Glossary

Term

Definition
Anion A negatively charged ion.
Blended fertiliser A fertiliser containing granules of several different products which have been blended together, giving it a heterogenous appearance.
Buffering capacity The ability of a soil to maintain the level of a nutrient in solution. In terms of potassium, it will depend on the ability of the exchangeable and fixed potassium pools to replenish the soluble potassium pool.
Capital applications Applications of fertiliser which are aimed at raising soil fertility to a targeted production level.
Cation A positively charged ion. The important nutrient cations include potassium (K), calcium (Ca) and magnesium (Mg). Sodium (Na) and ammonium (NH4) ions are also cations.
Cation exchange capacity The amount of negative charge on the surface of soil particles, and a measure of the ability of the soil to retain cations in a readily exchangeable form. Measured in units of centimoles of charge per kilogram of dry soil (cmol (+)/kg). It is also possible for soils to have an anion exchange capacity (cmol (-)/kg) but this is usually much smaller than the cation exchange capacity.
Clay minerals Mineral soil particles which are <2?m in diameter.
Colwell K soil test A soil extraction using 0.5M sodium bicarbonate to remove soil potassium. It has been widely adopted in Tasmania, Western Australia, New South Wales and South Australia, with results reported in mg/kg.
Compound fertiliser A fertiliser which is the result of several different products being chemically compounded prior to granulation, giving it a homogeneous appearance.
Critical value The nutrient availability below which unacceptable yield losses occur due to nutrient deficiency. The critical value is usually set to correspond with 90-97% of maximum yield.
Decision support systems Computer models which can be used to answer 'what if' scenarios. They assist in assessing options and making decisions.
Deficiency symptoms Visible plant symptoms which are the result of a nutrient deficiency.
Determinate growth Of specific duration, as compared to indeterminate growth which is unlimited. Crops that have determinate growth patterns will cease to grow and will begin to dry off after grain is produced. Crops with indeterminate growth patterns will continue to produce further shoots and seeds unless destructively harvested.
Dry matter A measure of physical plant material produced. It is measured by harvesting, drying plants to remove water and weighing.
Dry stock equivalents (DSE) A standard measure of animal numbers, based on the relative feed requirement of various classes of stock.
Duplex soils Soils with two horizons of contrasting texture. Duplex soils are usually a sandy topsoil overlaying a clay or gravelly subsoil.
Exchangeable potassium Potassium ions which are held on the charged surfaces of soil particles (usually clay and humus), and can be exchanged for other cations.
Fertigation Application of dissolved fertilisers in irrigation water.
Fertiliser burn Plant or seed scorching as a result of high concentrations of nutrients in solution in close contact with plant tissues.
Fixed potassium Potassium ions which are temporarily trapped between the expanding layers of some clay minerals. This pool of soil potassium is not readily available to plants but may be slowly released over time. Soils which have an abundance of suitable potassium fixing sites which are unoccupied may fix added fertiliser potassium in this temporarily unavailable form.
Granular fertiliser Fertiliser which has been produced so that particles are within a standard size range. Granulation ensures that different fertiliser products can be mixed without segregation, and improves handling and spreading.
Grass tetany Also known as hypomagnesaemia. It is a metabolic condition which develops in sheep and cattle when insufficient magnesium is absorbed from the diet.
Lactating Currently producing milk.
Leaching The downwards movement of nutrients or soil particles in draining soil water.
Legume A plant which forms a symbiotic relationship with Rhizobia bacteria. The bacteria form nodules on the root of the plant, and fix atmospheric nitrogen which is used by the plant. Excess nitrogen is returned to the soil in dead plant material or micro-organisms and can be used by accompanying non-legume plants, or stored in the soil for use by following crops.
Lignification The secondary thickening of cell walls with lignin.
Lodging The process of crop plants falling over due to weakened stems and/or adverse weather conditions. Lodging makes harvesting difficult and can cause a deterioration in grain quality.
Luxury uptake Absorption of nutrients by a plant in excess of that required for plant yield, but not causing toxicity. Luxury uptake of potassium can occur since potassium is not toxic to plants and the excess can be accumulated without affecting plant yield.
Maintenance applications Applications of fertiliser which are aimed at maintaining soil fertility at a given production level.
Maximum economic yield Marginal returns to added fertiliser become smaller as maximum biological yield is reached. The yield at which profit is maximised is called maximum economic yield, and may be less than maximum biological yield.
Muriate of potash (MOP) Potassium chloride, contains 50% potassium, and is the most common form of potassium fertiliser.
Nitric acid K test A soil extraction using nitric acid to remove soil potassium. It is used regularly to assess fixed potassium status in sugarcane soils.
Non-responsive A site which shows no, or little change in yield with added nutrient.
Nutrient budgeting The process of quantifying nutrient inputs and losses from a system to determine the net nutrient balance.
Nutrient response curves Graphical relationship between yield (or yield relative to a maximum) and the availability of a nutrient. It usually rises rapidly at low nutrient availability and flattens out at a maximum at high nutrient availability, although other forms are possible. It can be used to define critical values for nutrient availability, below which yield is lost.
OVERSEER™ A computer model developed by New Zealand pastoral research body AgResearch to assist in making fertiliser decisions for pastures.
Pasture composition The mixture of species which make up a pasture sward.
Pasture utilisation The proportion of pasture being consumed by stock.
Peat Soils which have accumulated a large (>20%) amount of undecomposed organic material under conditions of excessive moisture.
Petiole The 'stalk' section of a leaf, which attaches the leaf to the plant stem.
Photosynthesis The essential process by which plants in sunlight manufacture carbohydrates from carbon dioxide and water. The amount of carbon dioxide that is assimilated into carbohydrates is adversely affected in potassium-deficient plants (Smid and Peaslee, 1976. Agronomy Jnl, 68:907).
Plant uptake The absorption of nutrients and/or water through the roots.
Potash Potassium containing fertiliser.
Potassium nitrate Also known as saltpetre. It is classified as a Dangerous Good (oxidising agent) and therefore must be stored and transported according to set regulations.
Primary minerals Those minerals which are present in the parent material of the soil. Over time primary minerals will weather to form secondary minerals which are not found in the parent material of the soil.
Quick test K (QTK) A soil extraction using a neutral salt. It is used to assess exchangeable potassium in New Zealand with results reported in parts per 250,000.
Responsive A site which shows an increase in yield with added nutrient.
Runoff Rainfall which does not infiltrate into the soil but moves overland.
Salt index A measure of the potential of a fertiliser to cause burning. It is measured by the effect of a fertiliser on the concentration of the soil solution and reported relative to the effect of sodium nitrate. It is often more useful to examine the salt index per unit of nutrient element, than the salt index of the fertiliser itself.
Sedimentary soils Soils formed from sedimentary parent materials which have in turn been formed from the deposition and accumulation of sediments.
Seedbed utilisation (SBU) A term describing the physical spread of fertiliser bands over the seedbed as a percentage. SBU is calculated by dividing the spread width of the band (mm) by the row spacing between the centre of bands (mm) and multiplying by 100. SBU is expressed as a percentage.
Skene K soil test A soil extraction using 0.05M hydrochloric acid to remove soil potassium. It is used in Victoria, with results reported in mg/kg.
Soil solution The water contained in soil, including the compounds dissolved in it.
Soluble potassium The potassium dissolved in the soil solution
Spatial variation Variation across a field or landscape.
Specific gravity The weight of material per unit volume. It is used as a measure of quality for manufacturing potatoes where higher specific gravity is desirable.
Stocking rate The number of animals (or animal equivalents) being grazed per unit area.
Stomata The small openings in leaf surfaces through which carbon dioxide and oxygen are exchanged and water vapour is expired. The pores are surrounded by crescent-shaped guard cells which, through changes in turgidity, control the opening and closing of the pore. Potassium ions play an essential role in regulating the turgidity of these guard cells.
Subsoil Soil in the layers below the plough zone.
Substrate The substance upon which an enzyme or organism will activate.
Sulfate of potash (SOP) Potassium sulfate, contains 41% potassium and 18% sulfur. It is less soluble than potassium chloride or potassium nitrate.
Tetraphenyl boron K (TBK) A soil extraction using sodium tetraphenylboron. It is used to assess fixed potassium in New Zealand with results reported as cmol (+)/kg.
Transect A line along which samples are taken.
Vegetative plant material The non-reproductive parts of plants which includes leaves and stems, but not grain.
Water use efficiency The efficiency with which available water is converted to plant yield. At the field scale, WUE can be measured by dividing crop yield by the amount of water used in evapo-transpiration (evaporation and transpiration) and is measured in kg/mm.
Waterlogging The instance of soil pores being filled with water for an extended period. Waterlogging can occur as a result of irrigation, excessive rainfall or high water-tables. It prevents the exchange of gases from plant roots and can result in plant death.
Windrow The piling of crop plants or residues in rows along the field.
Yield potential

 

 

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The yield that could be achieved given the prevailing conditions. Yield potential is often not achieved due to production limitations, some of which can be controlled (nutrition) and others that cannot (rainfall).