Rewriting PTR salinity, alkalinity, chemical toxicity and drainage based on the wrb-standard
Review of available information in the SGDBE for chemical toxicity estimation
The estimation of chemical toxicity due to sulphur or gypsum can be derived from the soil name (FAO85-FULL, FAO90-FULL, WRB-FULL) and the agricultural limitation (AGLIM1 and AGLIM2).
Attribute FAO85-FULL
In the FAO-UNESCO 1974 legend, presence of sulphur or gypsum appears in Thionic Fluvisol, Gypsic Yermosols and Gypsic Xerosols. Thionic Fluvisols are defined as Fluvisols having a sulphuric horizon or sulphidic materials, or both, within 125 cm from the soil surface. The sulphuric horizon forms as a result of artificial drainage and oxidation of mineral or organic materials which are rich in sulphides. It is characterised by a pH (H2O) less than 3.5 and jarosite mottles. Sulphidic materials are waterlogged mineral or organic materials containing 0.75% or more sulphur (dry weight), mostly in the form of sulphides, and having less than three times as much carbonate (CaCO3 equivalent) as sulphur. These soils are generally permanently saturated. When these soils are drained, the sulphides oxidise to form sulphuric acid and the pH drops below 3.5.
Gypsic Yermosols or Gypsic Xerosols are soils having a gypsic horizon within 125 cm from the soil surface. A gypsic horizon is a horizon of secondary calcium sulphate enrichment that is more than 15 cm thick, and that has at least 5% more gypsum than the underlying C horizon, and in which the thickness of the product in cm and the percentage of gypsum is 150 or more.
In the Soil Map of European Communities, Thioni-humic Gleysols were defined as Humic Gleysols having sulphuric horizon or sulphidic materials, or both, within 125 cm from the soil surface.
In the SGDBE, Thionic Fluvisol and Thioni-humic Gleysol are described, as well as Salo-thionic Gleysol for which no definition is available in the FAO-UNESCO 1974 legend, neither in the Soil Map of European Communities.
Table 4-16: Values of the FAO85-FULL attribute that give information about chemical toxicity
Attribute FAO90-FULL
In the FAO-UNESCO 1990 legend, the presence of sulphur or gypsum appears in Thionic Fluvisol, Thionic Gleysol, Thionic Histosol, Gypsisol, Gypsic Vertisol, Gypsic Solonetz, Gypsic Solonchak, Gypsic Kastanozem, and Gypsiric Regosol.
Thionic Fluvisol, Thionic Gleysol and Thionic Histosol are defined as soils having a sulphuric horizon or sulphidic materials, or both, within 125 cm from the soil surface.
A sulphuric horizon forms as a result of artificial drainage and oxidation of mineral or organic materials which are rich in sulphides. It is at least 15 cm thick and characterised by a pH (H2O, 1:1) less than 3.5 and has jarosite mottles.
Sulphidic materials are waterlogged mineral or organic materials containing 0.75% or more sulphur (dry weight), mostly in the form of sulphides, and having less than three times as much calcium carbonate equivalent as sulphur, and having a pH above 3.5. Sulphidic materials accumulate in a soil that is permanently saturated and having a pH above 3.5, generally with brackish water. When these soils are drained, the sulphides oxidise to form sulphuric acid and the pH drops below 3.5. At this point, these materials become a sulphuric horizon.
Gypsisols are soils having a gypsic or a petrogypsic horizon, or both, within 125 cm from the soil surface. Haplic, Calcic and Luvic Gypsisols have no petrogypsic horizon. Petric Gypsisols have a petrogypsic horizon. Gypsic Vertisol, Gypsic Solonetz, Gypsic Solonchak and Gypsic Kastanozem are soils having a gypsic horizon within 125 cm from the soil surface. Gypsiric Regosols are Regosols which are gypsiferous at least from 20 and 50 cm from the soil surface. Nevertheless, Calcic Gleysols should be also considered because a gypsic horizon can be present (the gypsic horizon, when exists, must be within 125 cm from the soil surface). A gypsic horizon is a horizon enriched with secondary calcium sulphate, is 15 cm or thicker, and has at least 5% more gypsum than the underlying C horizon. The thickness of the product in cm and the percentage of gypsum must be of 150 or more. A petrogypsic horizon is a gypsic horizon that is so cemented with gypsum that dry fragments do not slake in water and roots cannot enter. The gypsum content is commonly far greater than the minimum requirements for the gypsic horizon and exceeds usually 60%. The term ‘gypsiferous’ applies to soil material which contains 5% or more gypsum.
In the SGDBE, there are no STUs that are thionic or gypsic.
Attribute WRB-FULL
In WRB, presence of sulphur or gypsum appears in thionic soils, Gypsisols, gypsic soils, petrogypsic soils and gypsiric soils.
Thionic soils are defined as soils having a sulphuric horizon or sulphidic materials within 100 cm from the soil surface. Two specifiers can be used and defined:
- orthithionic soils: having a sulphuric horizon within 100 cm from the soil surface;
- protothionic soils: having sulphidic soil material within 100 cm from the soil surface.
A sulphuric horizon is an extremely acidic subsurface horizon in which sulphuric acid is formed through oxidation of sulphides. It must have a pH (H2O, 1:1) less than 3.5.
Sulphidic soil material is a waterlogged deposit containing sulphur, mostly in the form of sulphides, and only moderate amounts of calcium carbonate. It must have a pH (H2O) of more than 3.5.
Gypsisols are soils having:
- a gypsic or a petrogypsic horizon within 100 cm from the soil surface,
- or, 15% (by volume) or more gypsum, which has accumulated under hydromorphic conditions, averaged over a depth of 100 cm.
A gypsic soil is a soil having a gypsic horizon within 100 cm from the soil surface. Several specifiers can be used to define:
hypergypsic soils: the gypsic horizon has more than 60% of gypsum;
hypogypsic soils: the gypsic horizon has less than 25% of gypsum.
A gypsic horizon is a non-cemented horizon containing secondary accumulations of gypsum (CaSO4.2H2O) in various forms. It must have 15% or more gypsum. If the horizon contains 60% or more gypsum, it becomes a hypergypsic horizon.
A petrogypsic soil is a soil having a petrogypsic horizon within 100 cm from the soil surface. A petrogypsic horizon is a cemented horizon containing secondary accumulations of gypsum (CaSO4.2H2O). It must have 60% or more gypsum and cementation to the extent that dry fragments do not slake in water. It cannot be penetrated by roots.
A gypsic soil is a soil having a gypsiric material at least between 20 and 50 cm from the soil surface. Gypsiric soil material is mineral soil material which contains 5% or more gypsum.
In the SGDBE, there are Thionic Fluvisols, Gypsisols, Gypsic Solonchaks and Gypsic Solonetz. There are no petrogypsic, neither gypsiric soils (Table 4-17).
Table 4-17: Values of the WRB-FULL attribute that give information about chemical toxicity
Attributes AGLIM1 and AGLIM2
There is no information about sulphur in the phase. On the contrary, there is a phase that gives information about gypsum. The petrogypsic phase marks soils in which the upper part of a petrogypsic horizon occurs within 100 cm from the soil surface (FAO-UNESCO, 1974). A petrogypsic horizon is a gypsic horizon that is so cemented with gypsum that dry fragments do not slake in water and roots cannot enter. The gypsum content in the petrogypsic horizon is commonly far greater than the minimum requirements for the gypsic horizon and usually exceeds 60%.
In the SGDBE, there are some STUs having a dominant phase as petrogypsic (Table 4-18) but there are no STUs having a secondary phase as petrogypsic. The STUs with a petrogypsic phase are coming from the Digital Soil Map of the World. As the petrogypsic phase doesn’t exist in the European part of the SGDBE, it was not mentioned as an option for phase-naming in the Instructions Guide of the SGDBE. Thus, the phase was not used in the Mediterranean countries that give data for the SGDBE.
