Australian Agriculture Assessment 2001 - Glossary
Acidic soil
Soil with a pH < 7.0 in a soil–water suspension.
Agricultural lime
A soil conditioner containing calcium carbonate (commonly from limestone) used to neutralise soil acidity and in some soils to provide calcium.
Algal blooms
A proliferation of microscopic algae in rivers and lakes, stimulated by input of nutrients such as phosphorus and nitrogen.
Alkaline soil
A soil with a pH > 7.0.
Aquifer
A rock layer that holds water
Alluvial
Sediments deposited from flowing water into floodplains.
Alluvial fan
Material deposited by a stream where it emerges from the constriction of a valley to a plain.
Arid zone
Those areas in Australia that receive less than 250 or 350 mm of rainfall each year in the south and north respectively.
Annual cropping
A system where one crop is grown each year. Refer also to double cropping.
Biomass
A mass (weight) of plant material.
Broadacre farms
Commercial farms over a large area. Produce includes crops, wool, beef and sheep meat. Farming is usually under dryland conditions.
Buffering capacity
The ability of the soil to resist changed conditions.
C3 & C4 plants
C3 plants comprise more than 95 percent of the plant species on earth. (Trees, for example, are also C3 plants.). C4 plants, such as the common marsh grasses and other herbaceous plants, are abundant in arid, hot environments. They include such crop plants as sugar cane, corn, and soybeans, and are the second most prevalent photosynthetic type. The C3 and C4 refer to how these classes of plants assimilate carbon dioxide into their systems. During the first steps in CO2 assimilation, C3 plants form a pair of three carbon-atom molecules. C4 plants, on the other hand, initially form four carbon-atom molecules. The important difference between C3 and C4 species for rising carbon dioxide levels is that photosynthesis in C4 species is saturated with carbon dioxide at present levels, while C3 species continue to increase for photosynthesis as carbon dioxide rises.
Catchment
An area of land where run-off from rainfall goes into the one river system.
Clay
Soil particles < 0.002 mm in diameter.
Climate variability
The natural year to year, and season to season variation of the climate system.
Codes of practice
Sets of agreed guidelines adopted by rural industries and the agricultural service sector to minimise the impacts of farming operations on the environment.
Conservation farming
A farming system that creates a suitable environment for growing crops and pasture with an emphasis on conserving soil and water resources, and consistent with sound economic practices.
Crop management
A series of management options (e.g. choice of crops within a rotation, variety of plant, length and type of fallow, time of sowing, residue management, pesticide, soil conditioner and fertiliser practices, and type and number of tillage operations).
Denitrification
The chemical or microbial conversion of soil nitrate or nitrite to gaseous nitrogen or an oxide of nitrogen.
Deposition
Occurs when the sediment load of a given particle type exceeds the energy available to move it. This often results from a reduced gradient, flow velocity or discharge or an increase in the hydraulic resistance the flow induced by vegetation. Deposition results in sedimentation.
Detachment
Detachment of soil particles occurs when the erosive forces of raindrop impact or of flowing water exceed the soil’s resistance to erosion. It is influenced by the forces of impact and flowing water, how likely the soil is to erode, the presence of plants or other material that reduces the magnitude of eroding forces, and management of the soil that makes it less susceptible to erosion. Detachment can also be caused by soil organisms such as ants or burrowing animals.
Digital elevation model (DEM)
A geographic grid of an area where the contents of each grid square represent the height of the landscape in that cell.
Direct sowing
Any system of sowing, or crop or pasture establishment where seed is placed into soil that has not been ploughed. Sometimes termed zero tillage.
Double cropping
Growing a summer and a winter crop on the same land within a 12-month period.
Deep drainage
Movement of soil water and solutes through the soil and beyond the root zone.
Dryland cropping
Cropping without irrigation.
Dryland salinity
Where water balance has been altered due to changing land use (e.g. clearing of native vegetation for broadacre farming or grazing), excess water entering the watertable mobilises salt which then rises to the land surface. Movement of water drives salinisation processes and may move the stored salt towards the soil surface or into surface water bodies.
Effective rainfall
Rainfall that is available for plant growth.
Erodibility
How likely the soil is to erode.
Essential chemical elements
Elements required by plants and animals to complete their life cycles.
Estuary
An inlet or river mouth that is influenced by tides from the sea and fresh water from land. The area where fresh and salt waters mix.
Eutrophication
Process whereby waters become enriched with nutrients (mainly phosphorus and nitrogen), stimulating growth of aquatic flora and/or fauna.
Erosion
The continuing process of landscape development as a smoothing or levelling of the earth’s surface by removal of weathered material. Natural erosion is due only to the forces of nature; accelerated erosion occurs as a result of human activities. In each case the same processes operate and the distinction is often only a matter of degree and rate.
Erosivity
The potential ability of an agent to cause soil erosion.
Fallow
The practice of maintaining land free of plant growth. Land is left either in a cultivated or herbicide-treated state for a period before sowing a crop or between successive crops. It is mainly carried out to conserve soil water and mineralise soil organic nitrogen reserves. The period of fallow can vary from between on to three months (short fallow) to 14 months (long fallow).
Farm-gate nutrient balance
The difference between the total amount of a nutrient applied to land as fertiliser, soil conditioners and legume nitrogen fixation and the total amount of that nutrient exported in harvested farm products.
Fertiliser requirement
The extra amount of a particular nutrient needed to increase plant growth to a designated level.
Foot slope
The lower part of a slope above the gentler gradient of a valley floor or plain.
Flux
The rate at which energy, water, nutrients and radiation flow across an area.
Geo-morphological processes
Processes that make up the physical and chemical interactions between the Earth’s surface and natural forces (e.g. gravity, ice, water, wind, waves) that produce landforms.
Groundwater
Water occurring below the ground surface
Gully density
The linear extent of a gully, measured as kilometres of gully per square kilometre of land.
Gully erosion
Removal of soil by running water which results in the formation of deep channels (gullies) that tend to form in upland areas, have steep sides , and usually transport surface run-off to relatively small drainage areas. Gullies are at least 50 cm deep. They erode unchannelled valleys and dips, and eventually become vegetated and infill, distinguishing them from depressions that have permanent streams.
Gypsum
The common name for calcium sulfate, used to supply calcium and sulfur to plants and to ameliorate sodic soils.
Headcuts
A sharp ephemeral waterfall cut into soil at the head of a gully or incised stream. Over time the headcut migrates upslope by the scouring and toppling of the soil.
Hillslope
All the land surface above a stream or channel edge.
Incised streams
Permanent streams which have deepened and widened by several metres as a result of plants being removed or increased forces of flow. These streams have high, bare vertical banks with headcuts incised into floodplains. They resemble large gullies.
Infiltration
Passage of water through the soil surface and into the soil.
Intensive agricultural land use(s)
Areas described as intensive agriculture generally include Horticulture; Semi-intensive (irrigated and non-irrigated) – sugar, cotton, rice, potatoes; Broadacre crops (irrigated and non-irrigated) – cereals, wheat, oilseeds, pulses, hay; Pastures (irrigated and non-irrigated) – livestock, dairy production from improved pastures.
Leaching
Movement of materials in solution from the soil.
Ley-farming
A farm rotation that specifically includes a legume-based pasture to improve soil fertility as well as to provide grazing for livestock. This system of land use is confined mainly to southern Australia.
Lime requirement
The amount of lime required to change the soil to a specified state of pH or soluble aluminium content.
Macro-nutrient
The essential plant nutrients nitrogen, phosphorus, potassium, sulfur, calcium and magnesium.
Maintenance application
Applications of fertilisers in amounts and intervals to maintain available soil nutrients at levels necessary to produce desired yields.
Mineralisation
The conversion of an element from an organic form to an inorganic state as a result of microbial activity.
Monitoring
Routine counting, testing or measuring environmental factors to estimate their status or condition
Net primary productivity
The difference between the levels of plant photosynthesis and respiration, that determine how much plant is produced—typically measured as a mass per unit area.
Nitrification
Oxidation of ammonium to nitrate or nitrite.
Nitrogen fixation
Conversion of gaseous nitrogen into more complex organic molecules that can be used by plants and other organisms. The process is usually carried out by soil micro-organisms in association with leguminous plants.
Nutrient availability
The ease with which plants can absorb a particular nutrient from the soil. Different fractions within the total nutrient pool will have different availabilities, depending on solubility, rates of dissolution and diffusion to plant roots.
Off-site impacts
Consequences of an action or decision that occurs beyond the area under consideration.
Perennial plant
Plants that live more than one year.
Photosynthesis
The process that plants use to convert carbon dioxide and water into plant organic matter. Photosynthesis is powered by energy from the sun.
Plant nutrient
An element absorbed by plants that is necessary for completion of the life cycle.
Rangelands
Areas of native grasslands, shrublands, woodlands, and tropical savanna woodlands that cover a large proportion (75%) of the arid and semi-arid regions of (outback) Australia.
Recharge
Rainfall that moves through the soil, beyond the roots of plants, to replenish the aquifer.
Regolith
The unconsolidated covering of weathered rock and soil on the earth’s surface. It consists of loose earth materials above solid rock.
River basins containing intensive agriculture
The catchments of the east coast of Australia from Cape York to the Eyre Peninsula, of Tasmania, of south-west Western Australia, and of the Ord Basin. These river basins include forests and rangelands as well as intensive agriculture.
Reduced tillage
Any procedure for preparing land for sowing, where herbicides partially replace cultivation. Also known as minimum tillage.
Residue
Portion of plant or crop left in the paddock after harvest. Often referred to as crop stubble or pasture residue. Residues can be retained, incorporated into the soil or burnt.
Revised Universal Soil Loss Equation (RUSLE)
The RUSLE calculates mean annual erosion (tonnes/ha/yr) as a product of rainfall erosivity, soil erodibility, hillslope length, hillslope gradient, ground cover and land use. However, because the slope steepness factor of the original equation (the USLE) overestimates erosion from slopes steeper than 9%, the RUSLE applies a different slope steepness equation to determine the hillslope gradient factor.
Rill erosion
Erosion where concentrated wash causes the formation of tiny channels or rills, a few centimetres to 50 cm deep, which usually carry water only during storms and which can be removed by tilling.
Run-off
The proportion of precipitation that is not immediately absorbed by the soil and thus flows across the surface.
Salinisation
The process whereby soluble salts accumulate in the soil.
Salinity
The total amount of water-soluble salts present in a soil horizon.
Sand
Soil particles between 0.005 and 2.0 mm in diameter.
Silt
Soil particles between 0.05 and 0.002 mm in diameter.
Siltation
Deposition of sediments from water in channels, reservoirs and harbours
Sediment
Solid material (predominantly small particles of sand, silt, rock and vegetable material) that have been transported by water and deposited or settled out of suspension.
Sediment delivery ratio (SDR)
SDR is measured as the ratio of gross erosion upstream to the sediment yield at a particular point and measures efficiency of transport and intensity of deposition upstream. Gross erosion is rarely measured and typically sediment yield of hillslope plots is the measure of erosion.
Sediment transport
The entrainment and movement of sediment from its original location after it has been detached from the soil. It is a function of the energy of the flowing water and size of particles; deep, fast flows have a greater capacity to transport sediment, fine particles are moved more easily than larger or heavier ones.
Sediment yield
The amount of material transported past a given point (usually a measuring device in a stream or a point on a hill slope). It is the net result of erosion, transport and deposition upstream or upslope.
Semi-arid zone
Lands where rainfall is too low and unreliable for crops to be grown with certainty.
Sheetwash or surface wash erosion
The removal of a relatively uniform layer of soil by raindrop splash and/or by diffuse surface run-off during intense storms. It occurs on land where soil is not protected by a surface cover such as vegetation.
Soil acidification
A gradual increase in the acidity of a soil as a consequence of a variety of natural processes and management actions.
Sodic soil
Soils containing a high proportion of sodium. Sodic soils cause poor physical conditions for plant growth. They are typically considered unstable and, as a consequence, have high erodibility and often present problems for soil conservation strategies.
Soil creep
Imperceptibly slow but continuous movement or displacement of soil or subsoil, evidenced by leaning trees and fences, and bowed walls.
Soil fertility
The ability of a soil to supply the nutrients essential to plant growth.
Soil organic matter
The organic fraction of the soil. Organic matter does not include undecayed plant and animal residues.
Soil pH
A measure of soil acidity or alkalinity. It is expressed as the negative logarithm of the hydrogen ion activity of a soil—typically between 3.5 and 8.5.
Soil test
A chemical, physical or biological procedure that estimates a property of the soil to gauge its suitablility to support plant growth.
Stocking rate
The number of animals over a specified land area.
Stream bank erosion
The removal of soil from stream banks by the direct action of water in the channel. It typically occurs under high flow conditions by scour and mass failure processes, and particularly by undercutting of the toe of the bank.
Stream link
The division of a river into lengths of stream between tributary junctions.
Surface run-off
Most soil eroded by water is transported downslope by surface run-off.
Terrace
A flat or gently inclined land surface bounded by a steeper ascending slope on its inner margin and a steeper descending slope on its outer margin.
Tillage
Mechanical disturbance of the soil using various implements to alter soil structure. Tillage is usually done to create a seed bed, control weeds or to improve water infiltration into soil.
Turbidity
How clear water is. Water clarity can be affected by suspended and colloidal particles, such as clay and organics.
Universal Soil Loss Equation (USLE)
The USLE (Y) calculates mean annual erosion (tonnes/ha/yr) as a product of: rainfall erosivity factor (R), soil erodibility factor (K), hill slope length factor (L), hill slope gradient factor (S), ground cover factor (C) and land use practice factor (P): Y = R*K*L*S*C*P The precise form of each factor is based on soil loss measurements on hill slope plots, mainly in the USA. Refer to Revised Universal Soil Loss Equation (RUSLE).
Water-repellent soil
Soils, which when dry, do not allow drops of water to spread spontaneously over surfaces and into soil pores.
Waterlogging
The saturation of soil with water; often associated with insufficient oxygen for good plant growth.
Watertable
A surface defined by the level to which water rises in an open well or piezometer.
Woodland
An area with scattered trees, where the portion of land surface covered by the crowns of trees is more than 30% (open woodland), but less than 60% (forest).
Yield
The amount of specified substance produced (e.g.. grain, straw, meat, total dry matter) per unit area.
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