Soils of the European Union - European Soil Portal - Europa

4.11 GypsisolsGeographical distributionGypsisols cover just over 4,000 km 2 in the European Union which makes up only a one per thousand of its total soilresources. Gypsisols are present only in Spain forming dominant soil reference group in 33 cases, being associated soil in25 and as inclusions in one time in soil associations (Table 4.11, Figure 4.11).Table 4.11 Area of the second level units of GypsisolsUnits in the Reference Soil Groupin the EUCodes ofsoil unitsArea in the EUkm 2Aridic Gypsisol GYad 4110Based on the 1:1 M scale database all Gypsisols fall into the Aridic Gypsisol unit.GYad100%Figure 4.11 Share of the second level soil units in the area of GypsysolsGlobal referenceGypsisols can only be found in arid regions, in level or hilly land and depression areas (e.g. former inland lakes). Worldwideextent of Gypsisols is approximately 1 million km 2 .Gypsisols have substantial secondary accumulation of gypsum in the subsurface. Most Gypsisols formed when gypsum,dissolved from gypsiferous parent materials, moved through the soil with the soil moisture and precipitated in anaccumulation layer. Where soil moisture moves predominantly upward (i.e. where a net evaporation surplus exists for anextended period each year), a gypsic or petrogypsic horizon occurs at shallower depth than a layer with lime accumulation(if present). Gypsum is leached from the surface soil in wet winter seasons. In arid regions with hot, dry summers, gypsum(CaSO 4 .2H 2 O) dehydrates to loose, powdery hemihydrate (CaSO 4 .0.5H 2 O), which reverts to gypsum during the moistwinter. Gypsum precipitates in the soil body as fine, white, powdery crystals in former root channels (gypsumpseudomycelium) or in pockets, or as coarse crystalline gypsum sand, or in strongly cemented petrogypsic horizons. Inplaces it forms pendants below pebbles and stones or rosettes (desert roses).The natural vegetation is sparse and dominated by xerophytic shrubs and trees and/or ephemeral grasses. However, deepGypsisols located close to water resources can be planted to a wide range of crops. Yields are severely depressed where apetrogypsic horizon occurs at shallow depth. Nutrient imbalance, stoniness, and uneven subsidence of the land surfaceupon dissolution of gypsum in percolating (irrigation) water are further limitations. Irrigation canals must be lined toprevent the canal walls from caving in. Most areas of Gypsisols are in use for low volume grazing.As Gypsisols occur in the driest parts of the arid climate zone, therefore leading soil classification systems label themDesert soil (USSR), Aridisols (Soil Taxonomy) and Yermosols or Xerosols (FAO).32