Soils of the European Union - European Soil Portal - Europa

that under arid conditions acicular clays are not produced but only preserved, provided they exist in the parent material orin the dust that falls on the soil.Continuous hard rockDefinition. Continuous hard rock is material underlying the soil, exclusive of cemented pedogenetic horizons such as apetrocalcic, petroduric, petrogypsic and petroplinthic horizons, which is sufficiently coherent and hard when moist to makehand digging with a spade impractible. The material is considered continuous if only a few cracks 10 cm or more apart arepresent and no significant displacement of the rock has taken place.Geric propertiesGeneral description. Geric properties (from Gr. geraios, old) refers to mineral soil material which has a very low effectivecation exchange capacity or even acts as an anion exchanger.Diagnostic criteria. Mineral soil material has geric properties if it has either:1. 1.5 cmolc or less of exchangeable bases (Ca, Mg, K, Na) plus unbuffered 1 M KCl exchangeable acidity per kgclay; or2. a delta pH (pHKCl minus pH water ) of +0.1 or more.Gleyic propertiesGeneral description. Soil materials develop gleyic properties (from the Russian local name gley, mucky soil mass) if theyare completely saturated with groundwater, unless drained, for a period that allows reducing conditions to occur (this mayrange from a few days in the tropics to a few weeks in other areas), and show a gleyic colour pattern.Diagnostic criteria. Reducing conditions 10 are evident by:1. a value of rH in the soil solution of 19 or less; or2. the presence of free Fe 2+ as shown by the appearance of either:a. a solid dark blue colour on a freshly broken surface of a field-wet soil sample, after spraying it with apotassium ferric cyanide (K 3 Fe(III)(CN) 6 ) solution; orb. a strong red colour on a freshly broken surface of a field-wet soil sample after spraying it with a a,a, dipyridylsolution in 10% acetic acid; and3. a gleyic colour pattern 11 reflecting oxirnorphic 12 and/or reductomorphic 13 properties either:10 The basic measure for reduction in soil materials is the rH. This measure is related to the redox potential (Eh) andcorrected for the pH as shown in the following formula:11 A gleyic colour pattern results from a redox gradient between the groundwater and capillary fringe causing an uneven distribution ofiron and manganese (hydr)oxides. In the lower part of the soil and/or inside the peas the oxides are either transformed into insolubleFe/Mn(II) compounds or they are translocated both processes leading to the absence of colours with a Munsell hue redder than 2.5Y.Translocated iron and manganese compounds can be concentrated in oxidized form (Fe(III) Mn(lV)) recognizable by a 10% H 2 O 2 test inthe field on ped surfaces or in (bio)pores ("rusty root channels"), and towards the surface even in the matrix.12 Oximorphic properties reflect alternating reducing and oxidizing conditions as is the case in the capillary fringe and inthe surface horizon(s) of soils with fluctuating groundwater levels. Oximorphic properties are expressed by reddish brown(ferrihydrite) or bright yellowish brown (goethite) mottles or as bright yellow (jarosite) mottles in acid sulphate soils. Inloamy and clayey soils the iron (hydr)oxides are concentrated on aggregate surfaces and the walls of larger pores (e.g. oldroot channels).13 Reductomorphic properties reflect permanently wet conditions and are expressed by neutral (white to black: N1/ to N8/)or bluish to greenish (2.5Y, 5Y, 5G, 5B) colours in more than 95 percent of the soil matrix. In loamy and clayey materialblue-green colours dominate due to Fe (II,III) hydroxy salts (green rust). If the material is rich in sulphur blackish colours81