pedogenic processes-ppt 604.ppt

Soil Forming Processes

1. CHAUDHARY SARWAN KUMAR HIMACHAL
PRADESH KRISHI VISHVAVIDYALAYA
PEDOGENIC PROCESSES, STABILITY AND WEATHERING SEQUENCE
COURSE CODE: SOILS-604
DEPARTMENT OF SOIL SCIENCE
Presented by: Sagun Mahajan

2. Content…
Pedogenic Processes: Introduction
Classification of Pedogenic processes
Stability and Weathering Sequence

3. Pedogenic Processes
Introduction
•Pedogenic/soilformingprocessesaretheprocesseswhichleadstothedevelopmentoftrue
soil/maturesoil.Theseactstobothcreateanddestroyorder(anisotropy)withinrocks/soils.These
alterationsleadtothedevelopmentoflayers,termedsoilhorizon,distinguishedbydifferences
incolor,structure,texture,andchemistry.
•Thesoilformingprocessesareverycomplexbecauseofsimultaneouslyoperatingvarious
chemical,mechanicalandbiologicalreactionsundertheinfluenceofsoilformingfactors.

4. Soil Formation
•Theevolutionoftruesoilfromrockcompletesmainlyundertwosteps:
•Thefirststepisaccomplishedbyweathering(disintegration&decomposition)
•Thesecondstepisassociatedwiththeactionofsoilformingfactorssuchas:
1.Climate
2.Organisms
3.ParentMaterial
4.Relief
5.Topography

5. Pedogenesis
Processofthedevelopmentofsoilfromtherockycrustoftheearth
Basic soil forming
processes
Addition
Losses
Transformation
Translocation

7. Classification of Pedogenic Processes
Pedogenic Processes
A. Fundamental B. Specific
Zonal
Intrazonal
C. Other

8. A. Fundamental Pedogenic Processes
Found in all soils and operate simultaneously
1.Humification
•Itreferstotheprocessof
transformationofraworganicmatter
intohumusoverthesoilsurface.
•Decompositionofraworganic
materialsbyvariousorganisms
producessimpleorganicacids.
•Furtherbacterialpolymerizationof
theseorganicacidsproducesadark
browncolloidalsubstanceresistantto
microbialattackiscalledhumus.

9. 2. Eluviation –Process of removal (wash out)
•Here soil constituents held in
suspension/solutionremovedbypercolating
waterfromtheupperlayer(A-horizon)to
lowerlayer(B-horizon),resultingtextural
differenceswhich leadstohorizon
differentiation.
•ThisprocessoccursinA-horizonofsoilprofile.
•E.g.RemovalofFeandAloxides.
3. Illuviation –Process of deposition (Addition)
•Soilconstituentsremovedfromupperlayer(eluvial
layer)depositedintothelowerlayer(zoneof
accumulation)istermedasilluviation.
•ThisprocessoccursinB-horizonofsoilprofile.
•E.g.depositionofclaymineralsandcalciumcarbonate.

10. B. Specific Pedogenic Processes
ZonalsoilformingProcesses
•Thesoilformingprocessesthatareoccurringundertheprevailing
conditionsofclimateandbiosphereinaspecificregion.
1. Calcification:
•Theprocessofprecipitationandaccumulationofcalciumcarbonate
(CaCO
3)insomepartofthesoilprofile(B-horizon)iscalled
calcification.
•Thisisacommonprocessinaridandsemiaridregions,whichare
lowinrainfall.
•TheilluviatedhorizonofCaCO
3isdesignatedascalcichorizon.
•CO
2+H
2O------>H
2CO
3(carbonicacid)
•H
2CO
3+Ca------>Ca(HCO
3)
2(soluble)
•Ca(HCO
3)
2----Temp.---->CaCO
3+H
2O+CO
2

11. 2.Decalcification
•ItisthereverseofcalcificationthatistheprocessofremovalofCaCO3orcalciumionsfrom
thesoilbyleaching.
•Thisprocessoccursinthehumidclimates.
•CaCO
3+CO
2+H
2O----Temp.---->Ca(HCO
3)
2(soluble)
3.Podzolization
•ThetermpodzolisderivedfromRussianword-PodmeansunderandZolameansashlike.
•Podzolizationistheprocessofaccumulationofsilicaandremovalofsesquioxides(FeandAl
oxides)andtheymovedownanddepositedinB-horizon.
•Climate-ColdandHumid
•Vegetation-Coniferous(acidnature)
•Parentmaterial-Sandy(eg.quartz)
•Mainlyseeninhillyareas.

12. Podzol soil
profile

13. 4. Laterization
•Thetermlateriteisderivedfromthewordlatermeaningbrickor
tileandwasoriginallyappliedtoagroupofhighclayIndiansoils
foundinMalabarhillsofKerala,TamilNadu,Karnatakaand
Maharashtra.
•Laterizationistheprocessthatremovessilica,insteadof
sesquioxides(FeandAloxides)fromtheupperlayersandthereby
leavingsesquioxidestoconcentrateinthesolum.
•Itrefersspecificallytoaparticularcementedhorizonincertain
soilswhichwhendried,becomeveryhard,likeabrick.Suchsoils
(intropics)whenmassivelyimpregnatedwithsesquioxidesimparts
characteristicredcolourtosoilprofilearecalledlaterites(Oxisols).
•Climate-warmandhumid(Tropical)
•Vegetation-Rainforestsoftropicalareas(Broadleaved)
•Parentmaterial-richinferromagnesiammineral.

14. IntrazonalsoilformingProcesses
•Thesoilformingprocessesaremoreinfluencedbycertainlocal
conditionssuchasrelieforparentmaterialthanclimateand
vegetation.
1. Gleization
•ThetermgleiisofRussianoriginmeansblue,greyorgreen
clay.
•TheGleizationisaprocessofsoilformationresultinginthe
developmentofaglei(orgleyhorizon)insomepartofthesoil
profileduetopoordrainagecondition(lackofoxygen),
imperviousparentmaterialandwherewaterloggedconditions
prevail.
•Suchsoilsarecalledhydromorphicsoils.
•The process is not particularly dependent on climate (high
rainfall as in humid regions) but often on drainage conditions
(Lower topographic position).

15. 2. Salinization (White Alkali Soils)
•Itistheprocessofaccumulationofsalts,suchassulphatesandchloritesofcalcium,
magnesiumandpotassiuminsoilsintheformofasalty(salic)horizonandalsocalledas
solonchaks.
•Itisquitecommoninaridandsemiaridregionswhereevaporationlosesaremorethan
precipitation.
•Itmayalsotakeplacethroughcapillaryriseofsalinegroundwaterandbyinundationwith
seawaterinmarineandcoastalsoils.
•Salinesoilshave;highosmoticpressure
•EC=>4.0dSm
-1
•pH=<8.5
•ESP=<15

16. 3. Alkalization (Black Alkali Soils)
•The process involves the accumulation of sodium ions on the exchange complex of
the clay, resulting in the formation of sodic soils (Sdic/Solonetz).
•These soils contain mostly CO
3
-2
and HCO
3
-
of Na.
•Mostly found in arid and semiarid regions.
•Ca {clay + 2Na ------------
Na
Na
{clay + Ca
2+
•Alkali/Sodicsoilshave;
•EC=<4.0dSm
-1
•pH=>8.5
•ESP=>15

17. 4. Pedoturbation
•It is the process of mixing of the soilmaterials not by the illuviation.
•The most common types of pedoturbation are:
•Faunal pedoturbation: It is the mixing of soil by animals such as ants, earthworms, moles,
rodents, and man himself.
•Floral pedoturbation : It is the mixing of soil by plants as in tree tipping that forms pits and
mounds.
•Argillic pedoturbation: It is the mixing of materials in the solum by the churning process
caused by swell shrink clays as observed in deep Black Cotton Soils.
•Cryopedoturbation :Frost churning (in gelisols) mixing due to freezing or thawing.

18. Pedoturbation

19. Other Pedogenic Processes
1. Clay migration (Lessivage):
•Removalofclay,particularlyoffineclayinsuspensionfromtheupperpartofsoil
profileanditsaccumulationinlowerpart.
•Lessivage term was given by Dachafour.
2. Braunification/ Rubufication/ Ferruginisation:
•Releaseofiron(Fe)fromprimarymineralsandtheirdispersalascoatingsonsoil
particlesorascomplexeswithorganicmatter/clayorasdiscreteaggregatestoimpart
browntoredcolourtosoil.
3. Regur formation:
•Formationofintensedarkcolourcomplexofsmectiteclayandhumus.
•Itisdominantprocessinblackcottonsoils.

20. Stability and Weathering Sequence
•Goldich(1938)wasthefirstpersontodrewastabilityseriesofminerals.
•Thisseriessummarizestherelativeresistanceofprimarymineralstoweatheringonearth
surface.

21. Why do rocks weather:
•Mostrocks(andminerals)formathightemperatureand
pressureinsidetheearthsurfaceandthereforeareatequilibrium
withthehightemperatureandpressureenvironments.
•Whenrocksareexposedtoearth’ssurface,theirequilibriumis
disturbedandtheirmineralsreactandexperiencetransformation
soastoadjusttolowtemperatureandpressureandwater
conditions.

22. Goldich Stability Series
Stability of
minerals vary due
to silica
tetrahedral linkage
decreasingdistortion
ofthelatticedueto
differentsizesof
cations

23. •S.SGoldichcameupwiththisseriesin1938afterstudyingsoilprofiles.
•Hefoundthatmineralsthatformunderhighertemperatureandpressurearelessstableonthe
earthsurfacethanmineralsthatareformedatlowertemperatureandpressure.
•ThepatternfollowsthesamepatternoftheBowen’sreactionseries,withthemineralsthatare
firsttocrystallizearealsothefirstthatundergochemicalweathering.

24. Weathering index (Jackson 1968)

25. Why some minerals are susceptible and some are resistant to weathering
•Ithasbeenfoundthatthehigherresistancetoweatheringofcertainmineralsareattributed
totheirhighsilicon:oxygenratio.
•Soitcanbetoldthathigherthesilicon:oxygenratiooftheminerals,higherisits
resistancetoelementsofweathering.
•Silica-tetrahedrallinkageincreasesthestability(Quartzhavingcompletesilicatetrahedral
linkage,whileolivinecomposedofsingleunhooksilicatetrahedral).
•Inrighthandorfeldsparbranch,thereisdecreasingdistortionofthelatticefromcalcicto
thepotassicfeldspar.Thebivalentcalciumdoesnotfitwellintothefeldsparchain
structure,butmonovalentKwellsuitstherolesatisfyingchargeimbalanceandfitsnicely
intolatticeoffelsparchain.
•Claysizemineralsweatheratslowratethansandandsiltparticles.

26. Mineral Silicon
Tetrahedron
Anion Forms Si:O
2
Olivines Isolated Sio
4
-1
.25
Pyroxenes Single chain SiO
3
-2
.33
AmphibolesDouble chain Si
4O
11
6-
.36
Micas Sheet Si
2O
5
-2
.40
Feldspar (K)Framework Si
3O
8
-1
.38
Feldspar
(Ca)
Framework Si
2O
8
-2
.25
Quartz Framework SiO
2 .50