LC Ag Science flashcards

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

Independent variable

The factor deliberately changed by the investigator between treatments in an experiment, so its effect on the measured response can be isolated and compared.

Reliability

The extent to which repeated measurements or repeats of an experiment give consistent results; improved by replication, standardised method, and averaging.

Soil texture

The relative proportions of sand, silt, and clay particles in a soil, determined by particle size and used to assign a texture class.

Cation exchange capacity

The total quantity of exchangeable cations a soil can hold on clay and organic matter surfaces, expressed in cmol(+)/kg and rising with clay and humus content.

Bulk density

The oven-dry mass of soil divided by its total volume, including pore space; high values indicate compaction and reduced porosity for roots and air.

Soil structure

The arrangement of soil particles into aggregates or peds, which determines pore size and continuity and therefore drainage, aeration, and root growth.

Mineralisation

The microbial conversion of organic nitrogen in soil organic matter and residues into inorganic plant-available forms such as ammonium, releasing nutrients during decomposition.

Transpiration

The loss of water vapour from plant leaves through stomata, creating the tension that draws water and dissolved nutrients up the xylem from the roots.

Apical dominance

Suppression of lateral bud growth by auxin produced at the shoot tip, which concentrates growth in the main stem until the tip is removed.

Rumen fermentation

Microbial breakdown of fibrous plant material in the rumen into volatile fatty acids, providing the main energy source for cattle, sheep, and other ruminants.

Heritability

The proportion of total phenotypic variation in a trait attributable to genetic differences; low heritability means selection produces slow genetic progress.

Stomatal control

Opening and closing of leaf pores to balance carbon dioxide uptake for photosynthesis against water loss, closing under drought stress via abscisic acid signalling.

Law of the minimum

The principle that crop yield is limited by the essential nutrient in shortest supply relative to need, so other nutrients added will not increase yield.

Integrated pest management

A decision framework combining cultural, biological, and physical controls with monitoring and thresholds, using pesticides only when justified.

Economic threshold

The pest population density at which the value of crop loss avoided equals the cost of control, marking the point where intervention becomes worthwhile.

Seed germination requirements

Viable seed needs adequate moisture, oxygen, and a suitable temperature range to break dormancy and begin growth, with sowing depth matched to emergence energy.

Post-harvest losses

Reductions in quantity or quality of harvested produce caused by respiration, moisture, temperature, pests, and handling, reduced by cooling, drying, and storage.

Feed conversion ratio

The mass of feed consumed divided by liveweight gain over a period; a lower ratio indicates more efficient conversion of feed into animal product.

Estimated breeding value

A prediction of an animal's genetic merit for a trait, based on its own performance and that of relatives, used to rank candidates for selection.

Heterosis

The superior performance of crossbred offspring compared with the average of their parents, exploited in commercial livestock and crop production.

Five freedoms

A welfare framework covering freedom from hunger and thirst, discomfort, pain injury or disease, fear and distress, and freedom to express normal behaviour.

Limiting amino acid

The essential amino acid present in the diet in shortest supply relative to requirement; it restricts protein synthesis and growth until supplemented.

Nutrient budgeting

Accounting for nutrient inputs to a farm against outputs in produce and losses to water and air, revealing surplus and the main loss pathways.

Eutrophication

Nutrient enrichment of water bodies, usually by nitrogen and phosphorus runoff, causing algal blooms, oxygen depletion, and harm to aquatic life.

Water-use efficiency

Marketable yield produced per unit of water applied or transpired, improved by scheduling irrigation to match crop evapotranspiration demand.

Carbon sequestration

Net storage of carbon in soil organic matter or vegetation, increased by organic matter inputs, residue retention, and reduced tillage; gains are reversible.

Gross margin

Enterprise gross output, including sales and valuation changes, minus variable costs; fixed costs are excluded because they do not vary with enterprise scale.

Break-even yield

The yield required for total revenue to equal total costs, calculated as total costs divided by the price received per unit of output.

Opportunity cost

The value of the next best alternative forgone when a resource such as land, labour, or capital is committed to one enterprise rather than another.

Price elasticity of demand

The responsiveness of quantity demanded to a change in price; demand for staple foods is inelastic, so price falls sharply reduce farm income.

Risk assessment

Identification of hazards in a practical investigation, the people at risk, and the control measures applied to reduce likelihood and severity of harm.

Validity in investigations

The extent to which a method actually tests the stated hypothesis and measures the intended variable, requiring adequate controls and appropriate measurement.