I85PREP
⌘ K
SACE Stage 2 Agricultural Systems study materials
SACE Stage 2 Agricultural Systems study resources

SACE Stage 2 Agricultural Systems practice questions

One question at a time. Build your SACE Stage 2 Agricultural Systems 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 systems

In a crop rotation, which practice most directly reduces the build-up of a soil-borne pathogen that survives on a single host species?

  1. Applying a nitrogen fertiliser before sowing
  2. Increasing the seeding rate of the same crop
  3. Growing a non-host crop in the following season Correct answer.
  4. Cultivating the soil to a greater depth

Explanation

Rotation works by removing the susceptible host, so a pathogen that depends on that host has no tissue to colonise and its population declines over successive seasons. Fertiliser, sowing density and tillage depth alter growth or soil condition but do not break the host cycle.

Question 2Agricultural systems

Which soil property is most improved by adding organic matter such as compost or retained stubble?

  1. Depth to the watertable
  2. Water-holding capacity Correct answer.
  3. Soil pH
  4. Bulk density of the parent rock

Explanation

Organic matter increases aggregation and pore space, which raises the soil's ability to retain plant-available water. It can buffer pH slightly but is not a liming agent, and it has no influence on bedrock or watertable depth.

Question 3Agricultural systems

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

  1. Deep ripping to break compaction
  2. Applying lime to raise soil pH
  3. Irrigating once at the start of summer
  4. Retaining stubble as surface cover Correct answer.

Explanation

Surface stubble protects soil aggregates from the wind and slows the wind speed at ground level, so particles are not lifted. Lime, ripping and a single irrigation do not provide lasting protection of the soil surface.

Question 4Agricultural systems

In a legume-based pasture, which process supplies nitrogen to the associated grasses?

  1. Mineralisation of rock phosphate in the subsoil
  2. Leaching of nitrate from adjacent paddocks
  3. Volatilisation of ammonia from the legume leaves
  4. Biological nitrogen fixation by rhizobia in root nodules Correct answer.

Explanation

Rhizobia in nodules on legume roots convert atmospheric nitrogen into forms the plant can use, and nitrogen is later released to companion grasses through root turnover, grazing and decomposition. The other processes either do not supply nitrogen or remove it from the system.

Question 5Agricultural systems

Which statement best describes the purpose of a break crop in a cereal rotation?

  1. It permanently removes the need for fertiliser
  2. It is grown purely to provide grain for livestock
  3. It is planted only when the cereal crop fails
  4. It interrupts pest and disease cycles between cereal crops Correct answer.

Explanation

A break crop is a different species grown between cereal crops to disrupt the life cycles of cereal-specific pathogens and weeds. It may also be grazed or harvested, but its defining role is to break the continuity of the cereal host.

Question 6Agricultural systems

Which factor most directly determines the plant-available water capacity of a soil?

  1. The mix of pore sizes and texture Correct answer.
  2. The number of earthworms present
  3. The colour of the surface horizon
  4. The slope of the paddock

Explanation

Available water is held in the intermediate-sized pores, so texture and pore-size distribution largely set how much water a soil can store between field capacity and wilting point. Colour, fauna and slope influence other properties but are not the primary control.

Question 7Agricultural systems

A producer wants to reduce nitrate leaching into groundwater beneath an irrigated crop. Which practice is most appropriate?

  1. Growing the crop on a sandy soil with no cover
  2. Matching nitrogen applications to crop demand and avoiding excess irrigation Correct answer.
  3. Increasing irrigation depth to push salts below the roots
  4. Applying all nitrogen in a single large dose before planting

Explanation

Leaching losses rise when nitrate is present in the soil and water drains beyond the root zone, so timing nitrogen to crop demand and avoiding over-irrigation keeps nitrate where roots can capture it. Large single doses and excessive irrigation both increase the risk of loss.

Question 8Agricultural systems

Which of the following is an example of a biological control agent used in an integrated pest management program?

  1. A predatory mite released to feed on pest mites Correct answer.
  2. A broad-spectrum insecticide
  3. A herbicide applied to the whole paddock
  4. A synthetic pyrethroid sprayed on calendar dates

Explanation

Biological control uses living organisms such as predators, parasitoids or pathogens to suppress a pest population. The other options are chemical controls, which act directly rather than through a living natural enemy.

Question 9Agricultural systems

A paddock has a soil test showing pH 4.6 in the topsoil and the grower plans to sow a pH-sensitive crop. Which action best addresses the constraint before sowing?

  1. Apply gypsum to supply calcium
  2. Apply agricultural lime and allow time for it to react Correct answer.
  3. Deep rip the paddock to improve aeration
  4. Increase the sowing rate to compensate for poor establishment

Explanation

Agricultural lime raises soil pH by neutralising acidity, but it reacts slowly and must be applied and incorporated well before sowing. Gypsum supplies calcium and sulfur without raising pH, and the other options do not correct acidity.

Question 10Agricultural systems

In a grazing system, rotational grazing is introduced instead of continuous set stocking. Which outcome is most likely?

  1. Elimination of the need for any fertiliser
  2. Increased selective grazing of preferred species
  3. Higher rates of soil erosion from trampling
  4. More even pasture utilisation and rest periods for regrowth Correct answer.

Explanation

Rotational grazing concentrates stock on a paddock for a short period and then moves them, which gives pastures a rest period to recover and reduces patchy overgrazing. Continuous stocking tends to allow more selective grazing and less uniform use.

Question 11Agricultural systems

Which combination best describes an integrated weed management strategy for a cropping paddock?

  1. Relying on one herbicide group applied every year
  2. Combining rotation, competitive crops, cultivation and rotation of herbicide groups Correct answer.
  3. Applying the maximum herbicide rate whenever weeds appear
  4. Removing all crop residues to expose weed seeds

Explanation

Integrated weed management combines cultural, mechanical and chemical tactics and rotates herbicide groups to slow the selection of resistance. Relying on a single herbicide group or reactive spraying increases the risk of resistance and does not address the weed seedbank.

Question 12Agricultural systems

A farmer applies 150 kg of urea (46% nitrogen) per hectare. Approximately how much nitrogen is applied?

  1. 150 kg N/ha
  2. 46 kg N/ha
  3. 69 kg N/ha Correct answer.
  4. 326 kg N/ha

Explanation

The nitrogen content is the product of the product rate and its nitrogen concentration: 150 kg/ha multiplied by 0.46 equals about 69 kg N/ha. The other values either mistake the concentration for the mass or divide rather than multiply.

Question 13Agricultural systems

Which practice is most likely to increase soil organic carbon in a cropping paddock over several years?

  1. Retaining stubble and including a pasture phase Correct answer.
  2. Burning all crop residues each autumn
  3. Applying nitrogen without any carbon input
  4. Continuous cultivation with a disc plough

Explanation

Soil organic carbon rises when carbon inputs exceed losses, so retaining residue and adding a pasture phase increases organic inputs and root material. Burning, frequent cultivation and nitrogen-only strategies either remove carbon or fail to add it.

Question 14Agricultural systems

A pest population develops resistance to a foliar insecticide. Which management response best slows further resistance development?

  1. Rotating to insecticides with different modes of action and using non-chemical controls Correct answer.
  2. Applying the same insecticide more frequently
  3. Increasing the dose of the same insecticide
  4. Spraying only when the pest population is at its highest

Explanation

Resistance is selected when the same mode of action is used repeatedly, so rotating chemical groups and integrating non-chemical tactics reduces selection pressure on any one mechanism. Higher doses and more frequent applications increase selection pressure.

Question 15Agricultural systems

Which statement correctly describes the role of a cover crop in a vineyard between vine rows?

  1. It competes with vines for all water and should be avoided
  2. It guarantees a higher yield every season
  3. It replaces the need for any pest monitoring
  4. It protects soil from erosion and can improve soil structure and biology Correct answer.

Explanation

A cover crop between rows reduces raindrop impact and surface runoff, protecting soil from erosion while adding organic matter and supporting soil biology. It may compete for water, which requires management, but it does not guarantee yield or remove the need for monitoring.

Question 16Agricultural systems

Which soil structure problem is most directly indicated by a hard, dense layer about 20 cm below the surface that restricts root growth?

  1. A rising saline watertable
  2. A phosphorus deficiency
  3. A plough pan or compaction layer Correct answer.
  4. An acidic surface horizon

Explanation

Repeated tillage or traffic at a consistent depth can create a compacted layer, often called a plough pan, with high bulk density that restricts roots. Salinity, phosphorus and acidity are chemical constraints that do not produce a distinct dense layer at a set depth.

Question 17Agricultural systems

A cereal is sown into a paddock that grew the same cereal for the previous three seasons. Which risk is most likely to increase?

  1. Loss of soil phosphorus through volatilisation
  2. Reduced effectiveness of rhizobia on the cereal
  3. Increased nitrogen fixation by the cereal roots
  4. Take-all and other residue-borne cereal diseases Correct answer.

Explanation

Growing the same cereal repeatedly allows residue-borne pathogens such as take-all to survive and multiply on stubble and roots, raising disease pressure. Cereals do not fix nitrogen, and phosphorus does not volatilise from soil in this way.

Question 18Agricultural systems

Which measurement would best indicate whether an irrigation schedule is supplying water efficiently to a crop?

  1. The colour of the crop leaves
  2. The number of irrigation events per week
  3. The price of water in the district
  4. The soil moisture deficit compared with crop water use Correct answer.

Explanation

Efficiency is assessed by comparing the water applied with the crop's actual water use and the soil moisture deficit, so that applications match demand and avoid drainage below the root zone. Leaf colour, event counts and water price do not quantify efficiency.

Question 19Agricultural systems

A farmer wants to reduce the risk of herbicide resistance in a grass weed population. Which tactic is least likely to help?

  1. Using harvest weed seed control
  2. Delaying sowing to manage early weed flushes
  3. Including a competitive break crop in the rotation
  4. Using the same herbicide group each season Correct answer.

Explanation

Repeated use of one herbicide group is the main driver of resistance selection, so it is the tactic least likely to help. Rotation, harvest seed control and delayed sowing all reduce the number of weeds exposed to a single chemical.

Question 20Agricultural systems

Which statement best explains why a legume pasture can improve the nitrogen supply to a following cereal crop?

  1. Nitrogen fixed in legume residues is released during decomposition Correct answer.
  2. Legume roots exude nitrogen directly into the soil during growth
  3. Legumes absorb nitrogen from the atmosphere through their leaves
  4. Legume plants convert soil nitrate into atmospheric nitrogen

Explanation

Nitrogen fixed by rhizobia is stored in legume shoots, roots and nodules, and mineralises during decomposition to become available to the next crop. Legumes do not absorb nitrogen through leaves or convert nitrate back to atmospheric nitrogen.

Question 21Agricultural systems

A paddock shows patchy crop growth, poor response to fertiliser and a high soil pH of 8.8 with visible white surface crusts. Which constraint is most likely?

  1. Severe phosphorus deficiency alone
  2. Salinity or sodicity associated with an alkaline soil Correct answer.
  3. Waterlogging from a perched watertable
  4. Acidity in the subsoil

Explanation

White surface crusts combined with a strongly alkaline pH point to salinity or sodicity, which restrict water uptake and cause patchy growth that does not respond well to fertiliser. Phosphorus deficiency, waterlogging and acidity do not produce these alkaline crusts.

Question 22Agricultural systems

A producer is comparing two nitrogen strategies for a cereal crop. Strategy A applies all nitrogen at sowing; Strategy B splits applications between sowing and stem elongation. Under a wet winter, which outcome is most likely and why?

  1. Strategy B reduces leaching losses because nitrogen is supplied closer to peak demand Correct answer.
  2. Strategy A stores more nitrogen in the profile because it is applied earlier
  3. Strategy A increases nitrogen fixation by the cereal
  4. Both strategies lose identical amounts because leaching depends only on rainfall

Explanation

Splitting nitrogen aligns supply with the period of rapid crop uptake, so less nitrate sits in the profile during the high-drainage winter and leaching losses are reduced. Early single applications are more exposed to winter drainage, and cereals do not fix nitrogen.

Question 23Agricultural systems

In an integrated pest management program, a pest is monitored and the decision to spray is delayed until the population reaches a defined threshold. What is the main purpose of this threshold?

  1. To eliminate the pest population completely from the paddock
  2. To avoid unnecessary sprays when the pest population causes less damage than the cost of control Correct answer.
  3. To ensure pesticides are applied at regular calendar intervals
  4. To increase the dose required at each application

Explanation

An economic threshold is the pest density at which the cost of control equals the value of the damage prevented, so spraying below it wastes money and adds selection pressure. Thresholds are not calendar schedules, eradication targets or dose recommendations.

Question 24Agricultural systems

Two paddocks have the same rainfall and soil type, but Paddock X has been continuously cropped with stubble burnt, while Paddock Y has retained stubble and included a legume pasture phase. Which difference in soil function is most defensible?

  1. Paddock Y will have lower water-holding capacity
  2. Paddock X will have higher aggregate stability and higher organic carbon
  3. Paddock Y will have higher organic carbon and better infiltration Correct answer.
  4. Paddock X will have greater microbial biomass

Explanation

Retaining residue and including a pasture phase adds organic carbon and root material, which supports aggregation, biological activity and infiltration. Burning and continuous cropping deplete organic matter and tend to degrade these functions.

Question 25Agricultural systems

A grower observes that a herbicide that previously controlled a weed well now gives poor control, and the weed is present at the recommended label rate. Which conclusion is most justified?

  1. The weed has become a different species
  2. The weed population has likely evolved resistance to that herbicide group Correct answer.
  3. The soil pH has permanently changed the herbicide's mode of action
  4. The herbicide has degraded because the container was opened

Explanation

Poor control at a full label rate, after previous effective use, is the classic sign of evolved resistance, which should be confirmed and managed by changing modes of action and integrating non-chemical tactics. Container storage, species identity and soil pH do not explain a consistent decline in control.

Question 26Agricultural systems

Which term describes the practice of growing two or more crop species together in the same paddock at the same time?

  1. Monoculture
  2. Fallow rotation
  3. Contour banking
  4. Intercropping Correct answer.

Explanation

Intercropping deliberately combines two or more species in one field during the same season so that their different growth habits and resource demands are used together. Monoculture is the opposite arrangement, and fallow and contour banking are unrelated to species mixing.

Question 27Agricultural systems

A producer wants to reduce wind erosion on a bare, sandy paddock over summer. Which approach is most appropriate?

  1. Burning stubble to remove loose material
  2. Increasing cultivation passes to level the surface
  3. Retaining crop residue as a surface mulch Correct answer.
  4. Grazing the paddock heavily to compact the surface

Explanation

Surface residue shelters the soil from wind and reduces the wind speed at the soil surface, so fewer particles are lifted. Cultivation, burning and heavy grazing all expose or loosen soil and increase the risk of erosion.

Question 28Agricultural systems

Which organism is a legume root nodule bacterium that fixes atmospheric nitrogen in symbiosis with pasture legumes?

  1. Rhizobium Correct answer.
  2. Trichoderma
  3. Mycorrhiza
  4. Azospirillum

Explanation

Rhizobium bacteria enter legume roots and form nodules where they convert atmospheric nitrogen into forms the plant can use. The other organisms listed are associated with other functions such as free-living nitrogen fixation, nutrient uptake or disease suppression.

Question 29Agricultural systems

Which statement describes the main purpose of a windbreak in an agricultural landscape?

  1. Removing nutrients from the soil profile
  2. Raising the water table beneath adjacent paddocks
  3. Increasing the rate of surface runoff downslope
  4. Reducing wind speed to protect soil, crops and livestock Correct answer.

Explanation

A windbreak is a permeable barrier of trees or shrubs that lowers wind speed downwind, reducing erosion, crop damage and stock stress. It does not raise water tables, speed runoff or strip nutrients from the profile.

Question 30Agricultural systems

Which animal is a ruminant and therefore digests forage mainly through microbial fermentation in a specialised stomach?

  1. Sheep Correct answer.
  2. Chicken
  3. Pig
  4. Horse

Explanation

Sheep are ruminants with a multi-chambered stomach in which microbes ferment fibrous plant material before digestion. Pigs, horses and poultry have different digestive systems and do not use a rumen.

Question 31Agricultural systems

Which practice is a form of conservation tillage?

  1. Rotary hoeing to a depth of 20 cm
  2. Direct drilling seed into undisturbed stubble Correct answer.
  3. Repeated discing until the soil is bare
  4. Mouldboard ploughing to bury all residue

Explanation

Conservation tillage keeps most of the previous crop residue on the surface and disturbs only a narrow band or slot for the seed. Ploughing, repeated discing and deep rotary hoeing all bury or mix residue and leave little cover.

Question 32Agricultural systems

What is the main role of a buffer strip of vegetation along a drainage line on a farm?

  1. Raising soil pH across the paddock
  2. Trapping sediment and nutrients before they reach waterways Correct answer.
  3. Supplying nitrogen directly to the adjacent crop
  4. Increasing the rate of water flow into the creek

Explanation

Vegetated buffer strips slow overland flow, allowing sediment to settle and nutrients to be taken up or filtered before water reaches a waterway. They do not speed flow, supply nitrogen to crops or change soil pH.

Question 33Agricultural systems

Which product is typically used to raise the pH of an acidic soil?

  1. Gypsum
  2. Ammonium sulfate
  3. Agricultural lime Correct answer.
  4. Superphosphate

Explanation

Agricultural lime, mainly calcium carbonate, neutralises soil acidity and raises pH. Gypsum adds calcium without changing pH much, while ammonium sulfate and superphosphate are fertilisers that do not correct acidity.

Question 34Agricultural systems

A producer wants to estimate the amount of pasture dry matter available in a paddock before setting stocking rates. Which method is most appropriate?

  1. Measuring the height of the tallest grass with a ruler
  2. Recording the number of grazing days from last season
  3. Cutting quadrat samples, drying and weighing the herbage Correct answer.
  4. Counting the number of plants in a single square metre

Explanation

Cutting known-area quadrats, drying the herbage to remove moisture and weighing it gives a direct estimate of dry matter per unit area. Counting plants, measuring only the tallest grass or relying on past records does not measure the feed available.

Question 35Agricultural systems

A grower wants to reduce the risk of stored grain being damaged by insects. Which action is most suitable?

  1. Cooling and drying the grain to a safe moisture level before storage Correct answer.
  2. Storing freshly harvested damp grain in sealed bags
  3. Leaving the silo open to allow air circulation and rain entry
  4. Mixing the grain with soil to dilute the insects

Explanation

Insects and moulds multiply rapidly in warm, moist grain, so drying and cooling grain below safe thresholds greatly reduces their activity. Damp storage, contamination with soil and open silos all increase the risk of spoilage.

Question 36Agricultural systems

A cereal crop shows pale yellow leaves with the older leaves affected first, and a soil test shows adequate phosphorus. Which nutrient deficiency is most likely?

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

Explanation

Nitrogen is mobile within the plant, so when supply is short the plant moves nitrogen from older leaves to new growth, causing older leaves to yellow first. Calcium, boron and copper are largely immobile or affect younger tissue and are not the most likely cause here.

Question 37Agricultural systems

Which practice best reduces the risk of soil compaction in a paddock that is being grazed during a wet period?

  1. Driving heavy machinery across the wet paddock
  2. Increasing stocking rate to shorten the grazing time
  3. Cultivating the wet soil to aerate it
  4. Removing stock from the paddock until the soil drains Correct answer.

Explanation

Wet soils are weakest and most easily compacted, so keeping stock off until the profile drains protects soil structure. Higher stock numbers, heavy machinery and cultivating wet soil all increase the load or disturbance on saturated soil.

Question 38Agricultural systems

A producer wants to reduce evaporative losses from a farm dam used for irrigation. Which measure is most effective?

  1. Pumping water out and back in each day
  2. Increasing the surface area of the dam
  3. Removing vegetation from around the dam
  4. Covering the dam surface with a floating shade structure Correct answer.

Explanation

Evaporation occurs from the exposed water surface, so a floating cover or shade reduces the area exposed to sun and wind and cuts losses. Enlarging the surface, clearing vegetation and recirculating water do not reduce evaporation.

Question 39Agricultural systems

A grower is planning a rotation for a paddock with a history of cereal root diseases. Which sequence is most appropriate?

  1. Cereal, break crop, legume pasture, cereal Correct answer.
  2. Cereal, cereal, fallow, cereal
  3. Cereal, cereal, cereal, cereal
  4. Cereal, cereal, cereal, legume pasture

Explanation

A non-host break crop and a legume pasture between cereal crops reduce the build-up of cereal-specific pathogens and improve soil nitrogen. Continuous or near-continuous cereals allow pathogens to persist and multiply.

Question 40Agricultural systems

Which statement best explains why a legume pasture in a rotation can reduce the amount of nitrogen fertiliser needed by the following crop?

  1. Legume roots physically pump nitrogen fertiliser from deep subsoil
  2. Fixed nitrogen is returned to the soil in roots and residues and mineralised for the next crop Correct answer.
  3. Legumes acidify the soil so that nitrogen becomes more available
  4. Legume residues immobilise nitrogen and release it slowly to the next crop

Explanation

Rhizobia in legume nodules fix atmospheric nitrogen, which is incorporated into plant tissue; when roots and residues break down, mineralisation releases nitrogen for the following crop. This reduces reliance on bagged nitrogen fertiliser.

Question 41Agricultural systems

A producer is choosing a pasture species for a paddock that is waterlogged for several weeks each winter. Which trait is most important in the chosen species?

  1. Requirement for frequent summer irrigation
  2. Very high drought tolerance
  3. Tolerance of waterlogging and poor aeration Correct answer.
  4. Ability to grow on highly saline soil

Explanation

In waterlogged soil, oxygen is depleted in the root zone, so species that tolerate poor aeration and waterlogging persist better. Drought tolerance, salinity tolerance and summer irrigation needs do not address the main limitation of that paddock.

Question 42Agricultural systems

Which approach best describes integrated pest management for a vegetable crop?

  1. Combining monitoring, thresholds, cultural controls and selective chemicals Correct answer.
  2. Removing all beneficial insects before spraying
  3. Spraying a broad-spectrum insecticide on a fixed calendar
  4. Applying the maximum label rate whenever any insect is seen

Explanation

Integrated pest management combines monitoring, economic thresholds, cultural and biological controls and selective chemicals used only when needed. Calendar spraying, spraying on any sighting and removing beneficials all conflict with the principles of IPM.

Question 43Agricultural systems

A farmer is comparing two ways to apply phosphorus: broadcasting on the surface each year versus banding near the seed at sowing. Which statement best explains the advantage of banding?

  1. Banding allows much higher total rates to be applied safely
  2. Banding places phosphorus close to developing roots and limits contact with soil that fixes it Correct answer.
  3. Banding removes the need for any soil testing
  4. Banding increases leaching of phosphorus to groundwater

Explanation

Phosphorus is relatively immobile in soil and is readily fixed by soil minerals, so placing it in a band near the seed improves root access and reduces the volume of soil that fixes it. Banding does not remove the need for soil testing or increase leaching.

Question 44Agricultural systems

A grower wants to estimate the economic threshold for a pest in a crop. Which concept best defines this threshold?

  1. The maximum number of pests that can ever be present in a paddock
  2. The date on which spraying must always begin
  3. The rate of pesticide required to kill all pests present
  4. The pest density at which the cost of control equals the value of the damage avoided Correct answer.

Explanation

The economic threshold is the pest population level at which the value of crop loss prevented by control equals the cost of that control. Above this level, control is expected to be worthwhile; below it, spraying is unlikely to pay.

Question 45Agricultural systems

A producer wants to reduce nitrate leaching beneath a legume pasture that is being grazed heavily. Which practice is most appropriate?

  1. Matching stock numbers to pasture growth and avoiding heavy grazing in high-rainfall periods Correct answer.
  2. Increasing stocking rate to consume the pasture faster
  3. Removing all pasture cover so that rainfall runs off the surface
  4. Applying additional nitrogen fertiliser to boost growth

Explanation

Matching stock numbers to growth limits the amount of nitrogen-rich urine and dung deposited and reduces the surplus that can leach when rainfall exceeds plant demand. Higher stocking rates, more nitrogen fertiliser and bare ground all increase the risk of nitrate loss.

Question 46Agricultural systems

Two paddocks have the same soil and rainfall, but Paddock A has been continuously cropped with stubble retained, while Paddock B has been continuously cropped with stubble burnt. Which difference is most likely after several years?

  1. Paddock A has more soil organic carbon and better aggregate stability Correct answer.
  2. Paddock A has more soil organic carbon but poorer aggregate stability
  3. Paddock B has more soil organic carbon because ash is returned
  4. Both paddocks have identical organic carbon because rainfall is the same

Explanation

Retaining stubble returns carbon to the soil and supports biological activity, which builds organic carbon and improves aggregate stability. Burning removes most of the carbon and leaves only mineral ash, so soil carbon and structure decline.

Question 47Agricultural systems

A grower wants to reduce the risk of surface runoff carrying phosphorus into a nearby lake. Which combination of practices is most effective?

  1. Increasing the phosphorus rate to build up soil reserves quickly
  2. Applying phosphorus at recommended rates, incorporating it into the soil and maintaining vegetated buffers Correct answer.
  3. Clearing vegetation from drainage lines to speed water away
  4. Applying phosphorus just before heavy rain on bare, sloping ground

Explanation

Phosphorus loss is greatest when erodible sediment and runoff carry surface-applied fertiliser away. Applying recommended rates, incorporating fertiliser and using vegetated buffers together reduce the amount of phosphorus reaching waterways.

Question 48Agricultural systems

A producer is comparing a perennial pasture with an annual pasture on the same soil type. Which statement best explains why the perennial pasture may use rainfall more efficiently?

  1. Annual pastures have deeper roots and use more of the summer rain
  2. Perennial roots remain active for most of the year and can use out-of-season rainfall Correct answer.
  3. Annual pastures fix more nitrogen and therefore need less water
  4. Perennial pastures transpire less water than annual pastures

Explanation

Perennial species keep roots and leaf area active across seasons, so they can capture rainfall that falls outside the short growing season of an annual pasture. This reduces water loss to deep drainage and improves overall water use efficiency.

Question 49Agricultural systems

A crop is showing poor growth despite adequate rainfall and fertiliser, and a soil test shows a high sodium adsorption ratio with dispersive clay. Which management approach is most appropriate?

  1. Applying gypsum and improving drainage to stabilise the clay Correct answer.
  2. Increasing irrigation without improving drainage
  3. Cultivating the wet dispersive soil repeatedly
  4. Applying more sodium fertiliser to balance the clay

Explanation

High sodium relative to calcium and magnesium causes clay dispersion and poor structure. Gypsum supplies calcium that displaces sodium, and good drainage allows the sodium to be leached away, improving structure.

Question 50Agricultural systems

A producer wants to reduce greenhouse gas emissions from a grazing enterprise while maintaining productivity. Which change is most likely to achieve this?

  1. Applying more nitrogen fertiliser without changing stocking rate
  2. Burning pasture residues each autumn
  3. Increasing the number of animals held per hectare indefinitely
  4. Improving pasture quality and matching stocking rate to feed supply Correct answer.

Explanation

Better pasture quality and correct stocking rates improve feed conversion and reduce the methane produced per unit of product, while avoiding overgrazing and land degradation. Simply adding animals, fertiliser or burning does not achieve the same emission intensity improvement.