Biosphere Biosphere SoilsSoils

Soils — properties and formation processes: ♦ properties of podzols, brown earths and gleys — horizons, colour, texture, drainage ♦ the influence of soil-forming processes on profiles as demonstrated by podzolisation, gleying, organic and nutrient movement

SQA

SoilsBiosphere Terminology

Pedalfer soil: soils where precipitation exceeds evaporation– wet areas.

Pedocal soil: soils where evaporation exceeds precipitation – dry areas.

mor: acidic humus associated with coniferous forests/tundra areas

mull: chemically neutral humus associated with deciduous forests

anaerobic : without oxygen

gleying : waterlogging

illuviation : Deposition of humus, chemical substances, and fine mineral particles in the lower layers of a soil from upper layers because of the downward movement of water through the soil profile

eluviation : movement of humus, chemical substances, and mineral particles from the upper layers of a soil to lower layers by the downward movement of water through the soil profile

Soil is a mixture of weathered rock, decayed organic matter, water and gases.Mineral matter. This consists of minerals from chemical and physical weathering of the parent material.Organic material. Material from decaying plants and organism.Air and water. Ever changing and fills the voids or spaces in the soil.

SoilsBiosphere What is soil?

Soils is a mixture of...

40%

10%23%

22%

5%Decayed organicmatter

Leaves

Water

Air

Dead soil biota

SoilsBiosphere Soil forming processes

Soil Soil formationformation

ClimateClimateReliefRelief

VegetationVegetation

HumansHumansTimeTime

DrainageDrainageParent Parent

materialmaterial

Soil biotaSoil biota

SoilsBiosphere Soil forming processes Climate

Climate Climate

Temperature and precipitation have a major influence on the soil. Higher temperatures encourage soil biota activity whilst the opposite is true.

In wetter areas where, precipitation is greater than evaporation, this causes the leaching of the soil and the removal of soluble minerals and humus. However where evaporation is greater than precipitation, water actually moves upwards through the soil, called capillary action, and this brings minerals from deeper down up to the surface.

SoilsBiosphere Soil forming processes Relief and drainage

Relief and drainageRelief and drainage

A steep slope will allow water to run-off and increase the chances of soil erosion. Flat land is usually poorly drained and this waterlogging can prevent soil forming properly.

Aspect can lead to south-facing slopes being warmer and encouraging biota activity and vegetation more so than in north-facing slopes.

The ease with which water can pass through as soil can also affect its development.

SoilsBiosphere Soil forming processes Vegetation

VegetationVegetation

Vegetation provides plenty of humus aiding soil fertility. Soil biota activity is encouraged and these areas are more likely to be warm and moist further improving soil fertility. The type of vegetation present will affect the type of soils that develops.

SoilsBiosphere Soil forming processes Humans

HumansHumans

People increasingly cause change in soils. By clearing woodlands in one area, planting trees in another, growing crops, adding chemicals and fertilisers, draining marshes the soil is altered much more quickly than would occur naturally.

SoilsBiosphere Soil forming processes Soil biota

Soil biotaSoil biota

This is all the animals living in the soil. Bacteria, worms, plants, roots and insects all absorb nitrogen, mix the soil by burrowing through it, and also aerate it (create air pockets that can be filled by water). The decaying humus in the topsoil makes this the most fertile section of any soil.

SoilsBiosphere Soil forming processes Parent material

Parent materialParent material

This is the main rock type under the soil, usually the bedrock (regolith). The parent material affects the colour, texture and chemical make-up of the soil. Eg red sandstone bedrock produces red, “sandy” soil.

SoilsBiosphere Soil forming processes Time

TimeTime

Long periods of time are needed for soils to reach maturity by the processes already mentioned (about 1000 years for one cm - in many parts of Britain we have had only 10,000 years since the last Ice Age stripped the original surface soils away). It is thought that 10 000 years are needed for a soil to settle and mature.

SoilsBiosphere Soil profiles

TopsoilTopsoil

SubsoilSubsoil

RegolithRegolith

The A HorizonThe A Horizon: This is the main layer and consist of a mixture of organic and inorganic material. This is usually nutrient rich and fine textured. Often referred to as topsoil.

AHorizon

Soil profile

BHorizon

CHorizon

The B HorizonThe B Horizon: This is the subsoil, which contains less organic matter and is coarser in texture, reflecting the importance of weathering.Nutrients may leach out of the A Horizon.

The C HorizonThe C Horizon: This is the zone of regolith (fragments of rock). Large particles sit on the underlying bedrock.

A soil profile is a vertical section from the surface vegetation to the bedrock. By examining the different layers or horizons it is possible to work out the soil type.

Soil profile can vary in depth. In Britain the average depth is 1.5m

SoilsBiosphere Brown Earth forest soils

SoilsBiosphere Brown Earth forest soils

SoilsBiosphere Brown Earth forest soils

LocationLocation: Temperate deciduous forests of Central Europe, Russia and North America. Further south than podsols.

Relief & drainageRelief & drainage: Gently rolling landscape, allows soil to drain well.

The A horizon is greasy due to its high organic content and is a light brown colour due to the humus. Leaching occurs but is less than in other soils from wetter areas, but where it is more pronounced an iron pan may develop in the B horizon.

ClimateClimate: Moderate climate. Milder winters, cooler summers and lower precipitation, allowing more rapid decomposition – although it is still exceeds evaporation (pedalfer). Good conditions for vegetation growth/soil biota.

Soil biotaSoil biota: Warmer temperatures encourage soil biota activity, making horizons less distinct. Leaf litter is more rapidly decomposed.

SoilsBiosphere Brown Earth forest soils

Type of soilType of soil: Horizons here a less distinct due to more soil biota activity mixing the layers. A pedalfer soil, but less acidic.more alkaline soil due to leaf litter type.

ProcessesProcesses: Climate is less of a negative influence – mixing is promoted vis biota and some gentler leaching may occur, possible leading to the development of an ironpan.

Human useHuman use: More fertile and useful than the other main soil types and populations here are greater. With the addition of manure and fertilisers these soils support grain crops and grazing cattle.

Natural vegetationNatural vegetation: Deciduous forests (ash, beech, oak). Plentiful supply of leaf litter. The resulting humus is deep and only slightly acidic (mull).

Parent materialParent material: Weathering of the parent material contributes to the soil forming process here.

SoilsBiosphere Brown earth soils

Thick leaf debris

Mild acid humus with plant foods

Dark brown layer

Merging boundary due to mixing by biota

Parent material

Lighter brown layer

AHorizon

BHorizon

CHorizon

Deep brown layer

Deciduous trees/heathers/shallow roots

Precipitation = evaporation approx

No marked horizons

Brown layer – well aerated

SoilsBiosphere Podsol soils

SoilsBiosphere World biomes - Podsol soils

SoilsBiosphere

LocationLocation: Northern coniferous forests.

Relief & drainageRelief & drainage: On mountain sides or tops, up to 350m. Precipitation and drainage leads to rapid leaching of iron and aluminium oxides (eluviation) from the A horizon leaving it rich in silica and ash-grey in colour.

The deposition of iron oxides in the B horizon (illuviation) creates a red-brown colouring and may concentrate to forma thin solid layer called an iron pan. This impedes drainage and can cause waterlogging.

ClimateClimate: Long cool/cold winters and short mild summers. Precipitation can be variable – low to fairly heavy. Considerable snowfall though leading to spring snow-melt.. Leads to low soil biota activity and slow decomposition.

Podsol soils

Soil biotaSoil biota: Not much activity here because of the cold climate and this means that the soil is not mixed, leading to clear horizons developing.

SoilsBiosphere

Natural vegetationNatural vegetation: Coniferous trees (pines, spruces, firs). Produces litter of needles and pines, creating a thin acidic humus (mor).

Type of soilType of soil: Heavy with aluminium and iron, leading to an acidic pedalfer soil. This soil has clearly defined horizons.

ProcessesProcesses: The climate has a strong influence here, ie lack of warmth limits soil biota activity restricts mixing of soil and causes humus to decay slowly; and leaching of iron and aluminium, as spring snow melts, and humus causes an iron pan to develop.

Human useHuman use: Mainly used for commercial forestry plantations (conifers). If lime were added, some cultivation could take place with oats, potatoes or hay. Waterlogging due to the ironpan is a major problem.

Podsol soils

Parent materialParent material: This only has a small influence with podsols.

SoilsBiosphere Podsol soils

AHorizon

BHorizon

CHorizon

Precipitation > evaporation

Coniferous trees/heathers/shallow roots

Parent material

Reddish brown layer

Raw,black acid humus (mor)

Ash grey layer

Iron pan – impedes drainage

Layer of needles and cones

Sandy texture

Denser texture

SoilsBiosphere Gley soils

SoilsBiosphere Gley soils

SoilsBiosphere

LocationLocation: Found in Tundra areas, or in places with poor drainage and low temperatures eg Dartmoor (SW England)

Relief & drainageRelief & drainage: Wet and exposed flat regions with very poor drainage - the soil is damp/waterlogged due to the permafrost. The presence of water here causes a lack of oxygen (anaerobic conditions), leading to a gleying of the soil, turning it blue-grey in colour and greasy to the touch.

ClimateClimate: Cold and wet. Summers are mild and brief and severe winters limit soil biota activity. The important factor here is the lack of warmth. The continual process of freezing and thawing, and consequent expansion and contraction, leads to vertical mixing of soil particles and poorly defined horizons. The presence of permafrost impedes drainage.

Gley soils

Soil biotaSoil biota: Severely restricted due to extreme cold and waterlogging. Soil is mixed by freeze/thaw action, but very slowly.

SoilsBiosphere

Natural vegetationNatural vegetation: Vegetation growth is limited due to lack of warmth and waterlogging. Typically mosses, lichens and marsh vegetation dominate. Larger plants can’t survive due top the shallow soils (permafrost). Produces a dark, acidic humus (mor).

Type of soilType of soil: Pedalfer soil. Clearly defined horizons.

ProcessesProcesses: As the soil is usually waterlogged it is deficient in oxygen, limiting soil biota activity. Litter is broken down very slowly in the cold temperatures. This soil is closely linked to the climate and vegetation.

Human responseHuman response: Limited potential for humans so populations are scarce. By ploughing, liming and fertilising/manuring this soil is still only capable of growing low value crops such as oats or potatoes. These areas are remote from population centres though so profits would be hard to make with such crops.

Gley soils

Parental materialParental material: Fragments of parent material are moved through this soil by freeze/thaw action.

SoilsBiosphere Gley soils

Parent material

Waterlogged blue grey gleyed mud

Black with acid humus (mor)

Grassy meadowland/small shrubs A

Horizon

BHorizon

CHorizon

Precipitation > evaporation

Waterlogged

Silty texture

Impermeable clay

Angular rock fragments

Permafrost

Mosses and lichens

SoilsBiosphere Brown Earth forest soils

Summary:

Precipitation is slightly greater than evaporation, leading to a downwards movement of water and moderate leaching. A narrow hard pan can sometimes develop.

Faster decomposition due to warmer temperatures and less water. Lots of soil biota activity – worms, rodents, insects.

Litter is mainly from deciduous leaves, leading to only a mild acid humus.

Clearly defined horizons.

Summary

SoilsBiosphere

Summary:

Precipitation is greater than evaporation, leading to a downwards movement of water and leaching.

An iron/aluminium hardpan is formed which acts as a barrier to drainage.

Low temperatures result in limited biota activity and a slow breakdown/decomposition of litter.

An acidic (mor) humus develops due to the layer of pine needles/fir cones.

Podsol soils

Clearly defined horizons.

Summary

SoilsBiosphere

Summary:

Damp waterlogged soils. Inadequate drainage. Permafrost layer may be present.

Limited soil biota activity due to waterlogging and low temperatures, so little biological activity. Humus decays very slowly.

Dark, acidic (mor) humus develops from the slowly decaying mosses, lichens and harsh vegetation.

Poorly defined horizons.

Gley soilsSummary