Common soil terms

Below is a list of common soils terms which may be referred to throughout the soil management section of this website.

Soils termDefinition
Acid sulfate soils The common name given to naturally occurring sediments and soils containing iron sulfides
Aluminum oxide A chemical compound of aluminum and oxygen with the formula Al2O3 
Alluvial Material deposited by water moving across the land surface
Anaerobic Soils which are deficient in oxygen, common in poorly drained or waterlogged soils
Anion See ions
Bicarbonate An anion with the formula HCO3- 
Bund A constructed wall or earth barrier designed to prevent inundation.
Capillary action Movement of soil moisture through fine soil as a result of surface tension forces between the water and individual soil particles

An anion with the formula CO32-

Catchment A catchment area or basin is land that is bounded by natural topographic features such as hills or mountains and from which all runoff water flows to a low point
Cation See ions
Clean fill Material usually consisting of soil, gravel and rock, used to raise or level land, which does not contain contaminants
Colluvial Material accumulated through the action of gravity, common on footslopes and drainage depressions
Columnar structure Vertical columns of soil that have a domed top; commonly found in sodic subsoils
Complexed Happens when an iron atom attaches to an organic molecule in a particular way. An unattached metal ion is not likely to stay dissolved in the water by itself under neutral pH conditions, but when it is attached to an organic molecule it is protected from reacting with other ions.
Deep drainage Water movement below the plant root zone
Digital Elevation Model (DEM) A model or 3 dimensional representation of the earth’s surface
Denitrification A process in which soil microbes, in the absence of oxygen, convert nitrates to atmospheric nitrogen
Discharge area An area in the landscape where groundwater moves to the soil surface. Evidence of this includes salt scalds, seepage or waterlogging. Salt may also accumulate in a discharge area.
Dispersible or dispersion Process by which clay particles are repelled by electrostatic forces and mechanical forces and separate from each other forming a suspension of clay particles in water
Dryland Dryland is land use that relies on natural rainfall, not irrigation. Dryland salinity occurs where irrigation water is not a factor in changing the water balance.
Electrical conductivity The measurement of how much electricity moves through a solution—the saltier the solution, the more electricity moves through it, and the higher the electrical conductivity reading.
Estuarine Estuarine environments are those where marine or oceanic water are diluted with freshwater run-off from the land.
Field pH pH of soil and deionised water
Field oxidised pH pH of soil and hydrogen peroxide
Flocculation Process where the attractive forces between clay particles are greater than the repulsive forces, resulting in the formation of larger aggregates (the converse process is dispersion)
Gilgai Surface microrelief associated with soils containing shrink-swell properties
Groundwater Water occurring below the surface of the landscape, at greater pressure than atmospheric, occupying spaces in regolith and bedrock. The upper surface of the groundwater is the water table.
Gypsum Calcium sulfate dihydrate (CaSO4·2H2O). It is often used as a soil amendment to improve structure.
Hard setting Soil which is compact and hard upon drying but softens upon wetting 
Infiltration The process by which water enters the soil from the soil surface
Ions An atom or molecule where the number of electrons does not equal the number of protons, giving the atom a net positive (cation) or negative (anion) charge
Iron Chemical element with the formula Fe
Jarosite Jarosite is an iron-and sulfur-containing mineral that forms in oxidising acid sulfate soil, with the formula KFe3+3(OH)6(SO4)2. It can only form in environments where the pH is less than 3.7, so it is considered very strong evidence of acid sulfate soil oxidation.
Massive A soil which appears to be solid or devoid of peds
Methane Chemical compound with the formula CH4 
Mottles/mottling In soils, spots, blotches or streaks of subdominant colours that differ from the soil matrix colour
Organic matter Plant or animal material in various stages of decomposition
Osmosis Osmosis is the movement of soluble molecules through a permeable membrane into a region of higher concentration. The direction of movement leads to equal concentrations on the 2 sides.
Perennial Species that live longer than a year and regenerate from root stock and seed
Plant available water The amount of water between field capacity and permanent wilting point which is available to a plant
Plastic limit The soil water content at which the soil becomes ‘plastic’; that is, capable of being deformed when external force is applied
Primary salinity Salinity that occurs naturally in soils and waters
Prismatic structure Vertical columns of soil that might be several centimetres long; usually found in lower horizons
Pyrite Pale-bronze or brass-yellow, isometric mineral (FeS2), the most widespread and abundant of the sulfide minerals
Recharge area An area where rainfall or flowing water infiltrates or leaks through soil, sediments and rock into groundwater. Generally areas with permeable soils and weathered or fractured rock are areas of higher recharge.
Regolith Part of the earth's surface including soil and weathered and fractured rock through which water and salts can flow
Riparian zone Part of the landscape adjacent to a waterbody that has a direct influence on waterbody margins and aquatic ecosystems contained within them
Saline soil Soil containing sufficient concentrations of soluble salts within the soil profile to result in reduced plant productivity or plant death. Climate, soil type, depth to salinity in the soil, and plant species influence the effect on plant productivity.
Saline water Water that contains sufficient concentrations of soluble salts to limit potential for domestic supply, industry, agriculture and environmental uses
Salinisation The process of salts accumulating in soil or water (also called salting)
Salinity The presence of soluble salts in soil or water
Salinity hazard The inherent characteristics of the landscape that predispose it to land and water salinity
Salinity risk The probability that land or water salinity may develop if certain management practices or land-use changes occur
Secondary salinity Salinity that results from human activities, usually land and infrastructure development and agriculture
Sedimentary Type of rocks that are formed by the deposition of materials on the earth’s surface or in waters
Self-mulching A strongly pedal loose surface mulch that forms on wetting and drying
Silicates Silicate minerals make up the largest rock-forming minerals. They contain different ratios of silicon (Si) and oxygen (O).
Siltation Pollution of water by silt or clay particles
Sodic A soil with a high percentage of sodium ions (in soluble or exchangeable form), exhibiting degraded soil behaviour such as dispersion when wet and crusting when dry
Stubble The stubs or stalks of a crop that remain in the soil after it has been harvested
Subsoil Usually referred to as the B horizon which can be clay rich but often is less fertile than the topsoil but can hold more moisture
Texture contrast An abrupt change in texture between the surface and subsoil
Tillage The preparation of land for growing crops
Topsoil Usually referred to as the A horizon where most plans, roots, earthworms, insects and microorganisms are active
Volatilisation Process by which solutions are changed into vapour, such as nitrates in the soil water changing to ammonia gas.
Water balance The amount of water in the different parts of the water cycle, including water inputs (precipitation and irrigation), runoff, infiltration, leaching, groundwater flow, evaporation and transpiration
Waterlogging Occurs when water cannot drain away through the soil
Water table Portion of the ground saturated with water, often used specifically to refer to the upper limit of the saturated ground
Water table salting Salinity that occurs where a shallow or seasonally shallow water table is sufficiently close to the soil surface for groundwater to move up to the surface by capillary action or seepage. This results in the evaporative accumulation of salts in the root zone or on the soil surface. Shallow water tables can also allow water and salt to leak into rivers and streams. Water table salting does not necessarily involve saline groundwater.