SACE Stage 2 Agricultural Production flashcards

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

Extensive production system

A farming system using large land areas with low inputs and outputs per hectare, typically based on natural pasture grazing and minimal supplementary feed or fertiliser.

Intensive production system

A system that raises output per hectare or per animal through high inputs such as irrigation, fertiliser, confinement housing or purchased feed, trading higher cost for higher yield.

Soil texture

The relative proportions of sand, silt and clay particles in a soil, which determine drainage, water-holding capacity, aeration and workability and cannot be altered by normal management.

Soil structure

The arrangement of soil particles into aggregates, creating pore space for air, water and roots; structure is degraded by compaction and cultivation and improved by organic matter and roots.

Field capacity

The water content remaining in a soil after free drainage has stopped, usually one to three days after saturation, when the soil holds water against gravity.

Permanent wilting point

The soil water content below which plants can no longer extract water and remain wilted, because remaining water is held too tightly by soil particles.

Plant-available water

The water stored between field capacity and permanent wilting point, calculated as the difference between the two contents multiplied by the depth of the root zone.

Law of the minimum

The principle that growth is limited by whichever essential resource is in shortest supply relative to demand, so other resources added in excess give no yield benefit.

Cation exchange capacity

A soil's capacity to hold positively charged nutrients such as calcium, magnesium and potassium on clay and organic matter surfaces, measured in centimoles per kilogram.

Soil pH and nutrient availability

Soil acidity or alkalinity measured on a logarithmic scale; most nutrients are most available near pH 6-7, while phosphorus locks up in acid soils and trace elements in alkaline soils.

Nitrogen fixation

Conversion of atmospheric nitrogen gas into plant-usable ammonia, performed biologically by rhizobia in legume root nodules or industrially by the Haber-Bosch process.

Nitrification

The microbial conversion of ammonium to nitrite and then nitrate in aerobic soil; nitrate is readily taken up by plants but is also easily leached and denitrified.

Denitrification

The conversion of nitrate to nitrogen gases by bacteria in waterlogged, oxygen-poor soil, representing a loss of available nitrogen and a greenhouse gas source.

Leaching

The downward movement of soluble nutrients, especially nitrate, below the root zone with drainage water, reducing fertiliser efficiency and potentially contaminating groundwater.

Crop rotation

A planned sequence of different crop species on the same land over successive seasons to interrupt pest and disease cycles, balance nutrients and reduce weed and resistance pressure.

Green manure crop

A crop grown specifically to be incorporated into the soil while green, adding organic matter and nutrients, particularly nitrogen if the species is a legume.

Cover crop

A crop grown between main crops to protect soil from erosion, suppress weeds and capture residual nutrients, rather than for harvest.

Stubble retention

Leaving crop residue on the soil surface after harvest to reduce erosion, conserve moisture, moderate soil temperature and return organic matter and nutrients.

Conservation tillage

Cultivation systems that minimise soil disturbance and retain residue cover, preserving structure and moisture and reducing erosion compared with full inversion ploughing.

Soil erosion by water

Detachment and transport of topsoil by raindrop impact and runoff; risk rises with slope, low ground cover and intense storms, and falls with residue cover and contour works.

Soil salinity

Accumulation of soluble salts in the root zone to levels that reduce water uptake by plants; often caused by rising water tables and irrigation with insufficient drainage.

Waterlogging

Saturation of soil pores with water, excluding oxygen from roots and reducing growth; on clay soils it also promotes denitrification and nitrogen loss.

Rumen fermentation

Anaerobic microbial breakdown of plant fibre in the rumen, producing volatile fatty acids as the main energy source and microbial protein as the main protein source for ruminants.

Metabolisable energy

The portion of feed energy available to the animal after losses in faeces, urine and fermentation gases; it drives growth, milk production and reproduction.

Crude protein

Feed nitrogen content multiplied by 6.25, used to estimate protein supply; it must be balanced against energy because rumen microbes need both for efficient fermentation.

Dry matter intake

The mass of feed consumed excluding water; it sets the ceiling on nutrient supply and is depressed by low feed digestibility and by excess protein relative to energy.

Stocking rate

The number of animals or animal equivalents grazed per hectare over a defined period; it influences pasture persistence, ground cover and per-head versus per-hectare production.

Rotational grazing

A system moving livestock between paddocks with rest periods, allowing pasture recovery, improving ground cover and often increasing total pasture utilisation and persistence.

Integrated pest management

A decision framework combining monitoring, economic thresholds and cultural, biological and chemical controls, using chemicals only when justified to slow resistance and limit harm.

Economic threshold

The pest population level at which the value of damage avoided equals the cost of control, marking the point where intervention becomes economically justified.

Mode of action rotation

Alternating pesticides with different biochemical modes of action across seasons to prevent selection of resistant pest or weed populations under repeated exposure.

Farm gross margin

Enterprise income minus variable costs, expressed per hectare or per head; it excludes fixed overheads and is used to compare the profitability of alternative enterprises.