WACE ATAR Agricultural Science and Technology cheat sheet

Agroecosystem inputs = solar energy, water, nutrients, seed/stock, labour and fossil energy; outputs = product, residues, leachate, greenhouse gases and biodiversity change.

Monoculture reduces within-paddock diversity and increases vulnerability to a single pest or pathogen; crop rotation interrupts pest life cycles and diversifies root-zone biology.

Nitrogen-use efficiency (NUE) = N removed in product ÷ N applied × 100; values below about 40% indicate large surplus N available for leaching or denitrification.

Eutrophication sequence: nutrient enrichment → algal bloom → shading and decomposition → dissolved oxygen depletion → fish kill; phosphorus is usually limiting in fresh water, nitrogen in marine systems.

Soil erosion risk rises with slope, low ground cover and high rainfall intensity; the Revised Universal Soil Loss Equation multiplies rainfall, soil, slope-length, cover and practice factors.

Riparian buffer strips trap sediment and nutrients and shade streams; effectiveness depends on width, vegetation type and whether flow is surface or subsurface.

Greenhouse gas sources in agriculture: enteric methane (ruminants), nitrous oxide (fertiliser and urine patches), carbon dioxide (fuel, land clearing); nitrous oxide has the highest warming potential per kilogram.

Salinity develops where rising water tables bring salt to the surface after native deep-rooted vegetation is replaced by shallow-rooted annual crops; recharge control and drainage are the two management levers.

Waterlogging reduces oxygen diffusion in soil, impairing root respiration and nutrient uptake; raised beds and subsurface drainage are structural remedies.

Yield components (grain crops) = plants per m² × heads or pods per plant × grains per head × grain weight; management targets the component most limiting at the current growth stage.

Dry matter accumulation follows the radiation-use efficiency model: biomass = intercepted radiation × radiation-use efficiency, with interception set by leaf area index and canopy architecture.

Phenology stages (emergence, tillering/branching, flowering, grain fill, maturity) determine when nutrients, water and pesticides are most effective; flowering is the most stress-sensitive stage in most grain crops.

Law of the minimum: growth is limited by the scarcest essential resource, so adding a non-limiting nutrient gives no yield response and risks off-site loss.

Critical soil pH range for most temperate crops is about 5.5–7.0; aluminium toxicity and phosphorus lock-up increase below pH 5.0 in acidic soils.

Photosynthetic pathway differences: C3 plants photorespire and suit cooler, wetter environments; C4 plants concentrate CO2, use water more efficiently and dominate hot, high-radiation zones.

Integrated weed management combines cultural (competition, row spacing, rotation), mechanical and chemical tactics to slow the evolution of herbicide resistance.

Herbicide resistance management: rotate mode-of-action groups, use mixtures and sequences with multiple effective groups, and prevent seed set of survivors.

Soil water balance: plant-available water = (field capacity − permanent wilting point) × rooting depth × bulk density, adjusted for stone and gravel content.

Feed conversion ratio = feed consumed ÷ liveweight gain; lower values mean more efficient conversion, and efficiency improves in younger animals and with higher-quality diets.

Ruminant digestion relies on microbial fermentation in the rumen; microbes synthesise microbial protein from non-protein nitrogen, so urea can partly replace dietary protein with a readily fermentable energy source.

Ration balancing matches energy, protein, fibre and minerals to animal requirements for maintenance, growth, pregnancy and lactation; energy is usually the first limiting nutrient.

Maintenance energy requirement scales with metabolic body weight (W^0.75), so larger animals need proportionally less energy per kilogram of body weight.

Heat stress reduces feed intake and fertility; indicators include panting, increased respiration rate and reduced milk yield, managed with shade, water and ventilation.

Reproduction efficiency: conception rate = females conceiving ÷ females joined; the calving or lambing interval combines conception, gestation and re-joining periods.

Genetic gain per year = (selection intensity × accuracy × genetic standard deviation) ÷ generation interval; shortening the generation interval accelerates progress.

Inbreeding depression reduces fertility and vigour; it rises when effective population size is small or related animals are mated repeatedly.

Animal welfare assessment uses the five domains: nutrition, environment, health, behavioural interaction and mental state.

Precision agriculture cycle: sense (yield, soil, canopy sensors) → map variability → interpret → apply variable-rate treatment → evaluate.

Variable-rate technology requires a prescription map, GPS/GNSS positioning and a controller that adjusts application rate by location; accuracy depends on positioning correction (RTK gives centimetre-level).

Remote sensing indices: NDVI = (NIR − red) ÷ (NIR + red); values near 1 indicate dense green vegetation, and the index saturates at high canopy cover.

Automatic milking and animal monitoring use activity, rumination and milk conductivity sensors to flag oestrus and mastitis earlier than visual inspection.

Drones and satellite imagery suit broad-scale monitoring; ground-based proximal sensors suit high-resolution soil and plant measurements at small scale.

Drip irrigation delivers water to the root zone with high application efficiency (often 85–95%) compared with furrow or overhead systems.

Data-driven decisions require calibration and validation; a sensor is only useful if its readings are repeatable and related to the decision variable.

Automation economics: compare annualised capital cost plus operating cost against the value of labour saved, yield gained and losses avoided.

The four soil condition components are physical (structure, porosity), chemical (pH, nutrients, salinity), biological (organic matter, microbes) and hydrological (infiltration, water holding).

Soil organic carbon is built by adding residues, reducing tillage and including perennial phases; it is lost through erosion, residue removal and continuous cultivation.

Water-use efficiency = biomass or yield produced ÷ water used (rainfall plus irrigation); it can be improved by reducing evaporation, runoff and deep drainage.

Irrigation scheduling based on evaporation pans or soil moisture probes applies water when the allowable depletion fraction of plant-available water is reached.

Whole-farm nutrient budget = nutrient inputs (fertiliser, feed, fixation, deposition) − outputs (product, leaching, volatilisation, erosion); a positive balance signals accumulation or loss risk.

Integrated pest management hierarchy: prevention, monitoring and thresholds, biological control, then targeted chemical control as a last resort.

Biodiversity on farms is supported by remnant vegetation, corridors, shelterbelts, diverse pastures and retention of woody debris.

Carbon farming options include soil carbon sequestration, reduced methane from livestock, plantation establishment and avoided clearing; permanence and measurement are key constraints.

Groundwater recharge control uses deep-rooted perennials and contour structures to lower water tables and limit dryland salinity.

Gross margin = gross income − variable costs; it excludes fixed costs and is used to compare enterprises on a per-hectare or per-head basis.

Gross margin per hectare = (yield × price − variable cost per hectare); ranking enterprises by this figure guides area allocation under limited land.

Break-even yield = total costs ÷ price per unit; break-even price = total costs ÷ expected yield.

Farm profit = gross income − variable costs − fixed costs; cash flow differs from profit because of timing of receipts, payments and inventory changes.

Partial budget format: added returns plus reduced costs versus added costs plus reduced returns; the net difference decides whether a change is worthwhile.

Opportunity cost is the value of the next best alternative forgone; it belongs in enterprise comparison even though no cash changes hands.

Price risk management tools include forward contracts, futures and options; forward contracts lock in price but remove upside and carry delivery obligations.

Supply and demand: a price floor above equilibrium creates surplus, while a price ceiling below equilibrium creates shortage.

Depreciation allocates the cost of a durable asset over its useful life; straight-line depreciation = (cost − salvage value) ÷ useful life in years.