|
|
|
Land Management & Natural
Hazards Unit |
SOIL |
|
|
|
Soil
Atlas of |
|||||
|
Soil classification Introduction to soil classificationFrom the previous pages of this atlas, one can understand how different characteristics can develop within soil profiles or in different geographical areas. Apart from bare rock, glaciers and water, soil covers the Earth's surface as a continuum. The gradual changes of soil characteristics across the landscape make the study and comparison of different soil types difficult. To overcome this problem pedologists (scientists who study soils) have developed various ways to characterise soil bodies, identify, label and group them according to certain names and rules called nomenclature. This important task is known as soil classification, one of the advanced branches of basic and applied soil sciences. Classification is the procedure to arrange soil into groups, categories or, as the word implies, classes, relevant to a specific purpose. For example, a fundamental soil scientist would consider soil classes matching the processes and mechanisms driving soil formation and geographical distribution; environmental scientists use soil types grouped according their ecological functioning, biological activity, buffering and water filtering capabilities; engineers need soil groups according to different building carrying capacities, roads construction, swelling and shrinking properties while agronomists wish to have information on crop suitability, responses to various chemicals and management practices. While classification schemes will group soil differently, classification also provides a common language to map soil types, exchange and compare knowledge about them. Early soil classifications were based on individual characteristics such as the texture of soil (e.g. loam, clay or sand) or the parent material (e.g. alluvial soil, gravelly soil, etc.). During the late 1880s the Russian geologist Vasili Dokuchaev - now regarded as the father of soil science was the first to suggest a more scientific classification based on the combination of soil characteristics in relation to their formation. This, so called genetic principle, remains the guide for most present day national soil classifications, distinguishing features resulting from soil-forming processes from those whose origin is geological. Since the 1950s, most European countries have carried out an intensive soil survey to optimise the efficient use of their land resources. This success was based on well-established national soil classifications and standards. The foundation of the European Union brought about an increased interdependency for the countries supplies of food and agricultural products.
Vasili Dokuchaev
(1846-1903) is widely regarded as the father of soil science. He was one of
the first people to investigate the properties of soil in a systematic and
scientific manner. He explained how soils reflect the environment in which
they are formed. He introduced the concept of five soil forming factors
(climate, organisms, topography, parent material, time) that are still
accepted in modern soil science. Most of his new ideas were published in his
classic book the "Russian Chernoziom".
The picture was taken in the |
In order to create a common understanding of soil resources in different countries, a new soil classification system, named World Reference Base for Soil Resources (WRB), has been developed. The WRB, the soil classification scheme used for the soil maps in this atlas, has been adopted as the official soil classification system of the International Union of Soil Science (IUSS) and the accepted common scheme of soil databases of the European Union. The WRB is not meant to replace national soil classification systems but serves as a common denominator through which national soil classification systems can be compared and correlated. The World Reference Base for soil resourcesThe WRB is a two-level system of soil classification with 30 Soil
Reference Groups (see below and Page 28) and a series of uniquely defined
qualifiers for specific soil characteristics (see box on Page 28). For describing and defining soils the WRB exploits the following
nomenclature:
Soil horizons and properties are used to describe and define soil classes
if they are considered as being "diagnostic". This means reaching a
certain degree of expression, as determined visually, by prominence,
measurability, importance and relevance for soil formation, soil use and
quantitative criteria. To be diagnostic, soil horizons also require a minimum
thickness. Soil Reference GroupsTwenty four soil reference groups represent the soil of Organic soils, such as peat, are brought together in one soil reference
group called HISTOSOLS while all man-made soils,
which vary widely in properties and appearance but have in common that their
properties are strongly affected by human intervention are aggregated to the ANTHROSOLS
soil reference group. Mineral soil whose formation is conditioned by the particular properties
of their parent material are subdivided in to the ANDOSOLS
of volcanic regions, the sandy ARENOSOLS of desert areas,
beach ridges, inland dunes or areas with highly weathered sandstone and the
swelling / shrinking heavy clayey VERTISOLS of back-swamps,
river basins, lake bottoms and other areas with a high clay content. Mineral soils whose formation was influenced by their topographic setting
(for example, soils associated with recurrent floods or on steep terrain)
range from the FLUVISOLS, which show stratification or other
evidence of recent alluvial sedimentation, non-stratified GLEYSOLS
in waterlogged areas and shallow LEPTOSOLS over hard
rock or highly calcareous material, to the deeper REGOSOLS,
which occur in unconsolidated materials that have a weak profile development
because of low soil temperatures, prolonged dryness or erosion. Soils that are only moderately developed on account of their young pedogenetic age or because of rejuvenation of the
soil material are referred to as CAMBISOLS. The wet tropical and subtropical regions where high soil temperatures and
ample moisture promotes rock weathering, rapid decay of soil organic matter,
a long history of dissolution and transport of weathering products has
produced five types of deep and mature soil types. PLINTHOSOLS
are marked by the presence of a mixture of clay and quartz ('plinthite) that hardens irreversibly upon exposure to the
open air while deeply weathered FERRALSOLS have a very low cation exchange capacity and are virtually devoid of weatherable minerals. ALISOLS have high cation exchange capacity and much exchangeable aluminium, NITISOLS have deep profiles
in relatively rich parent material, ACRISOLS
develop on acid parent rock with a clay accumulation horizon, low cation exchange capacity and low base saturation while LIXISOLS
possess a low cation exchange capacity but high
base saturation percentage. |
The soil of
|
|
Page
25 |
||
|
|
|
|