Gebruiker:De Geo/soil survey terminology

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GLOSSARY (adapted from FAO 1976 and Soil Survey Staff 1984)

Aeration, soil: The exchange of air in soil with air from the atmosphere. The air in a well aerated soil is similar to that in the atmosphere; the air in a poorly aerated soil is considerably higher in carbon dioxide and lower in oxygen.
Alluvium: Material, such as sand, silt or clay, deposited on land by streams.
Association. soil: A map unit of two or more kinds of soils occurring in a clear but intricate geographical pattern so that it is not practical to map them separately at the selected map scale. The soils of an association can be mapped separately on a larger map scale.
Available water capacity (available moisture capacity): The capacity of soils to hold water available for use by most plants. It is commonly defined as the difference between the amount of soil water at field moisture capacity and the amount at wilting point. It is commonly expressed as mm of water per meter of soil. The capacity, in mm, in a 100 mm profile or to a limiting layer is expressed as: very low: 50-100 mm; low: 50-100 mm; moderate: 100-150 mm; high:150-200 mm; very high: more than 200 mm.
Base Saturation: The degree to which material, having cation exchange properties, is saturated with exchangeable bases (sum of Ca, Mg, Na, K), expressed as a percentage of the total cation exchange capacity
Bedrock: Solid rock that underlies the soil and other unconsolidated material, or that is exposed at the surface.
Bench terrace: A raised, level, or nearly level strip of earth constructed on or nearly on the contour, supported by a barrier of rock or similar material, and designed to make the soil suitable for tillage and to prevent accelerated erosion.
Boulders: Rock fragments larger than 25 cm (10 inches) in diameter.
Calcareous soil: A soil containing enough calcium carbonate (commonly combined with magnesium carbonate) to effervesce visibly when treated with cold, diluted hydrochloric acid.
Cation: An ion carrying a positive charge of electricity. common soil cations are calcium, potassium, magnesium, sodium, hydrogen and aluminium.
Cation exchange capacity (CEO: The total amount of exchangeable cations that can be held by the soil, expressed in terms of milli-equivalents per 100 grams of soil at neutrality (pH 7, Nis more precise in meaning.
Clay: As a soil separate, the mineral soil particles less than 0.002 millimeters (2 microns) in diameter. As a soil textural class soil material that is 40 percent or more clay, less than 45 percent sand, and less H₄OAC method). The term, as applied to soils, is synonymous with base-exchange capacity, but than 40 percent silt.
Clay skin: A thin coating of oriented clay on the surface of a soil aggregate or lining of pores or root channels. Synonym: clay coating.
Coarse textured soil: Sand or loamy sand.
Colluvium: Soil material, rock fragments or both moved by creep, slide, or local wash and deposited at the base of steep slopes.
Complex, soil: A map unit of two or more kinds of soils occurring in such an intricate pattern that they cannot be mapped separately at the selected scale of mapping.
Concretions: Grains, pellets or nodules of various sizes, shapes and colours consisting of concentrated or cemented soil grains. The composition of most concretions is nuke that of the surrounding soil. Calcium carbonate and iron oxide are common compounds in concretions.
Conservation tillage: A tillage system that does not invert the soil and that leaves a protective amount of crop residue on the surface throughout the year.
Consistence. soil: The feel of the soil and the ease with which a lump can be crushed by the fingers. Terms commonly used to describe the consistence are:
- Loose: non coherent when dry or moist; does not hold together in a mass.
- Friable: when moist, crushes easily under gentle pressure between thumb and forefinger and can be pressed together in a lump.
- Firm: when moist, crushes under moderate pressure between thumb and forefinger, but resistance is distinctly noticeable.
- Plastic: when wet, rapidly deformed by moderate pressure but can be pressed into a lump; will form a "wire" when rolled between thumb and forefinger.
- Sticky: when wet, adheres to other material and tends to stretch somewhat and pull apart rather than to pull free from other material.
- Hard: when dry, moderate ly resistant to pressure; can be broken with difficulty between thumb and forefinger.
- Soft: when dry, breaks into powder or individual grains under very slight pressure.
- Cemented: hard; little affected by moistening.
Consociation: A map unit with 73 percent of one kind of soil (series) and 23 percent inclusions of other (minor) soils.
Contour, strip-cropping: Growing crops in strips that follow the contour. Strips of grass or close-growing crops are alternated with strips of clean tilled crops or summer follow.
Control section: The part of the soil on which classification is based. The thickness varies among different kinds of soil, but for many it is that part of the soil profile between depths of 23 and 100/200 cm.
Crotovinas: Old burrows that are filled in with humus-rich materials from the A horizon.
Diversion. terrace: A ridge of earth, generally a terrace, built to protect down slope areas by diverting runoff from its natural course.
Doline: A depression in the landscape where limestone has been dissolved (synonym: sinkhole).
Effective cation exchange capacity (ECEC): The total amount of exchangeable cations that is held by the soil (Ca, Mg, Na, K, H and Al), expressed in terms of milli-equivalents per 100 grams of soil at the pH value of the soil. Except for calcareous soils, the ECEC is lower than the CEC value determined with the NH₄OAC method atpH 7.
Erosion: The wearing away of the land surface by water, wind, ice or other geological agents and by such processes as gravitational creep.
Erosion, accelerated: Erosion much more rapid than geologic erosion (synonym: natural erosion), mainly as a result of the activities of man or other animals or of a catastrophe in nature, for example, fire that exposes the surface.
Fertility. soil: The quality that enables a soil to provide plant nutrients, in adequate amounts and in proper balance, for the growth of the specified plants when light, moisture, temperature, tilth and other growth factors are favourable.
Fine textured: Sandy clay, silty clay and clay.
Grassed waterway: A natural or constructed waterway, typically broad and shallow, seeded to grass as protection against erosion. Conducts surface water away from cropland.
Gravel: Rounded or angular fragments of rock from 2 mm up to 7.5 cm.
Gravelly soil material. Material that is 15 to 50 percent, by volume, rounded or angular rock fragments, not prominently flattened, up to 7.5 cm in diameter.
Ground water: Water filling all the unblocked pores and underlying material below the water table.
Horizon, soil: A layer of soil approximately parallel to the surface, having distinct characteristics produced by soil-forming processes. In the identification of soil horizons, an uppercase letter represents the major horizons. Numbers or lowercase letters that follow represent subdivisions of the major horizons. The major horizons in the survey area are as follows:
- A horizon: The mineral horizon at or near the surface in which an accumulation of humified organic matter is mixed with mineral material. Also, any ploughed or disturbed surface layer.
- B horizon: The mineral horizon below an A horizon. The B horizon is in part a layer of transition from the overlying horizon to the underlying C horizon. The B horizon also has distinctive characteristics, such as:
  - a) accumulation of clay, sesquioxides, humus or a combination of these,
  - b) granular. prismatic or blocky structure;
  - c) redder or browner colours than those of the A horizon; or d) a combination of these.
- C horizon: The mineral horizon or layer, excluding indurated bedrock, that is little affected by soil-forming processes and does not have the properties typical of the overlying horizon. The material of a C horizon may be either like or unlike that in which the solum formed. If the material is known to differ from that in the solum.an Arabic numeral, commonly a '2', precedes the letter C.
- R layer: Hard, Consolidated bedrock beneath the soil. The bedrock commonly underlines a C horizon but can be directly below an A or a B horizon.
Inclusion/Included soil: A soil that comprises less than 25 % of a mapping unit.
Infiltration: The downward entry of water into the immediate surf ace of the soil or other material, as contrasted with percolation, which is movement of water through soil layers or material.
Land characteristics: An attribute of land that can be measured or estimated, and which can be employed as a means of describing land qualities or distinguishing between land units of differ ing suitabilities for use.
Land evaluation: The process of assessment of land performance when used for specified purposes in order to identify and make a comparison of promising kinds of land use.
Land improvement: An alteration in the qualities of land which improves its potential for use.
Land qualities: A complex attribute of land which acts in a manner distinct from the actions of other land qualities in its influence on the suitability of land for a specified kind of use.
Land suitability: The fitness of a given type of land for a specified kind of land use.
Land suitability classification: An appraisal and grouping of specific types of land in terms of their absolute or relative suitability for a specified kind of use.
Land use requirement: The conditions of land necessary or desirable for the successful and sustained practice of a given land utilization type (subdivided in crop requirements and management requirements).
Land utilization type (LUT): A kind of land use described or defined in a degree of detail greater than that of a major kind of land use. In the context of rainfed agriculture, a land utilization type refers to a crop, crop combination or cropping system within a specified technical and socio-economic setting.
Loam: Mineral soil material that is 7 to 27 percent clay particles, 28 to 30 percent silt particles and less than 52 percent sand particles.
Major kind of land use (MLU): A major subdivision of rural land use, such as low technology rainfed farming or high technology rainfed farming with supplementary irrigation. In , MLUs are defined as crop/management systems: a particular crop is grown within a well defined technological and socio-economical setting.
Medium textured soil: Very fine sandy loam, silt loam or loam.
Metamorphic rock: Rock of any origin altered in mineralogical composition, chemical composition or structure by heat, pressure and movement. Nearly all metamorphic rocks are crystalline.
Mineral soil: Soil that is mainly mineral material and low in organic material. lts bulk density (kg/m3)is more than that of organic material.
Minimum tillage: Only the tillage essential to crop production and prevention of soil damage.
Moderately coarse textured soil: Coarse sandy loam, sandy loam and fine sandy loam.
Moderately fine textured soil: Clay loam, sandy clay loam and silty clay loam.
Mottling: Irregular spots of different colours that vary in number and size. Mottling generally indicates poor aeration and impeded drainage.
Munsell notation: A designation of colour by degrees of the three simple variables hue. value and chroma. For example, a notation of 5 YR 5/4 is a colour hue of 5 YR. value of 5 and chroma of 4. Each code corresponds with a specific name for the colour (5 YR 5/4 is reddish brown).
Parent material: The unconsolidated organic and mineral material in which soil forms.
Particle size class: Classes which refer to the grain size distribution of the whole soil, not only the fine earth. These classes are: fragmental, sandy-skeletal, loamy-skeletal, clayey-skeletal, sandy, loamy and clayey. The latter three classes can be read from a particle size triangle.
Permeability: The quality of the soil that enables water to move downward through the profile. Permeability is measured as the number of centimeters per hour that water moves downward through the saturated soil. Terms describing permeability are: very slow - less than 15 mm/hr.; slow - 5-15 mm/hr; moderate - 15-50 mm/hr; moderately rapid - 50-150 mm/hr; rapid -150-500 mm/hr; very rapid - more than 500 mm/hr.
Phase, soil: A subdivision of a soil series based on features that affect its use and management, For example, slope, stoniness and rockiness.
Profile. soil: A vertical section of the soil extending through all its horizons and into the parent material.
Reaction, soil: A measure of acidity or alkalinity, expressed in pH values. A soil that tests to pH 7.0 is described as precisely neutral in reaction because it is neither acid nor alkaline. The degree of acidic or alkalinity is expressed as: extremely acid (pH < 4.5), very strongly acid (4.5 < pH < 50), strongly acid (5.1 < pH < 5-5), medium acid (56 < pH < 6.0) slightly acid (6.1 < pH < 6.5), neutral (6.6 < pH < 7.3), mildly alkaline (7.4 < pH < 7.8), moderately alkaline (7.9 < pH < 8.4), strongly alkaline (8.5 < pH < 9.0) and very strongly alkaline (pH > 9.0).
Relief: The elevations or inequalities of a land surf ace, considered collectively.
Relief, intensity: The range between the average lowest and average highest point in a specific landscape as seen in relation to the horizontal distance (synonym: amplitude).
Rock fragments: Rock or mineral fragments having a diameter of 2 mm or more.
Root zone: The part of the soil that can be penetrated by plant roots.
Run-off: The water that flows off the surf ace of the land without sinking into the soil is called surface runoff.
Sand: As a soil separate, individual rock or mineral fragments from 0.05 mm to 2.0 mm in diameter. As a soil textural class, a soil that is 85% or more sand and not more than 10% clay.
Sedimentary rock: Rock made up of particles deposited from suspensions in water which have been hardened. The chief kinds of sedimentary rocks are conglomerate, formed from gravel; shale, formed from clay; and limestone, formed from soft masses of calcium carbonate. There are many intermediate types.
Series, soil: A group of soils that have profiles that are almost alike, except for differences in texture of the surface layer or the underlying material. All soils of a series have horizons that are similar in composition, thickness, and arrangement.
Shrink-swell: The shrinking of usually montmorillonitic soils when dry and the swelling when wet. Shrinking and swelling can damage roads, dams, building foundations, and other structures. It can also damage plant roots.
Silt: As a soil separate, individual mineral particles that range in diameter from 0.002 mm to 0.05 mm. As a soil textural class, soil that is 80 percent or more silt and less than 12 percent clay.
Slope: The inclination of the land surface from the horizontal. Percentage of slope is the vertical distance divided by horizontal distance, then multiplied by 100. Thus a slope of 30 percent is a drop of 30 meters in 100 meters of horizontal distance.
Soil: A natural, three-dimensional body at the earth's surface. It is capable of supporting plants and has properties resul tin g in the integrated effect of climate and living matter on earthy parent material, as conditioned by relief over periods of time.
Solum: The upper part of a soil profile, above the C horizon, in which the process of soil formation is active. The solum generally consists of the A, E, and B horizons. The living roots and plant and animal activities are largely confined to the solum.
Stones: Rock fragments 7.5-25 cm in diameter.
Stony: Refers to asoil containing stones in numbers that interfere or prevent tillage.
Structure. soil: The arrangement of primary soil particles into compound particles or aggregates.
Subsoil: Technically the B horizon; roughly the part of the solum below the plough layer.
Substratum: The part of the soil below the solum (C and R horizons).
Subsurface layer: Any surface soil horizon (A, AE, AB or EB) below the surface layer.
Surface layer: The soil ordinarily moved in tillage, or its equivalent in uncultivated soil, ranging in depth from about 10-25 cm. Frequently designated as plough layer or "Ap horizon".
Texture: The relative proportion of sand, silt and clay particles in a mass of soil. The textural class can be read from a textural triangle.
Textural group: (USDA) indication for a group of textural classes of part of the pedon (the control section, usually 25-100 cm) and comprises only the fine earth fracüon. The groups are: fine -, moderately fine -, medium -, moderately course - and course textured and strongly contrasting.
Textural group: (FAO/UNESCO) indication for a group of textural classes of the upper 30 cm of the profile. The classes are: coarse -, medium - and fine textured.
Tuff: A compacted deposit that is 50 percent or more volcanic ash and dust.
Variant, soil series: A soil largely similar to existing soil series, yet significantly different from it in some minor properties.

soil horizons

Master horizons: H an organic horizon formed or forming from accumulations of organic material deposited on the surf ace, that is saturated with water for prolonged periods (unless artificially drained) and contains i 30 % organic matter if the mineral fraction contains i 60 % clay, i 20 % organic matter if the mineral fraction contains no clay, or intermediate proportions of organic matter for intermediate contents of clay. O an organic horizon formed or forming from accumulations of organic material deposited on the surface, that is not saturated with water for more than a few days a year and contains i 35 % organic matter. A a mineral horizon formed or forming at or adjacent to the surface that either. a) shows an accumulation of humified organic matter intimately associated with the mineral fraction, or b) has a morphology acquired by soil formation but lacks the properties of E and B horizons. E a mineral horizon showing a concentration of sand and silt fractions high in resistant minerals, resulting from a loss of silicate clay, iron or aluminium or some combination of them. B a mineral horizon in which rock structure is obliterated or is but faintly evident, characterized by one or more of the following features: a) an illuvial concentration of silicate clay, iron, aluminium, or humus, alone or in combinations; b) a residual concentration of sesquioxides relative to source materials; c) an alteration of material from its original condition to the extent that silicate clays are formed, oxides are liberated, or both, or granular, blocky or prismatic structure is formed. 13 C a mineral horizon (or layer) of unconsolidated material from which the solum is presumed to have formed and which does not show properties diagnostic of any other master horizons. R a layer of continuous indurated rock. The rock of R layers is sufficiently coherent when moist to make hand digging with a spade impracticable. The rock may contain cracks but these are too few and too small for significant root development. Gravelly and stony material which allows root development is considered as C horizon. Transitional horizons Soil horizons in which the properties of two master horizons merge are indicated by the combination of two capital letters (for instance AE, EB, BE, BC, CB, AB, BA, AC and CR), The first letter marks the master horizon to which the transitional horizon is most similar. Mixed horizons that consist of intermingled parts, each of which associated with different master horizons, are designated by two capital letters separated by a slash (for instance: E/B, B/C). The first letter marks the master horizon that dominates. Letter suffixes A small letter may be added to the capital letter to qualify the master horizon designation. Suffix letters can be combined to indicate properties which occur concurrently in the same master horizon (for example Ahz, Btg, Cck). Normally no more than two suffixes should be used in combination. In transitional horizons no use is made of suffixes which qualify only one of the capital letters. A suffix may be used, however, when it applies to the transitional horizon as a whole (for example BCk, ABg). The suffix letters used to qualify the master horizons are as follows: a highly decomposed organic material (sapric organic material: rubbed fiber content less than 1/6 of volume). b buried horizon (for example Btb). c accumulation of concretions; this suffix is commonly used in combination with another which indicates the nature of the concretionary material (for example Bek, Ces). 14 e organic material of intermediate decompositlon (hemic organic material: rubbed fiber content 1/6 to 2/5 of volume). g mottling reflecting variations in oxidation and reduction (for example Bg, Btg, C'g). h accumulation of organic matter in mineral horizons (for example Ah, Bh); for the A horizon, the h suffix is applied only where there has been no disturbance or mixing from ploughing, pasturing or other activities of man (h and p suffixes are thus mutually exclusive). i slightly decomposed organic material (fibric organic material: rubbed fiber content more than 2/5 of volume). k accumulation of calcium carbonate. m strongly cemented, Consolidated, indurated; this suffix is commonly used in combination with another indicating the cementing material (for example Cmk marking a petrocalcic horizon within a C horizon, Bms marking an iron pan within a B horizon). n accumulation of sodium (for example Btn). p disturbed by ploughing or other tillage practices (for example Ap). q accumulation of silica (for example Cmq marking a silcrete layer in a C horizon). r strong reduction as a result of groundwater influence (for example Cr). s accumulation of sesquioxides (for example Bs). t illuvial accumulation of clay (for example Bt). u unspecified; this suffix is used in connexion with A and B horizons which are not qualified by another suffix but have to be subdivided vertically by figure suffixes (for example Aul, Au2, Bul, Bu2). The addltion of u to the capital letter is provided to avoid confusion with the former notations Al, A2, A3, B1, B2, B3 in which the figures had a genetic connotation. w alteration in situ as reflected by clay content, colour, structure (for example Bw). x occurrence of a fragipan (for example Btx). y accumulation of gypsum (for example Cy). z accumulation of salts more soluble than gypsum (for example Az or Ahz). Letter suffixes can be used to describe diagnostic horizons and features in a profile (for exampleargi 11 ie B horizon: Bt; natric B horizon: Btn; cambic B horizon: Bw; oxic B horizon: Bws; mottled layers: g).

Figure suffixes Horizons designated by a single combination of letter symbols can be vertically subdivided by numbering each subhorizon consecutively, starting at the top of the horizon (for example Btl-Bt2-Bt3-Bt4). The suffix number always follows all of the letter symbols. The number sequence applies to one symbol only so that the sequence is resumed in case of change of the symbol (for example Bt1-Bt2-Btr1-Btr2). A sequence is not interrupted, however, by a lithological discontinuity (for example Bt1-Bt2-2Bt3). Numbered subdivisions can also be applied to transitional horizons (for example AB1-AB2), in which case it is understood that the suffix applies to the entire horizon and not only to the last capital letter. Figure prefixes When it is necessary to distinguish lithological dlscontinuities Arabic (replacing former Roman) numerals are prefixed to the horizon designations concerned (for Instance, when the C horizon is different from the material in which the soil is presumed to have formed the following soil sequence could be given: A, B, 2C. Strongly contrating layers within the C material could be shown as an A, B, C, 2C, 3C, etc. sequence).