Climate, land and water glossary

Common climate, land and water terms

Many of the terms have links to other terms in this glossary, to help you understand the requirement for technical accuracy. Please enjoy the semantics!

A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z

A

• Absorption: the process where one substance enters the bulk, or volume, of another substance, e.g. a gas absorbed by a liquid. It involves atoms or molecules crossing the surface and entering the volume of the material. As in adsorption, there can be physical and chemical absorption (Chromatography Today 2014)

• Acidity: a measure of how acid is a soil or water. This is used for where the pH is less than 7.0, and the soil or water is termed acid. The lower the pH, the more acid is the sample. See alkalinity.

• Aerenchyma: a spongy tissue spaces or air channels in the leaves, stems and roots of some plants, to allow exchange of gases between the shoot and the root. The channels of air-filled cavities provide a low-resistance internal pathway for the exchange of gases such as oxygen and ethylene between the plant above the water and the submerged tissues. Aerenchyma is also widespread in aquatic and wetland plants which must grow in hypoxic soils (Wikipedia)

• Adsorption: the process where a gas or liquid accumulates on the surface of a liquid or solid, or molecules on a solid. Adsorption can be defined further based on the strength of the interaction between the adsorbent (the substrate onto which chemicals attach) and the adsorbed molecules (Chromatography Today 2014). For instance, clay minerals in the soil are negatively charged and adsorb the positively charged cations aluminium (Al³⁺), calcium (Ca²⁺), magnesium (Mg²⁺), potassium (K⁺) and sodium (Na⁺).

• Aggregates/peds (of soil): aggregations of clay, silt and sand within a soil into larger units. These are the basis of recognised soil structure. Soils that have stable aggregates are generally more productive than soils that have unstable aggregates. Stable aggregates allow movement of air and water to plant roots, can usually store more water, and retain their shape when subjected to rain and traffic.

• Agronomy: the science and technology of producing and using plants for food, fuel, fibre, and land reclamation (Wikipedia).

• Alien: belonging to another place (WAH Glossary)

• Alkalinity: a measure of how alkaline is a soil or water. This is used for where the pH is more than 7.0, and the soil or water is termed alkaline. The higher the pH above 7.0, the more alkaline is the sample. See acidity.

• Allelopathy: the beneficial or harmful effects of one plant on another plant, both crop and weed species, from the release of biochemicals, known as allelochemicals, from plant parts by leaching, root exudation, volatilization, residue decomposition, and other processes in both natural and agricultural systems  (https://edis.ifas.ufl.edu/hs186). Do not confuse this with competition between plants fro water, nutrients or light.

• Aquifer: an underground layer of water-bearing material (sand, fractured rock or other porous material) from which water can be extracted. Aquifers can be:
  confined – groundwater is confined between two impermeable layers
  semi-confined – groundwater is only partially restricted by low-permeability material, and can leak out
  unconfined – groundwater is unrestricted and rises and falls freely
  perched – groundwater sits on top of an impermeable or less permeable layer. Perched systems are often fresh.

• Artesian aquifer: a confined aquifer with a piezometric surface above the ground surface. See artesion pressure .

• Artesian pressure: the hydrostatic pressure in an artesian aquifer measured at the land surface. The pressure causes artesian water to be discharged from a relief well: the higher the piezometric head, the higher the pressure.

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B

• Basal area (ground cover by perennial grasses): in the rangelands, this term is used for the percent of ground covered by the base or butts of perennial tussock grasses. Basal area of tussocks is a consistent way of measuring the health of a tussock grassland from year to year. Tussock bases persist in both drought and good seasons and can be measured (basal cover %) despite being hidden by stems and leaves in good seasons. Foliar cover % varies with seasonal and grazing effects. See projected foliage cover for woody perennials.

• Batter: the sloped sides of a channel. This is usually described with a slope ratio, such as 1:6 (a rise of 1 unit in a lateral distance of 6 units).

• Bedload: sediment that moves along the bed of a drainage line or watercourse by a sliding or rolling action.

• Benthic environment: the habitat at the base of watercourses and waterbodies.

• Berm: a flat strip of land, on a raised bank or terrace, bordering a waterway or drainage channel. A berm is usually constructed to allow vehicle access. See levee.

• Bore: a hole drilled in the ground, with a bore casing that allows water inflow at the slotted end of the casing. Bores can be used to monitor groundwater, siphon water, act as a relief well, or be pumped to lower watertables or supply water for livestock, irrigation or domestic use. Bores to monitor groundwater can be observation wells (to monitor watertables in unconfined aquifers) or piezometers (to monitor hydraulic head in confined or semiconfined aquifers).

• Breakaway: a short scarp or cliff caused by erosion of an ancient land surface. Breakaways are scattered through the arid shrublands (rangelands) and erosional lateritic landscapes in the south-west of Western Australia.

• Bund: a secondary enclosure, of a wall or berm, to contain or redirect spills, leaks or overflows. See levee. Bunds can be used to separate and redirect saline inflows to lakes and other water bodies.

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C

• C3 plants: plants that produce a 3–carbon compound as the first stable product in the second phase of photosynthesis (the light-independent or dark reaction pathway). Most plants are C3 plants. An example is wheat.

• C4 plants: plants that produce a 4–carbon compound as the first stable product in the second phase of photosynthesis (the light-independent or dark reaction pathway). C4 plants – compared to C3 plants – have higher photosynthetic efficiency, have a higher optimal temperature, have higher water use efficiency at high temperatures. An example is sugar cane.

• Carrying capacity: the number of grazing units a paddock or management area can carry over the long term while maintaining or improving land condition. In the agricultural areas, this is usually expressed as dry sheep equivalents per hectare (DSE/ha), or DSEs per winter grazed hectare in mixed farming systems. Carrying capacity can be estimated from the quantity and quality (ideally in megajoules of metabolisable energy) of available forage in a given period. See the rangelands glossary for potential and present carrying capacity.

• Catch drain: a term used in raised bed systems to describe a drain that receives all the discharge from raised bed furrows. Catch drains discharge in waterways. Sometimes called a tailwater drain in irrigated agriculture.

• Cation exchange capacity (CEC; soil): the amount of positive charge that can be exchanged per mass of soil, usually measured in centimoles of charge per kilogram (cmolc/kg). Some texts use the older, equivalent units as milliequivalents per 100 grams (me/100g or meq/100g). CEC is measured in moles of electric charge, so a cation exchange capacity of 10cmolc/kg could hold 10cmol of sodium (Na+) cations (with 1 unit of charge per cation) per kilogram of soil, but only 5cmol of calcium (Ca2+) cations (2 units of charge per cation) (Wikipedia).

• Cattle unit (CU): this term is mostly used in the pastoral areas, and is based on the energy intake of 64 MJ ME/day to maintain a 450kg Bos taurus steer 2.25 years of age, walking 7 kilometers each day (Petty et al 2018, McLennan et al 2020). This is the equivalent of consuming an average of 8 kg dry matter per day, or 2920 kg of dry matter per CU per year (approximately 1.8% of body weight), of pasture averaging 7.75 megajoules of metabolisable energy per kilogram of dry matter (MJME/kgDM). This equates to 2920 kg DM/CU/yr.
  This is the same definition as an Animal Equivalent (AE), a term used by some other Australian States. The unit is used (1) to compare the feed requirements of different classes of livestock; (2) to assess the carrying capacity, stocking rate and potential productivity of a given area of grazing land.
  Based on the standard animal energy requirements, one CU is equal to 7.4 dry sheep equivalents (DSE): 64 MJ ME/day compared to 8.7 MJ ME/day. See Livestock comparisons for estimating grazing pressure in the rangelands for more detail.

• Cell or mob grazing: short duration, high density grazing with a longer than usual grass recovery period. These grazing systems are similar to rotational grazing, but are more intensive and involve more paddocks or 'cells'. The duration is regulated by feed on offer (FOO): grazing is usually between an upper and lower FOO value in kg DM/ha. The density (stocking rate) is usually determined by the need to have non-selective grazing by livestock.

• Chenopod: low shrub member of the family Chenopodiaceae, such as saltbush, bluebush, and samphire. Chenopods are common in the arid shrublands, around saltlakes and low-lying saline areas. The plants are usually palatable to livestock, and have a high salt content.

• Chill factor (plants): a requirement for a period of low temperatures to trigger particular plant development processes. Also known as vernalisation, and is common for many fruit crops.

• Chill units (plants): the units used to express the amount of chilling required to trigger particular plant development processes, such as germination or fruit set.
  All models for calculating chill units are based on hourly temperature records. There are different measures of chill factor, such as chill hours of Richardson units: a chill unit taking into account the nonlinear response to temperature by plants. A temperature of 4 degrees Celsius (ºC) for 1 hour produces 1 Richardson chill unit, which is the maximum chilling that can occur in 1 hour. Richardson chill units are calculated on an hourly basis and summed for the winter to provide an estimate of the amount of chilling affecting plants. In some models, there is an allowance for the negation of accumulated chill units that can occur when daily maximum temperatures go above 14ºC (Hortplus).

• Climate: the atmospheric conditions for a long period, and generally refers to the normal or mean course of the weather. Includes expectation of long-term weather, in the order of weeks, months or years ahead.

• Climate change: in recent times, the term has been used to mean the greenhouse effect, or global warming. Global climate varies naturally over a wide range of time scales for a variety of physical reasons. Recent use of the term assumes global temperatures moving to a new warmer equilibrium in response to a changing radiation balance, with attendant changes in regional climate.

• Compaction (soils): the process where soil grains are pushed closer together, displacing air and water. The result is higher-density soil, lower water-holding capacity, and poor plant root-growth conditions. Compaction can result from machinery and livestock pressure.

• Competent soils: resist settlement and compaction.

• Contour: a line on a map marking points that are of equal heights above sea level.

• Control measure: procedures designed to minimise the severity of erosion and sedimentation.

• Crop lower limit (soil): the extent to which a particular crop can extract water from a particular soil type – the minimal point of soil moisture the plant requires to not wilt. If moisture decreases to this or any lower point, a plant wilts and can no longer recover its turgidity when placed in a saturated atmosphere for 12 hours.
  Crops differ in their ability to extract water, determined by the length, density and osmotic potential of their roots, the duration of their growth, and their susceptibility to subsoil constraints.
  A theoretical lower limit can be measured in the laboratory equilibrating the soil at 1500 kilopascals (kPa) or 15 bar suction. Crops can vary greatly in their ability to extract water, and may be quite different to the 1500kPa value, especially at depth (APSIM).

• Cross drain: a term used in raised bed systems to describe a short drain to remove water ponding in raised bed furrows, where ponding is caused by small rises blocking flow. Cross drains discharge into catch drains.

• Crusting: sealing of the soil surface to form a protective layer against soil erosion, and may also reduce water infiltration and prevent germinated seeds from emerging.

• Cryptogamic crusts: a fragile, biological soil surface crust – found in arid and semi-arid environments – comprised of plants that have no true flowers or seeds, including ferns, mosses, liverworts, lichens, algae (cyanobacteria), and fungi (all cryptogams). Cryptogamic crusts protect the soil from erosion, provide nitrogen from cyanobacteria, and influence local water movement (hydrophobic when completely dry, then gradually absorbent).

• Cyclone (tropical): an intense low pressure system that forms over warm ocean waters at low latitudes. Tropical cyclones are associated with strong winds, torrential rain and storm surges (in coastal areas). Tropical cyclones can cause extensive damage because of the strong wind, flooding (caused by either heavy rainfall or ocean storm surges) and landslides in mountainous areas as a result of heavy rainfall and saturated soil. Tropical cyclones are also known (in other parts of the world) as tropical storms. If they attain maximum mean winds above 117 kilometres per hour (63 knots) they are called severe tropical cyclones. In the northwestern Pacific, severe tropical cyclones are known as typhoons and in the north-east Pacific and Atlantic/Caribbean they are called hurricanes.

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D

• Deep cultivation (of soils): any lifting, ripping, mixing or inversion of soils to greater than 20cm deep. In recent years, deep cultivation has moved from 20cm with discs, to 30cm with spading, to 60cm with delving, and over 60cm with single- or double-tyne rippers. Deep cultivation can be used to treat compaction, water repellence, acid subsoils (with lime incorporation), and dispersive soils (with gypsum incorporation).

• Deep drains (in agriculture): in most cases are more accurately termed groundwater drains, are deep excavated channels with sloping floors (on a grade) and sides, designed to intercept and drain groundwater (usually saline in Western Australia). Drains that are deep, drain surface water and do not drain groundwater, may not be notifiable under the Soil and Land Conservation Regulations 1992. Where watertables are within the rooting zone of plants, groundwater drains can be used to reduce waterlogging. See groundwater drains,  open deep drains and leveed deep drains.

• Delving (soil): the process of ripping deep into the soil profile and pulling up the clay-rich subsoil, incorporating it into the sandy surface soil. Delving uses specially designed rippers. Recommended where the subsoil is within 30–60cm of the surface. See spading.

• Denitrification: a microbially facilitated process where nitrate is reduced and ultimately produces nitrogen gas released to the atmosphere.

• Detention basin or structure: a structure that temporarily stores large volumes of water after a storm, which is designed to drain away at a controlled rate, to have the capacity to be ready for the next event. This is usually achieved by having an outflow point at the same level as the base of the structure that limits outflow. Detention structures are used to manage large inflows and regulate outflows to minimise downstream damage.

• Dioecious (plants): having the male and female reproductive parts on separate plants. This means that male (staminate) and female (carpelate) plants must be in proximity to produce fertile seed. See monoecious.

• Discharge (hydrology): the outflow of water from any body of water, such as a lake or aquifer. In Western Australia, the term is often used to mean the discharge of water (often saline) to the ground surface from an aquifer. See recharge for the other end of the process.

• Dispersity: the tendency of the clay fraction in a soil to go into colloidal suspension in water.

• Dispersive soils: soils in which the clay component disperses in water (a suspension of clay particles). When dry, these soils tend to form large cracks at the surface and usually appear grey and massive (little soil structure); when wet, these soils swell to some extent, and cracks and channels close and become hard for plant roots to penetrate. Dispersive soils are nearly always sodic soils that do not have conditions that limit dispersion. Dispersion of sodic soils is prevented by saline conditions. See sodic soils.

• Drained upper limit (soil): the amount of water that a particular soil holds after drainage has practically ceased. It is water held against gravity, and may be removed only by plants or direct evaporation. This replaces the term field capacity (APSIM).

• Drop structure: a structure allowing water to fall from one level to another, normally including an inlet, a drop and an outlet. Depending on the expected velocity, the outlet may incorporate an energy dissipater.

• Drought: a prolonged absence or marked deficiency of precipitation, usually over a period of months or years. Drought in general means acute water shortage, including above ground storage, soil water availability and groundwater depth. The term is also used in policy and legislation, with particular implications.

• Dryland salinity: saltland that develops in non-irrigated rain-fed systems. See irrigation salinity.

• Dry matter content (feedstuffs): a measure of the percentage of dry material in a feedstuff as fed. This measure is used to compare more accurately the value of feeds of different moisture content.

• Dry sheep equivalent (DSE): 1 DSE is based on the feed energy of 8.7 MJ ME/day required to maintain a 45 kilogram liveweight Merino wether with zero weight change, no wool growth additional to that included in maintenance, and walking 7 km/day (Petty et al 2018, McLennan et al 2020). DSEs can be used for small livestock types and classes, and cattle units (CU) are preferrred for cattle. See cattle unit.

• Duplex soil: also known as texture-contrast soils, where a sandy surface layer changes abruptly to a more clayey layer beneath. These soils are susceptible to waterlogging, and erosion when the surface soil is exposed and detached.

• Dykes (geology): a vertical sheet intrusion of rock through older rock. Dolerite dykes through granites are common in Western Australia. When weathered, these mafic dykes form red-brown, clay-rich soils that can act as barriers to aquifer flow.

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E

• Earth tanks: an earth structure on near-level land used to store water, in which part of the storage capacity is below ground level. On sloping land, the tank is often called a hillside dam or just a farm dam. The excavation can be rectangular or square – with 3 or 4 walls – or circular.

• Ecologically sustainable development (ESD): in the Australian Government's Environment Protection and Biodiversity Conservation Act 1999, ESD is based on the following principles:

  • decision‑making processes should effectively integrate both long‑term and short‑term economic, environmental, social and equitable considerations

  • if there are threats of serious or irreversible environmental damage, lack of full scientific certainty should not be used as a reason for postponing measures to prevent environmental degradation

  • the principle of inter‑generational equity – that the present generation should ensure that the health, diversity and productivity of the environment is maintained or enhanced for the benefit of future generations

  • the conservation of biological diversity and ecological integrity should be a fundamental consideration in decision making

  • improved valuation, pricing and incentive mechanisms should be promoted.

• Ecosystem services: are the benefits provided to humans through the transformations of resources (or environmental assets, including land, water, vegetation and atmosphere) into a flow of essential goods and services, e.g. clean air, water, and food (Department of the Environment and Energy).

• Edaphic: abiotic factors relating to the physical or chemical composition of the soil found (Encyclopedia.com). This includes factors such as drainage, physical and chemical barriers to root growth, soil pH and salinity.

• Electrical conductivity (EC – soil and water): Water and soil salinity can be estimated by passing an electric current between the two electrodes of a salinity meter in a sample of soil or water. Salts increase the ability of a solution to conduct an electrical current, so a higher EC value indicates a higher salinity level.
  EC units are commonly used as a 'measure' of salinity. See salinity.

• El Niño: in Australia (particularly eastern Australia), El Niño events are associated with an increased probability of drier conditions. The impact is often weaker over Western Australia, though El Niño reduces the chances of above-average winter and spring rainfall. Extensive warming of the central and eastern Pacific Ocean leads to a major shift in weather patterns across the Pacific. For more information, see Australian Climate Influences. See La Niña.

• Embankment: a long artificial mound of earth to hold back water or as protection from flooding. See levee, bund, or berm.

• Emerson class number: a soil classification system based on a soil's coherence in water.

• Endemic: having a natural distribution confined to a particular geographical region.³ See native.

• Energy dissipater: a device located usually at the outlet of pipes, spillways or drop structures for the purpose of interrupting discharged flows, dissipating their excess energy and thereby reducing the erosion potential.

• Engineering works: process of mechanically altering or seeking to manage lands and all they contain, using machinery, banks, drains, wells and other structures.

• Erosion (soil): the process by which soil particles are detached and moved from the land surface (usually called soil erosion) by the action of wind (usually called wind erosion) or water (usually called water erosion). Natural erosion occurs in undisturbed natural environments, and is usually a very slow process. Accelerated erosion occurs in disturbed environments, often resulting from human influence on soil, vegetation or landforms.

• Erosion risk assessment: the process of identifying the potential for adverse erosion effects.

• Eructation: belching or burping. Ruminants release significant quantities of methane through eructation.

• Eutrophication: enrichment of waterways with nutrients causing excessive growth of plants and algae. This process may lead to oxygen depletion and fish kills (Wikipedia).

• Evaporation: the process of turning a liquid into a vapour or gaseous state. Water on a surface can evaporate leaving any dissolved or suspended material on the surface.

• Evapotranspiration: the sum of evaporation and plant transpiration.

• Excavated tanks: see earth tanks.

• Exchangeable sodium percentage (ESP): the relative amount of the sodium ion present on the soil particle surfaces, expressed as a percentage of the total cation exchange capacity. See sodic soil.

• Exotic (plant): introduced from outside the area concerned (NSW Flora Glossary)

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F

• Feed On Offer (FOO): 'is the amount of pasture in a paddock at any given time, measured in kilograms of dry matter per hectare (kg DM/ha). FOO required to achieve production targets are available for different types of livestock. FOO levels can also be used to manage pasture composition and growth rate, ensure environmental protection and enhance pasture persistence. The appropriate FOO targets for a farm depends on the class of stock, production requirements and balancing the objectives for animals, pastures and environmental protection.' (AWI)

• Field capacity (soil): this term has been replaced by drained upper limit. See water holding capacity and plant available water.

• Filter fabric: synthetic material designed to allow water to pass through, but not soil particles, with the size of particle held back dependent on the fabric mesh size.

• Flatulence: release of gas from the bowel. Flatulence often contains some methane.

• Flocculation (soil): the process by which individual particles of clay in suspension aggregate into clumps or precipitate as a result of a chemical reaction between the clay particles and another substance, usually salt water. In water, flocculation results in the water changing from cloudy to clear.

• Flooding: water flowing outside its usual channel. Flooding can have short-term or long-term consequences: erosion, inundation, infrastructure damage, threats to human welfare. See inundation.

• Floodplain: an area close to a river that becomes flooded when the river rises after heavy rains. These areas are usually relatively fertile because of sediment deposition.

• Frost: a deposit of soft, white ice crystals or frozen dew drops on objects near the ground, formed when surface temperature falls below freezing point. In the Western Australian grainbelt, frost occurs on clear nights in early spring when the air temperature drops to 2°C or less. Crop damage from frost may occur at any stage of development, but is most damaging at or around flowering. All winter grain and oilseed crops are susceptible to frost.

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G

• Gabion: a purpose-built rectangular box made from steel wire mesh with wire crossties, into which rocks are placed. Gabions are used to stabilise embankments.

• Gilgai microrelief (soils): mounds and depressions on the soil surface associated with clays that shrink and swell. These formations are also called crabholes or melonholes, and can be circular, subcircular, linear or contoured.

• Global warming potential: the global warming potential of greenhouse gases is expressed in terms of how much carbon dioxide would be required to produce a similar warming effect over 100 years. This is termed the carbon dioxide equivalent value (CO₂-e).

• Grade bank: a drain – constructed with a channel and a downhill bank – running with a fall of a few degrees off a contour. Grade banks are a surface water management structure to reduce water erosion and to collect water.

• Grass: a plant belonging to the family Poaceae (NSW Flora Glossary)

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• Grassed waterway: a natural or constructed grassland strip to allow safe movement of surface water across the natural landscape, handling discharge from dams, the end of grade banks and other surface water disposal structures. Designed to minimise water erosion (Wikipedia).

• Grazing pressure: a relationship between animal demand for pasture forage and pasture forage supply over a given period; the number of livestock units grazing an area in relation to the forage supply (or available forage). If grazing pressure is high, demand is greater than supply, and pasture dry matter will decrease.

• Grazing systems: specialised forms of grazing management which defines the stocking rates and livestock movements, the periods of grazing and non-grazing (rest). Take care in using or applying these terms, as casual use often combines systems under one name. See set stocking; rotational grazing; cell grazing and tactical grazing.

• Greenhouse effect: a natural warming process of the earth. When the sun's energy reaches the earth, some of it is reflected back to space and the rest is absorbed. The absorbed energy warms the earth's surface, which then emits heat energy back towards space as longwave radiation. This outgoing longwave radiation is partially trapped by greenhouse gases, such as carbon dioxide, methane and water vapour, which then radiate the energy in all directions, warming the earth's surface and atmosphere. Without these greenhouse gases, the earth's average surface temperature would be about 33°C cooler. The main cause of atmospheric warming in recent decades is anthropogenic emissions of gases such as carbon dioxide and methane.

• Greenhouse gas: a gas that contributes to the greenhouse effect by absorbing infrared radiation and heating the atmosphere. Greenhouse gases include water vapour, carbon dioxide, methane, nitrous oxide, ozone and some artificial chemicals, such as chlorofluorocarbons (CFCs).

• Greenhouse gas emissions scenarios: from the Climate Change in Australia website. The climate modelling community has developed Representative Concentration Pathways (RCPs) to explore credible future options. The Australian climate change projections found on this site are derived from climate models forced by the RCPs. RCPs are prescribed pathways for greenhouse gas and aerosol concentrations, together with land use change, that are consistent with a set of broad climate outcomes used by the climate modelling community.
  There are 4 RCPS:

  • RCP8.5 – a future with little curbing of emissions, with a carbon dioxide (CO₂) concentration continuing to rapidly rise, reaching 940 parts per million (ppm) by 2100.

  • RCP6.0 – lower emissions, achieved by application of some mitigation strategies and technologies. CO₂ concentration rising less rapidly (than RCP8.5), but still reaching 660ppm by 2100 and total radiative forcing stabilising shortly after 2100.

  • RCP4.5 – CO₂ concentrations are slightly above those of RCP6.0 until after mid-century, but emissions peak earlier (around 2040), and the CO₂ concentration reaches 540ppm by 2100.

  • RCP2.6 – the most ambitious mitigation scenario, with emissions peaking early in the century (around 2020), then rapidly declining. Such a pathway would require early participation from all emitters, including developing countries, as well as the application of technologies for actively removing carbon dioxide from the atmosphere. The CO₂ concentration reaches 440ppm by 2040, then slowly declines to 420ppm by 2100).
    
    Note: RCPs are radiative forcing values found in the open literature, from 2.6 to 8.5 Watts per square metre (W/m²).

• Greenness index: also known as the Normalised Difference Vegetation Index (NDVI), is derived from satellite data. 'Live green vegetation absorbs visible light (solar radiation) as part of photosynthesis. At the same time plants scatter (reflect) solar energy in the near infrared. This difference in absorption is quite unique to live vegetation and provides a measure of the greenness of the vegetation. NDVI is an index which measures the difference between near-infrared (which vegetation strongly reflects) and red light (which vegetation absorbs), providing a measure of vegetation density and condition. See Normalised Difference Vegetation Index (Bureau of Meteorology).

• Groundwater: water that is located below the earth's surface. Over time, water from rain and rivers migrates through the ground and is stored in porous soils and rocks. The study of groundwater is known as hydrogeology (NCST 2009). Groundwater is accessible via bores, springs and wells. Water flows from recharge to discharge areas by gravity. Groundwater can be in aquifers that vary in scale from local to regional. Groundwater quality varies from fresh to hypersaline. Groundwater chemistry is influenced by geology and use, and varies between regions.

• Groundwater drains: any drainage system that intersects and removes groundwater. This can include open deep drains, leveed deep drains, mole drains and tile drains. 'When an owner or occupier of land proposes to drain or pump water from under the land surface because of the salinity of the land or the water and to discharge that water onto other land, into other water or into a watercourse, the owner or occupier shall, at least 90 days before the draining or pumping commences, notify the Commissioner in writing in a form approved by the Commissioner.' (Soil and Land Conservation Regulations 1992.)

• Growing season (south-west Western Australia): this term is based on winter rainfall in the Mediterranean climate of south-west Western Australia, and usually refers to the growth of annual crops and pastures.
  For the break of season, we use the FAO (Food and Agriculture Organization of the United Nations) crop factor method, estimated using a two-part rule, such that germination is assumed to occur if there is 25 millimetres (mm) of rainfall over 3 days after 25 April and before 5 June, and 5mm of rainfall over 3 days after 5 June.
  The beginning and end of a growing season are determined by plant available water, and therefore soil type has an influence.

• Gully: an open depression with short, precipitous walls and a moderately inclined floor or small stream channel, eroded by channelled stream flow with consequent collapse and water-aided mass movement (NCST 2009)

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H

• Hail: precipitation (falling) of particles of ice (hailstones). Hail can be spheroid, conical or irregular in form, and with a diameter generally varying between 5 and 50mm. Hail either falls from clouds separately or collected into irregular lumps. Hail is commonly formed in severe thunderstorms that generate sustained updrafts to support ice formation.

• Halophyte: a plant adapted to living in highly saline habitats; a plant that accumulates high concentrations of salt in its tissues. –halophytic, adj. (WA Herbarium Glossary).

• Hardpan: a hard layer in a soil horizon that is relatively impermeable to water or root movement. Hardpan layers can be formed by physical (traffic compaction, cultivation particle sorting) or chemical (silica, iron oxides, calcium carbonate) means.

• Herb: a plant that is non-woody or woody at the base only, the above ground stems usually being ephemeral. –herbaceous, adj.³

• Hydraulic conductivity (of a saturated soil): see soil permeability.

• Hydrograph: a graph of measured depth to water in a bore (observation well or piezometer) over time.

• Hydromulching: applying mulch, with or without seed and fertiliser, using a machine termed a hydromulcher. The hydromulcher sprays the mulch in slurry form under high pressure.

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I

• Inundation: where the soil surface or plants are completely covered by water. The effect on plant growth is severe because inundated plants cannot photosynthesise. Inundated soils are frequently also waterlogged.

• Irrigation: water from a source other than rain, applied to land or crops to improve plant growth. The water is typically moved through channels or pipes, and applied through sprinklers, drippers or flooding. See reticulation.

• Irrigation salinity: salinisation caused by concentration of salts in soil from irrigation water. The process is caused by evaporation or evapotranspiration of water, leaving salts in the root zone or on the surface.

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L

• Land conservation district (LCD): community groups constituted under section 22(1) of the Soil and Land Conservation Act 1945; comprise pastoral leasehold land, defined conservation areas (which may have formed part of the pastoral estate prior to declaration as conservation areas) and unallocated Crown land (UCL).

• Land degradation: includes soil erosion, salinity, eutrophication, flooding and the removal or deterioration of natural or introduced vegetation, that may be detrimental to the present or future use of land (adapted from the Soil and Land Conservation Act 1945). There is no definition of the term in the Environmental Protection Act 1986 or the Land Administration Act 1997.
  Most other definitions are based on human-induced or human-influenced change in the capacity for present or future use of that land:
  • changes that are additional to those occurring naturally and carries with it the notion of change that is undesirable and brought about by humans (The Australian Collaboration)
  • deterioration in the quality of land, its topsoil, vegetation, and/or water resources, caused usually by excessive or inappropriate exploitation (Business Dictionary)
  • the temporary or permanent decline in the productive capacity of the land, and the diminution of the productive potential, including its major land uses (e.g. rain-fed arable, irrigation, forests), its farming systems (e.g. smallholder subsistence), and its value as an economic resource (International Encyclopedia of the Social & Behavioral Sciences in Science Direct)
  • the loss of the economic and biological productivity of land, primarily through human activities (Enviropaedia)
  • the decline in quality of natural land resources, commonly caused through improper use of the land by humans (Soil Conservation Service NSW)
  • the many processes that drive the decline or loss in biodiversity, ecosystem functions or their benefits to people and includes the degradation of all terrestrial ecosystems (Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES))
  • a process in which the value of the biophysical environment is affected by a combination of human-induced processes acting upon the land. It is viewed as any change or disturbance to the land perceived to be deleterious or undesirable (Wikipedia).

• Landscape function analysis (LFA): a monitoring procedure that uses rapidly acquired field-assessed indicators to assess the biogeochemical functioning of landscapes at the hillslope scale.

  The procedure has been applied in natural landscapes and those rehabilitated after mining, in climatic regimes ranging from the arid zone (150mm annual rainfall) in Australia to tropical rainforest near the equator in Indonesia (4000mm annual rainfall) and in land uses ranging from traditional rangelands through mining to conservation of biodiversity.

  It uses visually assessed indicators of soil surface processes that gauge how effectively a hillslope is operating as a biophysical system. It is the synthesis of much published material from a variety of sources and is based mainly on processes involved in surface hydrology: rainfall, infiltration, run-off, erosion, plant growth and nutrient cycling. It is comprised of 4 components:
  A    a conceptual framework
  B    a field data acquisition
  C    a data reduction and tabulation
  D    an interpretational framework
  (Tongway & Hindley 2005).

• La Niña: La Niña occurs when equatorial trade winds become stronger, changing ocean surface currents and drawing cooler deep water up from below. This results in a cooling of the central and eastern tropical Pacific Ocean. The enhanced trade winds also help to pile up warm surface waters in the western Pacific and to the north of Australia. The warming of ocean temperatures in the western Pacific means the area becomes more favourable for rising air, cloud development and rainfall. As a result, heavy rainfall can occur to the north of Australia (Bureau of Meteorology).
  In Western Australia, La Niña can mean a reduced chance of having a dry winter. For more information, see Australian Climate Influences.

• Leaching: movement of water and soluble material below the root zone of plants. Leaching can result from heavy rainfall or from excess irrigation, and can result in groundwater recharge and possibly contamination, loss of plant nutrients, and increased soil acidification.

• Levee: a ridge of earth or embankment to prevent floodwater moving across the landscape. Often used on one or both sides of waterways and drainage lines. See berm, bund, embankment.

• Leveed deep drain: (in agriculture): in most cases are more accurately termed groundwater drains, are excavated channels with sloping floors (on a grade) and sides, and levees on one or both sides. They are designed to intercept and drain groundwater, which is usually saline in Western Australia. These drains are most effective where the channel is dug into a watertable in soils that allow good lateral drainage. Where watertables are within the rooting zone of plants, groundwater drains can be used to reduce waterlogging.

• Level bank: a sediment trap formed by constructing an earth channel with a downhill bund, on the contour. These are sometimes constructed below breakaways to slow the rapid run-off on bare clay surfaces. Level banks need a safe, level overflow.

• Logger: a device – usually electronic – used to capture measurements over time. Loggers are often attached to or have inbuilt sensors to enable measurement of specific properties, such as water level, soil moisture, temperature, or rainfall.

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M

• Massive (soil structure): where the entire soil horizon appears cemented in one great mass.

• Mediterranean climate: characterised by cool, wet winters (June to August in Western Australia) and warm to hot dry summers (December to February in Western Australia).

• MODIS (Moderate Resolution Imaging Spectroradiometer): 'is a key instrument aboard the Terra (originally known as EOS AM-1) and Aqua (originally known as EOS PM-1) satellites. Terra's orbit around the Earth is timed so that it passes from north to south across the equator in the morning, while Aqua passes south to north over the equator in the afternoon. Terra MODIS and Aqua MODIS are viewing the entire Earth's surface every 1 to 2 days, acquiring data in 36 spectral bands, or groups of wavelengths' (NASA MODIS). The data is recorded in pixels of 250 x 250m (6.25 hectares).

• Monoecious (plants): male and female reproductive parts are on the same plant. This can be as separate male (staminate) and female (carpelate) flowers, or as 'perfect' flowers with stamens and carpels in the same flower. Monoecious plants are self-fertile. See dioecious.

• Mulching: the application of plant residues or other suitable materials to the land surface to conserve moisture, hold soil in place, aid in establishing plant cover, increase infiltration, and minimise soil temperature fluctuations.

N

• Native: naturally occurring in the area, but not necessarily confined to it.⁴ See endemic.
• Naturalised: originating elsewhere but established and reproducing itself as though native to the area.⁴
• NDVI (Normalised Difference Vegetation Index): see Greenness index.

O

• Observation well: a bore with slotted casing from the bottom of the bore to above the watertable, and is not sealed above the slotted section, except for a collar at the surface to prevent water flowing into the drilled hole. Observation wells are suited to measure depth to the watertable in unconfined aquifers.

• Open deep drain: (in agriculture): in most cases are more accurately termed groundwater drains, are deep excavated channels with sloping floors (on a grade) and sides, designed to intercept and drain surface water (usually fresh) and groundwater (usually saline in Western Australia) from both sides of the drain. These drains are most effective where the channel is dug into a watertable in soils that allow good lateral drainage. Where watertables are within the rooting zone of plants, groundwater drains can be used to reduce waterlogging.

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P

• Palaeochannel: a remnant of an inactive river or stream channel that has been filled or buried by younger sediment. In Western Australia, these channels are often filled with sandy sediments, act as aquifers, and may be artesian. The sandy infill is usually covered by heavier textured soils, and may be confined or semi-confined. Palaeochannel aquifers are generally saline east of the Meckering fault line, and fresh to brackish west of the Meckering fault line.

• Permanent wilting point: this term has been replaced by crop lower limit.

• pH: a unit of acidity or alkalinity of a solution, on a logarithmic scale of hydrogen ions, on which 7 is neutral, lower values are more acid (down to pH 1) and higher values more alkaline (up to pH 14). The pH is equal to −log10 c, where c is the hydrogen ion concentration in moles per litre.

• Phosphorus buffering index (PBI): the agreed Australian measure to estimate how strongly a soil will retain phosphorus (P), and reflects soil type. PBI is used with the Colwell P test to determine a soil's phosphorus status.⁵

• Phosphorus retention index (PRI): a direct measure of P-sorption by a soil. A given quantity of soil is mixed in a solution with a single amount of phosphorus for a set period. The amount of phosphorus remaining in solution measures the soil’s ability to fix phosphorus. This measure has been replaced in Australia by the phosphorus buffering index (PBI).

• Piezometer: measure the pressure (sometimes referred to as hydraulic head or piezometric head) of the groundwater over a specific portion of a confined or semi-confined aquifer. An observation well only measures depth to the watertable. Piezometers are slotted over only a short section below the watertable, within the aquifer. The borehole is sealed directly above the slotted section, usually with bentonite clay and this arrangement allows measurement of groundwater pressure at the slotted interval. Assess vertical groundwater gradients and flow directions using multiple piezometers at and across a site.

• Piezometric head: the elevation to which water will rise in a piezometer connected to a point in an aquifer.

• Piezometric surface (potentiometric surface): the surface of piezometric head at all points in a given aquifer.

• Plant available water (PAW): the volume of water stored within a soil that is available to the plant at a point in time. It is the difference between the current volumetric soil water content (mm water / mm of soil) and the crop lower limit within a given rooting depth. Note that the actual plant available water in dryland systems is less than PAWC, and is dependent on rainfall, and abiotic edaphic factors – the soil may not be at its drained upper limit, soil texture may limit movement of water to the roots, and chemical and physical barriers may limit root development to make use of soil moisture.

• Plant available water capacity (PAWC): the difference between a soil's water content at the drained upper limit and the crop lower limit within a given rooting depth.

• Ponding: usually refers to limited low-lying areas filling with water, as in a pond. This is most common on clay soils, or water repellent soils on flat land or land with very low slope.

• Precautionary principle: The Precautionary Principle is defined by UNESCO as follows:
  When human activities may lead to morally unacceptable harm that is scientifically plausible but uncertain, actions shall be taken to avoid or diminish that harm. Morally unacceptable harm refers to harm to humans or the environment that is:
  • threatening to human life or health, or
  • serious and effectively irreversible, or
  • inequitable to present or future generations, or
  • imposed without adequate consideration of the human rights of those affected.
  
  The judgement of plausibility should be grounded in scientific analysis. Analysis should be ongoing so that chosen actions are subject to review. Uncertainty may apply to, but need not be limited to, causality or the bounds of the possible harm.
  Actions are interventions that are undertaken before harm occurs that seek to avoid or diminish the harm. Actions should be chosen that are proportional to the seriousness of the potential harm, with consideration of their positive and negative consequences, and with an assessment of the moral implications of both action and inaction. The choice of action should be the result of a participatory process (UNESCO COMEST report The precautionary principle).

• Precision agriculture: anything that producers use to make their work more accurate at a fine scale. Precision agriculture requires large amounts of data on crop or animal performance, and the attributes of individual production areas (for example, paddocks) at a high spatial resolution. Technology to collect and make use of that data includes global positioning systems (GPS), geographic information systems (GIS), yield monitors, soil sensors, various remote sensing systems, and variable rate machinery.

• Primary salinity: saltland caused by natural processes, and present in the environment before human land-use change. In Western Australia, strings of salt lakes existed before agricultural development.

• Projected foliage cover: the percentage of ground area occupied by the vertical projection of the foliage of woody vegetation (works best on fairly dense shrubs and trees). See basal area for perennial tussock grasses.
  Other terms used for this are: projected crown cover, canopy cover, foliar cover, and cover.

• Putrefaction: the process of anaerobic breakdown by bacteria or algae. In dams, organic materials provide ideal food for bacteria and algae. These organisms grow rapidly, using up all the free oxygen in the water, creating anaerobic conditions leading to putrefaction. Signs of putrefaction are dark water, a bad smell and black scum around the edge of the dam. See eutrophication.

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R

• Rainfall erosivity: a measure of the ability of rainfall to cause erosion and is dependent on total energy and rainfall intensity.

• Rainfall intensity: a measure of the amount of rain falling over a reference period, usually hours or minutes. Different periods are used for different design and impact assessment needs.

• Rainfall zones (south-west Western Australia): the most widely used classification is from the crop variety testing program zones, and is based on average annual rainfall isohyets and the length of growing season for cereal crops. Growing season for annuals is largely a function of rainfall (amount and timing), temperature and evaporation demand.
  Very high rainfall zone: >750mm
  High rainfall zone: <750mm – 450mm
  Medium rainfall zone: <450mm – 325mm
  Low rainfall zone: <325mm

• Raised bed system (agriculture): where soil has been pushed from a series of furrows, into beds of soil sitting above the usual ground surface. Raised beds are used to increase rooting depth above saturated (waterlogged) soil. Water is removed from the furrows by connecting drains that lead to a safe discharge point: usually a natural drainage line.

• Rational method: a probabilistic method of estimating the design peak flows from a given catchment area.

• Recharge: the process of infiltration of water into an aquifer – this may be fast in permeable soils and areas where macroporosity is high, such as cracks and fractures in soil and rocks. See discharge for the other end of the process.

• Regenerative agriculture (RA): the application of techniques which seek to restore landscape function and deliver outcomes that include sustainable production, an improved natural resource base, healthy nutrient cycling, increased biodiversity and resilience to change.
  Wikipedia has the definition 'Regenerative agriculture (RA) is an approach to food and farming systems that rejects pesticides, artificial fertilizers and aims to regenerate topsoil, increase biodiversity, improve water cycles, enhance ecosystem services, increase resilience to climate fluctuation and strengthen the health and vitality of farming and ranching communities.' There are other definitions and various principles and practices that contribute to RA.

• Relief well or bore: a free-flowing groundwater bore with discharge driven by artesian pressure. Such a bore allows groundwater to flow continuously up to the surface by the release of confined pressure stored within the aquifer at depth. This artesian pressure is renewed by a percentage of rainfall that infiltrates into the soil profile (at higher elevation) and recharges the deeper aquifers.

• Resilience: the capacity to recover from or adjust to shocks or changes to a system. Community resilience is the ability use available resources to respond to, withstand and recover from adverse situations. This allows for adaptation and growth after emergency incidents. Ecological resilience is the capacity of an ecosystem to respond to changes and disturbances, yet retain its basic functions and structures (Australia's Biodiversity Conservation Strategy 2010–2030).

• Retention basin or structure: a basin or structure for collecting and retaining water. This is usually achieved by having an outflow point above the base of the structure. Retention structures, such as dams and earth tanks, are used to collect inflow water for other uses. 

• Reticulation (water): a structure of pipes to move water from a source to a delivery system. In agriculture, the delivery could be to livestock water troughs, tanks, irrigation, domestic use.

• Revegetation: the process or result of planting vegetation – usually shrubs or trees, but can be forbes and grasses – on cleared or degraded land.for a specific benefit: commercial (timber, honey, firewood); hydrological (increased interception and discharge through transpiration); ecological functions (ecosystem services, habitat, biodiversity); amenity (dust suppression, shelter from winds, shade and temperature control, aesthetics and landscaping).

• Revetment mattress: a protective layer of erosion-resistant material placed along the banks of watercourses to prevent erosion. One type has grout pumped into a membrane cell to form a mattress conforming to the shape of the bank.

• Rhizosphere: the volume of soil that is directly influenced by root secretions and associated soil microorganisms.

• Riparian: 'The riparian zone can generally be described as the land that directly influences or is influenced by a watercourse. That is, the corridor of land in which a stream functions. The riparian zone includes the immediate vicinity of the stream, which consists of the bed, banks and adjacent land, as well as the floodplain, which carries large floods. The width of the riparian zone can vary greatly depending on the type of river or stream and the catchment. Therefore the area of the riparian zone that requires special management will also vary.' (Water Notes, Western Australia)

• Rock (or Reno) mattress: similar to a gabion, in that it is a wire, rock-filled mesh box, but more a mattress shape. It is used to line high-risk sections of drainage lines subject to substantial water flows.

• Rotational grazing: 'the practice of rotating livestock through a series of paddocks. By the time the last paddock in the series has been grazed, the first has been rested allowing sufficient pasture growth for the paddock grazing sequence to commence again.

  Rotational grazing involves higher paddock-by-paddock stocking rates than set stocking. It focuses on grazing plants intensively at the most nutritious stage in their growth cycle while allowing palatable species to continue to thrive by providing adequate rest time between grazing events.

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S

• Salinisation: the process of increasing soil or water salinity through natural processes or human activity.

• Salinity: the saltiness of water or soil, measured by the concentration of total dissolved solids (TDS) in a solution or estimated by various other measures (e.g. electrical conductivity, electromagnetic induction). The term is commonly used (incorrectly) to imply that the level of salt is high enough to cause problems, as in 'salinity is a problem in Western Australia'.

  The international standard (SI) unit for EC is siemens. The Department of Primary Industries and Regional Development expresses soil and water salinity in millisiemens per metre (mS/m).

  The Australian standard for water salinity is EC in microsiemens per centimetre (µS/cm), or milligrams per litre (mg/L), and for soil salinity, EC in decisiemens per metre (dS/m).
  
  Measures used by DPIRD are:
  EC_w: the electrical conductivity of a water sample.
  EC_1:5: the electrical conductivity of a mix of 1 part by weight of soil and 5 parts by volume of water.
  EC_e: the estimated electrical conductivity of the extract from a saturated soil paste, derived from the EC_1:5 measure and adjustment for the soil texture class.
  EC_se: a direct measure of the EC of the saturated extract of a soil sample. This measure is rarely used, as the measure is time consuming and expensive.
  EC_a: the apparent electrical conductivity estimated using an electromagnetic induction meter (EM), such as the EM38 or EM31.
  TDS: a measure by gravimetric analysis of the dissolved combined content of all inorganic and organic substances present in a liquid in molecular, ionised or microgranular suspended form. Generally, the operational definition is that the solids must be small enough to survive filtration through a filter with 2-micrometre (nominal size or smaller) pores. The unit for TDS is milligrams per litre (mg/L).

• Saltland: land that has a salinity level high enough to restrict growth of sensitive plants, and may have deleterious effects on infrastructure, biodiversity and some land uses. See primary and secondary salinity.

• Saprolite: a particular form of decomposed rock that preserves structures that were present in the parent rock. Granitic saprolite grit overlaying bedrock can be a highly transmissive layer for groundwater.

• Saturation: when all soil pores are filled with water. It may or may not be accompanied by anaerobic conditions, depending on whether there is biological activity to use the oxygen present. See waterlogging.

• Scald (noun): a hard, impermeable surface on saline or sodic soils as a result of wind or sheet erosion (dry scald) or by surface sealing through deposition of salts and clays following evaporation of surface water (wet scald) (data.gov.au).

• Seasonal variability: a measure of the variability of annual weather between years. Weather in the south-west of Western Australia follows a recognisable Mediterranean annual pattern, but the occurrence of weather events varies from year to year. This results in seasonal climate measures – such as total rainfall – being different each year. Variability is usually described in statistical terms, comparing the current season with a reference period of past years. Causes of seasonal variability are a combination of large-scale phenomena (such as El Niño) and shorter-term regional factors.

• Secondary salinity: saltland caused by human activity.

• Sediment: material that has been moved from its point of origin by erosive actions of wind, water or gravity, and deposited elsewhere.

• Sediment (or silt) trap: a structure designed to collect coarse sediment, ideally as close to the point of origin as possible. Sediment traps need to be regularly checked and cleaned out if necessary. Sediment traps are recommended in front of farm dams.

• Seep (noun): a place where water slowly oozes out of the ground. This means the piezometric head is above ground at that point. Seeps can occur at changes of slope, above groundwater barriers, and leaky artesian systems.

• Set stocking: 'the practice of grazing livestock in a particular paddock for an extended period of time. Under such a regime the paddock is rarely rested; the stocking rate is usually calculated so that the number of livestock can be grazed throughout the year; supplementary feeding may be used to correct seasonal imbalances in feed supply to demand' (MLA).

• Shrub: a woody plant usually less than 5m high and many-branched without a distinct main stem except at ground level.³

• Siphon: a structure for passively moving water from areas of higher hydraulic head to areas of lower hydraulic head. The siphon system consists of a siphon well into the aquifer, a siphon head, and a discharge pipe going downhill to a discharge point.

• Slaking (soil): the process when a soil aggregate is immersed in water, the pressure of the entrapped air causes the aggregate to break down into much smaller particles (i.e. micro-aggregates) within the soil matrix. Slaking is caused by a lack of physical bonds associated with organic materials, fungal hyphae and roots. Soils with low organic matter levels are most prone to slaking. See dispersive soils.

• Slope length: the effective distance across a site between control measures. The term is often used to describe the distance between grade banks.

• Sodicity: a measure of the exchangeable sodium percentage (ESP). This term is often used to refer to a soil with an ESP of more than 6%.

• Sodic soils: a soil with an exchangeable sodium percentage of more than 6% of the cation exchange capacity. Nonsaline sodic soils are usually dispersive in the presence of fresh water. Saline-sodic clays are less dispersive than nonsaline sodic soils, and have higher infiltration rates.

• Soil acidity: a measure of how acid a soil is. This term is often used to refer to a soil with pH of less than 7.0: that is, the soil is acid.

• Soil compaction: the process where soil particles are pushed closer together, reducing pore space, and increasing soil density. The process in agriculture is commonly from vehicle traffic and livestock movement causing a compacted layer in soils, that then reduces root penetration, water availability and potential yield.

• Soil erodibility: the susceptibility of a soil to detachment and transportation by wind or water (related to soil properties taken in isolation). See erosion.

• Soil erosion: see erosion.

• Soil health: also referred to as soil quality, is the continued capacity of a soil to provide ecosystem services appropriate to its environment that sustain plants, animals, and humans. There are various measures of soil health based on edaphic and/or biotic characteristics, or particular ecosystem services.

• Soil organic carbon (SOC): the carbon component of soil organic matter (SOM). SOC is easier to measure than SOM, and is therefore often used to estimate SOM because the proportion of carbon to other elements in SOM is fairly consistent.

• Soil organic matter (SOM): the organic component of soil, comprised of small fresh plant residue (<10%); small living soil organisms (<5%); decomposing organic matter, which may be soluble or particulate (33–50%); stable organic matter (33–50%); resistant organic carbon, such as char or charcoal (<2% to 20% depending on history). Decomposing organic material breaks down faster than other SOM components, releases nutrients for plant use, and is associated with high biological activity; it also responds more quickly to changes in management. The stable organic material (humus and other materials) provides the 'glue' for soil structure, and increases water- and nutrient-holding capacity.

• Soil permeability: a measure of the maximum potential for water to move through a soil or rock material – measured in units of time and distance, usually in metres per day (m/d). The value depends on soil porosity, connectedness of pathways and structure. High permeability is more than 1m/d, and low permeability is less than 0.01m/d. The actual speed of through-flow is determined by several site factors, including potential gradient and resistance.

• Soil structure: the arrangement of soil particles in various aggregates differing in shape, size, stability, and degree of adhesion to one another, resulting in an arrangement of particles and voids. Good soil structure means the soil has good soil permeability and good plant available water capacity.

• Soil water content: the total amount of water stored in a soil to a given depth or volume – expressed as percentage of water by weight or volume of soil, or centimetres of water per metre depth of soil. See plant available water capacity.

• Sorption: describes the actions of absorption and adsorption.

• Southern Oscillation Index (SOI): a value calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin.

• Spading (soil): the process of lifting seams of clay-rich subsoil to the soil surface while burying some surface soil, using low-speed rotary tillage tynes with 'spades' on the end. Recommended where it is less than 30cm to the subsoil.

• Spelling (of pastures): removal of all grazing animals for a period, to allow recovery of leaf area of mature desirable plants, germination of other plants in addition to desirable plants, and to allow seed production and release. Spelling is an integral part of pasture improvement.

• Spillway: an open or enclosed structure used to convey outflow water safely from a storage structure, such as a dam, into a stable drainage line.

• Stewardship (environmental resources): an individual's or group's care and management of the natural environment to achieve ecological sustainable development. "Aldo Leopold (1887–1949) championed environmental stewardship based on a land ethic 'dealing with man's relation to land and to the animals and plants which grow upon it.'" (Wikipedia).

• Stocking rate: the number of specific kinds and classes of animals grazing a unit of area for a specific period; normally expressed as animal type per unit area. To allow comparisons, the classes of livestock are usually expressed in standard livestock units: either dry sheep equivalent (DSE) or cattle unit (CU).

• Sum of excess water (SEW): a measure of the degree of waterlogging, that integrates the amount of saturated soil in the nominal rooting depth over a growing season. See Waterlogging for a full description.

• Sustainability: a measure of the ability of something to continue indefinitely at the same rate or level. 'Environmental sustainability is the ability to maintain rates of renewable resource harvest, pollution creation, and non-renewable resource depletion that can be continued indefinitely. Economic sustainability is the ability to support a defined level of economic production indefinitely.' (Thwink.org). In this sense, nothing is fully sustainable, but some things have higher sustainability than others do.

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T

• Tactical grazing: 'uses a range of grazing methods, including set stocking and rotational grazing (and spell grazing), throughout a single year or series of years, to meet different animal and pasture objectives at various times. This allows a balance to be struck between the demands of various classes of livestock for growth rate, reproduction and maintenance and feed supply.' (MLA) Tactical grazing usually requires more infrastructure (fences and watering points) than for set stocking.

• Taxon (plural is taxa): a scientifically classified group or entity. The taxonomic hierarchy is kingdom, phylum or division, class, order, family, genus, species. Species can then be separated in to subspecies, varieties and cultivars. Varieties and cultivars can be commercially protected by plant breeder's rights (PBR).

• Tensiometer: a sensor inserted into the soil to measure how hard it is to remove water from the soil, providing the best indication of available water for plants. Soil type and water content influence the suction pressure required to remove water from the soil. Tensiometers work by measuring suction pressure at the tensiometer's porous tip. Water is drawn out of or into the tip, depending on water availability. This creates a suction pressure representing the suction force required for a plant to obtain water from the soil.

• Total acidity: is a measure of the already free H⁺ (hydrogen ions) in solution (expressed as pH units) plus the potentially released H⁺ in solution. This is sometimes termed the titratable acidity, and 'is measured by reacting the acids present with a base such as sodium hydroxide (NaOH) to a chosen end point, close to neutrality, as indicated by an acid sensitive colour indicator' (Monash Scientific). The importance is that soil or water of the same measured pH can have very different requirements for neutralising.

• Total dissolved solids (TDS): a measure of 'salinity' in water – the total concentration of dissolved inorganic salts (usually the main component) and organic matter (usually a minor component). Common inorganic salts in water include calcium, magnesium, potassium and sodium, which are all cations, and carbonates, nitrates, bicarbonates, chlorides and sulfates, which are all anions. See salinity for other measures of salinity.

• Total grazing pressure (TGP): the demand for forage by all grazing animals, domestic and nondomestic, relative to forage supply.

• Total stocking rate: the sum of all grazers and browsers that eat the pasture, expressed in a single standard unit: usually dry sheep equivalent (DSE) or cattle unit (CU).

• Transient salinity: a measure of salt toxicity from salt accumulation in the root zone not influenced by groundwater or a rising saline watertable. This occurs on dispersive soils in low rainfall areas, where salt in rainfall accumulate in surface soils, because the hydraulic conductivity of dispersive clay soils is very low.

• Transmissivity (soil): a measure of how much water can be transmitted horizontally, such as to a pumping well. An aquifer may consist of several soil layers. The transmissivity for horizontal flow T_i, in a soil layer with a saturated thickness d_i and horizontal hydraulic conductivity K_i is:
  T_i = K_i d_i
  Transmissivity is directly proportional to horizontal hydraulic conductivity K_i and thickness d_i. Expressing K_i in metres per day (m/d) and d_i in metres (m), the transmissivity T_i is found in metres squared per day (m²/d).
  The transmissivity of an aquifer can be determined from pumping tests (adapted from Wikipedia).

• Transpiration: the process of water loss from plants. Soil water is taken up by roots and moves to small pores on the underside of leaves, where it changes to vapour and is released to the atmosphere.

• Turbidity (water): 'the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality.' (Wikipedia) There are several ways of measuring turbidity, and several units for reporting turbidity, all based on light transmission through the turbid water:
  nephelometric turbidity unit (NTU)
  Formazin turbidity unit (FTU).

U

• Utilisation (of pasture by livestock): the degree of conversion of pasture energy and nutrients into saleable product while leaving pasture residue in the best condition for rapid regrowth. The recommended utilisation of pastures is always less than 100%.

V

• Variable rate technology (VRT): technology that enables automated application of variable rates of materials in one pass. In agriculture, this means being able to apply different rates of chemical or fertiliser within a paddock in response to localised conditions. This technology is a component of 'precision agriculture', and relies on detailed spatial and other data. This approach is used in a range of farming systems, including viticulture, broadacre cropping, dairy and sugar farming.

• Volatilisation: evaporation or sublimation of a substance. Evaporation is when a liquid changes to the gas phase; sublimation is when a solid changes directly to a gas phase without going through a liquid phase

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W

• Water erosion: the process by which soil particles are detached and moved from the land surface (usually called soil erosion) by the action of water.

• Water-holding capacity (soil): the total amount of water a soil can hold at the drained upper limit.

• Waterlogging: excess water in the root zone accompanied by anaerobic conditions. The excess water inhibits gaseous exchange with the atmosphere and biological activity uses up the available oxygen in the soil air and water. Also called anaerobiosis, anoxia or oxygen deficiency. Soils do not have to be saturated for gas exchange to be inhibited (i.e. waterlogged).
  'Only one approach has been used to integrate intermittent waterlogging measurements in the natural environment, SEW30, and even this will be shown to have major limitations. Waterlogging throughout the year and at different soil depths can be integrated by the Sum of Excess Water that occurs each day in the primary root zone of the top 30 cm soil layer (SEW30).' (Setter & Waters 2003). This value, by itself, does not give an accurate influence on plant growth.

  Conditions which might substantially interact with SEW30 to affect growth include:

  • temperature
  • frequency of waterlogging
  • flooding
  • stage of development
    (McFarlane et. al 1989).

• Water repellence: a measure of the hydrophobic nature of soils that prevents infiltration. Water repellence develops in a susceptible soil when there is an accumulation of hydrophobic organic substances on the surface of soil particles. Hydrophobic compounds are derived from plant and microbial sources. Sands are more susceptible to developing water repellence than clays because they have a smaller soil surface area that is readily coated by hydrophobic substances. Water repellence results in poor water infiltration, variable soil wetting, increased erosion risk, and reduced and delayed crop, pasture and weed establishment.

• Water resources: sources of water that can be extracted and are useful or potentially useful to humans or for environmental services.

• Watertable: the level below which the ground is saturated with water, and is usually measured as the level to which water rises in an open well or bore at atmospheric pressure in an unconfined aquifer. In a confined or semiconfined aquifer, the water level is expressed as a piezometric surface.

• Waterway: in land management, any channel that carries water at some time of the year. Natural waterways include creeks, rivers, inlets; constructed waterways include grassed waterways, and channels and drains.

• Weather: the day-to-day atmospheric conditions, usually expressed in terms of temperature, rainfall and wind. See climate for longer-term weather conditions.

• Weather and climate modelling: construction of a mathematical description of atmospheric processes. Often very complex computationally and mathematically. Most modern models include other earth system processes from land, ocean and vegetation. Their design reflects their purpose, with smaller space and time scales (i.e. grid intervals and time steps) being important for simulation of regional and local processes. Simpler models can be developed for a broader view of the atmosphere.

• Wind erosion: the process by which soil particles are detached and moved from the land surface (usually called soil erosion) by the action of wind.

• Wind speed: a measure of the speed of wind movement at a given point over a given time. Wind is a continuous succession of gusts and lulls (quiet intervals) associated with changes of wind direction. Mean wind speed over a period is therefore the average of many gusts and lulls. Expressed using units of velocity, such as metres per second or kilometres per hour. Wind measurements should be referenced to the averaging period.

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References and bibliography

1. Chromatogrophy Today (2014) Adsorption, absorption and desorption — what’s the difference?, viewed 27 July 2021.
2. National Committee on Soil and Terrain (2009) Australian soil and land survey – Field handbook, 3rd edn, Australian Soil and Land Survey Handbooks Series 1, CSIRO Publishing, Melbourne, Australia.
3. Western Australian Herbarium (n.d.) Glossary of botanical terms, Department of Biodiversity, Conservation and Attractions, Perth, accessed 27 July 2021
4. New South Wales flora online (n.d.) Glossary of botanical terms, The Plant Information Network System of The Royal Botanic Gardens and Domain Trust, Sydney, accessed 27 July 2021.
5. Burkitt LL, Moody PW, Gourley CJP & Hannah MC (2002) 'A simple phosphorus buffering index for Australian soils', Soil Research, 40:497–513, accessed 27 July 2021.
6. National Centre for Groundwater Research and Training (n.d.) What is groundwater?, accessed 27 July 2021.
7. Tongway, DJ & Hindley, NL (2005) Landscape functional analysis: procedures for monitoring and assessing landscapes, CSIRO, Canberra, accessed 27 July 2021.
8. Setter, TL & Waters, I 2003, 'Review of prospects for germplasm improvement for waterlogging tolerance in wheat, barley and oats', Plant and Soil, 253:1–34, accessed 27 July 2021.
9. McFarlane, DJ, Barrett-Lennard, EG & Setter, TL 1989, 'Waterlogging: A hidden constraint to crop and pasture production in Western Australia', In Proceedings of the Fifth Australian Agronomy Conference, Perth, Western Australia, pp. 74–83.
10. Petty, S, Blood, D, Addison, J & Petty, E (2018) Potential carrying capacity review, Spektrum Consulting report for Landgate, Western Australia, accessed 26 July 2021.
11. McLennan SR, McLean I and Paton C (2020) Re-defining the animal unit equivalence (AE) for grazing ruminants and its application for determining forage intake, with particular relevance to the northern Australian grazing industries, Meat and Livestock Australia, North Sydney, Australia, accessed 26 July 2021.