To incorporate into something else, eg a gas into charcoal
A soil with a pH less than 6.5 (H2O) throughout most or all of
the parts of the soil that the plant roots occupy. A soil with
more hydrogen than hydroxyl ions in the soil solution.
Tiny thread-like bacteria that live in the soil.
The attachment of compounds or ions to a surface particles.
Nutrients in solution (ions) carrying a positive charge become
attached to (adsorbed by) negatively charged soil particles.
The clustering of soil particles into clods, crumbs, blocks or
prisms. The aggregate is bound by organic matter, plant roots,
fungal growth and exudates from roots, fungi and bacteria.
A primitive plant, which has no flowers or seeds, but has
A soil with a pH greater than 7.5 throughout the root zone. A
soil with more hydroxyl than hydrogen ions in the soil solution.
Substances (gypsum or lime) for improving the soil.
Living or functioning in the absence of air or free oxygen.
An ion carrying a negative charge of electricity, eg Nitrate
NO3- and Sulphate SO4-.
Nutrients in the soil that can be taken up by the plant in
amounts and at rates that will make the plant grow.
Water in the soil that can be taken up by the plant in amounts
and at rates that will make the plant grow.
A tiny, usually single celled organism. There are many bacteria
in the soil and they have a wide range of roles. Some break down
lignin, others convert nitrite to nitrate or sulphur to sulphate
and still others make nitrogen for the plant, eg Rhizobia for
The placement of fertilizer in the soil in narrow bands,
usually away from the seed or plant. The fertilizer bands are
covered by the soil but not mixed into the soil.
A ball of soil which has had water added.
The ability of a soil to absorb changes in the soil solution.
These changes may be of pH or increased salt concentrations from
Ratio of the mass or weight of dry soil to its volume or bulk.
Usually shown as grams per cubic centimetre.
A soil which has calcium carbonate or an alkaline reaction due
to the presence of calcium carbonate. A calcareous soil will fizz
when treated with dilute hydrochloric acid.
The elemental ratio existing within the soil organic matter
between atoms of carbon and atoms of nitrogen (C:N).
An ion carrying a positive electric charge, eg calcium,
hydrogen, magnesium, potassium, sodium.
The exchange of cations held by the soil adsorbing complex with
other cations. Thus, if a soil adsorbing complex is rich in
sodium, treatment with calcium sulphate (gypsum) causes some
calcium cations to exchange with some sodium cations.
A measure of the total amount of exchangeable cations that can
be held by a soil. It is expressed in terms of milli-equivalent as
per 100 grams of soil at pH7 unless stated otherwise.
The wrapping of an organic molecule around a metal ion.
Tiny soil particles less than 0.002mm in diameter. Clay is
sticky when wet. Clay soils have at least 40% clay in them with
less than 45% sand or 40% silt.
A soil texture with 27 to 40% clay and 20 to 45% sand.
A mass of soil produced by ploughing or digging which usually
breaks up easily.
How a ball of moist soil (bolus) behaves when squeezed in the
hand. The bolus is coherent if it sticks together when squeezed.
Very tiny clay particles less than 0.001mm in diameter. There
are two types of colloid - mineral colloids which are clay
particles and organic colloids which are humus or decomposed
The crushing and compression of a soil caused by vehicles or
A thin, brittle layer of hard soil which forms at the surface
of many soils when they are dry.
Decisiemens per metre - unit of salinity. dS/m x 1000 = EC
A bacterial action which reduces nitrates and/or nitrites in
the soil or organic compounds to free nitrogen. Nitrogen may be
lost to the atmosphere during this process.
The breakdown of soil aggregates on wetting into individual
particles which create a milky suspension.
A liming material which contains both magnesium as magnesium
carbonate and calcium as calcium carbonate.
Electrical conductivity - unit of salinity.
Proteins which act as a catalyst for chemical changes, eg
Urease catalyses for the splitting of Urea to ammonia and carbon
A state of balance between opposing soil forces or actions.
The cations that can be exchanged in the soil complex for other
cations. For example, when acid soils are limed, calcium ions
exchange for hydrogen ions in the soil complex OR when sodic soils
are treated with gypsum, calcium ions exchange for sodium ions
that can then be leached away.
Sodium that is attached to the surface of soil articles which
can be exchanged with other positively charged ions in the soil
solution, such as calcium or magnesium.
Any natural or manufactured material added to the soil to
supply one or more plant nutrients.
When the soil particles are holding all the water they can and
no drainage is occurring.
A primitive plant which has no flowers or seeds and is without
A granular, crystalline rock of quartz, felspar and mica.
Hydrated calcium sulphate.
As in soils which form surface crusts which inhibit plant
Colours or tints.
Soil organic residue which has been decomposed so much that it
no longer has any of its original structure. It is basically the
stable part of the organic matter.
The dominant ion in the soil solutions of alkaline soils. (OH-)
The threadlike growth from fungi.
A type of clay, which has considerable capacity to expand and
For legumes, inoculant is bacteria impregnated peat which is
applied to the legume seed before sowing to introduce new strains
Refers to substances occurring as minerals in nature or
obtainable from them by chemical means. Inorganic is all matter
except carbon compounds (carbon dioxide and carbonate compounds
Nitrogen in combination with mineral elements, not in animal or
vegetable form. Ammonium sulphate and sodium nitrate are examples
of inorganic nitrogen combinations, while proteins contain
nitrogen in organic combination.
In soils, an ion is an electrically charged element or
combination of elements resulting from the breaking up of an
electrolyte in solution. Since most soil solutions are highly
dilute, many of the salts exist as ions. For example, all or part
of the potassium chloride in most soils exists as potassium ions
and chloride ions.
The exchange of nutrients in the soil from clay particles and
organic matter to solution to plant roots.
A type of clay predominant in red soil which has little
expansion or shrinking.
Stiffening material in cell-walls of woody tissue.
Crushed limestone (predominantly calcium carbonate) or caustic
alkaline earth made by heating limestone. Used to reduce soil
A soil texture with moderate amounts of clay (7 to 27%), silt
(28 to 50%) and sand (less than 52%).
Refuse from stables or farmyards which includes animal excreta
An earthy mixture of calcium carbonate and clay which is found
in lakes and riverbeds.
A milliequivalent is 1/1,000th of the “equivalent weight”
of an element, which is the atomic weight of that element divided
by the number of charges on the cation (valence).
Life sustaining processes in the plant including nutrition,
production of energy (respiration) and the build up of food.
Conversion of soil organic matter through microbiological and
chemical processes into inorganic crop nutrients.
A type of clay.
Mega pascals. Unit of pressure.
Material such as straw, leaves, etc, applied to the soil
surface to conserve moisture and suppress weeds.
Fungi which grows onto plant roots and can increase the uptake
of plant nutrients.
The relative ability of different liming materials to
neutralise acidity is expressed on a percentage basis. Pure lime
(pure calcium carbonate) is given the value of 100%. Other liming
materials can be higher or lower.
The preferred nitrogen source of plants.
The formation of nitrites and nitrates from ammonia and ammonia
compounds by soil bacteria and enzymes.
The intermediate form of nitrogen between ammonium and nitrate.
The formation of small lumps on the roots of legumes by
nitrogen producing bacteria.
One of the basic molecules of life. DNA is a nucleic acid.
Central part of the plant cell including its genetic material.
Carbon based molecules derived from plants and animals.
A pressure exerted in living bodies as a result of unequal
concentrations of salts on both sides of a cell wall or membrane.
Water will move from the area having the least salt concentration
through the membrane into the area having the highest salt
concentration and, therefore, exerts additional pressure on this
side of the membrane.
A chemical change of an element or compound involving the
addition of oxygen to its chemical compound. A chemical change
that involves an increase of positive valence or a decrease of
A compound of any element (nutrient) with oxygen alone.
The unconsolidated mass of rock material (or peat) from which
the soil profile develops.
Unconsolidated soil material consisting largely of undecomposed
organic matter accumulated under conditions of excessive moisture.
The process in which the energy of light and chlorophyll are
used to manufacture carbohydrates out of carbon dioxide and water.
The water available to the growing plant; it is the difference
between the field capacity and wilting point.
The nutrients required by the growing plant.
Hard layer of soil which develops at the depth of ploughing.
Can restrict root movement.
A carbonate compound, for example starch or cellulose.
The fraction of the soil volume not occupied by solid
An organic compound built up of amino acids, essential to
Microscopic, single celled animals.
The shifting of a compound from a higher oxidation state to a
lower oxidation state, eg NO3- (nitrate) to NO2- (nitrite).
Plant’s absorption of oxygen and release of carbon dioxide.
A group of bacteria which ‘fix’ nitrogen from the
atmosphere in association with legumes.
A fungus which rots plant roots.
The length of wet soil when pressed out between the thumb and
Soil particles in the size range 0.02 to 2mm, they can
generally be felt when rubbed between the fingers.
Soil particles in the size range 0.002 to 0.02mm. Silt grains
cannot be detected by feel, but their presence makes the soil feel
smooth and soapy and only very slightly sticky.
The breakdown of soil aggregates on wetting, into smaller
Those soils with high (over 6%) exchangeable sodium levels.
They lead to soil structure breakdown, surface sealing and
Has a higher moisture and carbon dioxide level and a lower
oxygen level than atmospheric air.
The ability of a soil to provide nutrients for plant growth.
The creatures that live in the soil
Sand, silt and clay. They make up the texture of a soil.
pH is an indication of the concentration of hydrogen ions (H+)
in the soil solution. It reflects only the intensity of soil
acidity, not the actual amount of acid present. It is the negative
logarithm of the hydrogen ion concentration in the soil solution.
pH7.0 is neutral in terms of acid or base (Alkaline). pH8.0 is ten
times more alkaline than pH7.0.
The place, eg clay particles or organic matter, where nutrients
The accumulation of salts in the root zone of the soil.
It is the water in the soil which contains the soluble salts,
dissolved carbon dioxide and oxygen. It is found in the soil pores
or held as a film around the soil particles.
The way the soil particles are clustered together.
See soil solution.
The form of sulphur that is preferred by plants (SO4-).
The accumulation of water in a soil aggregate without causing
the aggregate to break down.
The ‘strength’ or ‘pressure’ with which soil particles
hold water in the soil.
The make up of sand, silt and clay in a soil.
The way the land lies.
The combining power which determines the number of other atoms
with which an atom of the element can combine, eg Sodium (Na) has
a valency of one, oxygen (O) has a valency of two which means that
two sodiums will combine with one oxygen, Na2O.
The loss of a substance in the form of a vapour.
A condition of the soil when the pores are more than 90% filled
The point when plants can no longer pull water from the film
around the soil particles.