Soils Flashcards
(38 cards)
Alluvial
Transported from original source via rivers and deposited further downstream
Consist of silt, sand, clay, gravel and large amounts of organic matter - very fertile soils.
Loess
Deposited large distances from their origin by the action of wind.
Tends to be light and fine and prone to erosion.
Primarily made up of fine sand and silt - generally quite fertile.
Sedentary
Have not been transported, formed from the parent rock directly beneath them.
Factors affection soil formation
Parent material
Parent material - rate of soil accumulation is dependent upon physical properties, pH and structure of underlying rocks.
Factors affection soil formation
Climate
Warm temperatures lead to more rapid decomposition, along with moisture provided from precipitation.
Factors affection soil formation
Biota (organisms)
Presence of flora leads to an accumulation of leaf litter - becomes humus layer after being broken down by activities of detritivores.
Factors affection soil formation
Topography
Weathering on exposed slopes removes any build up of soil but soil is accumulated where slope levels to flood plane.
Factors affection soil formation
Time
Time is crucial to the formation of soil, it can take 50yrs to form 1mm of new soil.
Soil profile and horizons.
When a vertical section is cut through a soil the result is a SOIL PROFILE.
The profile is divided into a series of HORIZONS, these run roughly parallel to the surface of the soil.
Soil horizons are relatively uniform and physically/chemically/ and/or bio locally distinct form the layer above and below.
O horizon
LGH layers
O- Organic material at the surface - living organic matter and leaf litter.
L - slightly comminuted litter
F - Fermented horizon
H - humidified layer
A horizon
Commonly referred to as top soil.
Mixed organo-mineral composition.
Often darker than lower layer as it contain partially decomposed organic matter.
Majority of root growth occurs here.
E horizon
Horizon where maximum leaching occurs (eluviation)
Minerals are washed down causing a layer of resistant minerals.
Most common in forested areas.
B horizon
Commonly referred to as subsoil.
High levels of minerals washed down from higher horizons.
Anoxic and greyer in colour.
C horizon & R horizon
Soil from parent material, weathered but otherwise not altered by pedogenesis.
R horizon is bedrock which has not been weathered.
Iron pan podzol
Infertile soils.
Formed beneath dense coniferous forests and Ericacaceous shrubs.
acid pH 3.0-6.5
Parent material often sand and gravel.
Limited organisms eg earthworms because of acidity. - this results in a layer of partially decomposed leaves in surface called mor.
Nutrients leach from A horizon.
Leaching from A horizon results in an iron pan just below, it is rusty brown in colour, has strong cohesion. Can be impenetrable barrier.
Layer below iron pan can be reasonably fertile.
Nutrient cycling is very slow under these conditions.
Very difficult to cultivate.
Brown Earth
Slightly acidic. ( pH4.5 to 8.0).
High fertility.
Formed under densely forested areas of native deciduous trees with herbaceous undergrowth - leaf litter, deposited on surface has been incorporated into the soil by fauna.
Occurs in areas of reasonable rainfall.
A horizon is rich in organic matter and organisms.
A & B horizons are dark brown in colour.
Under these conditions nutrient cycling is rapid - very productive land
Redzina
Shallow calcerous soil.
Derived from limestone and chalk parent rock.
pH generally greater than 8.0.
Soils remain shallow, sites often on incline.
Free draining, doesn’t retain water for long.
No B horizon, large weathered chunks of parent rock are present.
Plant growth limited to calcicoles.
Gleys
Greyed brown earths display some degree of water logging at depth.
Groundwater gley occur at depth due to high water table
Groundwater gley are formed where impermeable subsoil is present., often in association with large bodies of water.
Clay particles leaching from B horizon can cause a clay pan.
Cultivation at the wrong time or always to the same depth can cause a plough pan. Water cannot infiltrate down and a surface-water gley develops.
Surface water gleys present typical blue grey colouration immediately above pan in surface layers if soil.
Rain or irrigation water drain very slowly.
Problems with planting in gley soil.
Poor root activity - poor aeration/structure/AFP
Death of roots - anabolic aeration, alcohols produced.
Low levels of nutrients resulting in foliage problems.
Early wilting - indicative of root problems.
Improving gley soils
Drainage.
Breaking up of soil pans
Crumb
Very fine structure, characteristic of surface soils.
Units near spherical or ovoid but irregular faces.
Found on cultivated land, weathered sites or woodland.
Light soil, very conductive air and water content.
Fine filth is particularly important for germination of seedlings.
Prismatic
Sometimes referred to as columnar.
Vertical prismatic structures.
Mainly found in B horizons which contain large amounts of clay.
Most common in soils of arid and semi-arid regions.
Good drainage and root penetration.
Blocky
Associated with heavier clays dnd soils which have low organic matter content.
Mostly found in B horizons, sometimes in surface horizon.
Development of blocky structures is due to expansion and contraction of the clay component in soil by freezing and thawing, wetting and drying.
In B horizons they promote good drainage, aeration and root penetration.
Platey
Associated with areas of compaction eg plough pans or heavy leaching, commonly in the E horizon.
Units are flat, plate like.
Associated with poor drainage.
Horizontal orientation of the structure tends to hinder the penetration of roots.
