Install drainage and leach the profile with excess good-quality water Correct answer.
  3. Add gypsum without leaching and stop irrigation
  4. Apply more irrigation water in small frequent amounts without drainage

Explanation

Salt crusts indicate salinisation from evaporation concentrating salts at the surface. Reclamation requires adequate subsurface drainage so that excess salts can be leached below the root zone with good-quality water.

Question 37Soil science, soil management and conservation

Which process converts organic nitrogen in crop residues into plant-available ammonium?

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

Explanation

Ammonification is the mineralisation of organic nitrogen by heterotrophic microorganisms into ammonium. Nitrification then converts ammonium to nitrate, while denitrification and fixation involve different nitrogen transformations.

Question 38Soil science, soil management and conservation

A farmer practising conservation agriculture on a sandy loam wants to build soil organic matter. Which strategy is most likely to succeed?

  1. Continuous monoculture maize with complete residue removal
  2. Retaining crop residues and rotating with a legume cover crop Correct answer.
  3. Burning crop residues to return ash to the soil
  4. Annual deep inversion tillage

Explanation

Retaining residues adds carbon inputs, and legume cover crops add nitrogen-rich biomass, both of which build organic matter when combined with minimal disturbance. Removal, burning or excessive tillage deplete carbon.

Question 39Soil science, soil management and conservation

Which statement best explains why clay soils generally have a higher cation exchange capacity than sandy soils?

  1. Sand particles contain more organic matter.
  2. Clay minerals carry negative surface charges that attract and hold cations. Correct answer.
  3. Clay particles have larger diameters and greater mass.
  4. Clay soils have larger macropores that trap cations.

Explanation

Clay minerals such as smectite and illite carry permanent negative charges from isomorphic substitution and broken edges, which adsorb exchangeable cations. Sand has little surface charge, so its CEC is low.

Question 40Soil science, soil management and conservation

A farmer applies urea to the soil surface on a hot day and notices a strong ammonia smell. Which loss pathway is occurring?

  1. Denitrification to nitrogen gas
  2. Immobilisation into microbial biomass
  3. Leaching of nitrate below the root zone
  4. Volatilisation of ammonia from the soil surface Correct answer.

Explanation

Urea hydrolyses to ammonium carbonate, and on warm, moist, neutral to alkaline surfaces the ammonium converts to ammonia gas and escapes. Incorporating urea or applying it before rain reduces this loss.

Question 41Soil science, soil management and conservation

Which soil colour observation most strongly suggests poor drainage and reducing conditions in a subsoil?

  1. Grey or bluish-grey mottles with orange iron concentrations Correct answer.
  2. White calcareous nodules throughout
  3. Uniform light brown colour
  4. Uniform bright red colour

Explanation

Grey or bluish-grey colours indicate reduced iron under waterlogged, oxygen-poor conditions, while orange mottles show where oxidised iron has accumulated. Bright reds and browns indicate well-aerated, oxidised soils.

Question 42Soil science, soil management and conservation

Which practice most effectively reduces nitrate leaching from a field after harvest?

  1. Deep ploughing to bury residues
  2. Establishing a fast-growing catch crop to take up residual nitrate Correct answer.
  3. Leaving the field fallow and bare through the rainy season
  4. Applying additional nitrogen fertiliser after harvest

Explanation

A catch crop takes up residual soil nitrate and holds it in plant tissue, reducing the amount available to leach with drainage water. Bare fallow leaves nitrate in solution where it can move below the root zone.

Question 43Soil science, soil management and conservation

A farmer wants to improve the structure of a compacted clay soil before planting. Which approach is most appropriate?

  1. Cultivating when the soil is wet to break clods
  2. Applying lime regardless of the current pH
  3. Adding organic matter and using deep ripping when the soil is at the right moisture Correct answer.
  4. Increasing traffic across the field to press the soil firm

Explanation

Organic matter promotes stable aggregation and biological activity, while mechanical loosening by ripping can break a compacted layer if done at suitable moisture. Cultivating wet clay smears and compacts it further.

Question 44Soil science, soil management and conservation

Which statement about phosphorus behaviour in most agricultural soils is correct?

  1. Phosphorus availability increases as soil pH falls below 5.
  2. Phosphorus is relatively immobile and can be fixed by iron, aluminium and calcium compounds. Correct answer.
  3. Phosphorus is lost mainly through volatilisation as a gas.
  4. Phosphorus is highly mobile and leaches readily with drainage water.

Explanation

Phosphate ions react with iron and aluminium oxides in acid soils and with calcium in alkaline soils, forming less soluble compounds, so phosphorus moves little in the profile. Placement near roots and pH management improve its availability.

Question 45Crop production and management

A farmer wants to sow maize at a population of 53,000 plants per hectare using rows 0.75 m apart. What in-row spacing is required to achieve this target population?

  1. 0.50 m
  2. 0.25 m Correct answer.
  3. 1.00 m
  4. 0.75 m

Explanation

Plants per hectare equals 10,000 divided by (row spacing × in-row spacing). Rearranging gives in-row spacing = 10,000 ÷ (53,000 × 0.75) ≈ 0.25 m, so plants are spaced about 25 cm apart within the row.

Question 46Crop production and management

Which term describes the practice of growing two or more crops together in the same field in the same season?

  1. Monocropping
  2. Rotating
  3. Fallow
  4. Intercropping Correct answer.

Explanation

Intercropping is the simultaneous cultivation of two or more crops in the same field during one growing season. It differs from rotation, which sequences crops over time, and from monocropping, which uses a single crop.

Question 47Crop production and management

A soil test reports a pH of 4.8 for a field to be planted with maize. Which amendment is most appropriate to raise the pH into the optimal range?

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

Explanation

Agricultural lime (calcium carbonate) neutralises soil acidity and raises pH toward the range maize prefers, around 5.5 to 7.0. Gypsum adds calcium without changing pH much, while sulphur and ammonium sulphate acidify soil further.

Question 48Crop production and management

Which process converts atmospheric nitrogen into ammonia within the root nodules of legumes?

  1. Nitrification
  2. Biological nitrogen fixation Correct answer.
  3. Ammonification
  4. Denitrification

Explanation

Biological nitrogen fixation is carried out by rhizobia in legume root nodules, using the enzyme nitrogenase to reduce atmospheric N2 to ammonia. The other processes act on nitrogen already present in the soil.

Question 49Crop production and management

A seed lot has a laboratory germination of 85 percent and a purity of 98 percent. What sowing rate adjustment should the farmer make compared with a lot of 100 percent germination and purity?

  1. Use the same rate because purity does not affect field establishment
  2. Decrease the sowing rate because fewer viable seeds are needed
  3. Double the rate because germination is below 90 percent
  4. Increase the sowing rate to allow for the lower germination and purity Correct answer.

Explanation

The pure live seed percentage is 0.85 × 0.98, about 83 percent, so only that fraction of the sown weight will establish. The sowing rate must be increased proportionally to achieve the target plant population.

Question 50Crop production and management

Which irrigation method delivers water most efficiently to the root zone in a water-scarce vegetable enterprise?

  1. Drip irrigation Correct answer.
  2. Sprinkler irrigation
  3. Furrow irrigation
  4. Flood irrigation

Explanation

Drip irrigation applies water slowly and directly to the root zone, minimising evaporation, runoff and deep percolation. It typically achieves higher application efficiency than flood, furrow or sprinkler systems.