NREM 301NREM 30199--2222--0909Day 9Day 9Day 9Day 9

•• Quiz Answers from last ThursdayQuiz Answers from last Thursday –– up laterup laterQuiz Answers from last Thursday Quiz Answers from last Thursday up laterup later•• Wrap up discussion on soil texture and Wrap up discussion on soil texture and

porosity.porosity.•• Discuss weathering and soil chemistry/fertilityDiscuss weathering and soil chemistry/fertility•• Lab today Lab today –– “Identifying Soil Bio“Identifying Soil Bio-- and and TT ”” NOTE I di id l fNOTE I di id l fToposequencesToposequences.” .” NOTE: Individual paper from NOTE: Individual paper from today’s lab due in two weeks (October 6)today’s lab due in two weeks (October 6)

Individual 1Individual 1AA BB CC

a)a) Match the letters with numbersMatch the letters with numbers –– A3 B1 C2A3 B1 C211 22 33a)a) Match the letters with numbers Match the letters with numbers –– A3, B1, C2A3, B1, C2

For the following rank letters from high to low & give brief For the following rank letters from high to low & give brief WhyWhyb)b) Organic matter contentOrganic matter content –– A C B (prairie grasses have deeperA C B (prairie grasses have deeperb)b) Organic matter content Organic matter content –– A, C, B (prairie grasses have deeper A, C, B (prairie grasses have deeper

roots and put more organic matter into the soil)roots and put more organic matter into the soil)c)c) Amount of erosion occurring Amount of erosion occurring –– B, C, A (little structure, B, C, A (little structure,

surface litter or root matter in the crop field soil)surface litter or root matter in the crop field soil)surface litter, or root matter in the crop field soil)surface litter, or root matter in the crop field soil)d)d) Degree of structure development in the surface horizon Degree of structure development in the surface horizon –– A, A,

C, B (More roots and organic matter lead to better structure)C, B (More roots and organic matter lead to better structure)

1. What are these two soil features?1. What are these two soil features?2 What causes them?2 What causes them?

Individual 2Individual 2

2. What causes them?2. What causes them?

A BMottles, caused by oxdiation and Mottles, caused by oxdiation and reduction of iron due to a fluctuationreduction of iron due to a fluctuation

Clay coatings, Clay coatings, caused bycaused byreduction of iron due to a fluctuation reduction of iron due to a fluctuation

water tablewater tablecaused by caused by illuviation of clayilluviation of clay

Note: Feature B is waxy in appearance (not evident in the photo).

Individual 3Individual 3

Name the five soil forming factorsName the five soil forming factorsgg

Soils = f(CliPROT)Soils = f(CliPROT)

CliClimatemate

PParent Materialarent Material

RRelief (or Topography)elief (or Topography)

OOrganismsrganisms

TTimeime

Individual 4Individual 4

D fiD fi

Last Individual QuestionLast Individual Question

Define:Define:a)a) Aspect Aspect –– The cardinal direction that the slope faces.The cardinal direction that the slope faces.b)b) Bt horizon Bt horizon –– A subsurface horizon that has received A subsurface horizon that has received

ill i t d t i l f h i ti l lill i t d t i l f h i ti l lilluviated materials from upper horizons, particularly illuviated materials from upper horizons, particularly clays.clays.

c)c) Colluvium Colluvium –– Parent material deposited by gravity.Parent material deposited by gravity.d)d) Eluviation Eluviation –– Leaching or washing out of one horizon to Leaching or washing out of one horizon to

the next. Commonly happens in E horizons.the next. Commonly happens in E horizons.

Your classmates sampled soils last year in Your classmates sampled soils last year in MontanaMontana

Group 1Group 1

1.1. What slope position are they on? What slope position are they on? -- BackslopeBackslope

2.2. Because of the slope position, describe briefly what Because of the slope position, describe briefly what they might see in terms of soil development and why? they might see in terms of soil development and why? –– Very little soil development; high slopes do not allow Very little soil development; high slopes do not allow materials to rest in place long enough to undergomaterials to rest in place long enough to undergomaterials to rest in place long enough to undergo materials to rest in place long enough to undergo pedogenesis.pedogenesis.

Sketch the types of horizons and relative thicknesses Sketch the types of horizons and relative thicknesses Group 2Group 2 Last Group QuestionLast Group Question

ypypyou would find as time increases (assume temperate you would find as time increases (assume temperate forest veg. & all other soil forming factors are equal)forest veg. & all other soil forming factors are equal)

A A

B

A O

E

C CBw

Bt

E

C

CC

Time (years)Time (years)0 1,000’s

Soil TextureSoil TextureSandSand SiltSilt ClayClay

Holding Holding LowLow MediumMedium HighHighwaterwaterAerationAeration GoodGood MediumMedium PoorPoorOM levelOM level LowLow MediumMedium HighHighSpring Spring FastFast MediumMedium SlowSlowwarmwarm--upupCompactCompact LowLow MediumMedium HighHighErosionErosion LowLow HighHigh LowLowFertilityFertility LowLow MediumMedium HighHighGroup Group pH pH changechange

HighHigh MediumMedium LowLowExerciseExercise

Soil StructureSoil StructureAggregation ofAggregation of

Granular PedGranular Ped

Aggregation of Aggregation of Sand, Silt, Sand, Silt, Clay & OMClay & OMaa bb Clay & OMClay & OM

‘Glued’ ‘Glued’ together intotogether into

Peds or Peds or AggregatesAggregates

cc dd

ee ff

Strength of structure has a role in water movementStrength of structure has a role in water movement

Porosity and Bulk DensityPorosity and Bulk DensityPorosity and Bulk DensityPorosity and Bulk Density

Bulk Density = Bulk Density =

Weight of oven Weight of oven dry soil / dry soil / yy

Volume of whole Volume of whole soil (solids + airsoil (solids + airsoil (solids + air soil (solids + air

space)space)Nikki D’Adamo

Doolittle Praririe Soil (right) vs. Adjacent Crop Field (left)

Strength of structure also has a Strength of structure also has a l i il il i il irole in soil erosionrole in soil erosion

Jim Richardson/National Geographic Image Collection

Loss of Porosity and Structure by Loss of Porosity and Structure by Compaction by large equipmentCompaction by large equipmentCompaction by large equipmentCompaction by large equipment

Agricultural ActivitiesAgricultural Activities

Logging ActivitiesLogging Activities

What Happens to Soil Structure When What Happens to Soil Structure When --Forest (or Prairie) is replaced by corn & soybeans?Forest (or Prairie) is replaced by corn & soybeans?( ) p y y( ) p y y

Results of CultivationResults of Cultivation

S D dS D d

Infiltration rates drop fromInfiltration rates drop from

Structure DestroyedStructure Destroyed

Infiltration rates drop fromInfiltration rates drop from33--6 in/hr to 0.56 in/hr to 0.5--1.5 in/hr1.5 in/hr

R ff i 20R ff i 20 60%60%Runoff increases 20Runoff increases 20--60%60%Streams carry more waterStreams carry more water

Poor Soil Structure and TreesPoor Soil Structure and Trees

Porosity reducedPorosity reducedAeration reducedAeration reducedMoisture increasedMoisture increasedMicrobial activity reducedMicrobial activity reduced

Weathering in Weathering in SoilSoil

WeatheringWeathering refers refers to the alteration of to the alteration of

rocks and rocks and minerals at or minerals at or

near the Earth’snear the Earth’snear the Earth s near the Earth s surface.surface.

Two types:Two types:

PhysicalPhysicalPhysicalPhysical

& Chemical& Chemical

Physical WeatheringPhysical WeatheringDefinition: disintegration of rock material into smaller-sized

fragments. The general mechanism for physical weathering is the establishment of sufficient stress for theweathering is the establishment of sufficient stress for the rock material to break.

Common processes:Common processes:1. Expansion

a) Crystallization: freezing water, salt crystal growthb) Th l i / t ti diff ti lb) Thermal expansion/contraction: differential

expansion/contraction of minerals, effects of fire.c) Unloadingd) Plant and animal influences (e.g., roots, lichens)

2. Abrasion of material during transport by water, ice, wind, g p y , , ,and gravity.

Soil Parent Materials Soil Parent Materials –– the raw mineral material the raw mineral material soils are developing in.soils are developing in.

Rocks and Rocks and MineralsMinerals Deposited in oceans Deposited in oceans --marine sedimentmarine sediment

Deposited in lakes Deposited in lakes --------lacustrine sediment lacustrine sediment Deposited in streams Deposited in streams --alluviumalluvium –– floodplain, deltafloodplain, delta

terrace fanterrace fanterrace, fanterrace, fanice ice

transporttransportDeposited by ice Deposited by ice --------glacial till glacial till ------ morainesmoraines

Deposited by water Deposited by water ----outwash outwash –– alluvium, marine alluvium, marine lacustrinelacustrine

ResidualResidualparent materialparent material

lacustrinelacustrine

Deposited by wind Deposited by wind -- eolian eolian ------ loess, eolian sand, loess, eolian sand, sedimentsediment volcanic ashvolcanic ash

Deposited by gravity Deposited by gravity ––colluvium colluvium –– creep, landslidescreep, landslides

parent materialparent material(bedrock weathered (bedrock weathered in place)in place)

types of types of d itd it

examples of examples of

Modified from Brady and Weil. 2002. The nature and properties of soils. 13th edition. Prentice Hall.

depositsdeposits landforms or landforms or depositsdeposits

Chemical WeatheringChemical Weathering

Definition: weathering of rock material that results gin a change in chemical composition.

Common processes:1. Hydration2. Hydrolysis3. Oxidation/Reduction4. Dissolution

A id R i ( b i )5. Acid Reactions (eg. carbonation)6. Complexation/Chelation

1. Hydration: the chemical combination of water with another substance; binding of intact t l l t i lwater molecules to a mineral.

Example: Hydration of iron oxide to hydrous oxidesFe2O3 + H2O 2FeOOH (same as Fe2O3*H2O)(hematite) (goethite)( ) (g )Produces Red colors Produces Yellow and brown colors

2. Hydrolysis: reaction of minerals with split water molecules, leading to cation displacement.

Example: Hydrolysis of feldspar and production of kaolinite clay.2KAlSi3O8 + 2H+ + 9H2O Si2O5Al2(OH)4 + 4H4SiO4 + 2K+

(K-feldspar) (kaolinite) (soluble silica/silicic(K feldspar) (kaolinite) (soluble silica/silicic acid) + (potassium ions)

3. Oxidation/Reduction: process of substance losing (oxidation) or gaining (reduction) electrons (e-).Example: Oxidation and reduction of ironExample: Oxidation and reduction of iron2Fe2+ + 4HCO3 + 0.5 O2 + 2H2O Fe2O3 + 4H2CO3

(iron oxide or hematite, with Fe3+)

4. Dissolution: Water hydrates the cations and anions in a solid until they are dissociatedsolid until they are dissociated from one another and are completely surrounded by water molecules.

Example: Dissolution of salt

NaCl Na+ + Cl-

5. Acid Reactions: Strong or weak acids react with soil minerals to hasten weathering.

Example: CarbonationCaCO3 + CO2 + H2O Ca2+ + 2HCO3

-CaCO3 CO2 H2O Ca 2HCO3

(Calcium Carbonate + Carbon Dioxide + Water) yields (Calcium + Carbonic Acid)Acid)

6. Complexation/Chelation: Formation of metal organic complexes in which ametal-organic complexes in which a metal cation (e.g., Fe3+ or Al3+) becomes part of an organic ring structure

CH2 COOH

CCOOH

CH2 COOH

CCOO

structure.Example: Chelation of iron

OH + Fe(NO3)3

C

CH2 COOH

O Fe + 3HNO3

C

CH2 COO

citric acid

chelated iron

Physical Physical yyweathering by weathering by

root actionroot actionroot actionroot action

Ph i lPh i lPhysical Physical weathering weathering due todue todue to due to water and water and wind actionwind actionwind actionwind action

Slot Canyon, Slot Canyon, Zion National Zion National Park UtahPark UtahPark, UtahPark, Utah

Physical weathering Physical weathering –– wave abrasion of wave abrasion of limestone pebbles, Lake Michiganlimestone pebbles, Lake Michigan

Source: Sandor

Physical weathering – fire cracked rock Idahocracked rock, Idaho

Source: Jim Gubbels

Weathering till boulder, Sierra Nevada Mountains

Source: Sandor

Physical weathering – Unloading in granite, Sierra Nevada Mountains

Chemical and physical weathering rind in diorite till boulder, Des Moines Lobe

Source: Sandor

Deep biogeoDeep biogeo--Deep biogeoDeep biogeochemical weathering chemical weathering

in bedrockin bedrockin bedrockin bedrock

Ulti l i G iUlti l i G iUltisol in GeorgiaUltisol in Georgia

Source: Sandor

Common Igneous RocksCommon Igneous RocksIgneous rocks are formed from magma (molten rock)Igneous rocks are formed from magma (molten rock)

Common Primary Silicate Minerals

Common Primary Silicate MineralsCommon Primary Silicate MineralsPrimary minerals, the original minerals of the Earth, are formed at high temperature and/or

pressure in igneous and metamorphic rocks. They constitute the majority of sand and silt in soils.

Mineral Composition Si:O

Quartz Si02 1:2

Feldspar 1:2Feldspar K-feldspar (orthoclase)

KAlSi3O8

NaAlSi3O8

1:2(Si or Al:

O)

Plagioclase

3 8

CaAl2Si2O8

Mafic Minerals:

Mica (biotite) Fe, Mg aluminosilicates 2:5 Amphibole (hornblende)

Fe, Mg, Ca aluminosilicates

4:11

Pyroxene (augite) Fe, Mg, Ca aluminosilicates

1:3

Clay minerals have a layer silicate crystal tetrahedron

Clay building blocks:

y

structure consisting of tetrahedral and octahedral sheets tetrahedral sheet

octahedron

octahedral sheet

E l1 layer of1:1 clay

1 tetrahedral sheet bonded with1 octahedral sheet

Example:

1 octahedral sheet

Properties of Common Clay MineralsProperties of Common Clay Minerals

cmol(+)/kg or

Kaolinite mostly in highly-weathered, acidic soils like Ultisols and Oxisols

and exchangeable cations

Smectite mostly in less weathered, base-rich soils lik M lli l d Alfi lcations

and exchangeable

like Mollisols and Alfisols

exchangeable cations(Mg2+)

Cation Exchange Capacity (CEC) Cation Exchange Capacity (CEC) –– a key soil fertility property of a key soil fertility property of some clay minerals and humussome clay minerals and humus

CEC definition: the amount of exchangeable cations a soil can adsorb. Adsorption

Negatively charged clay Cation Exchangeplant root

refers to the holding of these cations near clay surfaces by electrical attraction.

exchange

plant root

exchange

reactions

Cations in the soil water solution

Several plant nutrients occur in soil as cations (positively charged ions),

Exchangeable cationsadsorbed to clay surface

Plant roots mainly take up nutrient ions from the soil solution

for example Ca2+, Mg2+, K+, Fe2+, Cu2+, Zn2+, and others. Negatively-charged clay and humus particles hold cations in soil, prevent leaching loss of these cations, and make them available for uptake by plants.

Origin of Cation Exchange Origin of Cation Exchange C i (CEC) i Cl Mi lC i (CEC) i Cl Mi lCapacity (CEC) in Clay MineralsCapacity (CEC) in Clay Minerals

tetrahedral sheet

Ca2+ K+

Exchangeable cations

• Mainly found in 2:1 clays

Two kinds of CEC:

octahedral sheettetrahedral sheet

Ca2+ K+

Two kinds of CEC:

• Permanent (through isomorphic substitution) at the time of clay mineral formationclay mineral formation

• pH dependant

Permanent CECPermanent CECCEC mainly results from process of isomorphous substitution during clay mineral formation.

Isomorphous substitution involves the replacement of one element for another inside the clay mineral at the time of formation It cannot be undoneformation. It cannot be undone.

Examples of isomorphous substitution: • Aluminum (Al3+) substitution for Silicon (Si4+) in Al3+Si4+Aluminum (Al ) substitution for Silicon (Si ) in tetrahedral sheet. • Magnesium (Mg2+) substitution for Aluminum (Al3+) in octahedral sheet.

Note in both cases a cation with lower valence replaces one of higher valence, resulting in a net negative charge, or layer charge. This negative charge is offset by the exchangeable cations.

pH Dependant CECpH Dependant CECpH Dependant CECpH Dependant CEC• Some variable or pH-dependent charge also occurs at

d l dexposed clay edges. • If pH rises, H+ dissociates from OH- at clay edges,

increasing the CEC. • If pH decreases, H+ can be attached to the clay surface

OH- groups, causing a decrease in CEC. • Under very acidic conditions such as in highly weathered

f ftropical soils, small amounts of positive surface charge can develop (i.e., anion exchange capacity. This variable charge is most important in kaolinite and aluminum and iron oxides which are abundant in highlyaluminum and iron oxides, which are abundant in highly weathered soils.

• The CEC of humus is also pH-dependent.

pH and Nutrient AvailabilitypH and Nutrient Availability

Base saturation Base saturation –– a soil property related to Cation Exchange a soil property related to Cation Exchange Capacity and also essential to soil fertilityCapacity and also essential to soil fertilityBase saturation % refers to the proportion of base forming cations (calciumBase saturation % refers to the proportion of base-forming cations (calcium, magnesium, potassium – all major plant nutrients, and sodium) on cation exchange sites. The remaining cation exchange sites are occupied by exchangeable acids (hydrogen and aluminum ions).

Base Saturation % = Ca2+ + Mg2+ + K+ + Na+ x 100CEC

Base saturation is positively correlated with pH. Acidic, highly weathered soils such as Ultisols and Oxisols have lower base saturation (and lower CEC) than less weathered, less acidic ( )soils such as Mollisols and Alfisols.

)EC

Site

s (%

)C

E

Soil pH Source: Birkeland 1999

Range of Soil pHRange of Soil pH

Relative concentration of H+ or OH -of H or OH

Acid Neutral Alkaline

pH 3 4 5 6 7 8 9 10

acid sulfate soils leached soils many fertile soils calcareous soil sodic soil

lemon juice pure water soap

Source: Jenny. 1980. The Soil Resource

Predict the Effect of Igneous Rock Parent Materials on Soil & Predict the Effect of Igneous Rock Parent Materials on Soil & Ecosystem Properties. Higher or Lower in Which One?Ecosystem Properties. Higher or Lower in Which One?

Igneous Rock Parent MaterialS il/E P G i ( i h i G bb ( i h i i

y p gy p g

Soil/Ecosystem Property Granite (rich in silica)

Gabbro (rich in iron and magnesium)

Clay Content

Sand Content

Available Water Capacity

CEC and Bases

Ecosystem Biomass

S il i ttSoil organic matter, nitrogen,fertility

Predict the Effect of Igneous Rock Parent Materials on Soil & Predict the Effect of Igneous Rock Parent Materials on Soil & Ecosystem Properties. Higher or Lower in Which One?Ecosystem Properties. Higher or Lower in Which One?

Igneous Rock Parent MaterialS il/E P G i ( i h i G bb ( i h i i

y p gy p g

Soil/Ecosystem Property Granite (rich in silica)

Gabbro (rich in iron and magnesium)

Clay Content Lower Higher

Sand Content Higher Lower

Available Water Capacity Medium Medium

CEC and Bases Lower Higherg

Ecosystem Biomass Lower Higher

S il i tt L Hi hSoil organic matter, nitrogen,fertility

Lower Higher

Effect of Parent Material on Soils and Ecosystems Effect of Parent Material on Soils and Ecosystems (A Lithosequence)(A Lithosequence)

Igneous Rock Parent Material

(A Lithosequence)(A Lithosequence)Example from Sierra Nevada Mountains, California (Jenny, 1980)

Soil Properties Silicic Rocks Mafic Rocks

Organic Carbon % 1 74 2 88Organic Carbon % 1.74 2.88

Total Nitrogen % 0.074 0.121

Clay % 12 21

Exchangeable 5 11Bases (cmol+/kg)

Today’s Lab Today’s Lab –– Reactor Woods Reactor Woods ––Identify and describe soil bioIdentify and describe soil bio-- and topoand topo--sequences sequences yy pp qq(logical orders of soils that are different because of (logical orders of soils that are different because of position in the landscape)position in the landscape)

• Wear long pants! (poison ivy)

E h ill h il b d il d i ti• Each group will have a soil probe and a soil description kit. You will describe three cores from different landscape positions (summitt, backslope, footslope)

• We will also walk down the hill to Onion Creek and look at soils along the way.

•• NOTE: Individual paper from today’s lab due in two NOTE: Individual paper from today’s lab due in two weeks (October 6)weeks (October 6)

Depth (cm)

BiBi f tf t20

BioBio--sequence sequence -- forest forest member. member.

40Hayden Hayden -- developed developed under deciduous forest under deciduous forest in Des Moines Lobe tillin Des Moines Lobe till

60in Des Moines Lobe till.in Des Moines Lobe till.

80

100100

120120

Source: Aandahl 1982

ApproximateApproximateDepth (cm)Depth (cm) BioBio--sequence sequence --

S M bS M b2020

Savanna Member Savanna Member

Lester Lester --4040 developed in developed in

deciduous forest deciduous forest –– prairieprairie

6060–– prairie prairie transition transition ecotone ecotone ( )( )

8080(savanna)(savanna)

100100

120120Source: Sandor

BiBiBioBio--sequence sequence ––Prairie Member Prairie Member

Clarion soil Clarion soil -- Shown Shown to 48 into 48 in

Source: Sandor

Landscape of toposequence:Landscape of toposequence: ClarionClarion -- wellwell--drained higher drained higher soils (lighter brown tones);soils (lighter brown tones); WebsterWebster –– dark, poorlydark, poorly--drained drained

t l t d ilt l t d il Ok b jiOk b ji d k i l l dd k i l l dwet elongated soils;wet elongated soils; OkobojiOkoboji –– dark, circular, closed dark, circular, closed depressions;depressions; HarpsHarps –– dark circular above Okoboji, more dark circular above Okoboji, more calcareous;calcareous; StordenStorden –– very light yellow tops of hillsvery light yellow tops of hills;; y g y py g y p

Thi k b tThink about the original

t tivegetation –recall your

i it tvisit to Doolittle P i i

Source: Lee Burras or Jerry Miller

Des Moines Lobe UplandDes Moines Lobe UplandPrairie

Drainage classesDrainage classes

•• Excessively drainedExcessively drained•• Somewhat excessively Somewhat excessively

draineddrainedW llW ll d i dd i d•• WellWell--draineddrained

•• Moderately wellModerately well--draineddrained•• Somewhat poorly drainedSomewhat poorly drainedSomewhat poorly drainedSomewhat poorly drained•• Poorly drainedPoorly drained•• Very poorly drainedVery poorly drainedy p yy p y•• Permanently wetPermanently wet

Compare the Webster to the Nicollet and Clarion.

Upland SoilsUpland Soils –– ClarionClarion--WebsterWebster--Nicollet AssociationNicollet Association

Note: Parent materials Note: Parent materials –– glacial till or local alluviumglacial till or local alluviumUpland depressional soil sequence from center out Upland depressional soil sequence from center out ––

Okoboji 6, Harps 95, Canisteo 507Okoboji 6, Harps 95, Canisteo 507Webster 107Webster 107 - depressional, nondepressional, non--circular soilcircular soil

Best drained soils Best drained soils –– Clarion 138 & Storden 62Clarion 138 & Storden 62 but Storden is erodedbut Storden is erodedNicolletNicollet – somewhat poorly drainedsomewhat poorly drained

Soil Landscape Model for Central IowaSoil Landscape Model for Central Iowa

HaydenHayden--LesterLester--StordenStordenHaydenHayden--LesterLester--StordenStordenAssociationAssociation

ClarionClarion--WebsterWebster--NicolletNicolletAssociationAssociation

ColandColand--SpillvilleSpillville--ZookZookAssociationAssociation