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Non-living, physical or chemical, includes solar radiation, temperature, humidity, and pH, used in context of an effect eg. abiotic damage.
In a system of moist air, the ratio of the mass of water vapour to the total volume of the system. Usually expressed as grams per cubic metre (g/m3).
A hypothetical temperature characterized by a complete absence of heat and defined as 0 K, -273.15 C, or -459.67 F.
Water held mechanically in a soil mass and having physical properties similar to ordinary water at the same temperature and pressure.
The penetration of a substance into the surface layer of a solid with which it is in contact eg. process by which pesticides are taken into plant tissues by roots or foliage (stomata, cuticle, etc.)
increased levels of acid (lowered pH) in water bodies which can be a result of changes in land use e.g. forestry.
The activity of hydrogen ion in the aqueous phase of a soil. It is measured and expressed as a pH value.
Change in an organism resulting from the action of natural selection on variation so that the organism is fitted more perfectly for existence in its environment.
An enzyme produced by an organism in response to the presence of its substrate or a related substance. It is also called an induced enzyme.
A thermodynamic change of state in a system in which there is no transfer of heat or mass across the boundaries of the system. Compression always results in warming, expansion in cooling.
An ingredient added to a pesticide formulation or mixture to improve its effectiveness. Includes wetting agents, spreaders, emulsifiers, dispersing agents, foam suppressants, penetrants and correctives.
Roots or buds arising from an unusual position on a stem eg. roots on stems, or buds produced elsewhere than in the axils of leaves or the extremities of stems.
The creation of holes in soil or turf by coring, slitting, grooving, hole punching, forking, sliding, spiking or other means to reduce compaction and improve water and air movement through the soil
Occurring only in the presence of molecular oxygen, as applied to certain chemical or biochemical processes such as aerobic decomposition.
A group of soil particles cohering in such a way that they behave mechanically as a unit.
A mechanical device in a spray tank to ensure uniform distribution of the toxicant during dilution and to prevent sedimentation.
The branch of agriculture/horticulture that deals with the theory and practice of field-crop production and the scientific management of soil.
Average Grain Size is used to denote the relative grading of sand. AGS is calculated using micron sieve sizes. In general, lower figures denote finer material.
A local wind which blows up a slope heated by sunshine. It is a feature which is less common than its converse, the kabatic wind
A negatively charged ion. An ion that carries a negative charge of electricity that interacts with cations (positive charges) in ionic bonding reactions
The tip of a growing plant root or shoot composed of cells from which subsequent growth develops climates.
A species having an articulated external skeleton such as an insect, spider or crustacean.
The portion of any element or compound in the soil that can be readily absorbed and assimilated by growing plants.
The clay, organic matter, and materials such as carbonates and phosphates that enable the soil to resist appreciable change in pH.
The cycle whereby carbon dioxide is fixed in living organisms by photosynthesis or by chemosynthesis, is consumed in carbohydrate, protein, and fat by most animals and plants that do not carry out photosynthesis, and ultimately is returned to its original state when it is freed by respiration and by the death and decay of plant and animal bodies.
Organic residues, or a mixture of organic residues and soil, that have been piled, moistened, and allowed to decompose. Mineral fertilisers are sometimes added.
The gradual reduction in volume of a soil mass resulting from an increase in compressive stress.
Tillage to prepare land for seeding or transplanting, and later to control weeds and loosen the soil.
To separate the individual components of compound particles by chemical or physical means or both.
The wearing away of the land surface by running water, wind, ice, or other geological agents, including such processes as gravitational creep.
Any organic or inorganic material of natural or synthetic origin that is added to a soil to supply certain elements essential to the growth of plants.
The guaranteed minimum analysis, in percent, of the major plant nutrient elements contained in a fertiliser material or in a mixed fertiliser.
The quantity of certain plant nutrient elements needed, in addition to the amount supplied by the soil, to increase plant growth to a designated optimum.
The percentage of water remaining in the soil 2 or 3 days after the soil has been saturated and free drainage has practically ceased. The percentage may be expressed in terms of weight or volume.
The process or processes in a soil by which certain chemical elements essential for plant growth are converted from a soluble or exchangeable form to a much less soluble or non-exchangeable form, for example, phosphate fixation.
A term with various meanings that usually refers to the mixture of organic substances that remains in solution when a dilute alkali extract from the soil has been acidified.
A mixture of various dark-coloured organic substances precipitated by acidifying a dilute alkali extract from the soil. The term is used by some workers to designate only the alcohol-insoluble part of this precipitate.
The processes by which organic matter decomposes to form humus. In humus the initial structures or shapes can no longer be recognized.
The fraction of the soil organic matter that is not dissolved when the soil is treated with dilute alkali.
The fraction of the soil organic matter that remains after most of the added plant and animal residues have decomposed
The process by which a substrate is split to form two end products by the intervention of a molecule of water.
A soil characteristic determining or describing the maximum rate at which water can enter the soil under specified conditions, including the presence of excess water.
Atom, group of atoms, or compound that is electrically charged as a result of the loss of electrons (cation) or the gain of electrons (anion).
A thin indurate soil horizon in which iron is a major constituent of the cementing material.
A chemical element necessary in large amounts, usually greater than 1 ppm in the plant, for the growth of plants and usually applied artificially in fertiliser.
The average moisture content of a disturbed sample of soil, 1 cm high, that is at equilibrium with a water table at its lower surface.
A microorganism growing best in the presence of small amounts of atmospheric oxygen.
A chemical element necessary in only small amounts, usually less than 1 ppm in the plant, for the growth of plants and the health of animals. Examples of these elements are boron, molybdenum, copper, iron, manganese, and zinc.
A homogeneous naturally occurring phase, sometimes restricted to inorganic, crystalline phases.
Any material such as straw, sawdust, leaves, plastic film, or loose soil that is spread on the surface of the soil to protect the soil and the plant roots from the effects of raindrops, soil crusting, freezing, and evaporation.
A mass of threadlike filaments branched or composing a network, that constitutes the vegetative structure of a fungus.
The sequence of biochemical changes by which nitrogen is used by a living organism, liberated upon the death and decomposition of the organism, and converted to its original state of oxidation.
The conversion of elemental nitrogen (N2) to organic combinations or to forms readily utilizable in biological processes.
An order of soils that have developed dominantly from organic deposits. The majority of Organic soils are saturated for most of the year, unless artificially drained, but some of them are not usually saturated for more than a few days. They contain 17% or more organic carbon.
The effective diameter of a particle measured by sedimentation, sieving, or micrometric methods. Has been called grain size.
Weight units of any given substance per one million equivalent weight units of oven dry soil; or, for soil or other solutions, the weight units of solute per million weight units of solution.
Unconsolidated soil material consisting largely of undecomposed or only slightly decomposed, organic matter.
A water table due to the "perching" of water on a relatively impermeable layer at some depth within the soil. The soil within or below the impermeable layer is not saturated with water.
Chemicals that kill organisms that are injurious to man or to the crops and animals upon which he depends for food, fibre, and shelter. These organisms include insects, mites, microorganisms, weeds, and rodents. Pesticides include insecticides, fungicides, herbicides, and others.
The versatility of the porphyrin ring, its molecular simplicity and its ubiquity in the biosphere suggest that it was developed a very long time ago. At that time life's chemistry was less elaborate than it is now, and one molecule may have performed many functions. A porphyrin molecule is a planar group of four connected rings, each of which contains a nitrogen atom that faces the center of the ring cluster. These four nitrogens provide an ideal environment for the insertion of a metal ion, such as iron or magnesium, which are extremely useful for a variety of oxygen-related reactions. A particular porphyrin ring containing magnesium is the organic molecule called chlorophyll, the substance in green plants that helps harvest the electromagnetic energy of sunlight for use in photosynthesis.
A vertical section of the soil through all its horizons and extending into the parent material.
Small heterotrophic bacteria of the genus Rhizobium capable of forming symbiotic nodules on the roots of leguminous plants. In the nodules, the bacteria fix atmospheric nitrogen that is used by the plants. The bacteria receive their energy from the plants.
In the lower plants, one of the unicellular or multicultural root like filaments that serve for attachment and absorption.
A classification of soil structure based on the shape of the aggregates or peds and their arrangement in the profile
The combination or arrangement of primary soil particles into secondary particles, units, or peds.
The moisture content of a soil at which plants (specifically sunflower plants) wilt and fail to recover their turgidity when placed in a dark, humid atmosphere. The wilting point is commonly estimated by measuring the 15-bar percentage of a soil.