Agleysol orgley soil is ahydric soil that unless drained is saturated withgroundwater for long enough to develop a characteristicgleyic colour pattern. The pattern is essentially made up of reddish, brownish, or yellowish colours at surfaces ofsoil particles and/or in the uppersoil horizons mixed with greyish/blueish colours inside the peds and/or deeper in the soil. Gleysols are also known asGleyzems,meadow soils,Aqu-suborders ofEntisols,Inceptisols andMollisols (USDA soil taxonomy), or asgroundwater soils andhydro-morphic soils.
The termgley, orglei, is derived fromUkrainian:глей,romanized: hlei, and was introduced into scientific terminology in 1905 by theUkrainian scientistGeorgy Vysotsky.[1]
Gleysols occur within a wide range ofunconsolidated materials, mainlyfluvial,marine andlacustrinesediments ofPleistocene orHolocene age, havingbasic toacidicmineralogy. They are found indepression areas and lowlandscape positions with shallow groundwater.
Wetness is the main limitation on agriculture of virgin gleysols;[citation needed] these are covered with naturalswampvegetation and lie idle or are used for extensivegrazing. Farmers use artificially-drained gleysols forarable cropping,dairy farming andhorticulture. Gleysols in thetropics andsubtropics are widely planted withrice.
Gleysols occupy an estimated 720 million hectares worldwide. They areazonal soils and occur in nearly allclimates. The largest extent of Gleysols is in northernRussia,Siberia,Canada,Alaska,China andBangladesh. An estimated 200 million hectares of gleysols are found in the tropics, mainly in theAmazon region, equatorialAfrica, and the coastal swamps ofSoutheast Asia.
They exhibit a greenish-blue-greysoil color because ofanoxicwetland conditions. On exposure, as the iron in the soiloxidizes colors are transformed to a mottled pattern of reddish, yellow or orange patches. Duringsoil formation (gleying), the oxygen supply in the soil profile is restricted due to soil moisture at saturation. Anaerobic micro-organisms support cellular respiration by using alternatives to free oxygen aselectron acceptors to supportcellular respiration. Whereanaerobic organismsreduceferric oxide toferrous oxide, the reduced mineral compounds produce the typical gleysoil color.Green rust, alayered double hydroxide (LDH) of Fe(II) and Fe(III) can be found as the mineralfougerite in gleysoils.[2][3]
Gleysoils may be sticky and hard to work, especially where the gleying is caused by surface water held up on a slowly permeable layer. However, someground-water gley soils havepermeable lowerhorizons, including, for example, some sands in hollows within sand dune systems (known as slacks), and in somealluvial situations.
Groundwater gleysoils develop wheredrainage is poor because thewater table (phreatic surface) is high, whilst surface-water gleying occurs whenprecipitation input at the surface does not drain freely through the ground. A reducing environment exists in the saturated layers, which become mottled greyish-blue or greyish-brown due to itsferrous iron and organic matter content. The presence of reddish or orange mottles indicates localised re-oxidation of ferrous salts in the soil matrix, and is often associated with root channels, animal burrows, or cracking of the soil material during dry spells.
In theWorld Reference Base for Soil Resources (WRB),[4] soils withredox processes due to ascendinggroundwater belong to the Reference Soil GroupGleysols. Soils with redox processes due tostagnant water areStagnosols andPlanosols.
