Factors influencing Factors influencing Soil FormationSoil Formation

Higher GeographyHigher Geography

BiosphereBiosphere

IntroductionIntroduction

There are six main interacting factors There are six main interacting factors in the formation of soil.in the formation of soil.

Parent Material – Biotic Factors – Climate – Relief – Time – Human

Activity

Parent materialParent material

Parent material is especially significant Parent material is especially significant in the early development of soil and its in the early development of soil and its mineral content. It can vary from solid mineral content. It can vary from solid bedrock to a wide range of bedrock to a wide range of unconsolidated deposits including unconsolidated deposits including alluvium, wind blown sand and glacial alluvium, wind blown sand and glacial till.till.

Parent material influences Parent material influences (1):(1): The rate of weathering:The rate of weathering: hard rocks (eg: hard rocks (eg:

schist) weather slowly often leading to thin schist) weather slowly often leading to thin soils. Softer, sedimentary rocks (eg: shale) soils. Softer, sedimentary rocks (eg: shale) weather more quickly.weather more quickly.

Chemical composition & soil colour:Chemical composition & soil colour: minerals derived from quartzite and minerals derived from quartzite and granite have a relatively high silica granite have a relatively high silica content and are acidic; soils on chalk and content and are acidic; soils on chalk and limestone are alkaline. The darker the limestone are alkaline. The darker the parent material the darker the soil.parent material the darker the soil.

Parent material influences Parent material influences (2):(2): Soil texture:Soil texture: is influence by the size is influence by the size

of soil material particles. This is of soil material particles. This is important because it helps determine important because it helps determine the permeability of the soil and the the permeability of the soil and the relative proportions of air (gases) relative proportions of air (gases) and water.and water.

Soil texture = the ‘feel’ of moist soil

Biotic FactorsBiotic Factors

Involves the action of vegetation and Involves the action of vegetation and a wide range of organisms, from a wide range of organisms, from bacteria to vertebrates.bacteria to vertebrates.

They all interact, influenced by They all interact, influenced by climate and the evolving nature of climate and the evolving nature of the soil itself, to produce the organic the soil itself, to produce the organic material or material or humushumus..

Humus may include: (1)Humus may include: (1) Mor humusMor humus - which mainly develops - which mainly develops

beneath coniferous forest or heather beneath coniferous forest or heather moorland is normally associated with a moorland is normally associated with a cooler, wet climate and acidic parent cooler, wet climate and acidic parent material.material.

The litter layer of pine needles, cones and / The litter layer of pine needles, cones and / or heather shoots further encourages acid or heather shoots further encourages acid soil reactions and discourages the soil reactions and discourages the breakdown of plant material.breakdown of plant material.

Earthworms are not common and there is a Earthworms are not common and there is a limiting mixing of organic and mineral limiting mixing of organic and mineral content.content.

Humus may include: (2)Humus may include: (2) Mull humusMull humus – frequently develops – frequently develops

beneath deciduous woodland whose beneath deciduous woodland whose leaves are rich in base materials.leaves are rich in base materials.

With a plentiful supply of litter and a rich With a plentiful supply of litter and a rich soil fauna, there is no clearly defined soil fauna, there is no clearly defined humus layer.humus layer.

Chemically the soil is almost neutral and is Chemically the soil is almost neutral and is the home to earthworms which are very the home to earthworms which are very active decomposers.active decomposers.

Humus may include: (3)Humus may include: (3)

Moder:Moder: is an intermediate humus is an intermediate humus between mor and mull.between mor and mull.

Climatic Factors (1)Climatic Factors (1)

ClimateClimate is particularly important, is particularly important, especially seasonal and daily variations especially seasonal and daily variations in temperature and precipitation.in temperature and precipitation.

At low temperatures the rate of soil At low temperatures the rate of soil formation is slower, especially organic formation is slower, especially organic decomposition. Equally, warmer decomposition. Equally, warmer temperatures encourage temperatures encourage decomposition.decomposition.

Climatic Factors (2)Climatic Factors (2)

The input of water percolating The input of water percolating through the soil is not the same as through the soil is not the same as precipitation but, providing precipitation but, providing precipitation exceeds evaporation, precipitation exceeds evaporation, leachingleaching is a particularly important is a particularly important process.process.

This occurs not just vertically but This occurs not just vertically but also downslope.also downslope.

Climatic Factors (3)Climatic Factors (3)

If evapotranspiration exceeds If evapotranspiration exceeds precipitation, water and minerals precipitation, water and minerals may be drawn upwards by the may be drawn upwards by the process of process of capillary movementcapillary movement. .

Relief (1)Relief (1)

ReliefRelief or topography of land or topography of land influences drainage and soil depth.influences drainage and soil depth.

Relief (2)Relief (2)Upper well drained shedding

site from which there is surface run off and through

flow.

The lower receiving site gains water,

organic and mineral matter.

If this site is particularly badly

drained, excess water accumulates and encourages the

formation of gleys and peaty soils.

Relief (3)Relief (3) Relief and aspect can also modify the Relief and aspect can also modify the

effect of climate on the soil.effect of climate on the soil.

Shady north-facing slopes are colder and wetter compared to those with a south-facing aspect. This can slow up organic decomposition and encourage peat formation.

TimeTime

Time is critical in the development of Time is critical in the development of soils before they are fully mature.soils before they are fully mature.

When they are young, soils retain the When they are young, soils retain the features of the parent material.features of the parent material.

Human ActivityHuman Activity

This should not be underestimated. It This should not be underestimated. It started around 3000 BC ago when started around 3000 BC ago when humans started to fell woodland and humans started to fell woodland and burn peat.burn peat.

More recently, blanket planting of More recently, blanket planting of coniferous plantations and coniferous plantations and modification of soil chemistry by modification of soil chemistry by applying fertilisers, lime and applying fertilisers, lime and pesticides have further altered soil pesticides have further altered soil characteristics.characteristics.