3.44b Soil Classification AK & BR Why look at soil? Because soil and its constituents are the base material for growing trees. History Why a Forestry Commission soil classification? There is a need for an objective site classification of United Kingdom soil / site types, upon which the growing and management of trees can be based. FC soil classification – Soil Classes Soils with well aerated subsoil Soils with poorly aerated subsoil main soil classes Flushed peatlands Unflushed peatlands Man-made mining / quarry spoil, brownfield sites etc. soils Rankers and bedrock present at < 30cm minor soil classes Skeletal soils Littoral soils adjacent to the coast, sands and gravels Typical soil constituents 20-30% AIR COMPONENT 45% MINERAL COMPONENT 30-20% WATER COMPONENT 5% ORGANIC COMPONENT What creates a soil? • Parent material - (type of rock) • Climate - (heat, water, wind) • Organisms - (bugs, insects, fungi, bacteria) • Topography - (landform) • Time Parent Material The parent material is the material from which a soil is formed, not necessarily the bedrock of a site. The geographic position of the parent material affects the potential water holding capacity, fertility and texture of a soil. Soil particles - texture SAND: coarse rough granular particles SILT: smooth spherical particles CLAY: flat, plate-like particles Soil texture Clay triangle Sand Silt FC soil classification – Soil Groups Soils with well 1 Brown earths aerated subsoil 3 Podzols 4 Ironpan soils 12 Calcareous soils Soils with 5 Ground-water gley soils poorly aerated subsoil 6 Peaty surface-water gley soils 7 Surface-water gley soils Flushed 8 Juncus (or basin) bogs peatlands 9 Molinia (or flushed blanket) bogs Unflushed 10 Sphagnum (flat or raised) bogs peatlands 11 Calluna, Eriophorum, Trichophorum (or unflushed blanket) bogs 14 Eroded bogs 2 Man-made soils 13 Rankers and Skeletal soils 15 Littoral soils Soil Horizons L – Litter (fresh litter from previous growth season) O – Organic material (humus or peat layers) A - Top soil (mineral with incorporated organic material) E – Elluvial (removed organic, clay and oxides) B – Mineral soil (altered parent material) C – Parent material (unaltered) A LAYER CAKE! Generic soil processes Podzolisation (ironpan formation) Gleying Build-up of partially decomposed vegetation (humus/peat) Brown earth Typical brown earth Slight podzolisation Slight gleying Slight build up of partially decomposed vegetation (humus/peat) Rooting is unrestricted by anaerobic conditions Brown earth Soils with brownish or reddish colours, free drainage and good aeration and moderate or strong acidity, throughout O the profile. Humified organic matter is incorporated into the mineral soil to give A a dark brown topsoil (A horizon). There is no E horizon. The B horizon is distinguished from the underlying C by a B richer brown colour due to weathering and the residual accumulation of iron oxides (Bw horizon). C Brown earth Soil Nutrient Regime Very Poor Poor Medium Rich Very Rich Carbonate moder, oligomull, Humus form mor mor, moder eumull eumull Soil oligomull eumull Rankers and shingle Moisture and Very Dry Rendzinas Gravelly or Gravelly or sandy sandy podzols brown earths Mod. Dry and ironpan Nutrient grid soils Sl. Dry Loamy brown Calcareous earths of high brown Loamy podzols Loamy brown base status earths Fresh and ironpan earths soils Moist Brown gleys of Calcareous Soil Moisture Regime Podzolic gleys Brown gleys high base brown and peaty status gleys ironpan soils V. Moist Surface-water Surface-water Calcareous gleys gleys of high surface- base status water gleys Wet Unflushed peaty gleys Flushed peaty Humic gleys of and deep peats gleys and deep high base status peats and fen peats Very Wet Podzol Podzol soil Acidic soil conditions Oxide leaching Humus movement Humus and oxide deposition Possible ironpan formation Possible surface gley formation Possible subsequent peat formation Podzol Podzols are free draining, well aerated, strongly acid soils with a surface accumulation of raw humus, an Ea O horizon from which iron oxides have been A removed, and B horizons in which E translocated humus or iron oxides have been deposited. The A horizon, which may not be well developed, consists of a B mixture of blackish humus particles and bleached sand grains. The Ea horizon consists largely of bleached sand grains and is whitish in colour. Both A and E C horizons have a friable consistence. Podzol soil Ironpan soil Ironpan The characteristic features of this group are an Eg horizon underlain by a thin ironpan (Bf horizon). The Eg horizon has a grey colour often with a O yellowish or greenish hue and ochreous or rusty mottles or streaks. These gley like symptoms are A caused by reduction and segregation of iron, E during frequent periods of waterlogging and Bf anaerobism. There is a surface accumulation of black greasy peat but this can be as little as a few centimetres thick or as much as 45 cm, the B maximum allowed in the group. The subsoil, beneath the ironpan, usually lacks gleying symptoms and is not affected by waterlogging or anaerobism. Ironpan soils are strongly acid C throughout the profile. The ironpan normally passes through stones, depending on their porosity, and also forms a conspicuous coating on the stones. Podzols and Ironpans Soil Nutrient Regime Very Poor Poor Medium Rich Very Rich Carbonate moder, oligomull, Humus form mor mor, moder eumull eumull Soil oligomull eumull Rankers and shingle Moisture and Very Dry Rendzinas Gravelly or Gravelly or sandy sandy podzols brown earths Mod. Dry and ironpan Nutrient grid soils Sl. Dry Loamy brown Calcareous earths of high brown Loamy podzols Loamy brown base status earths Fresh and ironpan earths soils Moist Brown gleys of Calcareous Soil Moisture Regime Podzolic gleys Brown gleys high base brown and peaty status gleys ironpan soils V. Moist Surface-water Surface-water Calcareous gleys gleys of high surface- base status water gleys Wet Unflushed peaty gleys Flushed peaty Humic gleys of and deep peats gleys and deep high base status peats and fen peats Very Wet Surface-water gley Typical surface-water gley Waterlogged soil becomes anaerobic (without oxygen). Soil loses bright, ochreous appearance and takes on a grey / black or mottled grey and yellow / blue / pink appearance. Rotten stones are found in the gleyed layers. Rooting is restricted by the anaerobic conditions. Surface-water gley A distinct topsoil or Ag horizon, grey coloured with rusty streaks, and some 15 - 25 cm thick, overlies a mottled grey and yellow subsoil, the Bg horizon. At a depth of about 100 cm the O mottling becomes less distinct, in the BCg horizon, and within another 50 cm the colour A becomes almost uniform in the C horizon. The profile may be attenuated by bedrock so that a true C horizon may be absent. Textures in the type are finer than sandy clay loam at least in the B Bg and BCg horizons although the Ag horizon is usually loamy and the C horizon is usually less clayey because it is less weathered. C Surface-water gley Soil Nutrient Regime Very Poor Poor Medium Rich Very Rich Carbonate moder, oligomull, Humus form mor mor, moder eumull eumull Soil oligomull eumull Rankers and shingle Moisture and Very Dry Rendzinas Gravelly or Gravelly or sandy sandy podzols brown earths Mod. Dry and ironpan Nutrient grid soils Sl. Dry Loamy brown Calcareous earths of high brown Loamy podzols Loamy brown base status earths Fresh and ironpan earths soils Moist Brown gleys of Calcareous Soil Moisture Regime Podzolic gleys Brown gleys high base brown and peaty status gleys ironpan soils V. Moist Surface-water Surface-water Calcareous gleys gleys of high surface- base status water gleys Wet Unflushed peaty gleys Flushed peaty Humic gleys of and deep peats gleys and deep high base status peats and fen peats Very Wet Peaty gley Peaty gley Waterlogged soil becomes anaerobic Litter breakdown is slowed by anaerobic conditions Build up of partially decomposed vegetation less than 45cm deep Rooting is restricted by the anaerobic conditions Peaty gley This is a soil with impeded drainage and surface peat accumulations between 5 - 25cm thickness. The peat is black or dark brown and amorphous or almost so. When O partially dried the peat shows a granular or fine blocky structure. Beneath the peat the Ahg horizon is black or dark grey and usually less than 10 cm thick. The Eg A horizon may be well developed, with pale grey colour E dominant and ochreous mottling associated with root channels and soft weathered stones. The Bg horizon has a roughly 50:50 mixture of grey and yellow or ochreous B mottling. Towards the bottom of the Bg horizon, which may be termed the BCg horizon, the mottling becomes less prominent, usually because the ochreous colour becomes less yellow and more khaki or olive and because the grey colour becomes darker. In the C horizon the C colours become less distinct and eventually merge, i.e. the original colour of the parent material is retained. Textures in the type are finer than sandy clay loam in the Bg horizon. Peaty gley Soil Nutrient Regime Very Poor Poor Medium Rich Very Rich Carbonate moder, oligomull, Humus form mor mor, moder eumull eumull Soil oligomull eumull Rankers and shingle Moisture and Very Dry Rendzinas Gravelly or Gravelly or sandy sandy podzols brown earths Mod. Dry and ironpan Nutrient grid soils Sl. Dry Loamy brown Calcareous earths of high brown Loamy podzols Loamy brown base status earths Fresh and ironpan earths soils Moist Brown gleys of Calcareous Soil Moisture Regime Podzolic gleys Brown gleys high base brown and peaty status gleys ironpan soils V. Moist Surface-water Surface-water Calcareous gleys gleys of high surface- base status water gleys Wet Unflushed peaty gleys Flushed peaty Humic gleys of and deep peats gleys and deep high base status peats and fen peats Very Wet FC soil classification – Soil Types A soil type defines a soil within a group of soils with similar characteristics.