Explanation of the C horizon of the soil profile
Answers
Answer:
C - (parent material) The deposit at Earth’s surface from which the soil developed.
The Soil Profile
Soil horizons
Soils differ widely in their properties because of geologic and climatic variation over distance and time. Even a simple property, such as the soil thickness, can range from a few centimetres to many metres, depending on the intensity and duration of weathering, episodes of soil deposition and erosion, and the patterns of landscape evolution. Nevertheless, in spite of this variability, soils have a unique structural characteristic that distinguishes them from mere earth materials and serves as a basis for their classification: a vertical sequence of layers produced by the combined actions of percolating waters and living organisms.
These layers are called horizons, and the full vertical sequence of horizons constitutes the soil profile (see the figure). Soil horizons are defined by features that reflect soil-forming processes. For instance, the uppermost soil layer (not including surface litter) is termed the A horizon. This is a weathered layer that contains an accumulation of humus (decomposed, dark-coloured, carbon-rich matter) and microbial biomass that is mixed with small-grained minerals to form aggregate structures.
The soil profile, showing the major layers from the O horizon (organic material) to the R horizon (consolidated rock). A pedon is the smallest unit of land surface that can be used to study the characteristic soil profile of a landscape.Encyclopædia Britannica, Inc.
Below A lies the B horizon. In mature soils this layer is characterized by an accumulation of clay (small particles less than 0.002 mm [0.00008 inch] in diameter) that has either been deposited out of percolating waters or precipitated by chemical processes involving dissolved products of weathering. Clay endows B horizons with an array of diverse structural features (blocks, columns, and prisms) formed from small clay particles that can be linked together in various configurations as the horizon evolves.
Below the A and B horizons is the C horizon, a zone of little or no humus accumulation or soil structure development. The C horizon often is composed of unconsolidated parent material from which the A and B horizons have formed. It lacks the characteristic features of the A and B horizons and may be either relatively unweathered or deeply weathered. At some depth below the A, B, and C horizons lies consolidated rock, which makes up the R horizon.
Soil horizon letter designationsBase symbols for surface horizonsOorganic horizon containing litter and decomposed organic matterAmineral horizon darkened by humus accumulationBase symbols for subsurface horizonsEmineral horizon lighter in colour than an A or O horizon and depleted in clay mineralsAB or EBtransitional horizon more like A or E than BBA or BEtransitional horizon more like B than A or EBaccumulated clay and humus below the A or E horizonBC or CBtransitional horizon from B to CCunconsolidated earth material below the A or B horizonRconsolidated rockSuffixes added for special features of horizonsahighly decomposed organic matterbburied horizoncconcretions or hard nodules (iron, aluminum, manganese, or titanium)eorganic matter of intermediate decompositionffrozen soilggray colour with strong mottling and poor drainagehaccumulation of organic matterislightly decomposed organic matterkaccumulation of carbonatemcementation or indurationnaccumulation of sodiumoaccumulation of oxides of iron and aluminumpplowing or other anthropogenic disturbanceqaccumulation of silicarweathered or soft bedrocksaccumulation of metal oxides and organic mattertaccumulation of clayvplinthite (hard iron-enriched subsoil material)wdevelopment of colour or structurexfragipan character (high-density, brittle)yaccumulation of gypsumzaccumulation of salts
The combined A, E, B horizon sequence is called the solum (Latin: “floor”).
Soils are natural elements of weathered landscapes whose properties may vary spatially. For scientific study, however, it is useful to think of soils as unions of modules known as pedons. A pedon is the smallest element of landscape that can be called soil. Its depth limit is the somewhat arbitrary boundary between soil and “not soil” (e.g., bedrock). Its lateral dimensions must be large enough to permit a study of any horizons present—in general, an area from 1 to 10 square metres (10 to 100 square feet), taking into account that a horizon may be variable in thickness or even discontinuous. Wherever horizons are cyclic and recur at intervals of 2 to 7 metres (7 to 23 feet), the pedon includes one-half the cycle. Thus, each pedon includes the range of horizon variability that occurs within small areas. Wherever the cycle is less than 2 metres, or wherever all horizons are continuous and of uniform thickness, the pedon has an area of 1 square metre.