1. Podzolization: Translocation of oxidized Fe, Al and/or humus to
Bs, Bh, or Bhs horizons
(Fe is NOT moving due to REDOX processes)
RUSSIAN school of thought:
"Podzolization" includes not only Fe+Al translocation,
but also clay destruction in the upper profile.
(creates coarser textures and thus enhances podzolization)

2. Main school of thought:
Cheluviation
organic acids (anions) combine with (oxidized)
Fe+++, Al+++ cations (that is, they CHELATE them),
to render them soluble and mobile
Forms an E-Bs horizon sequence
OC illuviates mainly into the
UPPER Bs, eventually leading
to an E-Bhs-Bs sequence

3. A E
Bhs Bs BC
Typic
Haplorthod

4. Organic acids:
humic (large ones, high-pH environs)
fulvic (medium ones, low-pH environs)
low molecular weight ones

5. Humic vs Fulvic acids FULVIC HUMIC C
Small-ish molecules Large molecules
Acidic soils Basic soils
Forest vegetation Grass vegetation
Fungi decomposition product Bacterial decomposition product
Indicative of low biological activity High biological activity
Chelates and renders mobile Fe & Al Forms stable Ca-humates
Cool, moist climates Warm, moist-dry climates
Accelerates weathering via chelation Inhibits weathering: an organic "paint"

6. Chelation – how does it work?
A +3 metal cation, like Fe+++
(not soluble)
Chelated metal cation,
now soluble

7. Fulvic acid chain molecule|
|--COOH
|--OH
|--COOH Carboxyl group (Structure before
|--OH Hydroxyl group dissociation of H+ and
| linkage to metal cation)
|--COOH + Fe H2O
|--COO--\___Fe(H2O)3 + H (Structure after metal
|--O------/ | cation (Fe+++) is
| OH chelated and one H+ is
| released, acidifying soil soln.)

8. From the top.......the podzolization process (cheluviation) is:
(Ch1a) Organic matter accumulates on the soil surface and decomposes,
releasing acidic organic compounds. 

9. TOO MUCH CLAY INHIBITS PODZOLIZATION
Acidification occurs
(Ch1b) Rainfall adds carbonic acid (CA) to the soil system
Additional CA is formed by oxidation of organic matter and
microbial respiration. 
Acidifies the surface horizons and initiates weathering.
(Ch2) Acids dissolve carbonate and other minerals (carbonation),
--byproducts are leached. 
pH gradient is established (acid in upper profile, non-acid below).
(Ch2a) If clays present, initiate lessivage.
(If sandy, proceed to step Ch3.)
TOO MUCH CLAY INHIBITS PODZOLIZATION

10. TOO MUCH CLAY INHIBITS PODZOLIZATION
Primary mineral
weathering
Fe+++
Adsorbed to
a clay mineral
Chelated by
organic acids
Aint goin’ nowhere!
Can be translocated
(PODZOLIZATION)
RUBIFICATION
(reddening in place)

11. Fe oxides adsorbed to clay minerals
Lessivage dominant here
E horizon
Red colors here due to
Fe oxides adsorbed to clay minerals
in Bt horizon
Bt horizon

12. Rubification:
-reddening in place
-forms Bw horizons

14. (Ch3) When upper profile pH drops <5.0,
ferromagnesian minerals really start to weather rapidly,
releasing lots of Fe, Mg, Al, and K cations.
(Ch4) Any “free” metal cations get chelated
(as long as clay doesn’t interfere, and as long as the “correct” acids are present)
Chelate complexes migrate with percolating water,
until immobilization and/or precipitation occurs, below.

15. (Ch5) Precipitation of chelate occurs due to:
(a) microbial breakdown of chelate
(b) loss of energy:
dessication (cessation of wetting front movement), or
loss of energy at water table, or
loss of energy at lith discontinuity
(c) increase in pH
(d) *saturation of chelate complex
ratio of > 0.1 for metal/acid wt will saturate it
Al max is deeper than the Fe max, due to greater solubility of Al at low pH.

16. (Ch6) Aluminum remobilized as pH lowers thru time
Al combines and
reprecipitates with Si
in the lower solum to
form Bsm horizons BELOW
Bh and Bhs horizons.

17. A E Al Fe Bs
Depth
Bsm BC C

18. E
Bsm Bs BC

19. Guess what
I am thinking!

20. Imogolite school (Anderson, Farmer and others)
… the inability of cheluviation to account for: 
(1) Al and Fe in Bs horizons that are predominantly in inorganic forms
(2) significant amounts of imogolite clay in Bs horizon
Where are
the organics
in the B?

21. Imogolite-type materials (ITM) theory:
Al (and to a lesser extent, Fe) migrates as hydroxyaluminum silcate
(proto-imogolite) sols (Al2O3-Fe2O3-SiO2-H2O),
Chelate complexes form LATER as Bh horizons, in situ,
when colloidal organics precipitate on the inorganic colloids
already present in the B horizon

22. The Imogolite Theory/Process
Stages Im1-Im3 same as Ch1-Ch3
(Im4) Sols and sesquioxides form due to liberation from PM
by organic acids.
They are electrostatically positive and migrate to the B horizon.
(Silica moves first because it is more mobile at higher pHs)
(Im5) pH increase in lower solum causes precipitation of sols.

23. (Im6) Organic colloids (electrostatically negative)
move from the E and flocculate on the positive sols
in the B, forming a Bhs horizon
(Im7) Continued acidification remobilizes Al from the Bs/Bhs horizon.
Al moves to greater depths, while Fe stays in the Bs/Bhs
(Im8) Additional humus is added to the Bs by root decomposition
and by continued illuviation of humus colloids.
Bhs forms above a Bs.

24. A E
Bhs Bs BC

25. Si-rich cutans surrounded by OM- and Al+Fe-rich cutans in B horizons
EVIDENCE in support?
Si-rich cutans surrounded by
OM- and Al+Fe-rich cutans in B horizons
Quartz grain
May be most common in soils/environments with little OM,
and in soils developed in volcanic parent materials
Not found in soils that have thick O horizons
or that have developed in pure quartz sand.

26. Wet Spodosols: Aquods Form by cheluviation, BUT
Fe in B horizon gets reduced
and leaves in groundwtaer

28. Very little Fe in B horizon