SOIL DEVELOPMENT SOIL DEVELOPMENT AND EROSIONAND EROSION

SoilSoil

SoilSoil is a combination of mineral is a combination of mineral and organic mater, water, and airand organic mater, water, and air

That portion of the That portion of the regolithregolith (loose (loose surface sediment of rock and mineral surface sediment of rock and mineral fragments produced by weathering) fragments produced by weathering) that supports the growth of plants that supports the growth of plants (Upper part of the regolith.)(Upper part of the regolith.)

SoilSoilFactors controlling soil Factors controlling soil

formationformationParent materialParent material

Residual soil – parent material is the Residual soil – parent material is the underlying bedrockunderlying bedrock

Transported soil – forms in place on Transported soil – forms in place on parent material that has been parent material that has been carried from elsewhere and carried from elsewhere and depositeddeposited

SoilSoil Factors controlling soil formationFactors controlling soil formation

TimeTime Important in all geologic processesImportant in all geologic processes Amount of time for soil formation varies Amount of time for soil formation varies

for different soils depending on geologic for different soils depending on geologic and climatic conditionsand climatic conditions

ClimateClimate Most influential control of soil formationMost influential control of soil formation Key factors are temperature and Key factors are temperature and

precipitationprecipitation

SoilSoil Factors controlling soil formationFactors controlling soil formation

PlantsPlants and and animalsanimals Organisms influence the soil’s physical Organisms influence the soil’s physical

and chemical propertiesand chemical properties Also furnish organic matter to the soilAlso furnish organic matter to the soil

SlopeSlope Steep slopes often have poorly developed Steep slopes often have poorly developed

soilssoils Optimum terrain is a flat-to-undulating Optimum terrain is a flat-to-undulating

upland surfaceupland surface

SoilSoilThe The soil profilesoil profile

Soil forming processes operate from Soil forming processes operate from the surface downwardthe surface downward

Vertical differences are called Vertical differences are called horizonshorizons – zones or layers of soil – zones or layers of soil

SoilSoil The soil profileThe soil profile

O horizonO horizon – organic matter – organic matter A horizonA horizon – organic and mineral – organic and mineral

mattermatter High biological activityHigh biological activity Together the O and A horizons make up Together the O and A horizons make up

the the topsoiltopsoil

E horizonE horizon – little organic matter– little organic matter Zone of Zone of eluviationeluviation and and leaching leaching

SoilSoilThe soil profileThe soil profile

B horizonB horizon – zone of accumulation – zone of accumulation C horizonC horizon – partially altered parent – partially altered parent

materialmaterial

The O, A, E, and B horizons The O, A, E, and B horizons together are called the together are called the solumsolum, or , or “true soil”“true soil”

SoilSoilSoil typesSoil types

The characteristics of each soil type The characteristics of each soil type primarily depend on the prevailing primarily depend on the prevailing climatic conditionsclimatic conditions

Three very generic soil typesThree very generic soil types PedalferPedalfer

Accumulation of iron oxides and Al-rich Accumulation of iron oxides and Al-rich clays in the B horizonclays in the B horizon

SoilSoilThree very generic soil typesThree very generic soil types

PedalferPedalfer continuedcontinued Best developed under forest vegetationBest developed under forest vegetation

PedocalPedocal High accumulations of calcium carbonateHigh accumulations of calcium carbonate Associated with dry grasslands and brush Associated with dry grasslands and brush

vegetationvegetation

SoilSoil Three very generic soil typesThree very generic soil types

LateriteLateriteHot and wet tropical climatesHot and wet tropical climatesIntense chemical weatheringIntense chemical weathering