soils (achieve) Flashcards
Explain the main conditions and processes involved in the formation of a podzol soil.
Podzol is a type of soil widespread throughout Scotland and is generally associated with acid parent material and semi-natural heath or coarse grassland vegetation and coniferous woodland.
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.
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.
The acid conditions are not liked by soil organisms which would normally mix/merge the boundaries of the horizons.
What is the formation of a podzol?
Low temperatures lead to slow decomposition.
Coniferous needles and cones produce acidic (mor) humus.
High precipitation leads to leaching which is the downward movement of the aluminium and iron oxides, this leads to formation of an iron pan between the A/B horizons.
This iron pan may impede drainage causing water logging .
Eluviation leaves an ash grey A horizon.
Illuviation leads to a reddish brown B horizon.
Limited soil biota leads to well defined horizons.
Found on steep slopes, this further encourages leaching.
Shallow roots mean limited absorption of deep leached minerals.
Shallow roots also mean limited nutrient recycling.
What are the 6 soil processes?
-Weathering
- Decomposition and humidification
-leaching-podsolization
- translocations (elevation and illuvaiton)
What is weathering?
Weathering is the wearing away or chaining of the the parent rock which forms the inorganic particles of a soil. Rocks are weathered by the sun, rain, wind ice and plants. Weathering I greatly affected by the climate - it can take place quickest in a hot, wet climate or very slowly in a cold, dry climate.
Decomposition and humification
This is the process by which organic matter is decomposed to form humus. It is most active in the the topsoil and the speed of humification depends on the amount of organic matter on the surface and the climate (organic matter decomposes fastest in a hot, wet climate. )
Leaching
This is there removal of soluble material in solution, dissolved by water passing through the soil. It occurs occurs when rainfall is greater than evaporation. Acids in the water dissolve minerals from the topsoil and redeposit them in the subsoil. Leaching makes soil infertile because the minerals it leaches downwards are foods for plants which there roots can no longer reach. Leaching is responsible for the different laters or horizons in a soil. Leaching is most active in sandy soils such as clays which have restricted pore spaces.
Podsolization
This is an extreme form of leaching and it occurs when rainfall is much greater than evaporation and when the water is very acidic. The acids in the water dissolve minerals (especially iron and aluminium) and leach them downwards from the A and E horizons to the B horizon, depleting the topsoil of all minerals leaving an infertile soil.
Translocation (Eluviation and alleviation)
Translation is simply the movement of something from one place to another. In terms of soils, we take bout eluviation and illuviation.
Elevation is the process in which material such as organic matter or minerals are transported downwards through the soil due to water. It differs from leaching as it affects suspended material whereas leaching is dissolved material.
Illuviation is the process in which elevated materials are deposited in one of the horizons.
what is does the podzol contain?
Ho Horizon
A Horizon
B Horizon
C Horizon
What is Ho Horizon composed of?
Ho Horizon is composed of slowly decomposing pine needles and cones. Decomposition is slow due to the cold temperatures that limit bacterial activity and as the pine needles have a waxy cuticle that is hard to break down. There is an acidic more humus of PH 3.5- 4 as few nutrients are produced from the decomposition of pine needles.
What is the A Horizon?
Downward movement of acidic water rapidly leaches nutrients dissolved in the soil water out of the A Horizon, especially during the spring thaw. Severe form of leaching is known as podsolisation. Iron oxides are washed downwards the alluvial horizon is left a pale ash grey colour. Smaller clay particles are lost through eluviation in suspension and as a result the A horizon has a coarse sandy texture.
B Horizon
Nutrients are re-deposited in the B horizon (illuvial horizon) well beyond the reach of plant roots - and some will be washed out of the soil and into rivers. Te B horizon has a denser texture as clay is re deposited here and a red brown colour as iron oxides are washed in. Iron oxides may form an iron pan a few cm thick within the B Horizon, this solid layer will implode root penetration and by prevention free drainage will cause water logging just above the iron pan.
C Horizon
The parent material may be acidic rocks or glacial till or fluvial glacial sands and gravels. Water filtering through may contribute to the chemical weathering of parent material. There may also be some freeze thaw weathering in the cold temperatures.
How are Podzols recognised?
Podzols are easily recognised by their distinct layers or horizons, The acidic conditions along with the cooler climate and heavy rainfall are not tolerated by soil organisms such as earthworms which would normally mix/ merge the boundaries of the horizons.
What are the 5 Major soil forming factors for a podzol?
climate
soil organsims
Relief and drainage
Parent Material (rock type)
Natural vegetation
