Glossary
Glossary of Terms adapted from Agriculture and Agri-Food Canada http://sis.agr.gc.ca/cansis/glossary/u/index.html and Krzic et al., 2013 SoilWeb200 http://soilweb200.landfood.ubc.ca/glossary/
4R
in fertilizer use, the 4Rs refer to (1) the right source of fertilizer, (2) the right rate of fertilizer, (3) the right timing of fertilizer application, and (4) the right placement of fertilizer to achieve efficient and timely uptake of fertilizer nutrients by growing crops. The goal is to properly nourish the crop and achieve the economically optimal crop yield, without any excess.
Active acidity
the activity of hydrogen ions in the aqueous phase of a soil. It is the acidity immediately measured in the soil solution.
Activity (a)
a measure of the “effective concentration” of a species in a mixture.
Adenosine triphosphate (ATP)
an energy storage compound common to all biological systems. The high-energy intermediate is formed during photosynthesis or by the breakdown of energy-containing material, such as glucose. Supplies the energy for many cellular reactions and functions.
Adhesion
the force that holds molecules of dissimilar substances together; e.g., the attraction of water molecules to soil particles
Adsorption
binding of a nutrient ion to a surface, such as surface complexation reactions on soil organo-minerals.
Adsorption
movement of a nutrient ion through the plasma membrane of a living organism (e.g., a plant or a microorganism).
Adsorption
the process in which one substance (e.g. soil water) adheres to a surface (e.g. soil particles)
Aerobe
organism requiring oxygen for growth.
Aerobic
(1) having molecular oxygen as a part of the environment.
(2) growing only in the presence of molecular oxygen, such as aerobic organisms.
(3) occurring only in the presence of molecular oxygen, as applied to certain chemical or biochemical processes such as aerobic decomposition.
Aerobic respiration
cellular respiration utilizing O2 as the terminal electron acceptor
Agroenvironmental (also agro-environmental; agri-environmental)
relating to the agricultural environment and the adjacent environments. In nutrient management, the agroenvironmental goal is to achieve the crop yield target without releasing excess nutrients into adjacent environments.
agroforestry
a land use system in which woody perennials are grown for wood production with agricultural crops, with or without livestock production. agroforesterie, agrosylviculture
amendment, soil
the addition of materials (e.g., lime, gypsum, sawdust, compost, animal manures, or synthetic soil conditioners) to soil to enhance plant growth. Fertilizers constitute a special group or soil amendments. amendement du sol
Amendment
any material that is added to improve soil condition but does not necessarily provide nutrients in the short-term (e.g., mulch, biochar).
Amorphous mineral
(1) A mineral that has no definite crystalline structure.
(2) A mineral that has a definite crystalline structure but appears amorphous because of the small crystallite size.
(3) A noncrystalline constituent that either does not fit the definition of allophane or it is uncertain that the constituent meets allophane criteria.
Amorphous Mineral
a mineral solid that lacks the long-range order characteristic of a crystal. The internal order of chemical bonds and atoms are either random or very short order. Individual mineral grains are typically very small and produce either no X-ray diffraction pattern or ones with very broad low intensity peaks.
Amphoteric
a metal oxide or hydroxide able to react both as a base and as an acid
Amphoteric
materials that can be both positively and negatively charged. The proportion of the charge sites depends on the pH of the environment. Amphoteric minerals are generally positively charged at low pH and negatively charged at high pH values. Oxides or hydroxides that have surface hydroxyl groups (e.g., Al(OH)3 or goethite) are usually amphoteric.
Anabolism
the metabolic process involving the conversion of simpler substances to more complex substances or the storage of energy. More generally, the synthesis of organic compounds within an organism. Also called assimilation, biosynthesis, or constructive metabolism.
Anaerobe
organism that lives in the absence of air (oxygen).
Anaerobic
(1) the absence of molecular oxygen;
(2) Growing in the absence of molecular oxygen (e.g., anaerobic bacteria);
(3) Occurring in the absence of molecular oxygen (e.g., a biochemical process).
Anaerobic respiration
a metabolic process for energy (often ATP) generation in which electrons are transferred from a reduced organic or inorganic compound to an inorganic acceptor molecule other than oxygen. The most common acceptors are carbonate, sulfate, and nitrate.
Anion exchange
a process in which anions in solution are exchanged with anions held on positively charged exchange sites on the surfaces of mineral or organic particles.
Anion Exchange
a process in which anions in solution are exchanged with anions held on positively charged exchange sites on the surfaces of mineral or organic matter.
Anion exchange capacity (AEC)
the total number of exchangeable anions that a soil can adsorb. It is expressed in cmol(+)/kg soil.
Anthroposol
an azonal soil, highly modified or constructed by human activity, with one or more natural horizons removed, removed and replaced, added to, or significantly modified. Defining features are severe disruption of soil forming factors and introduction of potentially new pedogenic trajectories. Disturbed layers are anthropic in origin and contain materials significantly modified physically and/ or chemically by human activities.
Arbuscular mycorrhizae
mycorrhizal association with intracellular penetration of the host root cortical cells by the fungus as well as outward extension into the surrounding soil.
Atterberg limits: see liquid limit and plastic limit
Available water storage capacity (AWSC)
corresponds to the water retained in the soil between the states of field capacity (FC) and permanent wilting point (PWP), i.e. AWSC = FC – PWP; considered as the portion of water in a soil that can be absorbed by plant roots
Base saturation percentage
The extent to which the adsorption complex of a soil is saturated with exchangeable cations other than hydrogen and aluminum; expressed as a percentage of the total cation exchange capacity.
Bioaccumulation
the process of a steady buildup of a contaminant in an organism over its lifetime (also see Biomagnification)
Bioaugmentation
inoculation of soil or other media with microorganisms to facilitate bioremediation; may refer to inoculation of a single organism or a group (consortium) of organisms.
Bioavailabile
the state of a compound being easily taken up by an organism, typically referring to an energy or anabolic nutrient source, or a pollutant or toxicant.
Bioavailability
in the context of bioremediation, refers to the relative availability of the contaminant to microbial decomposers or their enzymes; contaminants that are entrapped in soil aggregates or which are strongly sorbed to soil solids may have reduced bioavailability and may exhibit limited or slow biodegradation.
Biodegradation
the biochemical conversion of a parent organic compound to simpler forms; may or may not be complete conversion to inorganic constituents.
biodrilling
the creation of channels through layers of soil compaction by plant roots. When left undisturbed, these channels allow the roots for subsequent crops to growth through the compaction layer.
Biological control
a method of controlling pests or undesirable species by introducing or manipulating naturally occurring predatory organisms or their products, or by sterilizing them. In agriculture, biological control is used to reduce or replace mechanical or chemical means of controlling pests.
Biological nitrogen fixation
the transformation of atmospheric N2 into ammonia (NH3) through the reaction N2 + 8 H+ + 16 ATP + 8 e- 🡪 2NH3 (g) + H2 + 16 ADP + 16 Pi . The reaction is mediated by symbiotic, associative and free-living soil prokaryotes that possess the nitrogenase enzyme.
Biological Treatment
remediation strategies that facilitate growth of organisms, such as microorganisms and/or plants, to convert contaminants to non-hazardous or less toxic compounds or compounds which are more stable, less mobile, and/or inert.
Biomagnification
the increase (often exponential) in tissue concentrations of contaminants up trophic levels in food webs to apex organisms.
Bioremediation
remediation strategies that use of biological agents, such as microorganisms, to destroy, remove, or convert contaminants in soils, ground water or other contaminated media to less toxic forms.
Biostimulation
addition of nutrients to stimulate microbial activity including biodegradation of contaminants; commonly added nutrients include nitrogen and phosphorus.
Bottom-up processes
in reference to trophic interactions in a community, where the level of a primary resource determines the population of consumers.
Bulk density (ρb)
the mass of dry soil per unit bulk volume, i.e., ρb = Ms / Vt expressed in kg m-3 or g cm-3
Capillary (water)
the water held in soil micropores due to adhesion and cohesion; usually at soil tension >60 cm of water
Carnivore
an animal that obtains its nourishment by eating other animals.
Cation exchange capacity (CEC)
(plural) total number of exchangeable cations that a soil can adsorb. It is expressed in cmol(+)/kg soil.
Cation exchange
a process in which cations in solution are exchanged with cations held on negatively charged exchange sites on the surfaces of mineral or organic particles.
Cation Exchange
a process in which cations in solution are exchanged with cations held on negatively charged exchange sites on the surfaces of mineral or organic matter.
Charge density
amount of electric charge per unit length, surface area, or volume
Chemical Treatment
remediation strategies that involve chemical conversion of contaminants to non-hazardous or less toxic forms, or to compounds which are less mobile or inert. Includes chemical oxidation, chemical reduction, and neutralization of acidic or basic media types. Chemical oxidation and reduction are generally more applicable to contaminated waters or to soil slurries with high water content.
Cilia (plural)
Small hairlike projections found on the surface of some microorganisms and used for movement.
Clay Mineral
finely crystalline hydrous aluminosilicates and hydrous magnesium silicates with phyllosilicate structure.
Clay
(1) particle-size less than 0.002 mm in equivalent diameter;
(2) a textural class
Clay mineral
any naturally occurring mineral with equivalent particle diameter less than 0.002~mm (<2mm).
Coarse fragments
rock or mineral particles greater than 2.0 mm in diameter
Cohesion (soil water)
attraction between like molecules, e.g., the attraction of soil water molecules to each other
Colloid
any inorganic or organic soil particle <0.002 mm diameter.
Colloidal fraction
a particle 0.1 to 0.001 μm in diameter. Soil clays and organic matter are often called colloids because they fall within these size dimensions. In some soil science literature, colloids are also defined as any inorganic or organic soil particle <0.002 mm (2 μm) diameter.
Commensalism
interaction between two species in which one species derives benefit while the other is neither benefited nor harmed.
Community
all the organisms that occupy a specific habitat and interact with one another in time and space.
Compaction (soil)
increase in soil bulk density and corresponding decrease in porosity due to the application of mechanical or other stresses to the soil; commonly the result of heavy machinery compressing the soil, but can also occur due to foot or animal traffic.
compaction
increasing soil bulk density, and concomitantly decreasing soil porosity, by the application of mechanical or other forces to a soil. As soil compaction increases, a state of excessive compaction can be reached that adversely affects plant growth.
Complex ion
a charged species consisting of a metal ion surrounded by ligands (i.e., molecules or ions that donate a pair of electrons to a metal ion to form a complex).
compost
soil conditioner and fertilizers produced from organic residues or a mixture of organic residues and soil, that have been piled, moistened, and allowed to decompose. compost
conservation tillage
any tillage sequence, the object of which is to minimize or reduce loss of soil and water; operationally, a tillage or tillage and planting combination which leaves 30% or greater cover of crop residue on the surface. pratiques de conservation
Consistence (soil)
(1) the resistance of a soil to deformation or rupture;
(2) the degree of cohesion or adhesion of the soil mass
Consumer
an organism that gains energy by feeding on another organism. The place for a consumer in the food chain is defined by what it eats.
Contaminant(s)
chemical contaminants refers to any chemical substance whose concentrations exceed background concentrations or which is not naturally occurring in the environment or biosphere. Compare with pollutant.
controlled traffic
tillage [and all activities] in which all operations are performed in fixed paths so that recompaction of soil by traffic (traction or transport) does not occur outside the selected paths [called tramlines]. circulation limitée
conventional tillage
tillage operations normally performed in preparing a seedbed for a given crop grown in a given geographical area. travail du sol conventionnel
cover crop
a crop used primarily for the purpose of protecting and improving the soil between periods of regular crop production, or between rows of permanent standing crops (e.g., orchards and vineyards). culture de couverture
crop rotation
the practice of growing different crops in a planned regular sequence or succession on the same land. Usually established for economic considerations, especially to aid in the control of insects and diseases, maintain soil fertility, and decrease soil erosion. rotation culturale ou des cultures
Decomposer
a heterotrophic organism, chiefly a microorganism (bacteria or fungi), that breaks down the bodies of dead animals or parts of dead plants and absorbs some of the decomposition products while releasing nutrients usable by producers.
Denitrification
reduction of nitrate, nitrite to molecular nitrogen, or nitrogen oxides by microbial activity or chemical reactions involving nitrite. Microbial denitrification is an anaerobic respiratory process characteristic of facultative aerobic bacteria growing under oxygen-depleted conditions.
Detritivore
animal that feeds on particulate material derived from the remains of plants or animals, including large scavengers, smaller animals such as earthworms and some insects, and decomposers.
Diffusion (of gas)
the movement of a gas (e.g., CO2) from an area of high concentration to low concentration due to a difference in the partial pressure of the particular gas
Diffusion (of solutes)
the movement of a solute (e.g., K+) from an area of high concentration to an area of low concentration, tending to bring about a uniform distribution within the soil solution
Diploid (2n)
pertaining to cells or organisms having two sets of chromosomes.
ecological niche
the physical space in a habitat occupied by an organism; its functional role in the community (e.g., its trophic position). niche écologique
Ecological pyramid
a visual representation, resembling a pyramid, that depicts the total mass of organisms residing in each trophic level in a given area. The bottom bar of the pyramid represents the mass of plants, the top bar represents the mass of carnivores, and intermediate bars represent other forms of biota in the feeding structure of the community.
Ecological Restoration
the process of assisting recovery and management of ecological integrity. Ecological integrity includes a critical range of variability in biodiversity, ecological processes and structures, regional and historical context, and sustainable cultural practices.
Ecosystem
a functional unit consisting of all the living organisms (plants, animals, and microbes) in a given area, and all the non-living physical and chemical factors of their environment, linked together through nutrient cycling and energy flow
Ectomycorrhizal fungi
a mycorrhizal association in which the fungal mycelia extend inward, between root cortical cells, to form a network, and outward into the surrounding soil. Usually the fungal hyphae also form a covering or mantle on the surface of the roots.
Eh (see redox potential)
Electrical conductivity (EC)
the reciprocal of electrical resistivity. The conductivity of electricity through water or an extract of soil; expressed in decisiemens or (dS m-1) siemens per meter at 25°C. It is a measure of soluble salts content in solution.
Eukaryote
a cell that has a membrane-bound nucleus, membrane-bound organelles, and chromosomes in which the DNA is associated with proteins; an organism composed of such cells.
Exchangeable sodium percentage (ESP)
the fraction of the cation exchange capacity of a soil occupied by sodium ions.
Facultative anaerobe (or facultative aerobe)
the ability of certain organisms to harness energy from the environment under both aerobic and anaerobic conditions
fallow land
land not being used to grow a crop, but cultivated or left untilled during the whole or greater portion of the growing season to preserve water, kill weeds, and increase soil
Fermentation
a type of bacterial or yeast metabolism (chemical reaction) characterized by the conversion of carbohydrates to acids or alcohols, usually occurring in the absence of molecular oxygen.
Fertilizer
any material that supplies nutrients for crop production
Field capacity (FC)
the percentage of water remaining in the soil 2 or 3 days after the soil has been saturated and the rapid drainage phase has ceased
Fine earth fraction
the fraction of mineral soil consisting of particles <2 mm in diameter; includes sand, silt and clay
Fixation
the reaction that occurs when ions moves into the interlattice of an expanding lattice clay. This is more likely with K+ and NH4+ due to their 1+ charge and relatively small ionic radius.
Flagellum (plural flagella)
a flexible, whiplike appendage on cells, used as an organ of locomotion.
forage
(1) edible parts of plants, other than separated grain, that can provide feed for grazing animals or can be harvested for feeding, including browse, and herbage;
(2) to search for or to consume forage (of animals). (1) fourrage (2) fourrager
Formula Unit
the empirical formula of any solid compound used as an independent entity for stoichiometric calculations. Typically equivalent to a “unit half-cell” (see unit cell).
Friable
a descriptor of consistence, pertaining to the ease by which a soil crumbles
fumigant
a chemical compound in the form of a gas, particulate, vapor, or smoke, usually used to kill pests (e.g., fungi, insects, or rodents). fumigant
Generalist
a species that has very a broad feeding niche (e.g., a consumer in soil that will feed upon multiple types of living plant tissues or detritus as well as fungal hyphae)
Gravimetric water content (θw)
the ratio of water mass to dry soil mass, i.e., θw = Ml / Ms commonly expressed in g g-1
Gravitational potential
the attraction of water down the soil profile due to the pull of gravity
Gravitational water
water that moves into, through or out of the soil by gravity
green manure
any crop or plant grown and plowed under when green or soon after maturity to improve the soil by adding organic matter and subsequently releasing plant nutrients, especially nitrogen.
Haploid (1n)
A cell or organism that contains a single set of chromosomes.
heat capacity (soil)
the amount of heat required to raise the temperature of a unit volume of soil by 1ºC
Herbivore
a consumer that eats plants or other photosynthetic organisms to obtain its food and energy.
Horizontal gene transfer
the movement of genetic material by means other than parent to offspring.
Humus
(1) the fraction of the soil organic matter that remains after removal of macroorganic matter and dissolved organic matter. It is usually dark-colored;
(2) also used in a broader sense to designate the humus forms referred to as forest humus;
(3) all the dead organic material on and in the soil that undergoes continuous breakdown, change, and synthesis.
Hydraulic conductivity (K)
the proportionality factor describing the capability of a medium to transmit liquid; used in the calculation of the rate at which water flows in the soil (Darcy’s Law)
Hygroscopic water
corresponds to the soil water content below the permanent wilting point, i.e. below a matric potential of about -310 m (-3100 kPa); water lost from an air-dry soil when it is heated to 105 °C
Hyphae
branching filament structures in soil fungi and actinobacteria. The aggregated structures of hyphae are called mycelia.
Immobilization
a biological process whereby ions and low molecular weight compounds are absorbed from the environment (e.g., the soil pore water) into a biological organism (e.g., into a microbial cell).
Infiltration
the downward entry of water into the soil
intercropping
sowing [or growing] two or more crops simultaneously [often] in alternate rows. cultures intercalaires
Isomorphous Substitution
the replacement of one atom by another of similar size in a crystal structure without disrupting or seriously changing the structure. Occurs during the formation of the mineral. When a substituting cation is of a smaller valence than the cation it is replacing, there is a negative charge on the structure. Occurs during the formation of the mineral when elements of a similar size and valence are substituted for one another within a crystal structure. This commonly occurs in phyllosilicates where Al substitutes for Si in tetrahedral sheets and Mg or Fe substitute for Al in octahedral sheets. This substitution usually results in a charge deficit within the structure forming a surface charge site for cation exchange.
K strategists
K-selected species; from logistic growth curve equation referring to maximum carrying capacity of the ecosystem.
Species that are characterized by having few, slower slow-growing and long-lived offspring that flourish in stable environmental conditions.
Land Reclamation
the process of converting disturbed or damaged land to its former or other productive uses.
legume
a plant of the botanical family Leguminosae, (e.g., pea or bean), which has the ability to fix atmospheric nitrogen through a symbiotic association with nodule-forming bacteria of the genus Rhizobium. légumineuse
Lichens
organism resulting from the symbiotic relationship between a fungi and algae or cyanobacterium. They live in a wide range of habitats, from desert to polar regions and the tropics, but are commonly found in barren environments, and are dominant in tundra regions and mountains. Lichens are very sensitive to air pollution and serve as an indicator species. They occur in one of four basic growth forms: crustose- crustlike, growing tight against the substrate; squamulose- tightly clustered and slightly flattened pebble-like units; foliose- leaflike, with flat sheets of tissue not tightly bound; fruticose- free-standing branching tubes.
Lime
(1) a calcareous material containing anions that neutralize H+, such as agricultural limestone, CaCO3, calcium hydroxide, Ca(OH)2, calcium oxide, CaO, and dolomitic limestone, CaMg(CO3)2.
(2) calcium oxide (CaO). In agriculture, lime is defined as a soil amendment containing calcium carbonate, magnesium carbonate, and other materials, used to neutralize soil and furnish calcium and magnesium for plant growth.
Liquid limit (Atterberg limit)
the water content corresponding to a change from plastic to liquid states of consistence of a soil; the water content at which a soil will just begin to flow
loosening
(1) the increase in volume of voids in soils by plant, animal, and human activity, by freeze-thaw or other physical processes, and by removal of materials by leaching;
(2) decreasing soil bulk density and increasing porosity due to the application of mechanical forces to the soil
Macro-pores
also called aeration pores, are large pores (diameter > 0.08 mm) that occur between aggregates or between individual sand grains in coarse textured soil. They allow movement of air and the drainage of water, and accommodate roots and small animals to inhabit the soil
manure
the excreta of animals, with or without the admixture of bedding or litter, in varying stages of decomposition. It is also called barnyard manure or stable manure. This is the usual meaning in North America. In some countries manure is used to refer to any fertilizer. fumier, fumure, engrais
Mass flow (soil solution)
when an entire mass of soil solution moves from high to low pressure potential
Matric potential
the attraction of water molecules to the soil solids due to adsorption and capillarity forces
Meiosis
the process of nuclear division in a cell by which the chromosomes are reduced to half their original number; occurs during the formation of sex cells.
Metastable
having a state of apparent equilibrium although capable of changing to a more stable state
Methanogenesis
biological production of the reduced simple hydrocarbon (and atmospheric greenhouse gas) methane (CH4); carried out by anaerobic members of the domain Archaea using a limited number of simple substrates that are produced by symbiotic fermentative bacteria.
Methanotroph
a microbe that consumes methane (CH4). Typically, in soils methanotrophs are aerobic lithotrophic bacteria that gain carbon for anabolism and energy from CH4. Soil methanotrophs in wetlands prevent the release of CH4 to the atmosphere, while in upland soils, methanotrophs are sinks for atmospheric CH4.
Micro-pores
also called water-retention pores, are small pores (diameter < 0.08 mm) that occur within soil aggregates or between clay particles in fine textured soils. They are usually filled with water and are too small to permit significant air movement
Microbial biomass turnover
determined by microbial cell production and cell death.
Microbial grazers
consumers that feed on decomposers or plant pathogens
Mineral
a mineral species are crystalline compounds with a well-defined chemical composition and specific crystal structure.
Mineralization
the conversion of an organic compound to an inorganic form through microbial activity (e.g. conversion of a petroleum compound to CO2)
Mineralization
(1) a biochemical transformation that cleaves at least one covalent bond in an organic compound to release an ion;
(2) the conversion of an organic substance to an inorganic form, often as a result of microbial decomposition. Gross mineralization is the total amount converted, and net mineralization, the gross minus the growth demand or immobilization by the decomposer organisms, usually measured in laboratory incubations.
Mitosis
the process of cell division involving the replication and division of the cell nucleus; results in two genetically identical cells.
monoculture
(1) the repetitive growing of the same crop on the same land, season after season;
(2) the cultivation of a single crop. monoculture
Motile (motility)
capable of movement.
mulch tillage
a system of tillage and planting operations which maintains a substantial amount of plant residues or other materials are left to cover the surface; also called mulch farming, trash farming, stubble mulch tillage, plowless farming; operationally, a full-width tillage or tillage and planting combination that leaves > 30% of the surface covered with crop residue.
Mutualism
an interaction between two or more distinct biological species in which all members benefit from the association.
Mycelium (plural mycelia)
a mass of threadlike filaments, branched or composing a network, that constitutes the vegetative structure of a fungus.
Mycorrhizae
the association, usually symbiotic, of fungi with the roots of seed plants. Under favourable soil conditions, plants with mycorrhizae have been shown to produce up to four or five times as much growth as similar plants without mycorrhizae. The mycorrhizae absorb water and nutrients and pass them on to the plant, secrete hormones that stimulate plant growth, and help protect the plant roots from disease organisms. In return, the fungi depend on the plant for carbohydrates.
Mycorrhizal fungi
the fungal partners in mycorrhizae
no-till
a system whereby a crop is planted directly into the soil with no primary or secondary tillage since harvest of the previous crop; special seeding equipment is necessary to prepare a narrow, shallow seedbed immediately surrounding the seed being planted. No-till is sometimes practiced in combination with subsoiling to facilitate seeding and early root growth, whereby the surface residue is left virtually undisturbed except for a small slot in the path of the subsoil shank. zéro-labour, semis direct, système de culture sans labour [Note to Editor: this is from definition from Gregorich et al. 1999, which the authors feel is not reflective of the current definition. Our preference is to revise it for this textbook]
Nucleic acids
biopolymers present in all organisms responsible for genetic coding and storage, gene expression, protein synthesis, and even some catabolic activities. Nucleic acids encompass ribonucleic acid polymers (RNA) deoxyribonucleic acid polymers (DNA).
Nutrient stewardship
an approach that requires prudent and judicious use of all fertilizers, considering that soil fertility derives from the soil nutrient supply, crop residues, historical manure applications, on-farm nutrient sources and commercial fertilizers.
Nutrient
a chemical substance that is essential to life because its elemental form is required for energy relations, synthesizing the building blocks for repair and growth, and generating substances necessary to regulate biochemical processes
organic farming
crop production systems that attempt to rely solely on organic matter or natural materials for crop production. They avoid and largely exclude the use of synthetic fertilizers, pesticides, growth regulators, and livestock feed additives. Organic farming relies instead on crop rotations, crop residues, animal manures, legumes, green manures, off-farm organic wastes, mechanical cultivation, mineral-bearing rocks, and biological pest control to maintain soil productivity and tilth, to supply plant nutrients, and to control insects, weeds, and other pests.
Osmotic potential
the attraction of water to solutes
Oxy hydroxide minerals (see sesquioxides)
Parasitism
interactions between species where one benefits and one is harmed.
Particle density (ρp)
the mass per unit volume of the soil particles, i.e., ρp = Ms / Vs expressed in kg m-3 or g cm-3
Percolation (of soil water)
the downward movement of water through the soil in saturated or nearly saturated conditions
Permanent wilting point (PWP)
corresponds to the water content of a soil at which plants wilt and fail to recover; commonly estimated by measuring the soil water content at a tension of 1500 KPa (or 150 m of water)
Petroleum Hydrocarbon (PHC)
a broad range of chemicals that comprise crude oil and products refined from oil, such as gasoline and diesel.
Phyllosilicate
a silicate structure in which the SiO4 tetrahedra are linked together in infinite two-dimensional sheets and are condensed with layers of AlO or MgO octahedra in the ratio 2:1 or 1:1.
Phyllosilicates
a class or structural type of silicate in which the SiO4 tetrahedra are lined together in infinite two-dimensional sheets and are condensed with layers of AlO or MgO octahedral in the ratio 2:1 or 1:1. Also called layer silicate minerals.
Physical Treatment
remediation strategies that use physical properties of contaminants or contaminated media to separate, remove, or immobilize the contamination.
Phytoremediation
use of macroscopic plants to extract, degrade, contain, or immobilize contaminants in soil, ground water and other contaminated media.
Phytostimulation
the promotion of plant root growth facilitated by compounds released by rhizosphere microorganisms.
Plant available water (PAW) (see available water storage capacity; AWSC)
Plant growth promoting rhizo-organisms (PGPR)
bacteria or fungi living in or on roots or in the rhizosphere that enhance plant growth directly (e.g., biological nitrogen fixation) or indirectly by protecting plants from disease and abiotic stresses such as drought.
Plant-pathogens
microbes, primarily fungi and bacteria, that feed on living plant cells/tissues and cause harm to the host.
Plant-pests
invertebrate animals that feed on living plant cells/tissue and cause harm to the host
Plastic limit (Atterberg limit)
the water content corresponding to a change from plastic to semi-solid states of consistence of a soil; the water content at which a soil will just begin to crumble when rolled into a thread approximately 3 mm in diameter
plow pan
a pan created by plowing at the depth of tillage, largely the result of the common practice of dropping the tractor wheels of one side of the tractor into the dead furrow for steering while performing the plowing operation. semelle de labour
plowing
a primary broadcast tillage operation performed to shatter soil with partial to complete inversion. labour
Pollutant
a chemical or material out of place or present at higher concentrations that has adverse effects on organisms.
Polymerase chain reaction (PCR)
an in-vitro method for amplifying defined segments of DNA. PCR involves a repeated cycle of oligonucleotide hybridization and extension on single-stranded DNA templates.
Polymorphs
minerals with the same chemical composition but different crystal forms.
Population
All individuals of a species living in defined geographical area at the same time in association with each other.
pore
a void or space in a soil or rock not occupied by solid mineral material. The part of the bulk volume of soil not occupied by soil particles. Also called interstices or voids. pore
Pore-size distribution
the range in volume of the various sizes of pores in a soil
Porosity (f)
the volume percentage of the total bulk soil occupied by voids; f = Vf / Vt = (Vt – Vs) / Vt expressed in cm3 cm-3 or %
Primary producers
autotrophic organisms in an ecosystem, i.e., those capable of reducing the carbon molecule in CO2 to form new organic carbon molecules such as sugar. Primary producer biomass serves as the energy and carbon input to an ecosystem, fuelling all subsequent consumption.
Prokaryote
refers to single cellular organisms that typically lack internal membrane-bound organelles, and notably, never contain nuclei. Members of the domains of life Bacteria and Archaea are prokaryotes.
Pulse
the edible seeds of any leguminous plant.
pyrolysis
the thermal destruction of some material (e.g., coal, oil, wood, or other organic substance) in the absence of molecular oxygen. Also called destructive distillation. Pyrolise
r-strategists
r-selected species; from logistic growth curve equation referring to growth rate. Species that are characterized by having high growth rates, producing many offspring and flourish in resource-rich, less-crowded conditions that are unstable or fluctuating in environmental conditions.
Redox potential (Eh)
The potential generated between an oxidation or reduction half-reaction and the standard hydrogen electrode. In soils, it is the potential created by oxidation-reduction reactions that take place on the surface of a platinum electrode measured against a reference electrode minus the Eh of the reference electrode.
Remediation
improvement of a contaminated site, including contaminated soil, to prevent, minimize, or mitigate damage to human health or the environment.
Reserve acidity
acidity associated with the exchange sites
Respiration (cellular; chemiosmosis)
a metabolic process in an individual cell, tissue, or organism resulting in the release of chemical energy derived from chemically reduced organic or inorganic nutrients. Specifically, a series of reactions in a cell during which electrons removed during the oxidation of reduced substrates are transferred to an terminal acceptor.
Rhizosphere
the area of soil immediately surrounding plant roots in which the kinds, numbers, and activities of microorganisms differ from that of the bulk soil.
ridge tillage
a tillage system in which ridges are reformed atop the planted row by cultivation, and the ensuing row crop is planted into ridges formed in the previous growing season.
Rock
any naturally occurring solid mass or aggregate made up of physical mixtures of individual minerals or mineraloid matter.
Saline soil
A nonsodic soil containing enough soluble salts to interfere with the growth of most crop plants. The conductivity of the saturation extract is >4 dS m-1 at 25°C, the exchangeable sodium percentage is <15, and the pH is usually <8.5.
Saline-sodic soil
(1) a soil containing appreciable quantities of soluble salts with enough exchangeable sodium to interfere with the growth of most crop plants as well as an exchangeable sodium percentage >15, a conductivity of a saturation extract >4 dS m-1 at 25°C, and a pH 8.5 or less in the saturated soil;
(2) a soil that has a combination of harmful quantities of salts and either a high alkalinity or high content of exchangeable sodium, or both, so distributed in the profile that the growth of most crop plants is reduced.
Salinity
the amount of dissolved salts in a medium. Soil salinity is the amount of soluble salts in a soil; usually determined by measuring the electrical conductivity of a saturation extract.
Sand
(1) a soil particle between 0.05 and 2.0 mm in diameter;
(2) a soil texture class
Saprotroph
Any organism that derives its nutrition from dead or decayed organic material, in contrast to a parasitic organism that obtains its nutrition at the expense of a living organism.
Sodium Adsorption Ratio (SAR)
a measure of the amount of sodium ions (Na+) relative to calcium (Ca2+) and magnesium (Mg2+)ions in the water extract from a saturated soil paste;
SAR= [Na+] / [Ca2+ + Mg2+]1/2 where concentrations of ions, denoted by square brackets, are in millimoles per liter.
Saturated (water content)
all the voids between soil particles are filled with water
seedbed
the tillage-manipulated soil layer that affects the germination and emergence of crop seeds. lit de semence
Sesquioxides
any of the oxides and hydroxides of iron and aluminum.
Silt
(1) a soil separate consisting of particles between 0.05 and 0.002 mm in equivalent diameter;
(2) a soil texture class
Sodic soil
(1) A nonsaline soil containing sufficient exchangeable sodium to interfere with the growth of most crop plants;
(2) A soil having an exchangeable sodium percentage of 15 or more.
Sodicity
The level of exchangeable sodium and its influence on a soil.
Sodium adsorption ratio (SAR)
the relationship of soluble sodium to soluble calcium plus magnesium in water or the soil solution, expressed by this equation:
soil [health] quality attribute
properties that reflect or characterize a soil process, or processes that support a specific soil function.
soil amendment
Any material added to soil that [is intended to] enhances plant growth, via the nutrients they contain, or improves the soil condition (e.g., lime, gypsum, compost, animal manures, plant residues, certain industrial wastes, and synthetic soil conditioners). amendement du sol
soil degradation
The general process by which soil gradually declines in quality and is thus made less fit for a specific purpose, such as crop production. See erosion. dégradation des sols
Soil fertility
the inherent ability of soil to support crop growth, without human intervention.
Soil food web
the interrelationship among the organisms in a soil community according to the transfer of useful energy from food resources to organisms eating those resources.
soil function
the various roles that soil performs, or the tasks that are placed upon soil, that underpin the concept of soil quality. Soil functions in three main ways: as a medium for plant
soil health
an approach to soil condition analogous to human or community health, by which the condition of a soil’s properties and morphology are assessed against some optimum condition (i.e., soil-as-an-organism), or a soil’s functions assessed against the goals placed upon them (i.e., soil-as-a-community), or against an optimum functional state. Often soil health is used synonymously with soil quality, except that a soil may have poor inherent soil quality but still have good health.
soil management
the total of all tillage operations; cropping practices; and application of fertilizer, lime, and other treatments to a soil to produce plants and [ideally] improve soil condition. See tillage, soil management.
Soil productivity
the ability of soil to support crop growth when correctly managed (e.g., fertilized, irrigated, drained, etc.)
soil resiliency
the capacity of a soil to recover its qualitative functions and dynamic properties, generally in a relatively short time frame, after some disturbance; an aspect of soil [health/]quality.
Soil salinization
the process of accumulation of salts in soil.
Soil separates
the individual groups of soil mineral particles, i.e., sand, silt or clay
Soil solution
the aqueous liquid phase of the soil and its solutes, consisting of ions dissociated from the surfaces of the soil particles, and other soluble materials.
Soil solution
the aqueous liquid phase of the soil including ions in solution (i.e., solutes)
Soil structure
the combination or arrangement of primary soil particles into secondary particles, units, or peds
Soil water potential
the difference in energy levels between pure water in the reference state and that of soil water; the total potential of soil water consists of the sum of gravitational potential (hg) + matric potential (hm) + osmotic potential (ho) + pressure potential (hp)
Soil water tension
in soils partially saturated with water there is water tension, which is equal in magnitude but opposite in sign to the soil matric potential
soil-depleting crops
Crops that, under the usual management, tend to deplete nutrients and organic matter in the soil and permit deterioration of soil structure.
Specialist
A species that has a very selective feeding niche (e.g., that a nematode that only grazes on fungal hyphae)
Specific Surface Area (SSA)
The ratio of surface area to mass of a mineral, typically expressed as m2/g.
Specific surface area
The solid-phase surface area (of a soil or porous medium) divided by the solid-particle mass (expressed in m2 g-1), of by the soil-particle volume.
Stoichiometric
Quantitative relation between the number of moles (and therefore mass) of various products and reactants in a chemical reaction
strip tillage (partial-width tillage)
Tillage operations performed in isolated bands, separated by bands of soil essentially undisturbed by the particular tillage equipment.
subsoiling
Any treatment to loosen soil with narrow tools below the depth of normal tillage without inversion, and with minimum mixing of the soil. This loosening is usually performed by a lifting action or other displacement of soil dry enough so that shattering occurs.
sustainable soil management
Management regimes applied to soil that maintain the productive and renewal capacities as well as the genetic, species, and ecological diversity of soil ecosystems.
Symbiosis
An interaction between two different organisms living in close physical association.Interactions may be mutualistic, commensal, or parasitic
Tertiary consumers
Species that feed upon microbial grazers and plant-pests. They can be fully carnivorous or omnivorous (feeding on combinations of fungi, soil animals and living roots and other plant parts).
Texture (soil)
the relative proportions (%) of the various soil separates (i.e., sand, silt and clay size fractions) in a soil
Thermal conductivity (λ)
the proportionality factor describing the capability to transfer heat to or from a point in the soil; describes heat flow in response to a temperature gradient, expressed in units of J m-1 s-1 °C
Thermal Treatment
remediation strategies that make use of heat to separate contaminants from contaminated soil, destroy organic contaminants, and/or melt and then solidify the contaminated soil, thereby immobilizing contaminants and reducing their availability to potential receptors.
tillage
the mechanical manipulation of the soil profile for any purpose. In agriculture it is usually restricted to modifying soil conditions and/or managing crop residues and/or weeds and/or incorporating chemicals for crop production.
Top-down processes
in reference to trophic interactions in a community, where the levels of the predator determine that of the prey.
Trophic interactions
processes of energy and nutrient transfer from one or more organisms to others in an ecosystem.
underseeding
sowing a secondary crop [or cover crop] with the main crop to provide soil cover after the primary crop is harvested.
Unit Cell
the smallest number of atoms used to represent the chemical formula of a substance that included the overall symmetry of a crystal of that substance, and from which the entire lattice can be built up by repetition in three dimensions. Typically 2X the formula unit. See also formula unit.
Void
space in a soil mass not occupied by solid matter; may be occupied by air, water or other gaseous or liquid material
Volumetric water content (θv)
the ratio of water volume to total soil volume, i.e., θv = Vl / Vt commonly expressed in cm3 cm-3
Water content (θ)
the amount of water lost from the soil when it is dried to constant weight at 105oC; expressed either as the weight of water per unit weight of dry soil or as the volume of water per unit bulk volume of soil
Water table
the upper surface of groundwater or that level below which the soil is saturated
Zero point of charge
the pH at which the net charge of total particle surface is equal to zero.
