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Soil profiles

You need to be able to recognise the three British soils; podzol, brown earth and gley. For each of them, you should also be able to describe and explain their formation.

Podzol

Podzols are easily recognisable by their distinct layers or horizons. A grey or light-coloured 'E' horizon is the result of severe leaching or eluviation which washes out everything but quartz grains. The iron and aluminium oxides collect in the 'B' horizon (illuviation) where the iron oxides can accumulate to form a thin layer of hardpan, which impedes drainage through the soil. Some iron and aluminium oxides get through the iron/hardpan, giving this 'B' horizon its dull orange colour. These soils are found where there is good drainage and soil water is strongly acidic. They tend to be found on the upper slopes of upland areas where precipitation is heavy or where the vegetation is coniferous forest, producing an acid humus. The acid conditions are not liked by soil organisms which would normally mix/merge the boundaries of the horizons.

Climate - this should indicate an excess of precipitation (ppn) over evaporation (evap.) This should indicate cool/cold conditions leading to a slow breakdown of plant litter

Natural vegetation and soil organism - coniferous forest and associated plant litter of needles could be featured Limited soil biota and slow activity due to cool/cold climate A mor/ acidic humus would tend to develop from the plant litter

Relief and drainage - downward movement of water leading to translocation of minerals and leaching, possible formation of an iron pan

Parent material - Dependant upon area - glacially derived parent material is typical of many areas with podzolic soils

Brown Earth

Brown earth soils are widespread in Britain, except in highland areas. Soil organisms, like earthworms, mix the materials together, merging the boundaries between the horizons. These soils are leached, but not heavily, so the aluminium and iron oxides are dispersed through the soil to give the overall brown colour. The original vegetation was deciduous forest, resulting in a layer of decaying leaves giving a rich humus. The deep roots of these trees reached down to the 'B' horizon (unlike coniferous trees) tapping the nutrient supply and allowing good drainage.

Climate - ppn greater than evap during summer months, resulting in only moderate leaching. Warm summers

Natural vegetations and soil organisms - mixed broad leaf, much plant litter through this is more easily broken down by more active soil biota. A moderate or moder type of humus would develop from the plant litter

Relief and drainage - downward movement of water, moderate leaching likely

Parent material - strong influence on soil development

Gley

Gley soils represent the most extensive soil cover in Scotland. These soils are found on gentler slopes or in areas of high rainfall where the water does not drain away very readily. All the glacial tills of central Scotland are dominated by gley soils. Peaty gley soil is waterlogged for all or most of the year. This waterlogging denies the soil the oxygen that the soil organisms need to survive. The organisms left in the soil extract the oxygen they need to survive from the iron compounds and the soil gradually turns grey, blue or green as the oxygen is depleted. If only the surface is badly drained (in spring melt water areas), the soil is called a surface water gley. If the water permeates the soil all year, it is called a ground water gley. If construction work in urban areas disrupts the soil drainage it is called an urban gley

Climate - generally cool to cold

Natural vegetation and soil organisms - very limited specialised species can survive under the conditions. Soil organisms that can survive in anaerobic conditions. Very slow break down of plant material

Relief and drainage - often flat areas poor drainage Poor drainage is the key soil- forming feature for this soil type

Parent Material - generally impermeable in nature, often glacial drift and heavy clay deposited on the parent bedrock