Chapter 10Chapter 10

Global SoilsGlobal Soils

IntroductionIntroduction

►SoilSoil- the uppermost layer of the land - the uppermost layer of the land surface that contains organic matter surface that contains organic matter and support for plantsand support for plants VegetationVegetation ClimateClimate

►Chain reactionChain reaction: if soil loses portions of : if soil loses portions of any of three, then plants struggle, any of three, then plants struggle, animals that rely on plants are animals that rely on plants are affected, and animals that depend on affected, and animals that depend on those animals are in troublethose animals are in trouble

Important Factors in Important Factors in Soil FormationSoil Formation

► Parent materialParent material – mineral material – mineral material suitable for transformation into soilsuitable for transformation into soil

► OrganismsOrganisms – all flora and fauna living – all flora and fauna living on/in soil; trees, grasses, bacteria, on/in soil; trees, grasses, bacteria, worms, prairie dogs, etc.worms, prairie dogs, etc.

► ClimateClimate – mainly precip and temp that – mainly precip and temp that lead to physical and chemical lead to physical and chemical breakdown of parent material; wind also breakdown of parent material; wind also plays a roleplays a role

► TopographyTopography – elevation, slope, aspect of – elevation, slope, aspect of surfacesurface

The Nature of SoilThe Nature of Soil

► Contains all three phases of matterContains all three phases of matter SolidSolid

► Mineral matter: mainly from rock materialMineral matter: mainly from rock material► Organic matter: dead biological material and Organic matter: dead biological material and

excretions from living biological objectsexcretions from living biological objects► HummusHummus

Liquid: HLiquid: H22O and dissolved substances O and dissolved substances (nutrients)(nutrients)

Gas: COGas: CO22, CH, CH44, O, O22, etc., etc. _______is the physical and chemical process _______is the physical and chemical process

by which soils develop their properties and by which soils develop their properties and characteristics.characteristics.

► WeatheringWeathering

Average Composition of SoilAverage Composition of Soil

The Nature of SoilThe Nature of Soil

► Is soil static or dynamic?Is soil static or dynamic?► DYNAMIC! Numerous processes in soil DYNAMIC! Numerous processes in soil

involve the constant/continual interaction involve the constant/continual interaction of minerals, organic matter, water, and of minerals, organic matter, water, and gases at various scalesgases at various scales

► WeatheringWeathering All physical and chemical processes that lead to All physical and chemical processes that lead to

formation of soil properties and characteristicsformation of soil properties and characteristics Occurs on parent material both above and Occurs on parent material both above and

below current soil layer; below – bedrock and below current soil layer; below – bedrock and regolith; above – rocks, gravel, sand, silt, clayregolith; above – rocks, gravel, sand, silt, clay

Cross-section of a Patch of Cross-section of a Patch of LandLand

Soil Color and TextureSoil Color and Texture

► Why are soils different colors?Why are soils different colors? Inherited from parent material (composition)Inherited from parent material (composition) Dominant processes w/i soil (evaporation, Dominant processes w/i soil (evaporation,

oxidation)oxidation)► Soil textureSoil texture

Proportion of particles within soilProportion of particles within soil Described using a series of names emphasizing Described using a series of names emphasizing

dominant particle size (particles include sand, dominant particle size (particles include sand, silt, and clay)silt, and clay)

LoamLoam refers to mixture in which above particles refers to mixture in which above particles each account for > 10% of total compositioneach account for > 10% of total composition

Important b/c major determinant in water-Important b/c major determinant in water-retention capacity of soilretention capacity of soil

Soil Particles and Associated Soil Particles and Associated SizesSizes

Some Soil TexturesSome Soil Textures

Soil Texture TriangleSoil Texture Triangle

Structure and ColloidsStructure and Colloids

►Soil structure – how soil grains are Soil structure – how soil grains are lumped or held togetherlumped or held together

►ColloidsColloids Smallest particles (mineral or organic) in Smallest particles (mineral or organic) in

soil (< 0.00001mm) and are soil (< 0.00001mm) and are extremely extremely important in soil structureimportant in soil structure, as well as , as well as attracting nutrientsattracting nutrients that are used by that are used by plantsplants

Hold nutrients due to different charges Hold nutrients due to different charges (colloids are negative, nutrients are (colloids are negative, nutrients are positive)positive)

Soil Particles and Associated Soil Particles and Associated SizesSizes

Acidity and AlkalinityAcidity and Alkalinity

► How acidic or alkaline (basic) a soil is will How acidic or alkaline (basic) a soil is will affect the fertility of the soilaffect the fertility of the soil

► If positively-charged acidic ions get into If positively-charged acidic ions get into soil, can replace positively-charged basic soil, can replace positively-charged basic ions (the nutrients) ions (the nutrients) reduced soil fertility reduced soil fertility

► Measured using pH scaleMeasured using pH scale Ranges from 0 to 14Ranges from 0 to 14 7 is a neutral substance, e.g., distilled water7 is a neutral substance, e.g., distilled water < 7 is acidic, e.g., wine, lemon juice< 7 is acidic, e.g., wine, lemon juice > 7 is alkaline or basic, e.g., baking soda, > 7 is alkaline or basic, e.g., baking soda,

ammoniaammonia Best soil pH ranges from about 6.0 to 7.2Best soil pH ranges from about 6.0 to 7.2

pH Scale for Soil Acidity pH Scale for Soil Acidity and Alkalinityand Alkalinity

Soil MineralsSoil Minerals

►Two main typesTwo main types Primary: compounds found in unaltered Primary: compounds found in unaltered

rock; play no major role in sustaining liferock; play no major role in sustaining life Secondary: develop from primary Secondary: develop from primary

minerals via chemical weathering; minerals via chemical weathering; necessary for soil development and necessary for soil development and fertilityfertility

► Important minerals include clay for Important minerals include clay for fertility and mineral oxides (Alfertility and mineral oxides (Al22OO33 and and FeFe22OO33) for structure) for structure

Soil MoistureSoil Moisture► Importance: determine ability of soil to Importance: determine ability of soil to

support plants and can lead to weatheringsupport plants and can lead to weathering► How does moisture get to the soil?How does moisture get to the soil?► Precipitation, condensation, deposition, Precipitation, condensation, deposition,

snow and ice melt, irrigation, subterranean snow and ice melt, irrigation, subterranean water (aquifers), surface waterwater (aquifers), surface water

► Then three options: runoff, infiltration, Then three options: runoff, infiltration, evaporation/evapotranspirationevaporation/evapotranspiration

► Infiltration Infiltration soil water recharge soil water recharge saturation saturation soil reaches storage capacity soil reaches storage capacity (no more water drains due to gravity)(no more water drains due to gravity)

► Remember: storage capacity affected by Remember: storage capacity affected by texturetexture

Soil Moisture and TextureSoil Moisture and Texture

Soil Water BalanceSoil Water Balance► Similar concept to water balance in Similar concept to water balance in

hydrologic cycle and energy balance in hydrologic cycle and energy balance in entire earth Recharge – water added to soilentire earth Recharge – water added to soil

► Disposal/lowering – water removed from Disposal/lowering – water removed from soilsoil

► EvapotranspirationEvapotranspiration Actual (AE): amount of water usedActual (AE): amount of water used Potential (PE): amount of water neededPotential (PE): amount of water needed

► If AE > PE, then have shortage or deficit If AE > PE, then have shortage or deficit and water can be pulled from previous and water can be pulled from previous storage OR artificially addedstorage OR artificially added

► If PE > AE, then have an abundance of If PE > AE, then have an abundance of water which can be stored as excesswater which can be stored as excess

Soil Water BudgetSoil Water Budget

► ““Accounting” of water into and out of a Accounting” of water into and out of a systemsystem

► Pos. values: Precip (P), Change in Storage Pos. values: Precip (P), Change in Storage ((ΔΔSTST), Surplus (S)), Surplus (S)

► Neg. values: Actual Evapotranspiration Neg. values: Actual Evapotranspiration (AE), Potential Evapotranspiration (PE), (AE), Potential Evapotranspiration (PE), Water Deficit (D)Water Deficit (D)

► Over course of year, hopefully balances; if Over course of year, hopefully balances; if neg. are higher during growing season, neg. are higher during growing season, need irrigation to help crop growthneed irrigation to help crop growth

► See Fig. 10.9, p. 348See Fig. 10.9, p. 348

Soil HorizonsSoil Horizons► Distinctive horizontal layers with different Distinctive horizontal layers with different

physical or chemical composition or physical or chemical composition or different organic content or structuredifferent organic content or structure

► Develop by interaction of factors discussed Develop by interaction of factors discussed at beginning of class (parent material, at beginning of class (parent material, organisms, climate, topography, time)organisms, climate, topography, time)

► Distinguished by colorDistinguished by color► Soil profileSoil profile – cross-section of a sample of – cross-section of a sample of

soil that shows horizonssoil that shows horizons► Two types of horizonsTwo types of horizons

Organic: develop from accumulating organic Organic: develop from accumulating organic matter, Omatter, O

Mineral: combination of organic and mineral Mineral: combination of organic and mineral matter, A, E, B, C, (R)matter, A, E, B, C, (R)

Soil HorizonsSoil Horizons► OO – uppermost soil layer, – uppermost soil layer,

only organic matteronly organic matter► AA – minerals, organic – minerals, organic

matter, plant roots, and matter, plant roots, and humushumus

► EE – sand, silt, and plant – sand, silt, and plant rootsroots

► BB – clay, oxides, organic – clay, oxides, organic matter, plants rootsmatter, plants roots

► CC – regolith, clay, oxides, – regolith, clay, oxides, little organic matter; not little organic matter; not really part of soilreally part of soil

► RR – (not shown) bedrock, – (not shown) bedrock, little, if any, organic little, if any, organic matter; not really part of matter; not really part of soilsoil

Soil-forming ProcessesSoil-forming Processes

► EnrichmentEnrichment – material added to soil via – material added to soil via runoff, flooding, wind, humus runoff, flooding, wind, humus accumulationaccumulation

► RemovalRemoval – surface erosion of sediment – surface erosion of sediment

► TranslocationTranslocation – material moved w/i soil, – material moved w/i soil, usually from one horizon to anotherusually from one horizon to another Eluviation vs. IlluviationEluviation vs. Illuviation

► TransformationTransformation – conversion of minerals – conversion of minerals from primary to secondary typesfrom primary to secondary types

Soil TemperatureSoil Temperature

►Helps determine chemical Helps determine chemical development of soils and formation of development of soils and formation of horizons by controlling biologic horizons by controlling biologic activity, organic decomposition, and activity, organic decomposition, and intensity of chemical processesintensity of chemical processes

►Affected by topography, latitude, Affected by topography, latitude, longitude, and seasonlongitude, and season

►Plant growth generally require temp Plant growth generally require temp > 41> 41°°FF

Soil and TopographySoil and Topography► ElevationElevation

Influences temp and moisture of soilInfluences temp and moisture of soil Higher elevations tend to have cooler temps, Higher elevations tend to have cooler temps,

higher moisture content (Catalina Mountains)higher moisture content (Catalina Mountains)► SlopeSlope

Affects drainage of water and soil thicknessAffects drainage of water and soil thickness Steep slopes have more drainage, thinner soil Steep slopes have more drainage, thinner soil

horizonshorizons► AspectAspect

Influences temp and moisture contentInfluences temp and moisture content Toward sun (south slope in NH) means Toward sun (south slope in NH) means

warmer and dryer, away from sun means warmer and dryer, away from sun means cooler and more moisturecooler and more moisture

Soil and Biologic FactorsSoil and Biologic Factors

► HumusHumus – “finely divided, partially decomposed – “finely divided, partially decomposed organic matter;” affects soil fertility, organic matter;” affects soil fertility, maintains structure for infiltration of water maintains structure for infiltration of water and airand air

► PlantsPlants – protect vs. erosion, litter becomes – protect vs. erosion, litter becomes humushumus

► AnimalsAnimals (non-human) – affect accumulation (non-human) – affect accumulation time, accumulation rate, mixing, nutrient time, accumulation rate, mixing, nutrient cycles via burrowing/digging, travel, etc.cycles via burrowing/digging, travel, etc.

► HumansHumans – same effects as animals, but also – same effects as animals, but also via cultivation, irrigation, chemical and via cultivation, irrigation, chemical and mineral fertilizers, urbanization, recreation, mineral fertilizers, urbanization, recreation, etc.etc.

The Global Scope of SoilsThe Global Scope of Soils► Soil varies at many spatial scales – Soil varies at many spatial scales –

globally, country to country, region to globally, country to country, region to region, locallyregion, locally

► Type of soil linked to climate, parent Type of soil linked to climate, parent material, biologic processes (plant and material, biologic processes (plant and animal), time, and animal), time, and topography/landformstopography/landforms

► Classified into Classified into 3 groups3 groups, which contain , which contain 12 orders12 orders and and numerous sub-ordersnumerous sub-orders, , all of which are differentiated by all of which are differentiated by unique combinations of physical unique combinations of physical and/or chemical properties (see Fig. and/or chemical properties (see Fig. 10.2, p. 354)10.2, p. 354)