LC Ag Science key terms

Any factor in an experiment that is deliberately kept the same across all treatments so that it cannot influence the results. Examples include temperature, soil type, light duration and the age of plants or animals used.

The factor that the investigator deliberately changes or manipulates between treatment groups, such as fertiliser rate, stocking density or light intensity, so that its effect on the measured outcome can be observed.

The outcome that is measured in an experiment, such as yield, liveweight gain, germination percentage or soil pH. It is expected to respond to changes in the independent variable and must be measured consistently.

An independent repeat of a treatment within an experiment, using a different plot, pen or animal. Replication allows natural variation to be estimated and increases confidence that observed differences are real rather than chance.

The random allocation of treatments to experimental units such as plots or animals, so that unnoticed differences in soil, position or condition are spread evenly across treatments and do not bias the comparison.

An experimental design in which only the independent variable differs between groups, all other conditions are controlled, and sufficient replication and randomisation are used so that conclusions about cause and effect are justified.

Accuracy is how close a measurement is to the true value; precision is how closely repeated measurements agree with each other. A set of readings can be precise yet inaccurate if the instrument is poorly calibrated.

Checking and adjusting a measuring instrument against a known standard, such as a pH buffer solution or a set of certified weights, so that readings are trustworthy before data collection begins.

A vertical cross-section of soil from the surface down to the underlying parent material, showing distinct layers called horizons. Each horizon differs in colour, texture, organic matter and structure because of the processes forming it.

A recognisable layer within a soil profile, such as the organic-rich A horizon, the leached E horizon, the subsoil B horizon and the weathered C horizon. Horizons are named according to the processes that formed them.

The relative proportions of sand, silt and clay particles in a soil, determined by particle size rather than by how the soil behaves when squeezed. Texture strongly influences water-holding capacity, drainage and nutrient retention.

The way soil particles are bound together into aggregates or peds, giving a soil its crumbly, blocky, platy or massive arrangement. Good structure creates pore space for air, water and roots.

The capacity of a soil, mainly through clay and organic matter, to hold positively charged nutrient ions such as calcium, potassium and magnesium and release them to plant roots. It is usually expressed in centimoles of charge per kilogram.

A measure of the acidity or alkalinity of the soil solution on a scale from 0 to 14. It controls the availability of many plant nutrients and influences which crops and soil organisms can thrive.

The amount of agricultural lime needed to raise a soil's pH to a target level for a particular crop, determined from soil testing and the soil's buffering capacity. It corrects acidity and improves nutrient availability.

The downward movement of dissolved substances, especially nitrate and other mobile nutrients, through the soil profile with drainage water. Leaching removes nutrients from the root zone and can pollute groundwater and waterways.

The compression of soil into a denser mass with fewer large pores, usually caused by machinery traffic or grazing animals on wet soil. It restricts root growth, reduces infiltration and increases surface runoff.

The mass of dry soil per unit volume, including the pore space, typically expressed in grams per cubic centimetre. High bulk density indicates a dense, compacted soil with limited porosity for roots and drainage.

The living, dead and decomposed plant and animal material in soil. It improves structure, water retention and cation exchange capacity, and it is the main reservoir of soil nitrogen and carbon.

The conversion of atmospheric nitrogen gas into forms plants can use. Legumes do this through symbiotic bacteria in root nodules, while free-living soil bacteria and industrial processes also fix nitrogen.

A genus of soil bacteria that form nodules on the roots of legumes and convert atmospheric nitrogen into ammonia for the host plant. Correct inoculation of seed can improve legume establishment on soils lacking the bacteria.

A member of the pea and bean family, such as clover, lucerne, lupin or field pea, that forms a nitrogen-fixing symbiosis with rhizobia. Legumes are used in pastures and rotations to supply nitrogen and protein.

The planned sequence of different crops on the same land over successive seasons. Rotations help break pest and disease cycles, manage weeds, vary nutrient demand and maintain soil fertility and structure.

A decision-making approach that combines monitoring, thresholds, biological control, cultural practices and judicious pesticide use to keep pests below economically damaging levels while limiting environmental harm and resistance.

The pest or weed population level at which the cost of control equals the value of the crop lost if no action is taken. Control is justified only when pest numbers are expected to exceed this level.

The inherited ability of a pest population to survive a pesticide dose that would previously have killed it, arising when resistant individuals are selected and multiply. Rotating chemical groups and using non-chemical controls slow its development.

A digestive strategy in cattle, sheep and goats in which a large forestomach harbours microbes that ferment fibrous plant material before it is further digested. It allows efficient use of pasture and roughage.

The largest compartment of the ruminant stomach, where microbes ferment feed and produce volatile fatty acids, gas and microbial protein. Its health depends on adequate fibre, stable pH and gradual diet changes.

The energy in a feed that remains available to an animal after losses in faeces, urine and fermentation gases. It is the standard measure used to balance rations against the energy needs of stock.

The mass of feed consumed by an animal once its water content is excluded, usually expressed in kilograms per day. It limits nutrient supply and must be balanced against the animal's energy and protein requirements.

A prediction of the genetic merit an animal passes to its offspring for a particular trait, calculated from its own performance and that of its relatives. It allows fair comparison of animals across herds and flocks.

The proportion of the variation in a trait within a population that is due to genetic differences rather than environment. Highly heritable traits respond quickly to selection; lowly heritable traits need more records.

A weighted combination of estimated breeding values for several traits, with weights reflecting their economic importance in the breeding objective. It ranks animals on overall merit rather than a single trait.

The number of animals or animal equivalents carried on a defined area of land, usually expressed per hectare over a season. It links animal demand to pasture supply and is central to sustainable grazing management.

The maximum stocking rate an area can sustain over the long term without degrading pasture, soil and water resources. It varies with rainfall, soil fertility, pasture species and management.

The movement of dissolved or attached nutrients, especially nitrogen and phosphorus, across the soil surface into waterways with rain or irrigation. It can cause algal blooms and is reduced by buffer strips and careful fertiliser timing.

Managing agricultural systems so that production meets present needs without reducing the ability of soil, water, biodiversity and farm businesses to support future production. It balances economic, environmental and social outcomes.

The difference between the income from an enterprise and its variable costs, such as seed, fertiliser and animal health products. It measures enterprise profitability before fixed costs and helps compare alternative enterprises.

Costs that change in proportion to the size or output of an enterprise, such as seed, fertiliser, fuel, feed and casual labour. They are deducted from enterprise income to calculate a gross margin.

Costs of running the farm business that do not change with the level of output in the short term, such as depreciation, insurance, rates and permanent labour. They are covered by the combined gross margins of all enterprises.

The level of production or price at which total income equals total costs, so the enterprise makes neither profit nor loss. It is used to assess risk before committing to a production plan.

The layout of a field experiment, including plot size and shape, buffer areas, replicates, randomisation and measurement sites, planned so that soil variation and edge effects do not confound treatment comparisons.

Qualitative data describe qualities or categories, such as colour, disease presence or farmer opinions; quantitative data are numerical measurements such as yield or height. Both may be collected in a practical investigation and analysed differently.