Glossary of terms for Horticulture Soils A Acid A compound that releases free hydrogen ion (H+) when released in water. Adding an acid to water will cause the pH to decrease ActinomycetesGram positive filamentous bacteria that are produced by spores. Known by their earthy- musty taste and odour . Now often called Actinobacteria. Active acidityThe activity of hydrogen ions in the soil solution which is measured and expressed as pH. Active organic matterOrganic materials that decompose quickly after being added to the soil. Active organic matter is quickly recycled to provide food for microbes and plants. Aeration The process by which soil air is constantly replaced by oxygen rich air from the atmosphere. Aerobic Organisms that require oxygen for survival Aggregate a group of soil particles that clump together to form a unit. May be very small ( about 1mm) diameter to very large ( about 10cm) Aggregation The process by which small soil particles come together to form a larger unit. Alkaline A pH value greater than 7 AnaerobicOrganisms that live and function without oxygen (O2). Some bacteria are anaerobic Anion A negatively charged ion AspectThe downslope direction of a hillside. Hillsides sloping to the south accumulate more heat than those sloping to the north. AutotrophAn organism which is able to use CO2 as its source of carbon to build body tissue B BacteriaSingle celled organisms shaped like rod, spheres are spirals that are less that 1 micron (1 millionth of a meter) in length. Because of their diversity, some form of bacteria adapt to nearly any soil condition. BaseA compound that is capable of reacting with an acid to form a salt. Adding a base to water will cause the pH to rise. Bulk Density The mass of dry soil per unit volume. Soil with a lot of pore space will have lower bulk density than compacted soils. C CarbohydratesA class of energy compounds found in living organisms which are made up of carbon chains together with hydrogen (H+) and oxygen (O). Example: sugar, starch. Carbohydrates are a component of active organic matter. Cation A positively charge ion Cation exchangeThe reciprocal movement of cations between soil solution and negatively charged adsorption sites on colloid surfaces. Cation exchange The capacity of a soil to adsorb and exchange cations measured in units Capacity (CEC)of electrical charge per soil weight. Usually expressed as milliequivalents per 100 g of soil (meq/100g) Cementation The binding together of soil particles into stable aggregates Chroma The relative purity, strength or saturation of a colour. Clay Mineral soil particles with a diameter less than 0.002mm. Usually composed of crystalline structures that carry large amounts of negative electrical charge on their surface. C:N ratioThe ratio of carbon to nitrogen found in a given sample of organic material. Organic matter with C:N ratios of less than 30 generally provide a well balanced diet for microbes and will result in a surplus of plant available nitrogen when it is decomposed. Colloid, soilOrganic and inorganic matter with very small particle size and a correspondingly large surface area per unit of mass D Deglaciation The uncovering of an area from beneath glacier ice as a result of melting Discharge ZoneAn area where groundwater moves to the soil surface bringing with it soluble salts. Usually found along hillsides or hill bottoms. Dispersion The breaking up of soil aggregates into individual sand, silt and clay particles. DrainageThe loss of water from a soil due to gravity. It may refer to movement of water over the soil surface or downward through the soil profile Dynamic equilibrium A natural chemical process which establishes a steady relationship between the amounts of a given cation on adsorption sites and the amounts of mobile cations in soil solution. E Eluviation The transportation of fine soil material in suspension or in solution within the soil by the downward or lateral movement of water. Eolian DepositsSediments that have been deposited by wind. They generally consist of fine sand and coarse silt size particles. Essential nutrientA chemical element necessary for the normal growth and reproduction of plants. ErosionThe wearing away of the land surface by running water, wind, ice or other geological agents. Exchange complexThe zone surrounding soil colloids where adsorption and exchange of nutrients into soil solution occurs F Fine textureThe texture of soil containing large quantities of silt and clay. It includes all the textural classes of clay loams ( moderately fine) and clays. Flocculation The natural process whereby individual soil particles come together to form larger clumps or aggregates Fluvial DepositsSediments deposited by rivers and streams. They generally consist of gravel and sand size particles that have been rounded by tumbling action. Free limeCa or Mg carbonates present in a soil horizon that effervesce (bubbles) when dilute HCl is added Fungi a huge group of single or multi celled organism associated with decomposition of organic matter in the soil. Mold, mildew, smut, and mushrooms are examples of fungi G Glacial till Unstratified glacial drift deposited directly by the ice and consisting of a mixture of clay, sand gravel and boulders. Glaciation A collective term for the geological processes of glaciers and the resultingeffects on the earth’s surface. Glaciera large mass of ice formed on land by the compaction and recrystallization of snow, which remains from year to year. A glacier moves downslope or outward from its center due to the stress of its own weight. Gleying a Soil forming process that occurs under poor drainage conditions. Gleying is identified by the presence of gray soil colour and sometimes by the presence of bright red or yellow splotches. GranularAn aggregate of soil usually around 1cm in diameter, found in the A horizon of a grassland soil. H Hand Texturing A method of estimating the textural class of a soil by feel. There are several tests that can be used including the dry consistence test, the moist cast and ribbon test. HeterotrophAn organism which obtains its carbon from organic sources. Important in the decomposition of organic matter. Horizon A distinct layer of soil approximately parallel to the land surface. It differs from adjacent layers in properties such as colour, structure, texture, consistence, and chemical, biological, and mineral composition. HueThe tint of colour in terms of red, yellow, blue etc. that is determined by the wavelength of light. HumusThe stable part of the soil organic matter that remains after the majority of added residues have decomposed, usually amorphous ( no definite shape) and dark coloured. HydrolysisThe process by which a substance such as a salt is split by a water molecule to form two end products. Eg: NaCl = NaOH + HCl HydroxylThe negatively charged OH- ion consisting of one atom of hydrogen and one atom of oxygen I Immobilization The removal of plant available nutrients from the soil by soil microbes. Mineral compounds ( those that do not involve carbon chains) are immobilized as the microbes use them to construct the organic tissues needed for their growth. InfiltrationThe entry of water into the soil by gravity. Inorganic compoundComposed of matter other than plant or animal origin ( mineral). A chemical compound which does not usually contain carbon. IonAn atom or group of atoms that carry either a positive or negative electrical charge Ion adsorptionThe ability of soil colloids to hold ions near their surfaces, temporarily restricting their movement through the soil L Lacustrine Sediments deposited in lakes. Lacustrine deposits are usually made up of fine silt deposits and clay particles that settle out in lake beds but they also include coarser sands deposited on beaches by wave action. Leaching The removal of salts and fine particles form the upper portion of the soil profile by the downward movement of soil water. Lignin complex organic structures derived from plant cell walls which are slowly decomposed by soil microbes. An important component of the resistant fraction of organic matter. M Macrofaunalarge animals that are visible to the naked eye. Macrofloralarge visible plants that use chlorophyll to convert sunlight into chemical energy. Macronutrientsan essential plant nutrient required in large amounts usually measured by percent weight of plant dry matter. MediaMaterial used by gardeners as a soil substitute. Examples are peat, vermiculite and perlite. Medium texturethe texture of soil between fine- textured and coarse textured soils. It includes very fine sandy loam, loam, silt loam and silt. MicrofaunaAnimals too small to be seen without a microscope MicrofloraPlants that are too small to be seen without a microscope MicronutrientsAn essential plant nutrient required in very small amounts, usually measured in parts per million (ppm) of plant dry matter. MineralA naturally occurring inorganic element or compound having an orderly internal structure and characteristic chemical composition, crystal form and physical properties. MineralizationThe conversion of organic compounds ( those involving carbon chains) into plant available mineral compounds by microbial decomposition. Common mineral plant nutrients include ammonium (NH4+), phosphate (H2PO4-) and sulfate (SO4-) MottlesSpots or blotches of different colours or shades of colour (eg: yellowish-red/rusty spots) interspersed with the dominant colour. MottlingDistinct spots or blotches of different colour of shades of colour usually found in wet, poorly drained soils. MuckHighly decomposed organic material in which the original plant parts are not recognizable. MycorrhizaeA specific group of fungi which form a symbiotic ( partnership) relationship with the roots of many plants. The mycorrhizae provide phosphorus and other nutrients to the plant root in return for carbohydrates they need for energy. N Natural fertilizerA fertilizer derived from a living source, such as manure, composts and legumes incorporated into the soil. 0 OrganicMaterial derived from living organisms such as peat and humus Organic compoundsComposed of matter derived from living things. A chemical compound which contains carbon. Organic matterPlant and animal residues at various stages of decomposition. It includes cells and tissues of soil organisms and substances synthesized by soil organisms. OsmosisThe movement of water through a semipermeable membrane towards a solution with a higher concentration of salt. OxidationThe combination of an element or compound with oxygen. P Parent Material The unconsolidated (loose) and unweathered mineral or organism material from which soils develop.It is found in the C horizon of soil profiles. PedThe basic natural unit of soil structure such as a prism, block, or granule ( in contrast to a clod which is formed artificially by operation such as cultivation) PeatUnconsolidated (loose) soil material consisting of partly decomposed organic matter from mosses, sedges, shrubs, trees and other plants that grow in bogs or other wet places. PoresThe small spaces between the soil components of a soil that are usually occupied by water and air. Also called voids. PorosityThe total volume of pore space expressed as a percentage of soil volume. PrecipitationThe process whereby dissolved salts combine to form solid crystals. Usually brought about by evaporation. Primary mineralA mineral that has not been altered chemically since the original rock forming events such as crystallization from molten lava. ProfileA vertical section of the soil through all its horizons and extending into the parent material. ProteinA class fo organic compounds found in all living organisms. Contain a wide range of plant nutrients including nitrogen (N), phosphorus (P) and sulfur (S). Proteins are readily decomposed by soil microbes. ProtozoaSingle celled microscopic organisms which include amoeba, flagellates and ciliates. These organisms feed on organic matter including bacteria and fungi. Q QuaternaryThe most recent geological time period which began 2-3 million years ago. It includes the Pleistocene (glacial) era and the Holocene (historical) era which began only 8,000 years ago. R Recharge ZoneAn area where groundwater is replenished due to the downward movement of moisture from the soil surface to the water table. Usually found in upland areas. RepresentativeA soil sample that accurately reflects the average conditions of the field soil samplethat was sampled. Reserve acidityThe reserve of hydrogen and aluminum ions held by soil particles. These reserve ions help to maintain a constant pH in the soil solution by replenishing ions that are lost or neutralized. Aluminum ions released from the surfaces of soil particles react with the soil H2O then generate more hydrogen ions. Resistant organic organic compounds which are difficult for microbes to decompose matterincluding fats, waxes, and lignins which make up a large portion of the long term soil humus. Rhizobium A group of N-fixing bacteria which form symbiotic relationships with the roots of legume plants. Rhizobium converts atmospheric N2 into NH3, which is then available to the plant. In return, the plant root hosts the bacteria in specialized root cells called nodules where they receive carbohydrates. RocksA natural formed aggregate of two or more minerals. S Saline soilA soil that contains enough soluble salts to interfere with the growth of most crops. SaltA chemical compound made of a positive ion (cation) and a negative ion ( anion) that is at least slightly soluble in water. Sand duneswind-built ridges and hills of sand formed in the same manner as snow drifts. An obstruction (such as a bush or fence) causes an eddy where the wind velocity lessens and the sand is deposited. Once begun, the dunes themselves offer further resistance and grow to form various shapes. Secondary mineralA mineral resulting from the decomposition of a primary mineral or from the combination of products from the decomposition of a primary mineral. Sedimentary bedrockLayered bedrock formed by the compression of ancient materials that accumulated at the bottom of great inland seas and lakes. (eg: sandstone, shale, limestone) Sodium adsorptionThe ratio of sodium ions to calcium and magnesium ions in the soil ratio (SAR) SolumThe A and B horizons of a soil profile in which the most soil development has occurred. The ‘active’ portion of the soil profile. Soil buffer Soil components such as clay and humus which enable the soil to resist a compoundschange in pH when acidic and alkaline materials are added. Soil colloidClay or humus with very small particle size (usually a diameter of less than 0.002mm) and a very large surface area per unit of mass. Soil Formation The development of soil from parent material through the influence of climate, living organisms ,topography and time. Soil solutionThe liquid component of a soil consisting of water and all the materials dissolved in the water. Soil reactionThe measure of the acidity or alkalinity of a soil expressed as a pH value. Soil textureThe ‘feel’ of a soi which is determined by the relative percent of sand, silt and clay in a soil sample. Soil salinityThe measure of the amount of salts dissolved in a soil solution. Usually expressed in terms of electrical conductivity of the solution which is a direct function of salt content. Soil separatesThe individual mineral particles, less than 2.0mm in diameter which make up the soil. The main soil separates are sand, silt, and clay. SolubilityThe extent to which a solid salt compound will separate into positive and negative ions and thereby dissolve in water. SolumThe upper (A and B) horizons of a soil in which the parent material has been modified by processes of soil formation and in which most plant roots are contained. The ‘active’ portion of the soil profile. StructureThe organization of soil particles or aggregates (peds). Examples of structural types include granular, prismatic, platy, and columnar. Soil structures are classified on the basis of size, shape and degree of distinctness. SymbiosisThe living together of two dissimilar organisms, each of which depends for its existence on the other, such as the fungus and algae composing lichen. T TextureThe relative proportions of sand, silt, and clay found in a given soil. Texture triangleA diagram which illustrates the soil textural classes. It is a triangular shape indicating the clay percentage on the vertical axis and sand percentage on the horizontal axis. TilthThe physical condition of the soil as it relates to tillage. Soils with good tilth form good seed beds after tillage. These soils hold moisture while allowing emergence of seedlings and penetration by roots. TopographyThe surface features of a distinct or region, such as the relief and contours of the land. U UnconsolidatedSoil or sediment that is loosely aggregated and whose particles are not materialcemented together, recurring either at the surface of the earth or at a Depth. V ValueThe relative brightness of a colour between the extremes of white or black. Value could be compared to the brightness function on a computer. W Water tableThe groundwater surface or elevation. The upper surface of a completely saturated soil zone. Weathering The physical and chemical disintegration and alteration of rocks and minerals at or near the earth’s surface by agents such as wind, water, temperature change and chemical reactions.