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WACE ATAR Agricultural Science and Technology study materials
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WACE ATAR Agricultural Science and Technology practice questions

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Question 1Agricultural systems and the environment

In a crop rotation, which practice most directly reduces the build-up of a soil-borne pathogen that infects a single crop family?

  1. Growing a non-host crop in the following season Correct answer.
  2. Cultivating the soil more deeply before sowing
  3. Increasing the seeding rate of the susceptible crop
  4. Applying a broad-spectrum fungicide each fortnight

Explanation

A soil-borne pathogen survives best when its host is continually present, so inserting a non-host crop starves the pathogen of living tissue and interrupts its life cycle. Fungicides may suppress symptoms but rarely eliminate resting structures in soil. Deep cultivation spreads inoculum rather than removing it.

Question 2Agricultural systems and the environment

A farmer wants to reduce nitrate leaching below the root zone during winter. Which strategy is most effective?

  1. Establishing a deep-rooted cover crop after harvest Correct answer.
  2. Irrigating heavily after each fertiliser application
  3. Leaving the paddock bare and cultivated over winter
  4. Applying nitrogen fertiliser in late autumn at high rates

Explanation

A cover crop takes up residual soil nitrogen and holds it in plant tissue over the leaching season, releasing it later when decomposed. Bare, cultivated soil has no active root sink, so mobile nitrate moves down with drainage water.

Question 3Agricultural systems and the environment

Which soil property is most directly improved by maintaining high organic matter content?

  1. Depth to the water table
  2. Soil pH buffering against acidification
  3. Bulk density of the parent rock material
  4. Water-holding capacity and aggregate stability Correct answer.

Explanation

Organic matter binds mineral particles into stable aggregates and holds water in pore spaces, improving structure and plant-available water. Its effect on pH is indirect and modest compared with liming, and it does not change bedrock or water-table depth.

Question 4Agricultural systems and the environment

Which process in the nitrogen cycle converts ammonium to nitrate in aerobic soil?

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

Explanation

Nitrification is the two-step microbial oxidation of ammonium to nitrite and then nitrate, and it requires oxygen. Denitrification removes nitrate under anaerobic conditions, ammonification releases ammonium from organic matter, and fixation converts atmospheric nitrogen gas into combined forms.

Question 5Agricultural systems and the environment

A paddock shows sheet erosion after heavy rain. Which observation best indicates this form of erosion rather than rill erosion?

  1. A single large gully at the bottom of the slope
  2. Deposition of coarse gravel in a fan shape
  3. A thin, even layer of topsoil removed across the slope Correct answer.
  4. Deep channels that cannot be crossed by machinery

Explanation

Sheet erosion removes soil as a relatively uniform thin layer by raindrop impact and shallow overland flow, leaving no defined channels. Rills and gullies are concentrated-flow features with visible incised channels.

Question 6Agricultural systems and the environment

Which greenhouse gas is released from waterlogged paddy soils as a result of anaerobic decomposition?

  1. Carbon dioxide only
  2. Sulfur dioxide
  3. Methane Correct answer.
  4. Carbon monoxide

Explanation

In flooded, oxygen-depleted soils, methanogenic archaea decompose organic matter and release methane, a potent greenhouse gas. Aerobic decomposition instead produces mainly carbon dioxide, and sulfur dioxide and carbon monoxide are not the characteristic products of paddy soils.

Question 7Agricultural systems and the environment

In a Mediterranean climate such as the south-west of Western Australia, which rotation principle best conserves soil water for the following grain crop?

  1. Using a legume or break crop with early maturity Correct answer.
  2. Planting a high-biomass crop through the dry summer
  3. Delaying sowing until the soil profile is saturated
  4. Leaving a long fallow with repeated cultivation

Explanation

An early-maturing break crop uses less water through the season and leaves residual moisture for the next crop, while also interrupting disease cycles. Repeated cultivation fallow loses water through evaporation and degrades structure.

Question 8Agricultural systems and the environment

Which statement best describes the purpose of a riparian buffer zone on a farm?

  1. It traps sediment and nutrients before they enter a waterway Correct answer.
  2. It lowers the water table to improve paddock drainage
  3. It increases the area available for cropping up to the water's edge
  4. It provides a surface for machinery access during harvest

Explanation

Vegetated strips beside waterways slow overland flow, filter sediment and take up nutrients, protecting water quality. They are not designed for drainage, machinery access, or expanding cropped area.

Question 9Agricultural systems and the environment

Soil pH (CaCl2) of 4.6 is measured in a paddock. Which management response is most appropriate for a wheat crop sensitive to acidity?

  1. Apply elemental sulfur to increase cation exchange
  2. Flood the paddock to leach aluminium upward
  3. Apply gypsum to displace sodium from the clay
  4. Apply agricultural lime and incorporate it into the topsoil Correct answer.

Explanation

A pH of 4.6 in calcium chloride indicates strong acidity, and lime neutralises acidity by supplying carbonate that consumes hydrogen ions and reduces toxic soluble aluminium. Gypsum treats sodicity, sulfur acidifies further, and flooding does not remediate subsoil acidity.

Question 10Agricultural systems and the environment

A farmer applies 100 kg of urea (46% nitrogen) per hectare. How much nitrogen is applied?

  1. 100 kg N/ha
  2. 46 kg N/ha Correct answer.
  3. 460 kg N/ha
  4. 4.6 kg N/ha

Explanation

The nitrogen content is found by multiplying the product mass by the nutrient percentage, so 100 kg multiplied by 0.46 equals 46 kg of nitrogen per hectare. The percentage refers to nutrient concentration, not the total mass applied.

Question 11Agricultural systems and the environment

Which combination of conditions most strongly favours wind erosion of a sandy paddock?

  1. Dry, bare, finely aggregated soil and strong wind Correct answer.
  2. Moist soil, full crop cover and low wind speed
  3. Wet clay soil with a dense pasture sward
  4. Stubble retention with rough, cloddy surface

Explanation

Wind erosion requires detached, dry particles small enough to be lifted, a smooth bare surface, and wind above the threshold velocity. Moisture, vegetation cover and rough surfaces all raise the threshold and reduce transport.

Question 12Agricultural systems and the environment

Which statement best explains why legume pastures increase nitrogen availability for a following cereal crop?

  1. Legume roots exude nitrate directly into the soil solution
  2. Legume roots absorb nitrogen from deep subsoil and concentrate it at the surface
  3. Rhizobia fix atmospheric nitrogen in root nodules, which is later released in residues Correct answer.
  4. Legumes release nitrogen from fertiliser applied in the previous season

Explanation

Symbiotic rhizobia in legume nodules reduce atmospheric dinitrogen to ammonia, which is assimilated into plant protein and returned to the soil in residues and roots. Mineralisation of those residues then supplies nitrate to the following crop.

Question 13Agricultural systems and the environment

A grower uses minimum tillage with retained stubble. Which outcome is most consistent with this system?

  1. Faster stubble breakdown and lower soil carbon
  2. Increased soil disturbance and loss of aggregate stability
  3. Higher evaporation and greater surface crusting
  4. Improved infiltration and reduced erosion, with more stubble-borne disease risk Correct answer.

Explanation

Retaining stubble and reducing cultivation protects aggregates, improves infiltration and reduces erosion, but the retained residue can harbour pathogens such as crown rot organisms. The other options describe outcomes typical of intensive cultivation or residue removal.

Question 14Agricultural systems and the environment

A paddock has a high exchangeable sodium percentage and disperses readily when wet. Which amendment is most appropriate?

  1. Superphosphate
  2. Agricultural lime
  3. Urea
  4. Gypsum Correct answer.

Explanation

Gypsum supplies calcium, which displaces sodium from clay exchange sites and allows flocculation and improved structure. Lime treats acidity, while urea and superphosphate supply nutrients but do not address sodicity.

Question 15Agricultural systems and the environment

Which farming practice most directly reduces the risk of dryland salinity developing in a catchment?

  1. Replacing deep-rooted perennials with shallow-rooted annuals
  2. Clearing remnant vegetation to increase runoff
  3. Irrigating with saline water on low-lying land
  4. Establishing deep-rooted perennial pastures in recharge areas Correct answer.

Explanation

Dryland salinity arises when rising water tables bring salt to the surface, and deep-rooted perennials use more water over the year, reducing recharge. Clearing and shallow-rooted annuals increase recharge, and saline irrigation adds salt.

Question 16Agricultural systems and the environment

Which measurement best represents plant-available water in a soil profile?

  1. The gravimetric water content at saturation
  2. Total porosity expressed as a percentage
  3. The difference between field capacity and permanent wilting point Correct answer.
  4. The bulk density of the surface horizon

Explanation

Available water is held between field capacity, the water retained after drainage, and the permanent wilting point, where plants can no longer extract water. Total porosity includes air-filled pores, and saturated water content is not fully available.

Question 17Agricultural systems and the environment

A grower notices a decline in wheat yield where the same variety has been sown for six seasons. Which explanation best fits a break-crop solution?

  1. Nutrient exhaustion that only a break crop can reverse
  2. Loss of soil structure that only cultivation can repair
  3. Increased soil pH that a break crop will lower
  4. Build-up of stubble-borne pathogens that a non-host break crop interrupts Correct answer.

Explanation

Continuous wheat allows residue-borne pathogens such as crown rot organisms to multiply on retained stubble, and a non-host break crop reduces their inoculum. Nutrient decline is better addressed with fertiliser, and break crops do not reliably lower pH.

Question 18Agricultural systems and the environment

Which practice most effectively limits phosphorus movement into a nearby river?

  1. Increasing application rates to compensate for runoff losses
  2. Applying phosphorus fertiliser just before heavy winter rain
  3. Spreading fertiliser on the soil surface beside the drainage line
  4. Incorporating fertiliser into the soil and maintaining vegetated buffers Correct answer.

Explanation

Incorporating phosphorus binds it to soil where it is less mobile, and vegetated buffers filter sediment-bound phosphorus before it reaches the waterway. Surface applications before heavy rain and applications near drainage lines increase loss.

Question 19Agricultural systems and the environment

Which characteristic of a farming system most contributes to its resilience to drought?

  1. Maximum stocking rate during dry periods
  2. High levels of stored soil water and diverse enterprises Correct answer.
  3. Continuous cultivation to conserve soil moisture
  4. Reliance on a single high-value crop

Explanation

Resilience comes from diversity of income and risk, plus stored soil water that buffers the crop against rainfall variability. Monoculture, heavy stocking and repeated cultivation all increase vulnerability to drought.

Question 20Agricultural systems and the environment

Which set of conditions most favours denitrification losses from a fertilised paddock?

  1. Dry sandy soil with ammonium fertiliser
  2. Dry soil with a high calcium carbonate content
  3. Waterlogged soil with nitrate present and warm temperatures Correct answer.
  4. Well-drained, aerated soil with nitrate present

Explanation

Denitrification is carried out by facultative anaerobes that use nitrate as an oxygen substitute when oxygen is scarce, so waterlogged, warm soil with nitrate is the highest-risk combination. Aerated or dry soils favour aerobic processes instead.

Question 21Agricultural systems and the environment

A farm plans to reduce greenhouse gas emissions while maintaining productivity. Which combination is most consistent with this aim?

  1. Increasing stocking rates on the same pasture area
  2. Increasing nitrogen fertiliser rates without soil testing
  3. Burning stubble after each harvest
  4. Improving nitrogen use efficiency and reducing waterlogging Correct answer.

Explanation

Matching nitrogen supply to crop demand reduces nitrous oxide emissions, and avoiding waterlogging limits denitrification, so productivity can be maintained with lower emissions. Over-application, burning and overstocking all increase emissions or reduce carbon stores.

Question 22Agricultural systems and the environment

A catchment shows rising saline groundwater after 60 percent of its perennial vegetation was cleared. Which intervention addresses the cause rather than the symptom?

  1. Applying gypsum to the salt-affected surface soil
  2. Planting salt-tolerant species on the discharge area
  3. Installing deep drains to dispose of saline groundwater
  4. Re-establishing perennial vegetation across recharge zones Correct answer.

Explanation

Clearing reduced evapotranspiration and increased recharge, which raised water tables; restoring perennials in recharge areas reduces that recharge at its source. Drains and tolerant species manage the discharge symptom, and gypsum addresses soil structure rather than hydrology.

Question 23Agricultural systems and the environment

Two paddocks receive the same annual rainfall, but one has 30 percent more plant-available water at sowing. Which factor most plausibly explains this difference?

  1. Higher bulk density in the wetter paddock
  2. Steeper slope on the wetter paddock
  3. Greater stubble cover and lower evaporation from the wetter paddock Correct answer.
  4. Higher clay content at the surface of the drier paddock

Explanation

Stubble cover reduces evaporation from the soil surface and can improve infiltration, so more of the same rainfall remains stored at sowing. Surface clay, steep slope and high bulk density would all tend to reduce storage or increase losses.

Question 24Agricultural systems and the environment

A paddock has a long history of legume pasture and is now cropped continuously with cereals. Which nitrogen trend is most likely over time?

  1. Mineral nitrogen will decline as removal exceeds inputs once fixation stops Correct answer.
  2. Ammonium will accumulate permanently because nitrification stops
  3. Soil nitrogen will continue to rise because legume residues persist indefinitely
  4. Nitrogen will remain constant because soil organic matter never mineralises

Explanation

Once the legume phase ends, biological fixation stops and nitrogen is removed in grain and lost through leaching and gaseous pathways, so mineral nitrogen and organic reserves decline unless fertiliser is applied. Organic matter continues to mineralise and does not persist indefinitely.

Question 25Agricultural systems and the environment

A grower wants to reduce both soil erosion and nitrous oxide emissions from a cropping paddock. Which strategy addresses both outcomes most effectively?

  1. Cultivating to a fine seedbed and applying nitrogen in autumn
  2. Retaining stubble and applying nitrogen in split applications matched to crop demand Correct answer.
  3. Applying urea immediately before heavy rain
  4. Burning residues and applying all nitrogen at sowing

Explanation

Stubble retention protects the surface from erosion, while splitting nitrogen to match crop demand limits the excess nitrate and waterlogged conditions that drive nitrous oxide production. Burning, fine cultivation and large single applications increase both erosion and emissions.

Question 26Agricultural systems and the environment

In the nitrogen cycle, which process converts ammonium (NH4+) in the soil into nitrate (NO3-)?

  1. Ammonification by decomposers
  2. Denitrification by anaerobic bacteria
  3. Nitrification by soil bacteria Correct answer.
  4. Nitrogen fixation by rhizobia

Explanation

Nitrification is the two-step aerobic conversion of ammonium to nitrite and then nitrate, carried out by bacteria such as Nitrosomonas and Nitrobacter. It matters agronomically because nitrate is highly mobile and easily leached, whereas ammonium is held on the cation exchange complex.

Question 27Agricultural systems and the environment

Which soil property is most directly improved by increasing organic matter content in a sandy cropping soil?

  1. Depth to the watertable
  2. Water-holding capacity and cation exchange capacity Correct answer.
  3. Bulk density of the parent rock material
  4. Slope gradient of the paddock

Explanation

Organic matter acts like a sponge and carries negative charge, so adding it raises both the soil's ability to retain plant-available water and its capacity to hold nutrient cations. Sandy soils are naturally low in both, which is why organic matter management is central to their productivity.

Question 28Agricultural systems and the environment

A farmer wants to reduce nitrate leaching into groundwater beneath an irrigated vegetable crop. Which strategy is most effective?

  1. Applying all nitrogen as a single large dose before planting
  2. Applying smaller nitrogen doses timed to crop demand and avoiding excess irrigation Correct answer.
  3. Increasing irrigation volumes to push salts below the root zone
  4. Growing the crop on a bare, cultivated fallow between seasons

Explanation

Leaching losses depend on the amount of nitrate present in the soil when water drains beyond the root zone. Matching nitrogen supply to crop uptake and avoiding over-irrigation minimises both the nitrate pool and the drainage volume, so the two factors are addressed together.

Question 29Agricultural systems and the environment

Which term describes the variety of living organisms and habitats present within and around a farm landscape?

  1. Turbidity
  2. Eutrophication
  3. Salinity
  4. Biodiversity Correct answer.

Explanation

Biodiversity refers to the range of species, genetic variation and habitat types in a given area, including remnant vegetation, shelterbelts and soil organisms. On farms it underpins services such as pollination, pest predation and nutrient cycling.

Question 30Agricultural systems and the environment

A hillside paddock is to be converted from continuous cropping to a phase of perennial pasture. Which environmental outcome is most likely?

  1. Higher rates of wind erosion during summer
  2. Greater export of dissolved phosphorus to streams
  3. Increased rates of soil acidification from legume growth
  4. Reduced deep drainage and lower watertable recharge Correct answer.

Explanation

Perennial pastures have deeper, longer-lived root systems that dry the soil profile through summer and use more of the rainfall that would otherwise drain past the root zone. This reduces recharge to groundwater, which is the driver of dryland salinity in cleared catchments.

Question 31Agricultural systems and the environment

Why does retaining crop stubble on the soil surface reduce erosion compared with burning or full cultivation?

  1. It increases the soil's clay fraction through decomposition
  2. It intercepts raindrop energy and slows surface water flow while anchoring soil particles Correct answer.
  3. It eliminates the need for any nitrogen fertiliser
  4. It raises the soil pH and flocculates the surface horizon

Explanation

Stubble protects the soil surface from raindrop impact, which otherwise breaks aggregates and seals the surface, and it slows runoff so water infiltrates rather than transporting particles. The residue also reduces wind speed at the surface, lowering wind erosion.

Question 32Agricultural systems and the environment

A soil test shows a carbon-to-nitrogen ratio of 60:1 in a residue being incorporated before sowing. What is the most likely short-term effect on the following crop?

  1. Immediate release of large amounts of plant-available nitrogen
  2. Reduced soil water storage because of lower bulk density
  3. Temporary nitrogen immobilisation as microbes draw on soil nitrate Correct answer.
  4. Increased soil pH leading to manganese deficiency

Explanation

When residue carbon greatly exceeds nitrogen, decomposing microbes must source extra nitrogen from the soil solution to build their biomass, temporarily tying up nitrate. The nitrogen is released later as the microbial population turns over, so the effect is a delay rather than a permanent loss.

Question 33Agricultural systems and the environment

Which practice best reduces the risk of soil acidification under a legume-dominant pasture system?

  1. Regular soil testing and applying lime to maintain target pH Correct answer.
  2. Applying gypsum to displace sodium from the exchange complex
  3. Burning pasture residues each autumn
  4. Increasing superphosphate rates to boost legume growth

Explanation

Legume pastures acidify soil because nitrogen fixation and the subsequent removal or leaching of nitrate leaves hydrogen ions behind. Monitoring pH and applying lime neutralises this acidity and maintains conditions suitable for sensitive species and rhizobia.

Question 34Agricultural systems and the environment

A grower plants trees in belts across a paddock on a windy, sandy farm. Which primary purpose do these belts serve?

  1. Reducing wind speed at ground level to limit erosion and crop damage Correct answer.
  2. Raising the watertable to improve summer moisture supply
  3. Increasing the exchangeable sodium percentage of the topsoil
  4. Increasing deep drainage beneath the cropped area

Explanation

Shelterbelts create a zone of lower wind speed downwind by absorbing momentum from the airflow, which reduces the wind's capacity to detach and transport soil particles and protects crops from physical damage. The protected zone typically extends several tree heights downwind.

Question 35Agricultural systems and the environment

Which process in the phosphorus cycle is mainly responsible for long-term loss of applied phosphorus fertiliser from plant availability in many Australian soils?

  1. Volatilisation of phosphorus gas to the atmosphere
  2. Sorption and precipitation of phosphate onto soil minerals Correct answer.
  3. Denitrification of phosphate under waterlogged conditions
  4. Leaching of phosphate rapidly through sandy profiles

Explanation

In acidic and iron- or aluminium-rich soils, and in calcareous soils, phosphate reacts with soil minerals to form less soluble compounds, so a large share of applied phosphorus becomes only slowly available. This is why phosphorus is applied strategically, often banded near the seed, rather than broadcast in large single doses.

Question 36Agricultural systems and the environment

A paddock under continuous cereal cropping shows declining yields, increasing weed pressure and rising nitrogen fertiliser requirements. Which change to the system best addresses all three problems?

  1. Removing stubble to reduce shading at sowing
  2. Introducing a break crop or pasture phase into the rotation Correct answer.
  3. Applying a longer-acting nitrogen fertiliser at the same rate
  4. Increasing the seeding rate of the same cereal variety

Explanation

A break phase interrupts the build-up of cereal-specific pathogens and grass weeds and, if it includes a legume, contributes nitrogen to the following cereal. Diversifying the rotation therefore addresses yield decline, weed pressure and nitrogen dependency together.

Question 37Agricultural systems and the environment

In a catchment where deep-rooted perennial vegetation has been largely replaced by annual crops, which change to the water balance is expected?

  1. Surface runoff declines and stream salinity falls
  2. Evapotranspiration increases, drying the profile
  3. Less rainfall infiltrates, lowering the watertable
  4. More rainfall becomes deep drainage, raising the watertable Correct answer.

Explanation

Annual crops use water only during a short growing season and leave the profile wetter at the end of spring than perennial systems do. The unused rainfall drains beyond the root zone and recharges groundwater, which can raise watertables and mobilise salt.

Question 38Agricultural systems and the environment

A farmer wants to reduce ammonia volatilisation losses after applying urea to a dry, alkaline surface soil. Which approach is most appropriate?

  1. Applying urea to the surface and leaving it undisturbed
  2. Incorporating the urea into the soil or applying it just before rain Correct answer.
  3. Applying urea together with lime to raise surface pH further
  4. Applying urea in the heat of the day to speed drying

Explanation

Urea is hydrolysed to ammonium carbonate at the surface, and on alkaline soils with little moisture this releases ammonia gas, especially when the surface stays dry and warm. Placing urea below the surface or ensuring it is washed in quickly by rain or irrigation keeps the ammonium where it can be taken up.

Question 39Agricultural systems and the environment

Two adjacent paddocks have the same soil type and rainfall, but one has been under a diverse pasture with high ground cover while the other has been repeatedly cultivated. Which difference in soil function is most expected?

  1. The pasture paddock has more stable aggregates, higher infiltration and greater microbial biomass Correct answer.
  2. The pasture paddock has a wider carbon-to-nitrogen ratio in its surface soil
  3. The cultivated paddock has higher organic carbon because cultivation mixes residues
  4. The cultivated paddock has greater macroporosity from root channels

Explanation

Continuous pasture builds organic matter and supports root and fungal networks that bind particles into stable aggregates, so the soil resists slaking and crusting and accepts water faster. Cultivation breaks these aggregates, oxidises organic carbon and reduces the biological community that maintains structure.

Question 40Agricultural systems and the environment

A mixed farm seeks to cut greenhouse gas emissions from its cropping enterprise while maintaining gross margin. Which combination of practices is most consistent with that goal?

  1. Increasing irrigation volumes and replacing legumes with continuous cereals
  2. Burning stubble and increasing cultivation intensity to speed residue breakdown
  3. Applying a single large nitrogen dose at sowing and extending bare fallows
  4. Reducing fallow periods, using legumes in rotation and applying nitrogen fertiliser in split, demand-matched doses Correct answer.

Explanation

Nitrous oxide is the dominant greenhouse gas from cropping soils, and its emissions rise with excess mineral nitrogen and wet, anaerobic conditions. Legumes fix nitrogen without fertiliser, split applications avoid surplus nitrate, and fewer fallows keep living roots in the system, all of which lower emissions per unit of output.

Question 41Plant production and management

Which soil characteristic most directly determines the water-holding capacity available to crop roots?

  1. Soil slope
  2. Soil colour
  3. Soil temperature
  4. Soil texture Correct answer.

Explanation

Texture describes the proportions of sand, silt and clay, and these particle sizes govern pore space and therefore how much water a soil can retain and release to roots. Clay-rich soils hold more water than sandy soils because of finer pores and greater surface area. Colour, slope and temperature influence other processes but do not primarily set water-holding capacity.

Question 42Plant production and management

A grower wants to reduce wind erosion on a bare paddock over summer. Which practice is most effective?

  1. Increasing irrigation frequency
  2. Deep ripping the soil surface
  3. Maintaining surface cover or stubble Correct answer.
  4. Applying nitrogen fertiliser

Explanation

Wind erosion removes loose surface particles when they are exposed to wind above the threshold velocity. Keeping stubble or a cover crop on the surface reduces wind speed at ground level and anchors soil particles. Ripping loosens soil and can increase erodibility, while irrigation and fertiliser do not protect the surface from wind.

Question 43Plant production and management

Which macronutrient is most closely associated with promoting root development and early seedling establishment?

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

Explanation

Phosphorus is required for energy transfer and is particularly important for root growth and early establishment, which is why it is often placed near the seed at sowing. Nitrogen mainly drives vegetative growth, while potassium regulates water relations and enzyme activity. Calcium supports cell wall structure but is not the primary driver of root initiation.

Question 44Plant production and management

Legume pastures are valued in rotations mainly because they:

  1. Eliminate the need for phosphorus fertiliser
  2. Release nitrogen fixed by rhizobia into the soil system Correct answer.
  3. Prevent all root diseases in the following crop
  4. Increase soil bulk density

Explanation

Legumes form symbiotic associations with rhizobia that convert atmospheric nitrogen into forms the plant can use, and residues and root material later release that nitrogen to following crops. This reduces reliance on synthetic nitrogen but does not supply other nutrients. Legumes also break some disease cycles, but they do not prevent all diseases.

Question 45Plant production and management

Which factor is the primary reason for using certified seed in a commercial grain crop?

  1. It makes the crop resistant to all pests
  2. It removes the need for weed control
  3. It ensures genetic purity and known germination Correct answer.
  4. It guarantees a higher market price

Explanation

Certified seed is produced under quality assurance so that varietal purity, germination percentage and seed health meet defined standards. This gives growers predictable establishment and crop performance. Certification does not confer pest immunity, reduce weed control needs, or directly set grain prices.

Question 46Plant production and management

A farmer measures soil pH as 4.8 in the topsoil. Which management action is most appropriate before sowing a pH-sensitive cereal?

  1. Apply gypsum to improve structure
  2. Apply agricultural lime to raise pH Correct answer.
  3. Apply elemental sulfur to lower pH
  4. Apply more nitrogen fertiliser

Explanation

A pH of 4.8 is strongly acidic and can reduce availability of nutrients such as phosphorus and molybdenum while increasing aluminium toxicity. Agricultural lime (calcium carbonate) neutralises acidity and raises pH over time. Sulfur acidifies further, and gypsum addresses sodicity and structure rather than pH.

Question 47Plant production and management

Which irrigation scheduling approach best matches water supply to crop demand in a field with variable soil types?

  1. Irrigating on a fixed weekly calendar
  2. Applying the maximum possible volume each event
  3. Monitoring soil moisture and crop water use Correct answer.
  4. Irrigating whenever the soil surface appears dry

Explanation

Scheduling based on measured soil moisture and estimated crop evapotranspiration matches applications to actual depletion and demand. This reduces both under-irrigation and deep drainage losses. Fixed calendars and surface appearance ignore differences in soil water storage and root-zone depletion.

Question 48Plant production and management

Which statement best explains why crop rotation can reduce the build-up of soil-borne pathogens?

  1. Rotation increases soil bulk density
  2. Rotation changes the host plant, depriving pathogens of their preferred host Correct answer.
  3. Rotation removes all soil moisture from the profile
  4. Rotation increases soil pH above pathogen tolerance

Explanation

Many soil-borne pathogens are host-specific and survive in soil or residues. Growing a non-host crop interrupts their life cycle and reduces inoculum levels. Rotation does not reliably raise pH, remove all moisture, or increase bulk density as a disease control mechanism.

Question 49Plant production and management

A wheat crop shows pale yellow older leaves with poor tillering, and tissue testing confirms a deficiency. Which nutrient is most likely deficient?

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

Explanation

Nitrogen is mobile within the plant, so deficiency symptoms appear first on older leaves as pale yellowing while the plant redistributes nitrogen to new growth. Poor tillering is also consistent with nitrogen shortage. Iron deficiency typically shows on young leaves, and boron and copper deficiencies have different symptom patterns.

Question 50Plant production and management

Which practice best reduces the risk of herbicide resistance developing in a weed population?

  1. Using the same herbicide group each season
  2. Increasing herbicide rates beyond the label
  3. Applying herbicide only after resistance appears
  4. Rotating herbicide groups and integrating non-chemical control Correct answer.

Explanation

Repeated use of one herbicide mode of action selects for resistant individuals. Rotating herbicide groups and combining them with cultural and mechanical tactics reduces selection pressure and removes survivors. Higher rates increase selection pressure and may be off-label, while waiting until resistance appears is too late.