SACE Stage 2 Agricultural Systems flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Negative feedback

A process in which a change in a system triggers a response that counteracts the change, promoting stability; an example is increased soil moisture leading to greater plant growth, which then depletes that moisture.

Positive feedback

A process in which a change amplifies itself, potentially causing rapid system change or collapse; an example is erosion reducing infiltration, increasing runoff and causing further erosion.

Trophic efficiency

The proportion of energy transferred from one trophic level to the next, typically about 10%; this loss limits food chain length and explains why livestock production requires more land than plant production.

Nitrogen fixation

The conversion of atmospheric nitrogen gas into ammonia by rhizobia in legume root nodules or by free-living soil bacteria; this supplies plant-available nitrogen and reduces fertiliser requirements.

Soil texture triangle

A triangular diagram used to classify soil into textural classes based on the relative proportions of sand, silt and clay particles; loam soils generally balance water retention, aeration and nutrient supply.

Liebig's law of the minimum

The principle that plant growth is limited by the resource in shortest supply relative to need, even when other resources are abundant; adding a non-limiting nutrient does not increase growth.

Integrated pest management

A decision framework combining biological, cultural, physical and chemical controls, using economic thresholds to justify intervention; it reduces pesticide use and slows the development of resistance.

Economic threshold

The pest population density at which the cost of control equals the value of crop loss avoided; intervention below this level is not economically justified.

Crop rotation

The planned sequence of different crop species on a paddock over seasons; it disrupts pest and disease cycles, balances nutrient use and improves soil structure.

Water use efficiency

The amount of biomass or grain produced per unit of water transpired or applied; improving it through canopy management, irrigation scheduling and soil improvement increases productivity per megalitre.

Stocking rate

The number of animals grazed per unit area over a defined period; it must be matched to carrying capacity to avoid pasture degradation and reduced animal performance.

Carrying capacity

The maximum stocking rate a pasture or rangeland can support sustainably without long-term decline in productivity, ground cover or soil condition under a given management system.

Metabolisable energy

The energy in feed available to an animal after accounting for losses in faeces, urine and methane; it must meet maintenance plus production requirements for growth, lactation or pregnancy.

Drench rotation

The practice of alternating anthelmintic chemical groups used for parasite control to slow the development of drench resistance in sheep and cattle gastrointestinal worms.

Harvest maturity index

A measurable indicator used to decide when to harvest, such as grain moisture, sugar content, firmness or acidity; correct timing balances yield, quality and storage risk.

Paddock records

Documented history of inputs, yields, grazing and observations for each paddock; they support traceability, benchmarking and evidence-based management decisions.

Three pillars of sustainability

Economic viability, environmental integrity and social acceptability; a practice is sustainable only when all three are maintained over time, not just one.

Dryland salinity

Salt accumulation in the root zone caused by rising water tables after deep-rooted native vegetation is cleared; management includes perennial pastures, deep-rooted crops and drainage.

Eutrophication

Nutrient enrichment of water bodies, especially by nitrogen and phosphorus runoff, causing algal blooms, oxygen depletion and harm to aquatic life; riparian buffers reduce nutrient loss.

Enteric methane

Methane produced by microbial fermentation in the rumen and released by belching; it is a significant greenhouse gas source from livestock and represents lost dietary energy.

Nitrous oxide emissions

A potent greenhouse gas produced from nitrogen fertiliser and manure through nitrification and denitrification; emissions increase with excess nitrogen and waterlogged soil conditions.

Riparian buffer

Vegetated strip beside a waterway that filters runoff, stabilises banks and provides habitat; it reduces sediment, nutrient and pesticide movement into streams.

Ecosystem services

Benefits people obtain from ecosystems, including pollination, pest control, nutrient cycling, water filtration and soil formation; biodiversity underpins the supply of these services.

Life cycle assessment

A method that quantifies environmental impacts per functional unit across all stages of production, processing, transport and waste, preventing burden shifting between stages.

Gross margin

Gross income minus variable costs for an enterprise; it measures returns per hectare or per head and is used to compare enterprise profitability and guide enterprise mix decisions.

Fixed versus variable costs

Fixed costs such as depreciation and permanent labour do not change with output in the short run; variable costs such as seed, fertiliser and fuel do.

Break-even yield

The yield at which total income equals total costs, calculated as total costs divided by price per unit and area; it indicates the minimum production needed to avoid a loss.

Precision agriculture

The use of GPS guidance, variable-rate technology, sensors and yield mapping to match inputs to within-paddock variability, improving efficiency and reducing over-application.

Variable-rate technology

Equipment that adjusts the application rate of seed, fertiliser or spray according to a prescription map or real-time sensor data, matching inputs to localised crop requirements.

NDVI

Normalised Difference Vegetation Index, calculated from red and near-infrared reflectance; it indicates vegetation vigour and biomass and is used in satellite and drone crop monitoring.

Forward contract

An agreement to sell a specified quantity of produce at a set price on a future date; it reduces price risk but removes the opportunity to benefit from later price rises.

Return on assets

Profit expressed as a percentage of total assets employed; it measures how efficiently farm assets generate profit and allows benchmarking against industry standards.