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Land Management & Natural
Hazards Unit |
SOIL |
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Soil
Atlas of |
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What is soil?
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Within the A, E and B horizons, various clods, aggregates and grains of different sizes can be seen. These are the building blocks of the soil that together form its architectural fabric or 'structure'. Soil structure determines the amount and rate of water and air movements. The structure of the soil results from natural processes such as seasonal cycles of wetting and drying and freezing and thawing and, especially in the topsoil, from interactions between the mineral components and substances derived from living and dead plants and animals. Structure in the upper parts of the soil is also affected by human
activities, in particular, agricultural cultivations, vehicle trafficking and
building operations. However, it is also important to remember that simply
walking over the soil surface alters its soil structure and the more
frequently this happens the greater the alteration. |
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These photographs show two very different soils in a mountain landscape. The profile on the right is a Leptosol where the dark, organic-rich A horizon lies directly over an R horizon of calcareous (lime rich) rock (IB). In contrast, the profile on the left, a Fluvisol on the river floodplain is a deep soil, with a thick, organic-rich A horizon merging downwards into the C horizon of relatively unaltered rich river silt over sands and gravels. The lower parts of the C horizon are periodically waterlogged by a rising groundwater table and show a similar grey and orange "mottled" effect to that in the E horizon of the soil shown on the previous page. Because of their fertility and reliable water supply, such river floodplain soils were usually the first to be exploited for agriculture by humans (JH). |
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Do you say earth, soil or dirt?According to the Oxford English Dictionary, the word "soil" is
an Old English term coming from the Latin, solium,
meaning seat but used to imply ground (solum).
The word soil can also be used in a derogatory sense to mean something is
damaged or unclean, "these clothes are soiled". However, this sense
of the word soil has a different derivation, coming instead from the Old
French word suiller, which in turn is
derived from the Latin for pig, sus. More
than likely, people who tended pigs generally had unclean clothes and were
identified by their soil-covered clothes. Over time the differences in
meaning were forgotten. Although the term "dirt" is an often used as a substitute for
soil, the word dirt often implies an unclean appearance. The word dirt
originates from the Old Norse, drit, meaning
excrement. The common meaning of the words dirt and soil probably relate to
the use of farmyard manure as a fertilizer to improve soil. Crops would be
planted in soil fertilized by dirt. The term, "earth" has a Germanic or Saxon origin that gave rise
to the Old English word, eorthe, while the
word for wet soil, "mud," also has a Saxon origin that became the
Old English word, mot, meaning a bog or a marsh. |
Key Facts You Should Know About Soil
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So many differencesThe characteristics and vertical arrangement of soil horizons can vary
greatly from place to place, often over surprisingly short distances. This is
because of the diverse range of surface geological materials across In addition to this variability, the environmental weathering processes
vary over time, both in the short term with seasonal weather and vegetation
cycles and in the long term, as climate and land use patterns change in
response to external drivers. It is this complexity across This then is soil; a dynamic body that acts as the home to a myriad of
organisms, responds to the changing seasons and weather patterns with
associated changes in its organic, liquid and gaseous composition and,
chameleon-like, gradually changes to reflect its local environment. |
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