Item 3: ST and WRB, an introduction
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The document discusses soil classification systems, specifically the Soil Taxonomy (ST) and World Reference Base for Soil Resources (WRB), highlighting their structural differences, categorical levels, and characteristics of various soil orders. It details specific soil types such as Entisols, Histosols, Gelisols, Andisols, and others, along with their geographic distribution, physical properties, and ecological significance. The classification process using diagnostic rules and qualifiers for soil description is also outlined.
Item 3: ST and WRB, an introduction
- 1. The IUSS (2014) endorsed both classification systems ST and WRB as international systems
- 2. Differences in structure and principles Number of categorical levels: ST has 6 levels 4 defined by key WRB has 2 levels in the system 1 defined by key On the highest level: ST has 12 orders, WRB has 32 reference soil groups (RSG) Soil moisture and temperature regimes: The WRB has no direct info on those
- 3. 1 piece of info 2 pieces of info 3 pieces of info 4 pieces of info lots of info no info, very regional 6 categories of classification Hierarchical system of information General Specific
- 4. Soil Orders (First 6) Soil Order Ending Characteristics, etc. Entisol -ent Absence of distinct pedogenic horizons (genetic profile A/C) Inceptisol -ept Weak develop (genetic profile A/Bw/C) Gelisol -el Permafrost, freeze-thaw Histosol -ist Very high OM, wet (organic soils) Andisol -and Volcanic soils Aridisol -id Salt accumulation (carbonates, gypsum, silica) – on larg dry areas of Earth! Lessdeveloped
- 5. Soil Orders (last 6) Soil Order Ending Characteristics, etc. Vertisol -ert Swelling clays, high fertility Mollisol -oll Dark, thick, grasslands Ultisol -ult Moist & warm, acidic (low base) Alfisol -alf Moist, forested, clay accumulation Spodosol -od cool, wet, coarse, acidic Oxisol -ox Extreme weathering, tropical forest, Fe, Al oxides, old, stable PM Welldeveloped
- 7. Entisols Entisols are soils of recent origin. Most soils developed in unconsolidated parent material with usually no genetic horizons except an A horizon. All soils that do not fit into one of the other 11 orders are Entisols. Thus, they are characterized by great diversity. Many Entisols are found in steep, rocky settings. However, Entisols of large river valleys (floodplains) provide cropland and habitat for millions of people worldwide. Globally Entisols are extensive, occupying ~16% of the Earth's ice-free land area.
- 9. Histosols Histosols are soils that are composed mainly of organic materials. They contain at least 20-30% organic matter by weight and are more than 40 cm thick. Bulk densities are quite low, often less than 0.3 g cm3. Most Histosols form in settings such as wetlands. Histosols are ecologically important because of the large quantities of carbon they contain. These soils occupy ~1.2% of the ice-free land area globally.
- 12. Gelisols Gelisols are soils of very cold climates that contain permafrost within 2 meters of the surface (freeze –thaw). These soils are limited geographically to the high-latitude polar regions and localized areas at high mountain elevations. Gelisols are estimated to occupy ~9.1% of the Earth's ice- free land area Because of the extreme environment in which they are found, Gelisols support only ~0.4% of the world's population - the lowest percentage of any of the soil orders. Low soil temperatures cause decomposition of organic materials to proceed very slowly. As a result, Gelisols store large quantities of organic carbon.
- 15. Andisols Andisols are soils that have formed in volcanic ash or other volcanic ejecta. They differ from those of other orders in that they typically are dominated by glass and poorly crystalline colloidal materials. As a result, Andisols have unique chemical and physical properties that include high water-holding capacity and the ability to 'fix' large quantities of phosphorus. Globally, Andisols are the least extensive soil order and only account for ~1% of the ice-free land area..
- 16. Stromboli 900 m
- 18. Inceptisols Inceptisols have minimal horizon development. They are more developed than Entisols, but still lack the features that are characteristic of other soil orders. Inceptisols are widely distributed and occur under a wide range of ecological settings. They are often found on fairly steep slopes, young geomorphic surfaces, and on resistant parent materials. A sizable percentage of Inceptisols are found in mountain areas and are used for forestry, and recreation. Inceptisols occupy an estimated 17% of the global ice-free land area. Inceptisols support ~20% of the world's population, also the largest percentage of soil orders.
- 20. Aridisols Aridisols are CaCO3-containing soils of arid regions that exhibit at least some subsurface horizon development. They are characterized by being dry most of the year and limited leaching. Aridisols contain subsurface horizons in which clays, calcium carbonate, silica, salts, and/or gypsum have accumulated. Aridisols occupy ~12% of the Earth's ice-free land area. Aridisols are used mainly for range, wildlife, and recreation. Because of the dry climate in which they are found, they are not used for agricultural production unless irrigation water is available.
- 22. Vertisols Vertisols are clay-rich soils that shrink and swell with changes in moisture content. During dry periods, the soil volume shrinks, and deep wide cracks form. The soil volume then expands as it wets up. This shrink/swell action creates serious engineering problems and generally prevents formation of distinct, well-developed horizons (with slicken sides) in these soils. Globally, Vertisols occupy ~2.4% of the ice-free land area.
- 25. Slicken sides
- 26. Alfisols Alfisols are moderately leached forest soils that have relatively high native fertility. These soils are well developed and have a subsurface horizon of clay accumulation. Alfisols are mostly found in temperate humid and subhumid regions of the world. Alfisols occupy ~10.1% of the global ice-free land area. Alfisols support about 17% of the world's population.The combination of generally favorable climate and high native fertility allows Alfisols to be very productive soils for both agricultural and silvicultural use.
- 29. Mollisols Mollisols are the soils of grassland ecosystems. They are characterized by a thick, dark surface horizon. This fertile surface horizon, known as a mollic epipedon, results from the long-term addition of organic materials derived from plant roots. Mollisols primarily occur in the middle latitudes and are extensive in prairie regions such as the Great Plains of the US. Globally, they occupy ~7.0% of the ice-free land area. Mollisols are among some of the most important and productive agricultural soils in the world and are extensively used for this purpose.
- 31. Spodosols Spodosols are acid soils characterized by a subsurface accumulation of humus with Al and Fe (spodic horizon). These photogenic soils typically form in coarse-textured parent material and have a light-colored E horizon overlying the reddish-brown spodic horizon. The process that forms these horizons is known as podzolization. Spodosols often occur under coniferous forest in cool, moist climates. Globally, they occupy ~4% of the ice-free land area. Many Spodosols support forest. Because they are naturally infertile, Spodosols require additions of lime in order to be productive agriculturally.
- 35. Ultisols Ultisols are „old” strongly weathered, leached and acid forest soils with relatively low native fertility. Intense weathering of primary minerals has occurred, and much Ca, Mg, and K has been leached from these soils (very low base saturation). Ultisols have a subsurface horizon in which clays have accumulated, often with strong yellowish or reddish colors resulting from the presence of Fe oxides. Ultisols occupy ~8.1% of the global ice-free land area and support 18% of the world's population. Agrcicilture is possible only with the use of fertilizer and lime.
- 37. Oxisols Oxisols are very highly weathered soils that are found primarily in the intertropical regions of the world. These soils contain few weatherable minerals and are often rich in Fe and Al oxide minerals. Oxisols occupy ~7.5% of the global ice-free land area. Most of these soils are characterized by extremely low native fertility, resulting from very low nutrient reserves, high phosphorus retention by oxide minerals, and low cation exchange capacity (CEC). Despite low fertility, Oxisols can be quite productive with inputs of lime and fertilizers.
- 41. Development of soil orders
- 42. 2006: ftp://ftp.fao.org/agl/agll/docs/wsrr103e.pdf 2014: http://www.fao.org/3/a-i3794e.pdf World Reference Base for Soil Resources
- 43. Basic principles It comprises two tiers of categorical level: 1st level: Reference Soil Groups (RSGs) The 32 RSGs are determined by key and serve to delineate the broad soil regions. 2nd level: Set of principal and supplementary qualifiers that are giving a precise description on important properties and are added to the name of the RSGs.
- 44. RULES FOR CLASSIFICATION (three steps) The expression, thickness and depth of layers are checked against the requirements of WRB diagnostic categories, defined in terms of morphology and/or analytical criteria. (overlapping or coinciding possible) Step 1 – the diagnostics
- 45. RULES FOR CLASSIFICATION The combination of diagnostics compared with the WRB Key in order to find the RSG, which is the first level of WRB classification. The user should go through the Key systematically!!!! The soil belongs to the first RSG for which it meets all specified requirements. Step 2 – the key
- 46. RULES FOR CLASSIFICATION For the second level of WRB classification, qualifiers are used. Step 3 – the qualifiers Principal qualifiers: are regarded as being most significant for a further characterization of soils of the particular RSG. They are given in a ranked order. Supplementary qualifiers: All other qualifiers (further details about the soil). They are not ranked, but listed alphabetically.
- 47. Qualifiers 2014 The principal qualifiers are added before the name of the RSG without brackets and without commas. Priority order → The uppermost qualifier in the list is placed closest to the name of the RSG. The supplementary qualifiers are added in brackets after the name of the RSG and are separated from each other by commas, following the alphabetical order. Qualifiers conveying redundant information are not added. Specifiers (→ subqualifiers) such as Epi-, Endo-, Amphi-, Panto-, Thapto- Bathy-, Supra-, and Proto- indicate a certain expression of the qualifier.
- 49. Page 79
- 50. Key to RSGs Principal qualifiers Supplementary qualifiers Definition ↓ Reference Soil Group (RSG) List of the RSG Priority list ↓ 1 2 3 4 5 6 7 8 List of the RSG Alphabetic list ↓ A B C D E F G H Classification name: → (B D) ← 4 1 RSG Specifiers can be used to indicate depth of occurrence, or to express the intensity of soil characteristics
- 51. example
- 52. Step 1 Diagnostics Mollic horizon Cambic horizon Argic Horizon Calcic horizon
- 53. Step 2 The key
- 54. No chernic
- 56. Step 1 Diagnostics Mollic horizon Cambic horizon Argic Horizon Calcic horizon 65 cm
- 57. yes
- 58. PHAEOZEMS Principal qualifiers Supplementary qualifiers Rendzic Chernic/ Someric Petroduric/ Duric Petrogypsic Petrocalcic/ Endocalcic Leptic Hortic/ Irragric/ Pretic/ Terric Gleyic Stagnic Fluvic Vertic Greyzemic Glossic/ Retic Luvic Cambic Skeletic Gypsiric Dolomitic/ Calcaric Haplic Abruptic Albic Andic Anthric Arenic/ Clayic/Loamic/ Siltic Aric Chromic Colluvic Columnic Densic Ferralic/ Sideralic Fractic Hyperhumic Isolatic Nechic Novic Oxyaquic Pachic Ruptic Endosalic Sodic Technic Tephric Tonguic Transportic Turbic Vermic Vitric Luvic Endocalcic Phaeozem (Siltic, Aric) Step 3 - The qualifiers