Higher Soil types
Podzols These are found on a large belt across the Northern Hemisphere – associated with the coniferous forest belt or Taiga (Canada, Scandinavia, Siberia)
Main Features Climate Long, cold winters, short summers with low rainfall, but severe leaching when spring snow melts and washes down Vegetation Pine needles provide only a thin leaf letter and inhibit the formation of humus The humus that is formed is very acidic Pine needles have adapted to the conditions – pine needles reduce water loss, especially in winter and root system is shallow, to survive in frozen subsoil
Organisms The cold climate discourages organisms and the soil is too acidic for earthworms Decomposition of leaf litter is slow and definite horizons develop as there are few mixing agents The downward movement of water, especially after snow melt leaches out iron and aluminium oxides from the A horizon This leaves a high silica content, giving the horizon an ash grey colour The transported iron and aluminium oxides are redeposited at the top of the B horizon This often results in the formation of an ironpan or hardpan – this can act as an impermeable layer and lead to waterlogging
Podzols are generally poor soils, but they can be improved by artificial drainage and the addition of lime Only the hardiest of crops can be grown in improved podzols
Podzol
Podzol
Grey Brown Forest Soils These soils are found further south than the podzols, the Temperate Regions such as Britain and much of the rest of Western Europe
Main Features Climate There are higher temperatures and a longer growing season in this part of the world The milder climate encourages more rapid decomposition ad as a result the humus is mild and more alkaline Vegetation This area is associated with deciduous forest, i.e. broad-leaved trees like the oak The thick leaf debris from these trees returns many of the nutrients removed by the trees This provides a plentiful supply of humus The deep roots of the trees help mix and break up the horizons They are able to shed their leaves in winter due to the long growing season
Organisms These are very active due to higher temperatures and quickly decay the humus Earthworms, insects and rodents mix and aerate the soil There are more of these due to increased food supply These soils are pedalfers (precipitation exceeds evaporation) – gradual leaching does occur and iron pans can develop where leaching is more active
These soils have much greater agricultural potential – soils are deep, more fertile, less acidic and better mixed. Can producer a wide range of cereal crops and good grazing land for cattle
Brown Earth
Brown Earth
Tundra Soils or Gleys Found in Northern Latitudes, in areas where the subsoil remains permanently frozen (permafrost), and tundra vegetation grows in the topsoil during the brief summer. These soils can also be found in areas that are waterlogged such as the foot of a north facing hill where water has gathered from the hillside but there is little sunshine to evaporate it. Or where parent rocks are of an impermeable type (such as mudstones, clays and any igneous rocks) impeding drainage thus forming a constantly waterlogged soil
Main Features Climate Winter temperatures range from -290C to – 400C, while summer temperatures barely reach 100C. Growing season is very short, often as short as 3 months Vegetation Vegetation is confined to low plants such as lichens, mosses and shrubs Underneath the vegetation there is a black mass of very slowly decaying plant material, which is very acidic
Organisms There is very little bacterial action in the very cold waterlogged conditions When the frozen topsoil thaws at the end of the winter, the ground becomes waterlogged or gleyed (due to permafrost) The continual seasonal freezing and thawing causes expansion and contraction, which leads to vertical mixing of the soil. This means that there are no clearly defined horizons Tundra soils are of very limited use to man
Gley Soil
Gley Soil