Soils Horizons Flashcards
What 2 processes form A horizons?
Leaching or eluviation of materials in suspension (Ae) or maximum in situ accumulation of organic matter (Ah) or both (Ahe).
How do you recognize Ae?
The removal of organic matter and iron and/or enhanced weathering of minerals that occur close to the soil surface are usually expressed by a lightening of the soil colour. The removal of clay from the upper part of the solum (Ae) is expressed by a coarser soil texture relative to the underlying subsoil layer.
What are the 3 processes/changes that indicate a B horizon?
Enrichment of organic matter, iron and aluminum, or clay; by the development of soil structure; or by a change of colour by chemical weathering processes such as hydrolosis, reduction or oxidation.
t suffix
Illuvial horizon enriched with silicate clay. It is used as Bt, Btg, Bnt, etc.
Describe Bn, Bm, and Bg horizons.
Bn=significant amounts of exchangeable sodium
Bm=changes in structure from the parent material. Colour changes include relatively uniform reddening or browning due to oxidation of iron.
Bg=Mottling and gleying of structurally altered material associated with periodic reduction due to water saturation.
What may Podzolic soils have?
Translocated organic matter (Bh) that has darker colors relative to the overlying A and underlying C horizon.
C horizons - compare to A and B. What processes may still go on?
Comparatively unaffected by the soil-forming processes operating in A and B horizons, except the process of gleying (Cg), the accumulation of calcium and magnesium carbonates (Cca) and more soluable salts (Csa), and turbation due to shrinking and swelling of clays (Css) or ice (Cz).
R horizon
A consolidated bedrock layer that is too hard to break with the hands (>3 on Mohs’ scale) or to dig with a spade when moist. It does not meet requirements of a C horizon.
Lithic Contact
the boundary between the R layer and any overlying unconsolidated material.
What type of soils do w horizons occur in?
This layer of water may occur in Gleysolic, Organic or Cryosolic soils. Hydric layers in Organic soils are a kind of W layer as is segregated ice formation in Cryosolic soils.
L (litter) horizon
This organic horizon is characterized by an accumulation of organic matter in which the original structures are easily discernible.
F (folic) horizon
Characterized by an accumulation of partly decomposed organic matter. The material may be partly altered by soil fauna (moder), or it may be a partly decomposed mat permeated by fungal hyphae (mor.)
What does an h horizon indicate? What are all the possible horizons containing h? Where might you find each of these possible horizons (grassland, forests etc.)?
Characterized by an accumulation of decomposed organic matter in which the original structures are indiscernible. This horizon differs from the F by having greater humification due chiefly to the action of organisms. It is frequently intermixed with mineral grains, especially near the junction with a mineral horizon.
Mull
In forest soils where burrowing faunal (primarily earthworms) activity is high, the F horizon does not form and instead a mull horizon (Ah) is found. This form of zoogenous, forest humus consists of an intimate mixture of well-humified organic matter and mineral soil with crumb or granular structure that makes a gradual transition to the horizon underneath.
Ahe
Higher organic matter (darker) than lower horizons AND salt and pepper effect when dry aggregates are crushed
Ap
Higher organic matter (darker) than lower horizons in layer mixed by humans in agricultural or forestry operations ie: previously disturbed soils. p can be used with A or O (Ap, Op).
Ah
Higher organic matter (darker) than lower horizons in undisturbed soil.
Ae
Grayish layer AND/OR less clay than underlying B horizon. A horizon characterized by the eluviation of clay, Fe, Al, or organic matter alone or in combination. When dry, it is usually higher in color value by one or more units than an underlying B horizon.
gj suffixes
The contrast of mottles with the matrix - horizons with faint or distinct mottles (rather than prominent) are typically designated as gj horizons.
t suffix
An illuvial horizon enriched with silicate clay. It is used with B alone (Bt) and B and g (Btg), with B and n(Bnt) etc.
Describe Bt layers. How thick are they? What horizon does it form below?
Contains illuvial layer lattice clays. Must be at least 5cm thick. If less than 5cm, it is a Btj horizon. Forms below an elvial horizon (Ae, Ahe), but may occur at surface of a soil that’s partially truncated by erosion.
f suffix
A horizon enriched with Fe and Al combined with organic matter. Most commonly found in sandy, acidic, forest soils. It is used with B alone (Bf), or as Bhf, Bfg, and other suffixes. These criteria do not apply to Bgf horizons. there are also specific chemical criteria that these horizons must meet.
g suffix
A gleyed horizon characterized by dull (low chroma) gray colours, or prominent mottling, or both, indicating intense reduction due to permanent or periodic water saturation. It is the diagnostic horizon of the Gleysolic order.
Aeg
This horizon must mee the definitions of A, e, and g. Ae horizons are normally grey (lighter than B layer), and prominent mottles must be present for the g suffix to be assigned. If only faint or distinct mottles are present the horizon is designated as an Aegj horizon.
Bg
Must have a change in structure from the C horizon AND prominent mottles must be present for the g suffix to be assigned. If only faint or distinct mottles are present the horizon is designated as an Bgj horizon.
h suffix
A mineral horizon enriched with organic matte. It is used as either Ah, Ahe, Bh, or Bhf. Ah horizons occur in grasslands and in forest soils where mixing of forest litter and the mineral soil surface occurs. Ahe horizons are associated with forest-grassland transition areas. Bh and Bhf horizons occur in sandy, acid forest soils and are associated with the Podzolic soil order.
j suffix
A modifier of suffixes e,f,g,n,t and v (ie: any suffixes defined by quantitative criteria). It is used to denote an expression of, but failure to meet, the specified limits of the suffix it modifies. It must be placed to the right and adjacent to the suffix it modifies. It is not used with an m suffix.
Bfgj
A Bf horizon with a weak expression of gleying.
Bfjgj
B horizon with a weak expression of both f and g features.
Aej
An eluvial horizon that is discontinuous or slightly discernible (ie: when dry, it is not higher in color value by one or more units than an underlying B horizon or the difference in clay with the Btj is minor.
Btj
Horizon with some illuviation of clay but not enough to meet the limits of Bt.
Bgj, Btgj, Bmgj etc.
These horizons are mottled or have dull chromas but do not meet the criteria of g. Typically they have faint or distinct mottles or they have prominent mottles but the chromas are too bright for a true g horizon.
Bfj
Horizon with some accumulation amorphous Al+Fe but not enough to meet the limits of Bf. In addition, the color of this horizon may not meet the color criteria set for Bf.
m suffix
A horizon slightly altered by chemical weathering (ie: hydrolysis, oxidation, or solution, or all three) to give a change in color or structure, or both. This suffix can be used as Bm, Bmk, and Bms. Bmj is not used (the j suffix is redundant). An m horizon has evidence of alteration in one or more of the following: a. Higher chromas and/or redder hues than the underlying horizons. b. Removal of carbonates either partially (Bmk) or completely (Bm). c. A change in structure from that of the parent material (ie-the IC horizon). d. Illuviation, if evident, too slight to meet the requirements of a Bt or a podzolic B. e. No cementation or induration and lacks a brittle consistence when moist.
n suffix
Soils high in sodium (Na), that are found on saline parent materials. It is used with B as Bn or Bnt. These horizons would usually overlay a saline (eg Csk, Cskg) horizon.
(F) Fluvial
Deposited by glacial meltwater - sorted, rounded course fragments, bedding planes, buried horizons. Sediment generally consisting of gravel and sand with a minor fraction of silt and clay. The gravels are typically rounded and contain interstitial sand. Fluvial sediments are commonly moderately to well sorted and display stratification, but massive, non-sorted fluvial gravels do occur. These materials have been transported and deposited by streams and rivers. Finer textured fluvial deposits of modern rivers are termed alluvium.
Colluvial
Massive to moderately well stratified, non-sorted to poorly sorted sediments with any range of particle sizes from clay to boulders and blocks that have reached their present position by direct, gravity-induced movement. They are restricted to products of mass-wasting whereby the debris is not carried by wind, water, or ice (excepting snow avalanches).
Eolian
Sediment, generally consisting of medium to fine sand and coarse silt particle sizes, that is well sorted, poorly compacted, and may show internal structures such as cross bedding or ripple laminae. Individual grains may be rounded and show signs of frosting. These materials have been transported and deposited by wind action.
Glaciolacustrine
Lacustrine materials deposited in contact with glacial ice. May contain a numerous ice-rafted stones.
Lacustrine
Sediment generally consisting of either stratified fine sand, silt, and clay deposited on the lake bed; or moderately well sorted and stratified sand and coarser materials that are beach and other near shore sediments transported and deposited by wave action. These are materials that either have settled from suspension in bodies of standing fresh water or have accumulated at their margins through wave action.
Lacustro till
Lacustrine deposits, modified / re-worked by subsequent glacial activity.
Morainal (Till)
Sediment generally consisting of well compacted material that is non-stratified and contains a heterogeneous mixture of particle sizes, often in a mixture of sand, silt, and clay that has been transported beneath, beside, on, within and in front of a glacier and not modified by any intermediate agent.
Describe brunisolic soils. What is the central concept? Describe drainage and gleying.
Soils of the Brunisolic order have sufficient development to exclude them from the Regosolic order, but they lack the degree or kind of horizon development specified for soils of other orders. The central concept of the order is that of soils formed under forest and having brownish-colored Bm horizons.
Most Brunisolic soils are well to moderately poorly drained, but some that have been affected by seepage water are poorly drained although not strongly gleyed. They occur in a wide range of climatic and vegetative environments including Boreal Forest; mixed forest, shrubs, and grass; and heath and tundra.
Gleysolic soils
Soils with prominent mottling within 50cm of the surface are classifies as Gleysols. Gleysolic soils are associated with a number of different moisture regimes that may change during the genesis of the soil. They commonly have peraquic or aquic regimes, but some have aqueous regimes and others are now rarely, if ever, saturated with water. Those that are rarely saturated now presumably had aquic moisture regimes in the past and were once under reducing conditions. Drainage, isostatic uplift, or other factors have resulted in a changed moisture regime in these soils.
Gleysolic soils occur in association with other soils in the landscape, in some cases as the dominant soils, in others as a minor component. In areas of subhumid climate, Gleysolic soils occur commonly in shallow depressions and on level lowlands that are saturated with water every spring.
Luvisolic Soils
Soils of the Luvisolic order generally have light-colored, eluvial horizons and have illuvial B horizons in which silicate clay has accumulated. These soils develop characteristically in well to moderately poor drained sites, in sandy loam to clay, base-saturated parent materials under forest vegetation in subhumid to humid, mild to very cold climates.
The Gray Luvisols of that area usually have well-developed, platy Ae horizons of low chroma, Bt horizons with moderate to strong prismatic or blocky structures, calcareous C horizons
The genesis of Luvisolic soils is thought to involve the suspension of clay in the soil solution near the soil surface, downward movement of that clay with the soil solution, and the deposition of the translocated clay at a depth where downward movement of the soil solution ceases or becomes very slow. Commonly, the subhorizon of maximum clay accumulation occurs above a Ck horizon. The eluvial horizon (Ahe, Ae) commonly
has platy structure due perhaps to the periodic formation of ice lenses. Any condition that promotes dispersion of clay in the A horizons and deposition of this clay in a discrete subsurface horizon favors the development of Luvisolic soils
Very poorly drained (VP)
Water is removed from the soil so slowly that the water table remains at or on the surface for the greater part of the time the soil is not frozen. Excess water is present in the soil for the greater part of the time. Groundwater flow and subsurface flow are major water sources. Precipitation is less important except where there is a perched water table with precipitation exceeding evapo-transpiration. These soils have a wide range in available water storage capacity, texture, and depth, and are either Gleysolic or Organic.
Poorly drained (PD)
Water is removed so slowly in relation to supply that the soil remains wet for a comparatively large part of the time the soil is not frozen. Excess water is evident in the soil for a large part of the time. Subsurface flow or groundwater flow, or both, in addition to precipitation are main water sources; there may also be a perched water table, with precipitation exceeding evapo-transpiration. Poorly drained soils have a wide range in available water storage capacity, texture, and depth, and are gleyed subgroups, Gleysols, and Organic soils.
Moderately Poor (MP)
Water is removed from the soil sufficiently slowly in relation to supply to keep the soil wet for a significant part of the growing season. Excess water moves slowly downward if precipitation is major supply. If subsurface water or groundwater, or both, is the main source, flow rate may vary but the soil remains wet for a significant part of the growing season. Precipitation is the main source if available water storage capacity is high; contribution by subsurface flow or groundwater flow, or both, increases as available water storage capacity decreases. Soils have a wide range in available water supply, texture, and depth, and are gleyed phases of well drained subgroups. These soils generally have mottling below the surface layers and generally have duller colors with depth, generally brownish grey with mottles of yellow and gray.
(MW) Moderately well drained
Water is removed from the soil somewhat slowly in relation to supply. Excess water is removed somewhat slowly due to low perviousness, shallow water table, lack of gradient, or some combination of these. Soils have intermediate to high water storage capacity within the control section and are usually medium to fine in texture. Soils are commonly mottled in the 50 to 100 cm depth. Colors are dull brown in the subsoil with stains and mottles.
Well Drained
Water is removed from the soil readily but not rapidly. Excess water flows downward readily into underlying pervious material or laterally as subsurface flow. Soils have
in texture and depth. Water source is precipitation. On slopes subsurface flow may occur for short durations but additions are equalled by losses. These soils are usually free of mottles within 100 cm of the surface but may be mottled below this depth. Soil horizons are usually bright colored
(RP) Rapidly drained
Water is removed from the soil rapidly in relation to supply. Excess water flows downward if underlying material is pervious. Subsurface flow may occur on steep gradients during heavy rainfall. Soils have low available water storage capacity within the control section, and are usually coarse in texture, or shallow, or both. Water source is precipitation.
(VR)
Water is removed from the soil very rapidly in relation to supply. Excess water flows downward very rapidly if underlying material is pervious. There may be very rapid subsurface flow during heavy rainfall provided there is a steep gradient. Soils have very low available water storage capacity within the control section and are usually coarse in texture, or shallow, or both. Water source is precipitation.
What are the possible aggregate sizes?
<2cm
2-5cm
5-10cm
>5-10cm
List the possible aggregate structures
Platy Prism Like Angular Blocky Sub Angular Blocky Granular Crumb Lenticular Massive Single Grain
What are the admixing categories?
0-10 10-20 20-30 30-40 40-50 >50
List the possible aggregate strengths
Loose Very Friable Friable Firm Very firm
Platy
Two long axes (usually horizontal) and one short
Prism-like
Soil particles arranged around a vertical axis and bounded by relatively flat surfaces. Includes Prismatic - All sufaces relatively flat
Columnar - The tops are rounded
Block - like
Three axes (approximately equal) and flat or rounded surfaces which are accommodated to the surfaces of adjacent peds. This includes Angular blocky and sub-angular blocky.
Angular blocky
The plane faces intersect at relatively sharp angles.
Sub-angular blocky
Mixed rounded and plane faces with vertices mostly rounded.
Sheroidal
Three axes (approx equal) but surfaces curved or very irregular and not accomodated to the adjacent surfaces. This includes granular and crumb.
Granular
Relatively non-porous (looks fairly solid)
Crumb
Very porous (looks like a bread crumb).
Lenticular
Lens-like. Curved surfaces meet in sharp vertices to form a lens.
Effervescence
Bubble in a liquid; fizz. When a weak solution of HCl (1N) is applied, the strength of effervescence (fizzing that occurs) is related to the presence of carbonates in the profile
Solum
Upper layers of a soil profile in which soil formation occurs. A and B horizons.
Lamellae
Distinguished at a subgroup level. In soil taxonomy, a lamella is an illuvial soil horizon less than 7.5cm thick that contains an accumulation of oriented silicate clay on or bridging sand and silt grains.
Soil Peds
Essentially the natural ‘lumps’ of soil. Natural, relatively permanent aggregates, separated from each other by voids or natural surfaces of weakness. Peds persist through cycles of wetting and drying. Peds can range in size from <5mm to more than 100mm in diameter.
Apedal
Soils without peds, eg. Sands.
Pedal
Soils with peds, eg. Loams and clays.
Loose consistence
Trouble picking out a single ped, and the structure falls apart as soon as you touch it.
Friable consistence
The ped breaks with a small amount of pressure
Firm consistence
The ped breaks when you apply a good amount of pressure - and dents your finger before it breaks
Very Firm Consistence
The ped can’t be crushed with your fingers, you need a tool.
