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Thesis Few 13319 Degree a? ‘35. D.
MiCfiESRH STATE UNIVERSEFY
Lloyd J. McKenzie

1957

This is to certify that the

thesis entitled

Oxidation-Reduction Studies on the Mechanism
of B Horizon Formation in Podzols

presented by

Lloyd J. McKenzie

has been accepted towards fulfillment

of the requirements for
‘\

Ph.D. degree in Soil Science

Major professor
Date €994 1‘: ¢f7
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OXIDATION-REDUCTION STUDIES ON THE MECHANISM
OF B HORIZON FORMATION IN PODZOLS

Lloyd J. McKenzie

A THESIS

submitted to the School of Graduate Studiee of Michigan State
University of Agriculture and Applied Science in partial
fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY

Department of Soil Science
Year 1957

ABSTRACT

Oxidation- reduction potentials in situ have been measured
over a period of two years at various depths in a wdrosequenco of
soils. The well drained soil studied was Kalkaska sand, the
imperfectly drained soil was Saugatuck sand, and the poorly drained
soil was Roscoe-on sand. The distribution of certain microorganisms
in the soil profile of the Kalkaska and Saugatuck sands was also
studied.

Variations in rodent potential with time were observed to
correlate with the soil moisture content and with temperature;
variations in redo: potential with space were observed 'to correlate
With soil horizons. The population of the ferric citrate oxidizing
organisms decreased with depth and filamentous, sheathed bacteria
resembling met-anus species known to be active in oxidation
of ferrous to ferric iron were isolated from the Bir horizons of
the Kalkaska and Saugatuck sands.

Evidence is given of possible mechanisms of mobilization of
iron oxides in the A horizon and precipitation of ferric twdroxide
in the B horizon of podzol soils.

ACHOWWM‘

The author is deeply grateful to Dr. E. P. Whiteside and
Dr. A. E. Erickson for their continued willingness to discuss the
problem and for assistance in preparation and testing of platinum
electrodes and to Dr. A. R. Welcott for discussion and much assist-
ance with the microbiological studios. The assistance of both
Dr. Jacob, statistician of the University of Illinois Agricultural
Experiment Station and of Dr. R. '1'. Odell of the Agronomy Department
of the University of Illinois is gratefully acknowledged. Dr. John
Himsl, instructor in the University of Illinois Chemistry Department ‘
contributed much in the way of discussion in the interpretation
of the redox potential data and the author is sincerely grateful.
Last but not least the author is grateful to Mrs. L. J. McKenzie for
typing of the manuscript.

TABLE OF CONTENTS

INDEKOFFIGURESAIDTABLES................iv
INTRODUCTION....................... 1
REVIEWOFLITERA'IURE................... 2
SIHMARYOFIITERATURE...................36
Theories of Podzol Developnent. . . . . . . . . . . . 36
Oxidation-reduction Potentials. . . . . . . . . . . . Al
RESULTS..........................l+7
SoilsStudied....................h7
Oxidation-reduction Studies . . . . . . . . . . . . . 52
MembiologicalStudies...............58
DISCUSSION........................68
SUMMARYANDCONCLUSION..................92
BIBLIOGRAPHY.......................9l+
APPENDIX.........................103

INDEX OF FIGU--?ES Ill-TD TABLES

Text

Figure 1. Photograph of a stronglyr developed Podzol Profile,
‘ Wallace Sande e e e e e e e e e e e e e e e e e e e e

\o
0\

Figure 2. Diagram of experimental site showing relationship
or the 5011 serieS. e e e e e e e e e e e e e e e e e

-\‘
4

Fw-
q-

Figure 3. Diagram of electrode installation . . . . . . . . . . 53

Figure 4. Seasonal variations in redox potential for five
horizonsofKalkaskasand. . . . . . . . . . . . . .55

Figure 5. Seasonal variation in redox potential for four hor-
izons Of Saugatuck sand e e e e e e e e e e e e e e e )6

Figure 6. Seasonal variation in redox potential for five
horizons of Roscommon sand. . . . . . . . . . . . . . 57

Figure 7. Kalkaska sand cumulative percentage composition
curves by horizons. e e e e e e e e e e e e e e e e e 59

Figure 8. Saugatuck sand cmmllative percentage composition
curves by horizons. e e e e e e e e e e e e e e e e e 60

Figure 9. Roscommon sand cumulative composition curves by
horizons. e e e e'e e e e e e e e e e e e e e e e e e 61

Figure 10. Sampler used in'sampling for distribution of
micro-organisms e e e e e e e e e e e e e e e e e e e 63

Table 1. Distribution of citrate oxidizing organisms
in KalkaSka and Saugatuck pr0f1135e e e e e e e e e e 65

Table 2. Distribution of isolates of filamentous sheathed
bacteria from Kalkaska and Saugatuck sands. . . . . . 66

Figure 11. Diagram of organisms observed on slides from the
isolates of the B11. horizons of Kalkaska and
Saugatuck e e e e e e e e e e e e e e e e e e e e e e 66

TELble 3. Statistical analysis of reds: potentials for
xhlkflfik.»‘nd 8.fl8£tuck . . e e e e e e e e e e e e e 68

Table A.
Table 5.
(Fable 6.

Ufable 7o
flflafile 80

Figure 12.

Figure 13.

Analysis of variance of A1 horizon of the
Roscqmmon series. 0 o o o o o o o o o o o o o o 0

Analysis of variance of Ga_1 horizon of the
Roscammon series. 0 o o o o o o o o o o o o o o 0

Analysis of variance of BG.1 horizon in the
Roacammon series. 0 o o o o o o o o o o o o o o 0

Analysis of variance of the Roscommon series. . .

Analysis of variance for 3 dates during winter
of 1953-1951» for Kalkaska and Saugatuck profiles.

Relation between redox potential and drainage
for Saugatuck and Roscomnon sands using mien

bIOCkaoooooooooooooooooooooo

Residual variation of redox potential with
temperature for Saugatuck and Roscamon sands . .

69

69

69

73

7h

Figure 1A.

{Fable 9.

UPable 100

anablfi 11.

Ihiba3 120

Table 13.

Uflaflble IA.

1331116 15.

APPEIDIX

Eh-pH curves for Kalkaska, Saugatuck and
ROBCGNNOD Bands by horizons. e e e e o e e e 0

Mechanical analysis percent composition by
separates. o e e o e o o o e e e e e o o e e 0

Some physical, chemical, mineralogical
characteristics or KalkBSka Band 0 o o o o e 0

Mean redox potentials by soil series, dates
and horizons o e o e e e e e e e e e e o e o o

Sorting analyses for all horizons of
Kalkaska, Saugatuck and Roscomon series . . .

Change in resistance of Beuyeucos moisture
blocks with dates in Kalkaska, Saugatuck and
Roscommon Sands. e o o e o e o o e e e e e e 0

En! or spontaneous oxidation or reduction
reactions with the saturated calemel electrode
at pH 5.0 from Latiner and DOvriOB o o e e e 0

Weather data from Cadillac weather station . .

101.;

105

106

107

108

109

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INTRODUCTION

Oxidation and solution are two chemical processes that are
involved in soil genesis. There is a differential solubility in
the oxidized and reduced state for several of the metallic ions such
as iron and manganese in soils. For example, ferrous hydroxide is a
million times more soluble than ferric hydroxide. Recentk, McKenzie
and Erickson (L9) have reported results of studies on the oxidation
status of soils by horizons which indicated that such elements as iron
and nengeneee could be nebilised in the A horizon, translocated into
the B horizon, and there precipitated due to a change in oxidation—
rodnction status within the soil profile. The present study is a
continuation of the work in which a more detailed stuck of a hydro-
eequence of soils has been carried out.

Oxidat ion- reduction potentials have now been studied in the
horizons of a hydrosequence of soils over a period of time using an ad-
‘Ptdtion of the technique developed by Quispel (65) and used by
McKenzie and Erickson (A9). Measurements were made from September 9,
1953 to August 10, 1955 in all seasons of the year. The results were
treated statistically to determine significant variations in the oxi-
dation reduction potentials observed.

Mechanical analyses and mineralogical analyses were also
can‘3.ed out. In addition, a special sampling was carried out designed
to 18Olate iron oxidizing microorganisms from the soils under study
“a to gain some information about the ability of soil organims
”meant in the soils to utilise organic complex forming compounds as .
source of energy.

REVIEWCF HTERATUBE

Marbut (1.3) discussed the early theories on the developnent
of Podzols. One theory seemed that iron was imediately converted
to ferric oxides on decomposition of the minerals in the A horizon.
Soil solutions containing acid organic matter reduced the ferric
oxide to ferrous oxide and famed organic acid-ferrous oxide con-
plcmes which were relatively more soluble than the ferric oxide.
These conplms were trenslocsted in the leaching waters to lower
regions in the soil. At relatively shallow depths the organic acid
complex was deconposed by cages and the ferrous iron on being
reloued was res-oxidised to ferric oxide and precipitated.

In 1910, Dr. Albert (1,2) in Gem studied the genesis of
Podnsols. He reported tbst the cenenting neterisl between the soil
Micles consists largely of clay-iron phosphate caplemes. Hume
netsrials nay not play an essential role in 1:0de fornstien because
Maole nay form without hqus nsterials. Dr. Albert showed there
was no variation in aeration within the profile and correlated
“attain" fornstion with depth of penetration of Mt rains.

Gillespie (27) about 1920 was one of the first investigators to
”Pk with oxidation-reduction potentials in soils. In lsborstory
““10- he found that soils becsne highly reduced when subject to
m°r10gging. This reduced condition was intensified by the addition
°‘ “actress. The ineresse in intensity of reduction was sccaspenied
b’ ‘ foul odor. He discussed the significance of reducing conditions
m °1‘ reduction potentials in soil study.

3

In 1911;, Morison and Sothsrs (51.) studied the fornation of iron
pan. hey reported that peat was a strong reducing agent but was not
capable of reducing ferric oxide to ferrous oxide and that the solu-
tion obtained by the action of peat on ferric oxide does not contain
ferrous hunats which appears to be acconpenied by the presence of
ferrous ions. Peat in the presence of water renoves considerable
quantities of minerals such as ferric oxide, calcium oxide, and
aluninun oxide fron the soil as colloidal suspensions. These colloid
sole are not very sensitive to changes in concentration but evapora-
tion to dryness destroys their capacity for suspension to acne extent.
In the case of iron the conpound forned is probably ferric Innate,
but nay be an adsorption complex of colloidal humus and colloidal
ferric hydroxide. They supported the theory that the pen fornation
in Podsols was due to the for-nation of colloidal tnmus cmpounds of
aha-inn and iron which are carried don into the soil and there
precipitated by soluble salts, loss of water or by a change of bases.

At the sane tine, Morison and Doyns (53) studied the nethed
of extracting iron fron. soils. They concluded that the lame: nethcds
were unsatisfactory for the determination of ferrous iron in soils,
and that the occurence of large ancunts of ferrous and ferric iron in
the soluble state in the soil was highly inprobable.

In 1922, Keller (56) reported that growing green plants acceler-
ated the oxidation processes in soils. He measured the increase in
carbon dioxide produced in planted cultures above that produced in
Implanted cultures and found it to vary for different plants. Work-
ing with buckwheat, field beans, and soy beans he found that a second

crop was more effective than the first crop.

About the same time Bowoucos (15) reported that different
chemical agents had decidedly different effects on the oxidation of
iron both as to rate and extent. The non-oxidizing effect of some
reagents could dainate the oxidizing effect of others; and the
effect could be observed in the absence of oxygen from the air.

In the late 1920's and early 1930's several important investi-
gators did nuch to develop the theory of oxidation-reduction
potentials. These were Clark and his co-workers (21) , Remesow (66) ,
and Hichaslis (52) who published a discussion of the theory of
oxidation and reduction in 1930.

In 1927, Halvorson and Starkey (29) developed a theory of
equilibriun for ferrous and ferric iron when present in both the
solid and soluble form. They showed that as pH increases ferrous
iron will tend to be converted to ferric iron and to precipitate as
ferric twdroxide. However if the pressure of onygen varies, then as
the pressure is reduced, ferric hydroxide will tend to go into
solution and ferric iron will be reduced to ferrous iron. If com—
plex ions are fenced, then ferrous iron will be renoved from solu-
tion, and the tendency will be for more ferric twdroxide to go into
solution. If there are enough couple: ions formed it is possible to
keep such larger quantities of iron in solution even at low mdrogen
ion concentrations then would be nomal if no caplemes were formed.

In 1927, Starlqy and Halvorson (76) studied the effect of micro-
organisns on the precipitation of iron in soils. Sons of the means by
which iron nay be precipitated were listed as follows:

(l) The activity of iron bacteria.

(2) The activity of heterotrophic microorganisms
decomposing organic compounds of iron.

(3) Activities of organisms causing changes in
ongen pressure or reaction and thereby

precipitating iron.

(4) Strictly chemical changes as a result of
changes in envimment.

They concluded that microorganism could be responsible for both the
reduction and solution of iron or its precipitation, either directly
or indirectly by decomposing the organic radical of complex organic
cmpounds of iron. However iron could be brought into solution in a
number of ways, some of which were not related to microorganinas.
Therefore it was necessary to understand more thoroughly the reactions
responsible for changes in the form of iron in the soil before
biological changes would have an significance.

In 1930, Tsmey and Wakaaan (80) studied the decanposition of
.chenical constituents of organic materials under anaerobic conditions.
They reported that in general, anaerobic decanposition was slower than
aerobic decomposition. In all cases there was a net gain in protein
and in some cases there was a net gain in lignin under anaerobic
deconpo sition. Under aerobic conditions, decomposition proceeded
completely to the production of 002 and water, while under anaerobic
conditions more alcohols and organic acids were produced. With oak
leaves, under aerobic conditions, much of the protein was deconposed
with production of amnia which escaped into the air; while under
anaerobic conditions, less protein was decomposed and losses in

mania were also lower.

6

In 1930, Who and Schmidt (73) studied the mode of combination
of iron with a number of organic complex forming empounds. They
studied the equilibrium between ammonium this cyanate and ferric iron
(Ferric iron complexes are more stable towards oxidation and decom-
position than the ferrous iron complexes), the stability of the iron
compounds to acid and alkali, and the migration of the iron under the
influence of an electric current. 'nleir results suggested that iron
could form stable complexes (undissociated compounds) with organic
materials which possessed a particular grouping within the molecule.
The following classes of substances were cited as having this
particular grouping: hydronmonocarbonlic acids (lactic, gluconic);
dicarbozwlic acids (onlic, malonic); hydroawdicarbocwlic and
hydron'tricarboxylic acids (tartaric, citric); amino acids which
are also rudrony or dicarboxylic acids (aspartic, serine); certain
inorganic acids (phosphoric, arsenic); certain phosphorus containing
cmpounds (nucleic acid, glycerophosphoric acid); and certain pro-
teins (casein, gelatin). They found a correlation of the amount of
iron bound by casein and gelatin with certain groupings which were
lmown to occur in the molecules of these proteins. They explained the
combination of iron with the organic molecules on the basis of the re-
sichlal charge of the atoms.

In 1930, Mattson (1.5) reported on a study of the laws of soil
colloidal behavior. Using cataphoresis methods, colorimetic pH
measures and chemical methods for determination of the reacting
components, he characterized a number of soil..colloida1 materials
including silica, sesquionbs, litmus and humates of iron and

aluminum. Silica and hums are electro-negative. The sesquiosddes
are electrical ampholytes, that is, they are electro-positive

in acid solution and electro-negative in alkaline solution. lhe
position of the isoelectric point depends on the nature of the acid
anion. The sesquioxides also adsorb both acids and bases.

The alloali Inmates are highly dispersable. They nay form true
solutions. Humates of divalent cations are less easily dispersed.
Alumna and ferric Inmates are amphoteric. They are non-dispersable
at the isoelectric point but are increasingly dispersable above or
below the isoelectric point with increasing negative or positive
charge. He also showed that ferric hydroxide is isoelectric at
pH 7.1 and that aluminum hydroxide is isoelectric at pH 8.1.
However, complexes of ferric hydroxide and phosphate and aluminum
wdroxide and phosphate and also silicates are isoelectric at such
lower pH's so that such complexes could be precipitated isoelec-
trically under conditions normally found in soils.

In a further study in 1931, Mattson (1.6) showed that ferric
humates are isoelectric at pH h.8-7.0 depending on the home
sesquioxide ratio. In addition, aluminum humates are isoelectric at
pH l..8-8.0 depending on the hms-sesquioxide ratio. He also found
that the clay colloids reacted with aluminum and iron forming
isoelectric precipitates in the same manner as the humus complex.

In another report in the same year, Hattson (h7) described the
colloidal behavior of the soil anpholytes. He found that soil
colloids in which the silica-sesquioxide ratio was low showed a
pronounced anphoteric behavior in the normal pH range of soils. When

the ratio is large, the soil colloids do not react in the normal pH
range in soils. A11 soil colloids react amphoterically with phos-
phates. The isoelectric point is not constant but varies with the
dissociation of the compounds formed by the colloid with the adsorbed
ions. The soil colloids react as acids above the isoelectric pH and
as bases below the isoelectric pa. Hattson calls the transition
point "the point of exchange neutrality." This point is not fixed
for the colloid but varies with the energy of displacement of the
anions and cations for the hydroxyl and hydrogen ions in the
electrodialised free mapholytoid.

Again in 1931, Hattson (158) reported on the colloidal behavior
of a number of proteins. They were found to be isoelectric at pH
h.8-5.2. Iron and aluminum hydroxides are isoelectric at xfl 7.1
and 8.1, respectively. A mixture of aluminum or iron with protein
was isoelectric at some point between pH 7.1-8.1 and pH 4.8-5.2
dependim on the relationship between the charge and relative con-
centration of the colloids. The mixture was isoelectric at the pH
where the total charge ratio was equal to 1. This could vary
depending on the relative concentrations of the charged colloids.
The protein complexes that were formed (aluminum and ferric pro-
teinates, protein hunates, bentonites and silicates) all obeyed
the fundamental principle of the colloidal behavior previously
described.

In 1931, anytime (72) studied the relative ease of oxidation of
ferrous iron in the ionic form by cozy-gen of the air as compared to
the unionized ferrous hydroxide in alkaline solution, or to the

complexes that could be formed with an organic anion. He showed

that ferrous iron was more readily oxidized as the complex or as the
unionized ferrous ludroxide in alkaline solution and that this
oxidation could take place regardless of the reaction of) the solution.
He discussed the catalytic effect of ferrous and ferric iron in
certain oxidations and gave an interpretation of the mechanics
involved.

In the same year Hichaelis and myths (51) studied the rela-
tionship between rate of oxidation and the property of autooxldation
of iron systems. Since the more negative the potential of the
system, the more highly autooxidisable it is, there should be a
relation between the rate of oxidation of an iron system and its
potential. They measured the rates of oxidation of a number of
iron complex systems and found there was a relationship between rate
of reaction and potential. Those canpleooss with the lowest potential
were most readily oxidised. On the basis of these observations they
were able to correct the potential of an iron system which had been
reported by another investigator.

In 1931, Halvorson (28) studied equilibrium conditions for
iron solutions under the influence of atmospheric organ and carbon
dioxide and developed equations to express the conditions. He
considered the activities of microorganisms associated with solution
and precipitation as well as with oxidation and reduction of iron in
relation to the equations developed. He observed several important
points. Under anaerobic conditions, heterotrophic organism could
dissolve metallic iron. They could also dissolve and reduce ferric

10
hydroxide. Such changes could take place fraa a decrease in oxygen
pressure and the formation of acid; and could occur even at reactions
close to neutrality. Ferrous carbonate could be precipitated under
anaerobic conditions when carbon dioxide was increased as a result
of organic matter decomposition. The activity of iron bacteria
appears to occur only under environmental conditions favorable to
spontaneous oxidation by chemical agencies. The solution and
precipitation of iron in nature are associated with equilibrium
conditions which depend on ongen tension, carbon dioxide tension,
acidity, and the presence of organic compounds. These conditions
may be. modified extensively by microorganims. The activities of
iron bacteria are confined solely to its precipitation. Halvorson
thinks that their activities have been overemphasised at the expense
of the heterotrophic bacteria.

In 1932, Willis (87) using Dunbar fine am loam, devised a
method for determining the Eh-pH relationship of the soil. He used
a nitrogen atmosphere. He found an inverse relationship between Eh
and pH, and estimated there was about 60 millivolts change in Eh for
each pH unit change.

Bradfield et a1 (17) studied the oxidation-reduction state of
the soil in relation to the production of fruit in 1931+. They found
that they could eliminate 80 to 90 percent of the low yielding trees
in apple orchards on the basis of the low oxidation-reduction
potentials observed in the spring. The low potentials tended to
disappear in the sumor months. They noted a general agreement
with Willis' work on the Eh-pH relationship. That is, there was a

11

generally linear relationship between Eh and pH except at low pH's
but they believed that 80 millivolts per pH unit was a more probable
factor. They used quinm'drons in 0.05 molar potassium acid
phthallate as a reference solution for standardizing electrodes.
Electrodes which failed to indicate a pH value of 3.98 1 0.05 were
disqualified for redox potential measurements. The potentials
obtained in soils had to be constant and had to be reproducible on
more than one electrode before they could be accepted with confi-
dence. Soil redox potentials w never prove to be absolutely
exact, but for practical purposes they were sufficiently reproducible
to merit consideration. They also studied the effect of past
history of the platinum electrodes on the redox potentials obtained.
It was found that the electrodes were affected by past treatment

but that the effect disappeared after a short time. This had the
effect of delaying the electrode in coming to equilibrium with the
soil in which it was placed. Subsequent readings agreed well with
untreated fresh electrodes once equilibrium was reached. The use of
a vacuum tube potentiometer eliminated the possibility of polarisation
of the electrodes when measurements were made. One tenth normal
H2801. was used as the suspension medium. It was claimed that the
8230,, medium was practically similar to the water suspension medium
but was better poised. The acid medium inhibited the action of the
microorganisms and shortened the time required for the electrodes to
reach equilibrium with the soil solution. However, if proper time
was allowed for equilibrium to be reached, and the electrodes were
properly cleaned so as not to be affected by past history, water

could be used to advantage as a suspension medium. There was no
apparent difference in redox measurements resulting from different
ratios of soil to suspension medium. Therefore a standardised
volume sample was used. The Eh value of the soil was calculated by
adding 0.250 volts to the value obtained from the soil when the
sample was measured against the standard saturated calomel electrode.
It represented the soil potential referred to the standard hydrogen
electrode.

At the same time Brown (18) reviewed the principles involved in
the stuck of soils by means of oxidation-reduction potentials. He
used a rapid method of measuring Eh in the laboratory and developed
the method of preparing electrodes which were later used by Quispel
(65), lemon and Erickson (w) and McKenzie and Erickson (1.9).

In 1931., Heintse (30) used the glass electrode instead of the
malomel electrode as the reference electrode to minimise polarization
and to facilitate instantaneous Eh-pfl measurements. She used water
as the suspension medians and reported that the ratio of soil to water
was of little importance in the measurement of redox potentials.

She also claimed that the presence of air or nitrogen did not effect
the potential. Soils that contained readily decomposable organic
matter dropped rapidly in potential on being waterlogged; but soils
that contained little organic matter tended to resist am drop in Eh.
Heintse recmnded that Eh and pH of soils should not be considered
separately since the Eh of a soil depended greatly on the pH.

In 193k. Kohnke (35) reported that the ongen supply of a soil
determines the oxidation-reduction potential. A high potential is

13
indicative of a well drained and oxidized soil and a low potential is
indicative of a poorly drained de-aerated soil. The principal
substances entering into the oxidation-reduction reactiais of soils
are colloidal clay, organic substances and humus, and cmpounds of
iron and managanese. He used 59 millivolts as the correction for
the Eh per pH unit. Aeration increased the potential and water-
logging lowered the potential. Surface soil horizons gave lower
potentials than subsurface or subsoil horizons in the spring. This
difference tended to disappear during the manor. Quantitative
determinations gave large and significant differences between well
and poorly aerated soils. He reported a large experimental error.

In the same year Peech and Batjer (59) made a critical study
of the methods used in msasuring oxidation-reduction potentials of
soils. They used shim platinum electrodes and found that cleaning
with chromic acid tended to give high results; but when the chraaic
acid treatment was followed by rinsing in alcohol and flaming to
dull red heat, the high results were not obtaimd. They reported
that the use of a vacuum tube potentialeter eliminated polarization
of electrodes. They used a sulphuric acid suspension medium because
the redox systems were better poised in 3280‘; and suggested that a
nitrogen atmosphere be used when water was used as the suspension
medium. They used the factor of so millivolts for correcting Eh
measurements for pH. They reported that little reduction occurred
in soils in the spring until the temperature had reached 55°F.

In 1936, Sturgis (79) reported that low potentials in water-
logged soils were caused by decomposition of fresh organic matter.

ll;
The solubility of phosphorus was reduced under conditions causing
low potentials in soils. In the absence of activek decomposing
organic matter, large amounts of iron cmnpounds precipitated around
the roots of rice plants. The presence of gypsum in a waterlogged
soil caused the production of sulphides which reduced rice yields.
The application of leguminous organic matter tended to increase
rice yields. He reported potentials as low as 80 millivolts in
soils containing actively decomposing organic matter.

In the same year Darnell and Eisemenger (22) found that there
was little or no change in potential with the addition of fertili-
sers containing nitrogen. The changes correlated better with changes
in pH. They reported a rapid fall in potential when fresh organic
matter underwent rapid decomposition and gave a rapid depletion of
ongen as the cause.

In 1936, karma and Gordon (so) reported that the type of
decomposable organic matter was an important factor in the determin-
ation of the reducing intensity that prevailed. They reported that
casein decomposition resulted in highly positive potentials while
carbotwdrate decmposition resulted in negative potentials not
unlike those produced in soils. They also reported that moisture
did not greatly affect potentials.

In the same year Willis (86) discussed the importance of
oxidation-reduction potentials of soils in soil fertility. He
pointed out that manganese deficiency caused by overliming could be
explained by consideration of Eh as well as pH. He also stated that
two soil canponents, ongen and organic matter, appeared to govern the

15
oxidation-reduction equilibrium in the soil. Both required
activation, the former by catalysis and the latter by microorganisms.
He suggested evidence that phosphorus, potassium, copper, maltose,
boron, silicic acid, organic matter, pH, aeration, and temperature
are to some degree interdependent variables.

In 1938, Stevenson et al (78) working with Oregon soils found
that different soil types under field conditions showed little
variation in oxidation- reduction potential by the methods used.

There was little variation in potential between horizons even when
there was a tight subsoil. They reported that fresh organic matter
alone did not cause a fall in potential, but waterlogging caused a
rapid fall in potential. They reported that oxidation-reduction
potentials were not reliable indicators of anaerobic conditions in
the soil.

In 1939, Buehrer et al (19) found that the Eh-pH relationship
could be determined by simply diluting a soil suspension with water.
They showed that the Eh change amounted to about 68 to 70 millivolts
per unit change in pH, and that bubbling nitrogen through the soil
tended to lower the sh value. PudeJng caused a drop in Eh which
they believed was due to factors other than oxygen depletion. An
abundance of oxygen tended to increase the Eh' The addition of
alfalfa to a soil suspension caused a marked decrease in Eh which was
taken to be indicative of the nature of the reduced compounds fomed
during its decomposition.

Volk (83), working with Alabama soils, did much to establish a
standardised technique for the measurement of oxidatim—reduction

16
potentials in the laboratory. Batjer, Bradfield, Kohnke, and Peech
all used 11/10 H2301, as the suspension medium to inhibit microbial
activity and to add poise to the redox system. Volk claimed that
sulphuric acid dissolved materials in the soil which were not
ordinarily active and therefore acid suspensions and water suspen-
sions were not comparable. Only Kohnke and Willis used a nitrogen
atmosphere, while others (17 , 30, 59) disregarded the effect of
cowgen entirely. Volk reported that arable soils changed little in
Eh with treatment but that reduced soils were rapidly oxidised unless
osygen was expelled with nitrogen. as reported that all preservatives
used to inhibit microbiological activity changed the Eh of the soil.
Volk cooled all samples to a point just above freezing, uad boiled
water saturated with nitrogen as the suspension medium, and per-
formed all analysis in a nitrogen atmosphere. He also reported
that potential drift was due to the past history of the electrode.
Wire electrodes were superior to foil electrodes. In a second
paper (81) he reported the results of extensive studies on Alabama
soils. He found that cultivated soils in general, had higher Eh
values than virgin soils in the O to 8 inch depth, but that subsoils
were similar. He found little difference in soil types. Differences
rarely exceeded fifty millivolts which he did not think important
since they could have been due to differences in soil material
rather than state of oxidation. Swampy soils often had higher Eh
values than did well drained upland soils. After rains the Eh tended
to rise for a time due to the oxygen carried into the soil by the
rainfall. Seasonal variations did not exceed 60 millivolts. Volk

17
did not think that Eh was a reliable indicator of the oxidation
state of the soil, since it was dependent not only on the ratio of
oxidized and reduced substances present, but also on the kinds and
amounts of ions present. He also studied the effect of varying the
Eh on the growth of plants (82). He was able to vary the Eh of the
soil from 525 to 325 millivolts by the use of m'droquinone. There
was no limiting effect of Eh on plants in the range of Eh studied.
He concluded that Eh was not limiting to plant growth in Alabama
soils.

In 191.0, Keaton and Kardos (31.) , studied the effect of various
materials on the arsenite-arsenate system. They found that ferric
oxide raised the potential and caused arsenite to be oxidized to
arsenate while clay shifted the equilibrium to the arsenite side.
Alumina had no effect. They used the Hernst equation as a basis for
their calculations. They concluded that ferric oxide in the soil
caused increases in plant growth because of the oxidative effect on
the arsenite-arsenate system which removed toxic arsenite by conversion
to arsenate. They further concluded that the oxidative character of
the soil was reflected in the redox potential and that the redox
potential of the soil was the function of many complex interlocking
systems. They therefore suggested that the redox potential was
useful in the study and interpretation of the general chemical
processes taking place in the soil.

In 191.5, Starkey and flight (77) made a very great contribution
to the knowledge of redox processes in soils in a stw for the
American Gas Association. They studied the effect of soil conditions

18

on the corrosion of iron gas lines buried in the soil.

The evidence which they obtained from various sources indicated
that sulphate reducing bacteria were very important in anaerobic
corrosion. The evidence indicated that the sulphate reducing bacteria
were able to utilise energy from the oxidation of hydrogen, a
redox reaction in which sulphate was reduced to sulphide. 0n the
basis of Eh and pH measurements it was possible to predict severity
of anaerobic corrosion of steel and cast iron in the soil. The
reaction range for §Erovibrio desulfuricans in a culture medium
was found to be 5.5 to 8.5. In soils, anaerobic comsion was most
severe at near neutral reactions. Soils more acid than pH 5.5 were
considered unfavorable for anaerobic corrosion and no evidence of
corrosion was noted in soils more acid than pH 5.5. The redox
potentials of culture media of g. desulfuricans was initially 300
to 1.00 millivolts and dropped to 300 to 300 millivolts during growth
of these sulphate reducing bacteria. Nearly as low potentials were
observed in a sterile medium to which sulphide was added. The Eh
of sterile media to which metallic iron was added became stabilised
at 1.00 millivolts and this potential remained unchanged even after
the growth of §. desulfuricans in the medium.

The Eh of rapidly decomposing plant residues was low even when
the materials were kept moist and were presumed to be decaaposing
aerobically, but slowly decomposing plant materials had higher
potentials. Similar plant residues decomposing under anaerobic
conditions had low potentials. In moist soils containing organic
matter, potentials remained high (above 1.00 millivolts) but similar

l9
soils in the waterlogged condition had low potentials (below 200 mv.).
Sibsoils, low in organic matter, showed scarcely am decrease in
redoc: potential except when organic matter was added.

Acid extracts from aerobic and anaerobic soils showed little
difference in redox potentials and little correlation with soil
reductiveness. Potentiomet ric titrations however, showed wide
differences between acid extracts from aerobic and anaerobic soils
and even large quantitative differences between strongly reduced
soils. These differences appeared to be due to chemical composition
of the soils, in particular the iron content.

It was decided to use Eh and pH as a method of distinguishing
corrosive soils and an instrument was devised for measuring the Rb
of soils at depths of 3 feet or more. It was adapted only to wet
soils. Electrodes were cleaned with an acid solution of a
synthetic detergent and a solution of twdrogen peroxide. A scale
of corrosiveness was set up based on soil redox potential. Each
site was classified as to severity of corrosiveness on the basis of
soil Eh and condition of the pipe.

The results of 1.8 test sites were tabulated. In 10% of the
cases Eh failed to indicate the corrosive nature of the soil. In
67% of the cases the prediction was correct and in the remainder
of the cases the degree of corrosiveness was predicted with only
fair accuracy. In another test, results were less favorable where
seasonal fluctuations in soil reductiveness occurred or where stray
current electrolysis occurred.

Anaerobic corrosion was most severe in soils that had redox

20
potentials between 0 and 100 out. and was not observed in soils with
redox potentials over 1.00 mv. Where water stagnated in poorly
drained areas, anaerobic corrosion occurred. Where the soil water
was in motion however, low redox potentials were not observed.

In 191.3, Norman and Bartholomew (57) studied the composition
of organic matter. They estimated the polyuronide content of soil
organic matter by boiling in 12% rcdrochloric acid and measuring the
carbon dioxide produced. The "s" horisons of a lumber of Podsol
soils were high in uronide content. Polyuronides occur in all plant
materials and are also produced by microorganisms. Uronic acids
(Indrolytic products of polyuronides) form soluble salts with
monovalent cations and insoluble salts with divalent cations. They
may act as agents of translocation in the Podsol weathering process.

In 191.5, Starkey (75) reported on the types of bacteria which
are active in oxidising ferrous iron. Siderocapsa, Sphaerotilus,
Clonothrix, Leptothrix, Grenothrix and Gallionella are all types of
iron oxidising organise. Species of Gallionella are autotrophic
and acquire energy strictly by undation of ferrous to ferric
hydroxide, forming twisted ribbons or stalks of Fe(OH)3. They are
the most canon type. They thrive at temperatures from 0°C to
22°C with an optimum at 6°C and are not sensitive to light. They
11-h a range in iron concentration of 0.1 ppm to 30 pp in a
Slightly acid reaction under aerobic conditions. They are most
Gallon on the surface of stagnant pools of water or near the roots of
true. Numerous heterotrophic organises other than the above may
“compo” complexing organic anions, thus releasing canplexed iron,

which may or may not be precipitated, depending on conditions,

+4».

pH, 02, Fe" :3 Ff”, concentration of Fe ion, etc. Starkey
performed a lumber of experiments and made several conclusions.
In general, the principal effect of microbial activity was in the
solution of iron. In precipitation experiments most of the iron was
precipitated by strictly chemical means as a result of variations
in oxygen and kudrogen content of the solutions.

In 191.7, Matclski and Turk (A1.) studied the heavy minerals
in sue Podzol profiles of Michigan. The soils studied were Wallace,
Kalkaska, met, Rubicon, Roselawn, Grayling and Eastport sands.
The heavy mineral suite was hornblende, garnet, epidote, zircon,
tourmaline, tremolite, mseovite and opaque minerals. Magnetite
made up 90% of the opaque minerals. Garnet was the most resistant
to weathering of all heavy minerals. They showed that organic
matter is an effective weathering agent in the formation of podzols.
The "B" horizon showed a greater loss in heavy minerals due to
weathering than the "A" horizon which in turn was more weathered
than the "C". The "B" horizon also was more able to support
vegetative growth than the "A" or "C".

In the same year Quispel (65), measured redox potentials
in situ. He studied the soils in Holland that were inundated during
World War II , and found potentials as low as -250 millivolts. He
used platinized platinum electrodes and found the results more
reproducible. Due to the great variance between measurements in situ,
Quispel reconmended that a great many readings be taken. He found
that oxygen affected the redox potential greatly and thus the redox

22
potential was determined in part by the state of aeration of the
soil. When the potential of the soil was determined in the field it
was possible to define the aerobic or anaerobic character of the soil
in terms of Eh.

In the same year Roberts (67) reported that _B__a_9_i_];l_u_s_ m
in the presence of glucose, reduced ferric oxides or ferric hydroxide.
The fermentation of glucose was more rapid in the presence of ferric
hydroxide and the production of hydrogen was reduced. Roberts
tested a number of cultures isolated from the soil and found that
only g. m and one culture of Clostrigium m. reduced iron
in considerable amounts. These were facultative aerobic bacilli.

Bertramson and White (A) give an excellent review of the
literature dealing with oxidation and reduction in recent years.

They concluded that the Eh of the soil represented the sum total of
the oxidizing and reducing tendencies in the soil and depended on
the nature of the system. The redoc: system varied with the nature
of the soil and varied from soil to soil. They were critical of
present laboratory techniques since there is no suitable method for
measuring Eh in a manner similar to the measurement of pH. They
suggest that the field quick test for ferrous iron may be more
suitable for the measurement of reducing conditions in the soil.

In 19h? , LaFonde (3Q reported on the redox characteristics of
several types of forest humus from Wisconsin and Quebec. He measured
pH, redox potential and the total quantity of reduced substances by
titration with permanganate solution. His results showed that mull
humus was characterized by a positive redox potential and a strong

23
acidity. He concluded that redox potentials could be used to
characterize forest humus types.

In the same year Wilde ct a1 (85) studied the clectro—chcmical
properties of the ground water in the four major types of organic
soils in Wisconsin. They measured pH, specific conductivity and
redox potential in moss peat, wood peat, sedge pest and muck. The
ground water underlying the foursoils possessed specific electro-
chemical properties. All results were highly significant. They
concluded that electro—chcmical analysis of ground water was
important in dealing with problems in drainage of muck or peat soils
and regulation of the water table.

In 1949, Joffe (33) gave a summary of the literature on
Podzol formation. He described the genesis of a Podzol as that process
which is initiated under the influence of a cool, humid climate
with a vegetative cover usually of forest. It is controlled in a
large measure by the plant food resources. The process is character-
ized by the rapid leaching of bases, dcvelopnent of an acid reaction,
release of silica through mineral decomposition, and finally the
removal of sesquioxides and their accumulation in the form of ortstein,
orterdc or concretions.

According to the literature, the "B" horizon may be soft and
easily friable in which case it has been called "orterdc". The
"ortstein" has been differentiated into 3 forms. "Brandcrde" is
a form of "B" horizon which is rich in organic matter but not
cemented. "Ortstein" may be dark brown to black, hard as a rock

containing organic matter or a dark brown ortstcin which is very hard

and contains only a very small amount of organic matter.

The iron and aluminum move as sols protected by organic sub-
stances and by silicic acid sols as well as by the cations Ca,

Mg, K, Na, and the anions SOL, FDA, and 603. If the amount of organic
matter present is small, iron ortstein low in organic matter forms.

If there is a large amount of organic matter, iron-organic matter
ortstein forms, poor in iron. Concretions should not be looked on

as inherent to the podzolization process.

Limonite and gibbsite are the usual forms of iron and aluminum
in the "B" horizon. They serve as cementing materials for ortstein
and concretion formation. Manganese also tends to accmmlate in
the "B" horizon. Some concretions contain both manganese and iron.
Phosphorous also tends to be fixed in the "B" horizon as phosphates
of the sesquioxides. A polygorskite mineral (magnesium alundnum
silicate) has also been identified.

The A2 horizon (bleicherde) has been strongly leached. The
removal of sesquioxides accounts for the white color. Most of the
literature describes it as being the most acid horizon in the profile.

Joffe suggests that concretions have formed as a result of a
change in the oxidation system in the soil.

In 1949, Deb (21.) reported on the movement and precipitation
of iron oxides in Podzols. He reviewed the mechanisms that have
been suggested. The movement of iron as a positive iron oxide sol
in association with alumina and humus cannot be established unless it
is shown that the A horizons of Podzols are positively charged. This
had not yet been established. It is not likely that iron oxide sols

could move as silica protected sols because the peptization of
silica occurs in alkaline conditions and is probably not important
in acid solution. The movement of iron as negatively charged iron
oxide sols protected by humus is explored further by Deb. It is
also proposed that iron may move in the form of ccmplexes with large
organic ions. Deb prepared a number of peat and muck extracts and
studied the mutual coagulation and peptization of the extracts with
ferric oxide sols, observing the relative concentrations, and the
reaction. He also studied the adsorption of iron by soils fran
complex organic salts of iron and organic acid. Deb found that humus
could peptiae iron oxide sols under conditions found in Podzols

and that any iron oxide formed as a result of weathering would
probably be fully peptized by organic matter. He found that the
amount of humus required to peptize iron oxide sols was not more
than one third of the amount of iron oxide which is a much lower
value than that which was suggested earlier.

He could find no evidence that the precipitation of iron from
humus protected sols was affected by exchangeable calcium in B
horizons of Podzols, or that the adsorption of iron by soils from
complex salts of organic acids is influenced by the pH or the amounts
01' exchangeable bases present in the soil. He suggested a micro-
b101egica1 mechanism for the precipitation of iron.

In 191.9, Bowoucoa (15) introduced the mlon blocks for measuring
803-1 moisture. nylon blocks are more resistant than plaster of
1’“1‘13 blocks to decomposition under wet conditions. Both the nylon
blocks and the plaster of paris blocks have very steep resistance-soil

26
moisture curves in sandy soils because of the poor ability of sandy
soils to maintain tension forces with water. The blocks could be
used, however, in sandy soils to indicate conditions of dryness or
extreme wetness.

E. W. Russel (68) discussed modern theories on the weathering
processes involved in the developent of Podzols. Little is known
about the chemistry of the Podzol process. It has long been
suspected that the movement of organic matter is connected in some
way with the solution and transport of sesquioxide s. The problem is
to determine what constituents of the organic fraction are responsible.
It has been shown that finely dispersed acid humus particles can
mobilize Indrated ferric oxide and carry it down into the subsoil.
It has been shown that from 3 to 10 times its om weight of hydrated
ferric oxide can be carried down into the subsoil by acid litmus
under the conditions that prevail in the Podzol.

Another possibility is the formation of complex co-ordination
compounds of polybasic carbouylic acids with iron. The presence of
these materials has been assumed, not demonstrated, in the downward
moving waters. It is possible that the mobilization of ferric oxide
by humic acids takes place by some similar mechanism.

The second problem concerns the precipitation of the trans-
located materials in the B horizon. It seems most likely that not
all the materials are deposited, but only a small portion, while the
remainder are carried away in the ground waters. There are mamr
analyses of ground water to support this reasoning. However some

people claim complete precipitation. The principal theories at

27
present assume that the primary cause of precipitation is the
increased pH in the B horizon. Mobilized soil colloids are
assumed to acquire a negative charge from humic or silicic acids.
That is, colloidal ferric hydroxide or aluminum hydroxide becomes
coated with humic acid and thereby acquires a negative charge.
These particles are precipitated out in the B horizon when they
come into a region of higher pH. In this case there could be no
formation of co—ordination compounds with organic acids because
such compounds would be soluble in less acid conditions than occur
at the top of the B horizon.

An alternative theory postulates the precipitation of clay
colloids in the B horizon during summer droughts. The mineral
particles would then acquire a negative charge which could then
adsorb the positively charged iron and aluminum co-ordination
compounds moving downwards in the percolating waters. The organic
acids would then be attacked by microorganims thereby releasing
the iron and aluminum hydroxides. The Ivdroxides, being positively
charged would then adsorb silicic or humic acid. This theory
approadmates Mattson's theory for he has shown that the precipitates
are isoelectric at the pH prevailing there.

Russel states that more factual information is necessary.

In Particular, information is needed about the forms of organic
matter that actually move down through the A2. The newer methods
°1 arsenic matter analysis should give better knowledge of the
cmPOnents of organic matter particularly those that move from
”’9 A0 into the B. There should also be more knowledge of the

28

products of weathering that are not precipitated in the B horizon,
but are carried away in the drainage water.

In 1950, Pierce (61) studied the prairie like mull of Downs
silt loam, one of the most conspicuous forms of mull in the prairie
forest region. Measurement of pH, specific conductance and redox
potential indicated an intermediate position between Carrington
silt loam and Miami silt loam which was taken to indicate that the
soil was originally a prairie soil which had undergone a slight
modification as a result of becoming forested.

In 1951, Bloomfield (5) studied the process of gleying. His
results indicated that reduction of iron in the absence of oxygen
may be partly due to the activities of microorganisms. His results
are interpreted as evidence that degradation products of plants are
in part responsible. He also discovered that ferric oxide was
capable of fixing ferrous iron in solution. He compared the fixing
properties of alpha, beta, and gamma varieties of ferric oxide using
ferrous sulphate. He found that weight for weight the alpha form
(goethite) had the greatest capacity for fixation and that a large
portion of the ferrous iron was adsorbed. This occurred under
aerobic conditions. Further experiments showed, that in the absence
of air, ferric oxide had no effect but that, in the presence of air,
the ferric oxide increased the degree of oxidation of ferrous iron
markedly above that which occurred in an open ferrous sulphate
solution. This suggests that ferric oxide in some way caused the
ferrous iron to be less stable and made it more easily oxidized by

oxygen in the air.

29

The above experiment also suggested a method whereby ferrous
iron could be oxidized on being adsorbed by ferric iron in the
B horizon of a podzol. The process is self renewing.

In 1952, Mackenzie (1.2) reported on studies of cold precipitated
tmirated ferric oxide, which is found widely distributed in soils
and soil clays, by means of differential thermal, X-ray, and electron
diffraction methods. He suggested that these oxides may be preci-
pitated from soil solution by ammonium kwdroxide or sane other
similar amoniacal material, or by hydrolysis of ferric salts in
the soil solution.

The same year, Leeper (39) discussed the factors affecting
availability of micronutrients in soils. The nature of primary
minerals, exchangeable ions, simple precipitates with anions,
oxidat ion- reduction processes, unavailable and available complexes
(soluble), aging and recrystallization, and competition by micro-
organisms are some of the factors discussed. He suggests that iron
and manganese are affected by the oxidation processes in the soil.

In 1952, Bloomfield (7) reported on further studies of the
gley process in soils. He concluded that the iron content of
mottled gley soils is essentially that of the ocherous mottles,
the formation of which is a secondary effect of the gley process.

In the gray portion of mottled gley soils, or in a peat gley, the
process causes extensive mobilization of iron. Almintm, in the
mottled gley soil, followed the distribution of iron but in the
gley soil it did not. This suggested a difference in the solubility

of aluminmn from that of iron in the gley process. He suggested

30
that the gley horizons in a soil consisted in part at least of a
sorption complex between ferrous organic compounds and the clay
fraction.

In 1953, Bloomfield (6) reported on a study of the effect of
aqueous extracts of Scots Pine needles on the iron.and aluminum in
the soil. He reported that an aqueous extract of the Scots Pine
needles was capable of dissolving ferric and aluminum oxides and
causing the iron to be reduced to the ferrous state. Solution and
reduction took place under neutral and aerobic conditions. The
ferrous iron was present in the form.of organic complexes and
possibly the aluminum also. The rate of oxidation of the ferrous
complex was low but increased at higher pH's. At pH 7.0 the
oxidation product was a soluble ferric complex and at pH 4.0 the
products were precipitated. The soluble ferric complex remained
in solution to a large extent and the ferrous complex.remained in
solution in relatively large amounts even at pH 8.0.

In 1953, Pierce (62) studied the pH, specific conductance,
and redox potential of ground waters in Wisconsin. He found a close
correlation between the redox potential, the oxygen content of the
ground water, and with the rate of tree growth. The specific
conductance influenced the forest type rather than the rate of
growth. Later studies in Hearst, Ontario confirmed these results.

In the same year Bloomfield (8) reported a study on the
mobilizing effect of Agathis Australis (Kauri) on the iron and
aluminum.in the soil profile. Results were similar to those for

the Scots Pine.

. 31

In 1951., Lag and Einevoll (37) in studies on the water permea-
bility of raw humus in podzol profiles, found that humus differed
greatly in permeability from place to place. They had already
shown a relationship between local microrelief and the thickness of
the A2 horizon of podzols. Under the surface depressions, the A2
was noticeably thicker. They explained that this was due to the
greater quantity of water percolating through the soil in the
depressions. In view of this, the permeability of the humus on the
surface would also affect the amount of water that could percolate
through the soil.

In 1951;, Bloomfield (9,10) also reported on further studies of
reduction and solution of ferric iron and mobilization of aluminum
by various leaf extracts. He used Rimu (Dacrydium cupressinum),

‘ NW Zealand species, Norway spruce, Sitka spruce, Douglas fir,
and Larch, which is a deciduous conifer. All gave similar results.
The iron oxides dissolved with the formation of organic complexes,
the 1' Orric iron undergoing reduction even in the presence of oxygen.
1”"ut'thcnr studies with leaf extracts from ash and aspen (1.1) also
"‘ct 0:! with ferric and aluminum oxides to form soluble metal
Mme, and the ferric iron was reduced to ferrous iron under
a.1“ch conditions. In contrast to the conifers, the aspen
continued its ability to carry out the process at high pH values.
3100:1121,“ also suggested that since aspen and ash leaves contain
ml‘tively large quantities of water soluble calcim, they may
"e‘muut for the high base saturation status of Grey-Wooded soils.
In a subsequent paper in the same year, Bloomfield (12)

32
studied the precipitation of the mobilized sesquioxide complexes.
Solution of the oxide reaches a maxim and subsequently declines
with the formation of coatings of adsorbed ferrous iron complex
on the ferric oxide particles. Leaching through sand coltmns
produced similar coatims on the sand particles. In other words,
iron and aluminum leaf leachate compounds or complexes were
adsorbed on soil colloids. The sorption was found to vary inversely
as the efficiency of the species as a mobilizing agent.

In 195’», Bloomfield and Gasser (13) studied the mobilization
of phosphate in waterlogged soils. The effect of anaerobically
fermenting plant material on the mobilisation of aluminum,
calcium and iron phosphates was studied. The alunimm phosphate
could not be mobilised. Calcium and iron phosphate could both be
mobilised. Basic ferric phosphate readsorbed phosphate. Kaolin
and montmorillonite fined phosphate from fermenting grass solution.
Phosphated clays released about half of the phosphate which had
been "fixed" on the clays to the fermenting grass solution. With
montmorillonite the amount remaining fined by the clays was equal
to the amount removed from fermenting grass solution by untreated
nontnorillonite.

Oxidation of fermentation solutions containing iron and phosphate
gave a precipitate of basic ferric phosphate together with organic
matter. They suggested that since this is a relatively stable
precipitate it accounts for the movement of phosphate in association
with iron within the soil profile.

In the same year McKenzie and Erickson (1,9) reported on the use

33
of redox potentials in studies of soil genesis. Radon: potentials
in soil profiles and in sand columns gave evidence that there was a
redox profile in the soil. Further studies were warranted.

In 1951., Brouficld (90) studied iron reducing organises. He
made isolations from a soil treated with sugar and artificially
gleyed, from a gleyed soil, and from fermenting grass. Organisms
from the genera Escherichia, Aembactg Bacillus and Paracolobactrun
were identified. All produced ferrous iron in ferric hydroxide
media.

The most active organisms, Bacillus m and Bacillus
circulans, were isolated for further stuck. Under anaerobic
conditions these organisms reduced iron. Under aerobic conditions
they also carried on reduction, but the amount of ferrous iron
produced varied as the surface area of the media used. Under anaerobic
conditions the organisms were unable to utilize the oczygen from
ferric oxide for growth, but in the presence of another oxygen
bearing compound capable of being utilized, reduction of ferric
oxide and growth occurred. Ferric iron reducing organisms were
present in the surface layers of gleyed soils but were not present
at depths of 10 feet.

In 1955, Sowden (71,) reported results of studies on estimation
0f amino acids in soil hydrolysates using the Moore and Stein
method. He found no distinctive difference in the amino acid
distribution of three soil types. The percentage of amino-N was
1’Clzher than expected.

In 1955, Flaig, Scharrer, and Judel (25), in Germain, reported

31+
investigations on the determination of redox potentials in soils.
They found that reproducible redox potentials could only be obtained
in aqueous solutions, and aqueous 8011 81131391131935: when the
dissolved oxygen in solution is displaced by an absolutely pure
inert gas like nitrogen. The reproducibility and the velocity at
which the redox potential is established depends mainly on the effect
Of the previous handling of the electrodes. Form and size of the
electrodes and the electrode vessels showed no special influence on
the redox potential. Likewise the error which arises through the
neslect or the temperature falls within the error limit of the
method. The establishment of potentials by the platinum electrode
18 an ecBailibrium reaction between the redox system and the electrode.
Through agitation and more intense introduction of nitrogen, the
diffusion within the solution being measured is improved and the
establl—iannent of the potential accelerated. In the case of all
Cited investigations a saturated calomel imnersion electrode was
used as the reference electrode. A potassium chloride diffusion
from the electrode into the measuring solution was maintained by a
Suitable construction of the potassium chloride bridge. The previous
history of the platinum electrode is very important in the reproduc-
ibility and the equilibrimn adjustment of the potential. The
connection between the previous handling and the effect on the redox
33’8th was discussed and examples cited. The redox potential was
higher, the greater the proportion of solid particles in the 5011
suspension. A definite soil-water ratio should always be militained.

Th
'3 length of time, during which the suspension was agitated, in

 

 

35
order to disperse the soil particles and to bring the water soluble
parts into solution was, within certain limits (1}; up to 2 hrs.),
without noticeable influence on the redox potential. In the case of
transferring the suspension to be measured from the sintered
container for agitation to the electrode container, care was required
that no sedimentation occurred. A continuous meamrement of pH
with a glass electrode during the redox determination was not
feasible because of the suspension effect. and the colloid adsorption.
On a similar basis a glass electrode could not be used as the
reference electrode for the redox measurement. It was shown that the
redox determination of air dry soil samples was of little value
since they were slowly oxidized in the air. In order for the redox
P°t°nt1al of the undisturbed soils to be obtained, the samples
5h°u1d be suspended and measured in the fresh unaltered state.

In a second paper (26) the authors discussed the results of
red”: Measurements and titrations from a study of a number of
Soils.

In 1955 (69) Schniteer'and De Long studied the ability of leaf
must: to mobilize and transport iron. The material present in ex-
tract-,3 of Populus grandideatata (poplar) was an acidic pclysaccharide.
Th." was no evidence of chelation.

In 1956 Schnitzer and Wright (70) reported on the results of
luchiig a calm of calcareous sand with ethylenedeaminetetraacetic
acid (EDTA) which is a strong chelatiag agent. Sesquiondes were
d""°°:5-‘l=ed in the B horizon in the column.

36
SUMMARY OF LITERATURE

A. Theories of Podzol Developnent

The Podzol profile is characterized by an ashy A2 horizon
which is strongly leached and is often the most acid part of the
profile (33). The A2 horizon changes abruptly into a sharply
contrasting brown to dark reddish brown B horizon which contains
an accumulation of sesquioxides and organic matter. Phosphate
also tends to accumulate in the podzol B horizon (33). The B
horizon changes gradually into the underlying light yellowish brown
C horizon forming a diffuse boundary between the B and C horizons
which is difficult to define. In some cases, the B horizon may be
subdivided into two parts, the upper Bhir horizon which is very dark
reddish brown and is the zone of maxim organic matter accmlation
and the Bi, horizon which is brown or reddish brown.

 

Figure 1. Photograph of a strongly developed Podzol Profile,
Wallace sand.

Overlying the ashy A2 horizon is a group of thin horizons, the

37
A00 which is composed of relatively fresh plant remains, the A0
horizon which is composed of decomposed plant materials, and the
A1 horizon which is a mixture of decued plant remains, hums and
soil particles. The A1 horizon may be absent (58 ). In any case
there is an abrupt change fm the A0 or A1 into the bleached A2
horizon.

The sharp boundary between the A2 horizon and the Bhir

horizon and the diffuse lower Bir suggest a more or less complete
precipitation of mobile materials which are largely organic, or a
complete mobilization of the sesquioxides in the A2 horizon and
translocation of the mobilized materials into regions lower in the B
where a gradual immobilization occurs. This suggests that the
process is the result of the downward movement of percolating waters
and that some or all of the mobilized materials are removed from
the percolating waters by some mechanism such as adsorption or
precipitation. Such a thesis would 'not suggest that the percolating
waters dissolve soil constituents from the A horizon, move downward
into the B horizon and remain there until a drying process occurs
during the summer to deposit and fix the soluble materials as
Dr. Albert suggested (1, 2) but that the percolating waters move
completely through the profile and the soluble or mobilized colloidal
materials are removed by some definite process or agency. The
tongued nature of the B horizon indicates the channels where most
of the percolating water travels through the soil into the under-
ground regions where it joins the ground water supply. Dr. Albert

in Germamr (l, 2) has shown that there is a relation between the

depth of penetration of summer rains and the depth of the B

horizon of the Podzol below the surface. It is not intended that
this thesis refute his work, but we must also account for those
periods in the year when the water in the upper soil horizons is
connected with the ground water supply. Under these conditions the
addition of surplus water to the surface horizons would lead to a
transfer of the excess water in the soil to the ground water supply.
Such a condition exists in the northern part of the lower peninsula
of Michigan during the winter and early spring months. During that
period, the soil, under a good snow cover, does not freeze but is
cool and moist all winter long. Such conditions are suitable for
solution of materials in the upper layers of the soil and for almost
continuous movement of water downwards to the ground water, laden
with mobilized soil constituents.

The shamess of the A1 - A2 boundary suggests a more or less
complete conversion of certain parts of the plant materials into
mobile or water soluble constituents which are carried beyond a
definite boundary, while the residue is quite imobile and remains
behind in the A1 in the form of humus. This form of reasoning leads
to the assumption that the water soluble, mobile constituents of the
organic matter together with the products of the metabolic activities
of the microorganisms in the surface horizons, are the mobilizing
agents for other constituents. The evidence in the literature
substantiates these observations (5, 6, 7, s, 9, 10, 11, 13, 75)-

It has been established by Bloomfield (5, 6, 7, 3, 9, 10, 11, 13)
that fresh organic materials have the power to reduce ferric oxide to

39
ferrous oxide and thereby mobilize iron in the A horizon. He has
also shown that the organic materials form complexes with iron which
are mobile or soluble and can move downwards in the soil. In general,
then the function of the organic matter in the podzolization process
is the mobilization of sesquioxides , in the A horizon.

It is also known that a shallow Podzol with a thin A2 horizon
can form in 20-25 years (68). This suggests that the process begins
near the surface and the early thin A2 gradually thickens downwards
through remobilisation of precipitated materials in the B horizon
until an equilibrium with the environnent is attained and the soil
has reached the stage of developnent which is recognized by pedal-

. ogists as the mature soil. Visible Podzols also tend to form more
quickly and to be more strongly developed on sandy soils than on
finer textured soils. Possible reasons for this are the relatively
lower total surface areas of sandy soils, their high permeability
and their higher aeration status.

Once the se squioxides , organic matter and silicates are
mobilized they are translocated to regions lower in the profile
and precipitated there. Several possible methods of precipitation
have been presented in literature. Hattson' s theory of isoelectric
precipitates (1.5, A6, 1.7) suggests a reasonable possibility which
can occur under the conditions of acidity prevailing normally in
soils. Silica and hulms are electronegative while seequioxides are
electrical ampholytes being electropeeitive in acid solution and
electronegative in alkaline solution. The position of the isoelectric
point relative to pH depends on the nature of the combining anion

1.0
which is present when the sesquioxides are in the electropositive
state. Oxides of almimm and iron can form precipitates with
silicates, humus and phosphoric acid under conditions comonly found
in soils. (hddation of adsorbed materials durim periods of stun-er
dryness may also play a part. It seems like]: that translocation
of dissolved sesquioxides in true solution must also plw an
important part (1.9). However it must be shown that conditions for
oxidizing ferrous iron in true solution do exist in the regions
of the B horizon. The presence of adequate ammmts of oxygen or
sue other material ondizing ferrous iron in the region of the B
horizon would supply the required conditions. Iron oxidizing
bacteria could also perform such a function.

The genesis of the Podzol profile seems therefore to be the
result of mobilisation of sesquioxides and organic matter possibly
through the activities of microorganias in part and also through the
process of iron-organic complex formation and the translocation of
these materials in solution or suspension to regions lower in the
soil where they are precipitated. The means of precipitation
suggested are precipitation of colloids in a region where soil
reaction conditions are isoelectric for the colloids, precipitation
by drying and resultant oxidation, precipitation from solution by
means of oxygen or some oxidizing agent other than omen, or
precipitation by means of microorganisms capable of acidizing iron
itself or organic complemes (75, 76) of iron.

B. Oxidation-reduction Potentials

Any anion or cation in equilibrium with its counterpart in a
different state of oxidation is a redox systan. It should be
explained that the word redox is a contraction of the words
oxidation-reduction for purposes of convenience and has been widely
adopted in the literature. An example of such a system is the
Fe+2 = Fe+3 + (e‘) couple. Fe"2 and Fe+3 are the ions involved in
the system; (e‘) is the electron change (the valence change in
the reaction) undergone by the reactants. The E.H.F. of the
electrode or couple camot be measured unless it is compared with
a standard electrode whose potential is known. The potential is a
measure of the tendency of the electrode to donate electrons and
thereby to be oxidized, or to accept electrons and thereby to be
reduced. The hydrogen electrode (82: 211+ + 2e") , where the
pressure of 32 is 1 atmosphere and the 11+ ion is 1 molal in
solution, has been chosen as the standard and its potential has been
set at zero. Thus, when some other electrode or couple is compared
With the hydrogen electrode, the potential observed is the potential
of the unknown electrode. Marv other electrodes have been compared
with the hydrogen electrode and their potentials have been tabulated.
Latimer (33 has prepared one of the most complete tabulations
available. When two such electrodes are compared, the resulting
system is known as a cell and each electrode is called a half-cell.
When one half-cell is a system of ions in solution, contact is made
by means of an inert noble metal which acquires the charge of the

1.2

half-cell. Platinum is preferred as the connector and may be either
8’11” or platinized. When two such electrodes are connected, a
current W111 tend to flow from one electrode to the other. The
POtOItia-l measured across the electrodes is known as the Eh of the
cell when it is compared with the standard hydrogen electrode. When
another standard cell is used a correction must be made to refer back
'00 thO hydrogen electrode. The saturated calomel electrode is such a
standard and is widely used since it is portable. In the convention
used by Latimer (38) the potential of the saturated calomel electrode
is «21.5 volts and must be applied algebraically to the measured emf
to compare with the standard hydrogen electrode. The saturated
calomol electrode has been used in this work and the potentials given
301' the soils studied are canpared to the saturated calmel electrode.
(Fig. 1., 5, 6 she appendix.)

The potential of a cell may be calculated by use of an equation
dev°1°ped from the Ne rnst equation -

Eh : Eo .. 3?. Ln $9.9.
nF (Red) (1)

“1°“ Eh is the emf of the cell, E0 is the standard potential of the
electrode being compared with the standard electrode, R is the gas
COnStant, T is the absolute temperature, n is the number of electrons
luv-(“Ned in the reaction, F is the Faraday (96,500 coulombs),
(OX) is the activity of the oxidant and (Red) is the activity of the
red"ltt‘tant. When at 25° (298° absolute) and converting from natural

1
033 to the base 10., the equation simplifies to -

.4222 103$) ,,
o n Log (Red) ( )

In the case of very dilute solutions it may be assumed that all
activities are equal to l and the actual concentrations may be used.

When the activities of the oxidant and reductant are equal, it can

be seen that -

£22 _(_o_x)__
n Log (Red)- 0

and therefore Eh = E0.

This means that when the reactants in the cell are 50%
oxidized and 50% reduced the E0 of the cell is a standard value which
can be compared with other systems. All known systems can.therefore
be arranged in a scale in order of their Eo values. The E0 value
of an electrode is a measure of its ability to donate or accept
electrons, it is a.measure of the tendency of a one system'to oxidize
or reduce another. In Latimer's convention those systems with high
negative Eo values are strong oxidizing agents and those with high
positive values are strong reducing agents. When the two electrodes
are coupled, the emf. measured is the algebraic difference of the
Eh's of the two electrodes. The magnitude of the Eh then is a
measure of the rate at which the reaction will proceed. Those
electrodes with high or low'Eo values are widely used by chemists in
redox reactions. In some cases catalysts can be used to accelerate
the reactions.

In the literature it has been reported (17, 19, 20, 22, 27,

3°: 35, #9, 51, 56, 62, 65, 77) that organic matter, humus, clay

minerals, iron, manganese, oxygen and sulphur are some of the
substances that take part in redox reactions and which may determine
the redox potentials observed in the soil. Each substance is present
in the soil in the form of a redox couple, that is, both an oxidized
and reduced form of each substance will be present in varying amounts
depending on the oxidation state of the couple. The oxidation state
of the couple depends on the nature of the other redox systems
present in the soil at the same time. Keaton and Kardos (31.) regard
the 5011 system as a composite of complex interlocking redox
S3’5515311’153. If the oxidation state of one redox system is changed,
due to the effect of microorganisms or removal of oxygen or some
other determining factor, all the other systems change until equili-
brium is again reached. The redox system of the soil should then be
regarded as a dynamic system affected by climate, topography and
microorganisms which is continually changing, never at equilibrium,
but 8Ll’Nays trying to reach equilibrium. The change is reflected in
the change in Eh. A
The redox potential of the soil is also affected by the hydrogen
ion Concentration. It increases directly as the hydrogen ion
concentration increases. That is, the Eh-pH relationship is an
Merge relationship. It was first reported by Willis (87) as being
about ~060 volts per pH unit, but later investigators (17, 59) have
Shown that it may vary for each soil or for each soil horizon.
Using the Nernst equation it can be calculated for a particular redox

react ion

Some redox systems are more resistant to 3h changes than others.

he
The resistance of a redox system to change in 3h is known as the
poise of the system. The poise of a redox system is similar to the
buffer capacity of soils. Every system will undergo a change in
Eh as the ratio of oxidant to reductant changes. The Eh curve is
relatively flat where the ratio of oxidant to reductant is approxi-
mately equal to 1.0 but becomes very steep when the ratio of oxidant
to reductant is extremely large or small. According to Clark et al
(21), the system is well poised when the curve is flat, and the
system.is poorly poised when the curve is steep.

In soil genesis it is considered that there are five factors of
Soil formation (32). me action of microorganisms and organic matter
on the soil particles, conditioned by the effect of climate and
drainage operating for a period of time, results in the morphological
exPression of a soil profile which is at equilibrium.with the
enVironment when at maturity. When the redox potential is measured
in the soil in situ, the effect of climate, microorganisms and organic
matter (vegetation), and drainage (topography) on certain mineral
Constituents of the parent material is expressed in the Eh. If the
redox potential is followed over a period of time, all the soil
formation factors are considered and the Eh of the soil is in part a
measure of soil formation. There should therefore be a redox profile
in the soil. Since the podzolization process, described above, is
Concerned with sesquioxides and organic matter which are complex
redox systems, the study of the redox potentials of a Podzol profile
is of interest, and may serve to indicate which of the theories are

likely to be most important in the profile development.

Previous studies of redox potentials of soils in situ
(35, A9, 65) have indicated that there is a large experimental error.
If enough replicates are used, it should be possible to determine
if the variance is due to experimental error or to the natural
variance of the oxidation-reduction processes in the soil. It was
therefore decided to use as many replicates as possible.

The effect of microorganisms is considered important as a part
of the biotic or vegetation factor of soil fermation. It was
therefore decided to devise a method whereby those organisms oxidizing
both organic matter and iron could be studied.

In.the discussion and interpretation of the redox potential data

a number of conventions are discussed. Those used.by Peters (60)

bass been adopted in this thesis.

47
RESULTS

Soils Studied

For the study of redoprotentials in situ it was decided to
measure redox potentials by horizons (depth); and observe the
changes in redox potential as they occurred with the seasons and
with drainage. For this purpose, three soils were selected in one
area forming a hydrosequence of soils developed on the same kind
of parent material. They differed in drainage and although all
three sites were under forest vegetation, the species on each site
differed from the others.

Figure 2 below shows the relationship of the soils in the
hydrosequence. Profile descriptions of the soils at each site are
given below. The soils selected for study were the well drained

\
\ -—-’ /
.... kALKASKA SAND § .--—' // /
t \ ... ... . \ /// {y‘V
KALKASKA SAND S e \\ 7—4_‘595:°-I$80§§+°£'§f$§fig:..:ml“, $3
~§ES:‘ “‘ ‘E’<F:"—‘- -"':: ——5-;"
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"E" TABL \ \ % '3AF-Di’i" w '5»
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Figure 2. Diagram of Experimental Site Showing Relationship of the
Soil Series.

48

Kalkaska sand, the imperfectly drained Saugatuck sand, and the poorly
drained Roscamon send. They form a hydrosequence of soils on the
slope. The Kalkaska series is a well drained sandy podzol with a
moderately developed B horizon. It was located at the top of the
slope (Fig. 2). Where the series intergrades to the Wallace
series it may contain some "ortstein" concretions (Fig. l). The
Saugatuck series is an imperfectly drained Podzol with a strongly
developed "ortstein." It was located near the foot of the slope
in the region of the fluctuating water table. The Roscomon series
is the poorly drained sandy associate of the soils of the Podzol
region of Michigan. The site was located at the foot of the slope,
approximately 50 ft. North of the Saugatuck site, adjacent to a
muck soil. The Roscomon series is slightly acid in reaction. The
parent material of all three soils in the ludrosequence is saw
outwash or till which is extensive in the northern lower peninsula
of Michigan.

location and mum: The soils selected for stw are
located in the region of the Podzol Great Soil Group in the northern
part of the lower peninsula of Michigan. The area is located in the
hilly interlobate norainic area in the northwestern part of Osceola
County. Elevations range from 1000 ft. to 1600 ft. above sea level,
and the drift ranges in thickness from 800 ft. to 1200 ft. It is
of late Cary age. A wide variety of textures and slopes occur. The
site where the stw was carried out was on an 842$ slope, located
in T 20 I - R 10 W (Burden Twp.) section 10, m, S. E. corner,
50 yds. west of the road.

1:9

Climate: The climate of the area is cool and humid (31, 84).
The annual precipitation is approadnately 30 inches. The winters are
of particular interest. The snow cover reaches 1 - 2 ft. in
thickness, and protects the soil from freezing, as well as supplying
enough meltwater to keep it moist. During the time the stub was
being carried on the soil was never frozen. The last frost in the
spring occurs from May 20 - 31, and the first frost in the fall
occurs from September 10 - 20 (31). The growing season is 110 - 11.0
days long. The stunner temperatures reach the low 90's. The manner
season nay be dry. The rainfall is of the thundershower type.

Vegetation: The vegetation consisted of sugar maple (Acer
saccharun) , aspen (Pomlus treuuloides) , with bracken (Pteris
aquilina) ,' blackberries and wintergreen on the well drained and
imperfectly drained sites and with hemlock (Tsuga canadensis) ,
white cedar (Thuja occidentalis) and scattered alders on the poorly
drained site. Profile descriptions of the series are presented
below.

Kalkaska sand: The Kalkaska sand is the well drained member of
the mdrosequence, developed on the brow of a 10% slope under the
crown of a large sugar maple. There was no sign of erosion although
later treatment of the surface horizon indicated the presence of
charcoal, suggesting that the area had been subject to fire in the

past.

Kalkaska Soil Profile

Horizon Death Descripg ion
A... A. 15-0" Dark grayish yellowish brown!- (10 IR

2/1); mat of organic matter with a thin
( inch) covering of fresh leaf litter;
1 inches thick.

A1 0-2" Brownish grey (10 YR L/l); sand; crumb
structure; very friable; pH 5.2;
2 inches thick.

A2 2-17" Yellowish grey (10 TR 7/2); sand:
loose; pH 5.1; 15" thick.

Bhir 17-23" Dark grayish brown (5 YR 2/1 - 2/2);

sand; coated with organic matter;
strongly cemented in places, but soft
and friable in others; pH 5.6;

6 inches thick.

Bir 23-31." Moderate brown (7.5 IR h/h); sand;
weakly cemented with scattered ortstein
concretions; firm; pH 5.3; 11 inches
thick.

C 31." Light yellowish brown (10 IR 7/3);

sand; loose; pH 5.5.

Muck sand: The Saugatuck sand is the imperfectly drained
member of the hydrosequence, developed at the foot of the slope, a
few feet in elevation above the Roscounon site. The site was
located six feet south of the trunk of a large aspen and under the
edge of its crown. Apparently because of the effect of a strongly
developed ortstein in the B horizon, and the presence of the high
water table, the roots were mostly concentrated in the A1 horizon
with a few in the Bhir horizon.

 

*I.S.C.C.-N.B.S. color names as given in national Bureau of
Standard Circular 553, 1955.

51
Saugatuck Soil Profile

Horizon Depth Descrimion
A00, A0 15-0" Dark grayish brown (5 IR 2/1); organic

layer with a 1; inch cover of fresh
leaf litter; 15 inches thick.

A1 0-5" Grayish yellowish brown (10 IR 5/2);
sand; weakly coherent; very friable;
medium crumb structure; with much organ-
ic matter; pH l..8; 5 inches thick.

A2 5-18" Brownish pink (7.5 IR 7/2); sand,
loose, very friable; pH l..6; 13 inches
th10ke

Bhir 18-22" Dark grayish brown (5 IR 2/1); sand;

weakly cemented with organic matter;
firm; pH 6.1; 4 inches thick.

311- 22.37" Moderate brown (7.5 m 4/1.) ; mottled
light brown (7.5 YR 6/h): and:
strongly cemented; pH 6.1; 15 inches
thiCke

C , 37" Light yellowish brown (10 IR 6/3) ;

sand; loose; moist; pH 6.5.

Roscomon sand: The Roscomon sand is the poorly drained member
of the Wdrosequence. It was located in the bottom of a drainage way,
at the foot of the slope in a clear space between alders and hemlock.
The site was usually saturated with moisture in the late winter and
spring. The water table was not normally much below the soil
surface until early July.

Roscommon Soil Profile

Horizon Defih Descrifiion
Aoo, A0 2.0" Dark grayish yellowish brown (10 IR 2/1);

moderately decomposed organic material
with a Q inch covering of fresh plant
residues; 2 inches thick.

 

 

 

52
Roscomon Soil Profile (Cont.)

Horizon Depth Description
A1 0-10" Brownish grey (10 IR 3/1); fine sand;
- very friable, medium crumb structure;
pH 5.l;; 10 inches thick.
GA 1 1046*! Light grayish brown (7. 5 m 6/2);
- sand; loose; very friable; pH 5.9;
6 inChOS thiCke
GB 1 16-18" Dark grayish yellowish brown (10 IR
‘ 3/2) mottled with 101m 5/6 and 4/1;

gravelly loanw sand; loose; pH 6.7;
2—4 inches thick. ’

GA_2 18-31" Light gr sh yellowish brown
(10 IR 6 3): sand; loose; pH 6.7;
13 inches thick.

GB_2 31-32" Grayish brown (7.5 YR M2) and very
dark grayish yellowish brown (10 IR
3/2); sand; cemented; pH 6.7; 1 inch

thiCke
01 32.31. Light grayish brown (7.5 IR 5/2); fine
. sand; loose; pH 6.7; 2 inches thick.
02 31." Light grayish yellowish brown

(10 IR 6/2); sand; loose; pH 6.7.

Cb:i.dation- reduction Studies

Electrodes were prepared as described by Quispel (65) and
McKenzie and Erickson (1.9). In order to make them more sturcw,
the glass tubing containing the wire leads was filled with castolite
resin which was allowed to harden slowly after heating to 60°C for
a short time. Treated in this manner, the castolite formed a flexible
rod which was less subject to damage during installation. It was
not necessary to remove the glass tubing. The electrodes were
then cleaned, platinized, and tested for reproducibility. Only

53
those electrodes checking within 2 to 3 millivolts were used.
The testing solution was a solution of quinhydrone in .05 molar
potassium-acid phthalate buffer which gave a pH of about 4.0. The
quinhydrone dissociates in equal amounts of oxidant and reductant
and therefore the Eh of the solution is constant. It thus serves as
a good testing solution for standardizing electrodes. The
electrodes were installed in the soils using the method described
by McKenzie and Erickson (A9). After installation, the tops of
the electrodes were clipped off at the level of the A horizon and
extensions of Belding 22 gauge insulated copper wire were soldered
to the electrode leads. The connections were waterproofed with tygon
paint. The extensions were connected to an instrument board mounted

on a 3% foot post. The installation pennitted the measurement of the

BECKMAN MODEL 6
POTENTIOMETER

  
  
    

STANDARD SATURATED
CALOMEL ELECTRODE

 
  

‘PLATINUM
ELECTRODES
,‘Isorsa SET)

 

 
 

Figure 3. Diagram of Electrode Installation.

51+

redox potentials during the winter, without disturbing the electrodes,
unhampered by the depth of snow. Connection with the saturated
calomel electrode was carried out by setting the calomel electrode

in a hole prepared in the soil near the site. The soil was first
moistened with a saturated solution of technical grade KCL.
Potentials were measured using the Beckmsn model G potentiomenter.
Figure 3 is a diagram of the installation. The electrode sets were
protected with a wire guard. A wooden cover was installed over

the wire leads at the electrode panel to protect them from the
weather.

At each site, thirty electrodes were installed, six electrodes
in each of five horizons. Measurements were made periodically over
a period of two years. At the end of the experiment the soils were
sampled, the electrodes were removed, examined, and the exact
location of each electrode in the soil profile was determined.

An Eh-pI-I measurement was run on each of the soil horizons using a
variation of the method of Willis (87) with a nitrogen atmosphere.
Results are recorded in the appendix. The correction was applied
to the redox potentials of the soil to standardise them at pH 5.0.
This experiment must be run on fresh soil samples since air drying
results in oxidation of some of the soil constituents and may thereby
Blur the potentials. Results of these experiments are shown
Plotted in Figures 1., 5, and 6.

Pmsical and Chemical Studies

Mechanical analyses by the pipette method and mineralogical
analyses were run on all three soils. For the mineralogical

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58
analyses, the fine sand fractions were used. The heavy-minerals were
separated.using s-tetribrenoethene adjusted to 8.0. 2.85 with nitro-
benseme. An additional check of the light mineral fraction.was
obtained by xeray analyses using the florelco xhray spectrometer.

In addition, volume weight, solution loss, total carbon by the
m'drogen peroadde method, permeability, porosity, the base exchange
capacity of the mineral fraction were run on the Kalkaska sand
profile. The results of the mechanical analyses are given in
Table 9 in the Appendix.and are shown in.cumu1ative percent compo-
sition curves in Figures 7, 8, 9. The values of sorting, kurtosis
and skewness were calculated for the horizons of the three soils.
Results (Table 12 in Appendix) indicate stratification in the
Roscommon and Saugatuck series. There is some variation in the
Kalkaska series also.
Kicrobiological Studies

In order to further characterize the soils, it was decided to
study the distribution of nicroorganisms in the profiles of both
the Saugatuck and Kalkaska series. Iron complex forming organic
anions may be important in the podzol process (5, 6, 7, 8, 9, 10, 11,
1h), and may determine soil redox.potentials in part (51, 72, 73). There
are microorganisms which can utilize such anions as a source of energy
(55,77).They may also contribute to the redox potential of the soil
(2? ). Citrate is such an anion. when ferric citrate agar medium
is used, the colonies of organisms are stained a reddish brown color
and can be counted. Therefore, ferric citrate agar medium was

selected to test for the presence of complex.forming organic anions

59

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62

on the one hand, and for the presence of organisms capable of
cuddizing such anions on the other hand.

Organisms capable of oxidizing ferrous iron have been shown to
be present in the water of stagnant pools and water pipes etc. (75).
It was decided to try and isolate them from the profiles of the
Kalkaska and Saugatuck series to find out if they were present in
soils as well. Accordingly, in late April 1956, the Kalkaska and
Saugatuck sites were sampled again. The procedure used was as
follows:

Pits were dug approximately three feet square and deep enough to
expose the soil profile. One side of the pit was cut vertically to
prepare a fresh face for sampling. The opposite side of the pit was
dug out with a slope, thus enlarging the working space. It was
decided to sample the A1, Bhir! Bir horizons. Therefore a fresh
face was opened on the vertical side of the pit with a knife. Using
the volume weights of each soil horizon the volume of soil required
to give a 10 gm sample of soil with five samplings was calculated
and set on a sampling tool which could be sterilized, and which had
been specially prepared for the purpose. A diagram of the tool is
shown in Fig. 10. Using the sampler, five samples were quickly
transferred asceptically to empty, sterile dilution bottles. The
dilution bottles were prepared in the laboratory and after sterili-
zation in an autoclave, they were placed in a tray used for carrying
coca cola bottles. The tray facilitated transportation of the

dilution bottles to and from the sample site.
The sampler used is made entirely of steel so that it can be

PLUNGER

   

--__ la... l .u_.

SCALE .'
FULL SIZE

PLUNGER ”STOP"

9/I6" 0.0. STEEL PIPE

FIGURE IO: SAMPLER USED IN SAMPLING
FOR DISTRIBUTION OF

MICRO-ORGANISMS.

61.
flamed. Sterilization was carried out by washing in alcohol and
flaming in a blow torch flame. In this manner, duplicate samples
were collected of each of the required horizons. An additional
duplicate set of samples was collected for moisture determinations
for each horizon with the sampler set at the same calculated volume.
These samples were later dried and weighed and used to calculate the
number. of colonies per gram of soil. The samples, in field moist
condition, were taken to the laboratory where they were suspended
in 90 c. c. of sterile distilled water and appropriate dilutions
made for counting citrate oxidizing organisms on ferric citrate
agar( 3 ) .

The dilutions prepared were l:lOT, 1:100T and lle. Inocu-
lations were made and triplicate plates were poured of each dilution
°n the Same day that the samples were taken. The cultures were then
°°°1°d and incubated at room temperature for five days. Colonies
“11°11 formed a brown halo and those which did not were counted
sepia"""Ei-"Z'OILv. Only the brown colonies precipitated iron. The remainder
Of the Organisms used citrate as a source of energy but did not
In“Scipitate iron. The reason for this is not understood. The counts
for the 1:10T dilution are given in Table I as organisms per gm of
soil.

In a. second experiment, two iron nails were placed in 500 c.c.
erlemneygr flasks with 200 c.c. of distilled water and glass slides
were a‘lgbended in the medium with iron wire. After sterilization
the Qaaka were inoculated with l c.c. of the 1:10 dilution of the

field
ea"“Illes. The cultures were incubated at room temperature for a

65

Table 1 Distribution of Citrate Oxidising
Organisms in Kalkaeka and Saugatuck Profiles

 

 

 

 

 

 

 

Soil Series and Horizon Sample Organisms (Thousanggég, 3011)
Brown rs
A 126 I2 63
1 125 16.33 2;.6
121.. e - e5
mum“ Bhir 123 0.03 1.1.
B 122 0 O
11' 121 0 0
a 1.32 1.7 1.0
1 131 1a5 32
Saugatuck Bhir 11323 0.01. t:
128 0 0.2
311‘ 127 o 0.9

 

 

 

 

 

 

month. Several slides were then emined. No growth was observed,
;O the incubation was continued. Several months later, the cultures
were opened, the slides were removed and treated with dilute
Marie acid to remove the ferric hydroxide precipitate. The
.1140! were then stained using the periodate—-Schift'e reagent
”fining procedure described by Lillie (Al) . Mild periodate oxidation
Bins rise to aldehyde groupings in microbial cell wall materials
”Id thus provides a basis for the Schiff color reaction. In the
Pmlimfinary H 01 treatment, the ferric hydrate was not completely
"loved but pink stained organisms were readily seen. Sears were
‘130 We of the voluminous precipitate of ferric hydrate at the
Mtoe of the flasks. After fixing with heat, iron was dissolved
With 1:2 H Cl and Gram's iodine applied as a stain. The slides were
“1°11 mined under the microscope using the oil innersion lense.
Results are shown in Table 2.

Ix. ,,¢Aiur\l...ar|¥arlfllll1a‘fl :

‘~c~‘-_¥

Table 2

66

Distribution of Isolates of Filamentous Sheathed

Bacteria from Kalkaska and Saugatuck Sands

 

 

 

 

 

 

 

Series Horizon Sample Observations
Kalkaska al 126 Nothing on incubated slides,
very few sheath fragments,
empty, on smears.
Bhir 124 Nothing on either slides or smears.
123 II II II II II II .
Bir 122 Numerous beaded fragments,
apparently branched, on slides.
121 Snort beaded fragments, no
branching in smears.
Saugatuck A1 132 Nothing on slides or snears.
Bill 130 II II II II II
r 129 II II II II II
Bir 128 Numerous sheathed, beaded filaments
with apparent branching on slides.
12? meathed, beaded fragments in

m‘rfl e

 

No positive identification of the organisms observed was made.

However, they were very similar to those described by Starkey (75)

and by Pringsheim (63). Drawings of the organims are shown below in

£4: %

Diagram of Organisms Observed on Slides from the Isolates
of the Bir Horizons of Kalkaska and Saugatuck.

Figure 11o

Figure 11.

Without further study, the organisms observed could not be identified

 

67
beyond the family Chlamydobscteriaceae (filamentous sheathed

bacteria); but they appeared similar to merotilus dichotoma as
illustrated by Starkey (77) . The organisms were found without
difficulty and were quite- numerous on the incubated slides fran the
Bir horizons; but were absent or found only with great difficulty on
slides from the other horizons. The same was true for the smears. No
other types of organisms were observed. This indicates that the
medium was restrictive for all types of organisms but the ferrous
iron oxidising types.

68

DISCUSSION

The results of the study on redox potentials are shown plotted by
horisons snddates for each of the soils in the twdrosesquence in
Figures 1., 5, and 6. Statistical analyses by horizons and dates
indicate that dates are highly significant. Table 3 shows the
statistical analyses of the results from the Kalkaska and Saugatuck
series. Table llin the Appendix shows the means of the replicates
for each soil by horizons and dates.

Table 3. Results of Statistical Analysis of Redo:
Potentials for Kalkaska and Saugatuck.

 

 

 

 

 

 

Treatment D.F. 5.3. $1.8. F. Nec.F.

11 5%
Dates 13 1,061.,662 81,897 M31; 2.23 1.77
Horisons 8 1,017,680 12,721 2.23 2.65 2.01
Error 101; 591M309 5,712
Total 125
L.S.D. for dates :- 71.2vlillivolts -
L.S.D. for horizons - 57.2 millivolts.

A chi-square test of the variance of the A1, A8 and 3"8 horizons of
the Roscmon series indicated that an uncontrolled factor was
affecting the potentials in these horizons. This was not true of the
other soil horizons. Therefore, the three horizons were analysed
for significance between replicates. The results of the analysis are

shown below in Tables 1., 5 and 6.

69

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 1.. Analysis of Variance of the A1 Horizon
of the Rosconon Series.
Tm‘mnt Dope So So Me So Fe “0098“” F
1% 5f
Replicates ‘5 155,999 38,999e8 19.95 Zeta 1088
Dates 1h 6,698,899 £78,493 24h.8 3.68 2.5L
Error 56 109.h63 1,955
Total 31;
Table 5. Analysis of Variance for the 6a.; Horizon
of the Rascal-on Series.
Treatnent DJ. 3.5. 14.3. F. Necessary F
1% 5%
Replic.t. 5 L 293 , 6m 73 . 1.10 3. 18 20 ‘03 10 88
D‘tOB u A,288,h77 306,32) 1303 3e68 2e 5“
Error 56 l,29h,2hl 23,111
Total 81.
Table 6. Analysis of Variance in.BG;1 Horizon
in.the Rosccuson Series.
Tro‘mnt DJ 0 So So Me So F e NOCCBSM F
1% Si
Replicates 1 147,298 1L7,298 28.1h 8.86 b.60
Betas 1h» 3,238,795 231,363 hha19 3-70 2-h8
Error 11. 73,287 5,235
Total 29

 

 

70
The variance between replicates in all three horizons is signi-

ficant. Due to the small thickness in the 354 only two electrodes
were successfully installed there. The F values for replicates in
this horizon is larger than in the other two horizons where five
replicates were used. This suggests that more replicates should be
used. Increasing the amber of replicates would allow more degrees
of freedom and thereby reduce the mean square values for the
replicate comparisons. It is also interesting that replicates are
here variable in the A1 horizon than in the A61 horizon. This
suggests that the variance is connected in scale way with organic
matter. The activity of nicroorganisu, varying from place to place
in the horizon could be responsible. The effect of excess water was
no doubt also a contributing factor. There may have been leakage in
the insulation of some of the leads. Danage to the electrodes during
installation is not a contributing factor in this case, however,
since the surface horizons are most effected and they would receive
the least danage during installation. Another contributing cause to
the variance between electrodes in the A1 horizon nay have been the
effect of alternate freezing and thawing in the spring season which
resulted in some heaving of the electrodes. Analysis of variance

of the redox potentials observed in the soil at the Ros-

conmon site is shown by itself in Table 7. Differences in

71
Table 7. Analysis of Variance of the Rosconnon Series.‘

 

 

 

 

Treat-eat D.F. 5.5. 11.3. F. Nos. 1“
E 5%

Horizons 5 " 429,151 85,830 3.11 3.29 2.35

Dates 11. 1,995,638 11.2, 51.6 5.16 2.35 1.8:.

Error 70 1,934,081 27.630

Total 89 5,358,870

 

 

rehszpotentials between horizons are significant as are differences
between,dates.

In the analysis of variance for the three soil series there
were significant differences between dates at the 1} level and between
horizons at the 5% level.

It was suggested, that since there is a cyclic variation in.the
redox potential due to clisate, the results are skewed rather than
synaetrically distributed about the lean. It was therefore decided
to select a series of dates in one season for analysis. Three dates
of the winter season of 1953 and 195h'were used.

Table 8. Analysis of variance for 3 dates during winter of
l953-5h for Kalkaska and Saugatuck Profiles.

 

 

Treatment 13.3. 3.3. 11.5. Nee. F
F. ‘11——
Erizons a 591,515 73,939 60.1.1 3.89
Dates 2 12,035 6,018 b.92 6.23
Error 16 19,577 1:22“
Total 26 623,127

 

 

‘-‘

 

72

It can be seen that analysis of variance of results for only
three dates tends to increase the significance of horizons and
reduce the significance of dates. Examination of Figures A, 5, 6
shows that some horizons vary more than others so that the graphs
for jmfkvidual horizons tend to cross. Results for horizons should
therefore be comparable, although the absolute values for the redox
v potentials no doubt vary scnewhat from the true values. Such varia-
tion is included in the error tern. Variation with season or
climate , indicating seasonal trends in redox potential, should be
”Present“ ive regardless of the possible variation of the absolute
redox values from the true values. Table 11. in the Appendix shows
”19 redox potential for a number of oxidation-reduction couples
that estint in soils. They are shown compared to the calcmel electrode
”“1 ‘dJusted to pH 5.0 using the Hornet equation. Values used were
0““th from Latiner (38). Examination of these equations shows
‘1‘“: m E, values fall within the range of redox potentials measured
in the Kalkaska, Saugatuck and Rosccanon series.

Figure 12 shows a comparison of the moisture determinations for
8“staining and Rosco-ion series with redox potentials. The moisture
cmt‘ents of both series were measured with wlon blocks (16) and are
therefore comparable. The moisture variations for the Kalkasks
””198 were measured with plaster of paris blocks. They are not
Show“ Plotted since they are not comparable to those obtained for the
Salsa-tuck and Roscomon series which were measured with m'lon blocks.
Stub 0f the values in Table 13 of the appendix shows that the
Kuk‘Bka series behaved sinilarly although it was better drained at

L06 RESISTANCE IOHMSI

 

700,000 I I I I

FIGURE I2
RELATION BETWEEN REDOX
POTENTIAL AND DRAINAGE
FOR SAUGATUCK AND

ROSCOMMON SANDS USING
NYLON BLOCKS

noo,ooo --
O
O

Ascuavs PLOTTED mow
MEAN VALUES 0 /

B = VISUAL CURVE

0 = SAUGATUCK

El ‘-' ROSCOMMON
[0,000 —

 

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.DD 0 I/ 0
1,000 — . 'I': I" D on .—
' D
/ D D
m I L 1 J
200 o 200 400 soo soo

REDOX POTENTIAL Imv)

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75
all times. Since the moisture content changes only a small amount

for a large change in resistance of the nylon blocks, the moisture meter
readings are shown plotted as the logarithm of the block resistance
in ohms rather than as actual moisture percentages. It can be seen
that there is a general relationship between redox potential and
the moisture content of the soil. These results suggest that relief and
climate have a great influence on the oxidation-reduction status of
the soil. Table 15 (appendix) shows the rainfall and temperature at
the Cadillac station for the years 1953, 1951+ and l955 over the period
that the experiment was in progress. The data were obtained from
Climatological Data for the Michigan section for the period from
1953 to 1955 Published by the U. S. Weather Bureau. The Cadillac
station is approximately fifteen miles from the experimental site
and therefore should be fairly representative. The residual varia-
tion in the redox potentials from the mean curve A for the Rosccmmon
and Saugatuck series are shown plotted in Figure 13 against the mean
temperature for the two week period prior to the date of the reading.
An asymmetrical sine curve was obtained which indicates that a great
part of the variability (residuals) in redox potential about the mean
misture line in Figure 12 was due to temperature variation.
Examination of the results from Figures 1., 5, 6 suggest that the
climate greatly affects the redox potential of the soil and that both
moisture and temperature should be measured in conjunction with redox
Potentials.

The remaining residual variation not due to temperature is no
doubt due largely to soil variation. Note also that the curves in

76
Figure 13 show a sharp dip at the high temperature end. The activities
of microorganisms are probava responsible for the high temperature
dip in this curve. Since microorganisms would be most active during
periods when moisture was favorable as well as temperature, one would
expect that they would be most active in the spring and fall when the
soil was both moist and warm (above 50°F). The low potentials
observed while the temperature was low (50°F or lower) are probably
due in large part to chemical reduction in the soil rather than to
the activities of microorganisms. It was observed that at no time
during the course of experiment was the soil frozen. During the winter
period while it was covered with snow it was also moist. Thus, the
late winter and earl“,r spring peried is the most favorable time of
year for chemical reduction due to the presence of a fresh supply of
water soluble plant materials from the previous summer's vegetative
grot-rth, high moisture and rising temperatures. This may account for the
sudden drop in the redox curve around 20°F air temperature (in early
January) show in Figure 13.

However some organisms may be active at these low temperatures.
Certain psychrophilic (cold loving )organisms include some of the iron
caidizing bacteria described by Starkey (75) and Pringsheim (63, 6A).

The results of the lie robiological studies indicate that iron
musing organisms were present in the Bir horizons of both the
Wash and Saugatuck series. According to Starkey, sane of the
Organisms are most active at temperatures ranging from 32°F to 70°F.
For Gallionella the optimum temperature is given as 43°F. The

Organisms observed grew under aerobic conditions since they were

77
distributed.most densely on the glass slides near the surface of the

distilled water in the iron.medium of the second experiment. The
falsely branched filaments observed however were more like the type
described by Starkey as Sphaerotilus dichotoma.

According to Stanky, these organisms obtain energy from the

oxidation of ferrous iron in accordance with the Molloxing reaction

(75):
la.FOLICCB)2‘l'AI .1“: *0: i I; Fe<ClD3 + $002 4" energy.

In the absence of organic materials they utilize the carbon from
dissolved 303. The above reaction suggests that the mineral siderite
( FeCC'q) Some other forr of iron carbonate ma y be present in the
B ho~izons of podzols. These results are interpreted as evidence
that under the conditions observed in the soils under study, iron
oxidizing organisms were present in the soils and could be active in
the development of the Podzol E Ziorizcns. Examination of the results
from the fir.t e1 eriment (T ble 1) indicate tJQt organisms in detect-
able nunbe rs :ere present in the Al and Bhir horizons which could
oxidize the ferric citrate and precipitate ferric hydroxide or

which could neilize citrate as a source of carbon or energy without
zecipitating iron. The ability to at lize citra tea as he sole
energy source is sufficiently limited among bacterial species to
permit its use in selective media for isolating certzin nutritional
8r01W(55 filthougb the evidence is not highly opecific,t ,he prp

Of organisms capable of utilizing ferric citrate,vith or without iron

precipitation,on artificial mcii: infe1s the presence or appropriate

78
substrates in the soil horizons studied. The nunibers of organisms
recomred on ferric citrate age: provide indirect evidence that
citrate or related tricarbom'lic and dicartom'liC acids may be
included wrong the native substrates present in traeae soils. Both
ferrmfis and fesric iron are knee-r31 to for? ::o~.:iplef: corvxpounds with
may of these rtateriels ('5, la, '32., 73, 5’3). Iron tends to he
reduced on flu-ring oraplex orgnic cmpounds in the soil (4, 1.4),
therefore it is t.- be expected that iron in solution is present in
both the ferrous and ferric state. It has been observed here that
citrate utilizing orgnims c most n‘rrez‘om in the A1 horizons,
present ‘in the ”hi.“ ‘."\:‘izrns “Z17“. descent, or very scarce, in the Sir
horizons of the Kali-asks. and Saugatuck series. This suggests that
many of the iron complexes formed in the A1 horizons are decomposed
there and some are carried to the Bhir horizon before they are
utilized by microorganisms. Some of the iron, mobilized in the A
horizons, must therefore be released into solution in the free state
either as the ferrous or ferric form in the A and upper B horizons.
It has also been observed here that iron oxidizing organisms are
present almost exclusively in the Bir horizons of both 8011!. This
means that ferrous iron not be present in the Bir horizon in
sufficient anounte to serve as the source of energy for the iron
oxidizing bacteria. The nobilization of iron oxides in the A
horizon- of podzols by the fornation of water soluble couple:
organic compounds accompanied by reduction of some of the ferric
iron to the ferrous form, the release of the ferrous and ferric

iron in the free state through decomposition of the organic couplers

79

by nicroorganisns in the A and Bhir horizons, translocation of the
.0me materials to the region of the Bir horizon by percolating
waters, and precipitation of the free ferr ic iron there by iron
oxidizing organisms is a possible nechmisn of Podzol formation.

Mechanical Analysis

Results of the mechanical analyses show that ell three soils
were essentially sands. Both the Saugatuck and Roscanon sites
were somewhat lore stratified than the Kalkesh site, see Table 12
intheippendixendrigures 7, 8, end9inthetext. This suggests
that there hes been some soil loss from the Kelkaske site by erosion
and some soil gain at the Saugatuck and Hosea-on sites as a result
of erosion of the surrounding areas or that the naterials were
originally nore stratified at the Saugatuck and Rosco-on sites. To
further substantiate this observation, there is a relative loss in
silt and very fine send in the Kalkaske and an enrichzent in come
sand, while the Saugatuck and Roscomon series show a relative gain
in very fine sand and silt and a relative decrease in coarse sand.
However all soils show a trend to increasing amounts of fine or
medium sand with depth in the profile. Comparison with the redox
profiles suggests that the variation in porosity due to differences
in texture as a result of stratification is not the deter-ining
factor as far as the redox profile is concerned. The rods: profile
correlates better with the organic matter distribution, the degree
of oxidation in the B horizon, and the variation in noisture content
as determined by a. rainfall and the season. Such variations in

texture nay contribute somewhat to the experimental error. The
variations shown in texture are not so great that the poorly drained
or the imperfectly drained soils would be considered different from
the Kalkaska series and not included in the catena or hydrosequence.
The presence of charcoal in the A horizon of the Kalkaska. series
indicates that a forest fire passed over the area. There has also
been some accumulation of clay in the A1 and B horizons of all three
soils. The color of the A2 horizons of new podzol sites in northern
Michigan is pinkish gray (7.5 TB 6/2). As a matter of interest, on
dispersion of the soil senples during nechanical analyses, the
pinkish gray color remained in the suspension after the sands and
silts had settled out. This indicates that the pinkish gray color
is associated with the thin coating of clay on the sand particles.

The Moisture Measurements

Wtion of the data for the Kalkaska site shows that at
no tile in the period of the study did the moisture content of the
profile exceed h% of the dry weight of the soil (16). This means
that about 12% of the pore space was filled with water and suggests
that aerobic conditions existed in the profile at all tiles. On
the sane basis, the Saugatuck was approxinately 20$ saturated at
its wettest point and the Rosan approxinately 1.0% saturated.
The figure for the Rosco-Ion seens low because the site was covered
with water at tines when the neasurenents were taken and the soil
should have been nearly 100% saturated. Examination of the weather

data for the period over which the moisture measurements were nade

81
shows that there was a deficiency of 3.65 inches of rainfall on

January 1, 1951. and an excess of 2.98 inches by April 30, 1951..

This neans an increase in the water content of the soil during the
period which was observed while the moisture blocks showed a
decrease. The weather data also shows a net difference of 6.57
inches of water in the four months of the fall of 1953 as compared
to the fall of 1951.. This difference in rainfall caused a difference
in the amount of water on the Roscommon site and was reflected in

the redox potential for all three sites during the winter montE-m

(see Figure 6).

The Redox Profile

The analysis of variance indicates that there are significant
differences in the redox potentials between horizons. The A horizon
of the Kalkaska site was lowest of all the horizons in the Kalkaska
profile except during the winter of 195k and 1955. Then the A2
horizon and the Bhir horizon were lower. At all tines the B11. and
the C horizons were significantly higher than the other three
horizons.

The redox profile suggests that ferrous iron, moving downward
in the percolating water from horizons of low redox potential, was
oxidized to ferric iron as it entered the region of higher redox
Potential. According to Latimer (38) the ferrous-ferric couple

as shown by the equation,
2 _
Fe -.-——- Fe 3 + s

has an Eh of -771 millivolts. Compared with the saturated calmel

82
electrode at pH 5.0 the Be would be -526 millivolts. The negative

sign means that the couple tends to go spontaneously to the left or
to the reduced side and that the couple tends to be more oxidizing

than the calomel electrode. In order to make the value positive the

equat ion should be reversed as follows.

Fe

11

Fe3+e

J.

This means that 5. large ...3"‘:"‘J31;, o

H:

energy is repaired t ~ reroxe the
third electron from the iron atom and suggests that some other
31001181113111 of oxidation of ferrous iron may be more important in
30118. The formation of water soluble iron-organic complexes tends
to reduce the amount of energy required to remove the third

electron (72), and would make the ferrous iron more susceptible to
easy Oxidation. The mechanism called valence induction described

by $0le (71) and lentioned by Bloomfield (5) would also cause

”’9 oJELdation of ferrous iron to take place more readily. Herkle

(5°) discussed the work by Peters (60) with ferrous and ferric

iron. According to this work, the Eh of the ferrous-ferric couple

1‘ 713 millivolts. Comparing with the saturated calmel electrode
‘ a pH 5.0 the Be of the ferrous-ferric couple would be 468 millivolts.
This Value is comparable to Latiner's value of -526 millivolts. It
“It." nunerically from Latiner's value because of the different

E0 “lines used and differs in sign because the conventions in the
Europe“ system were used by Peters. At the potentials observed

in the A and B horizons of the Kalkaska site, the ferrous-ferric

“me could have been operative there during most of the tins of

83
the study except for the winter of 195h-55. The sane couple could
have been operative in the A2 and BM, horizons in the Saugatuck
site. Potentials in the Bir horizon of the Saugatuck site were too
low for the ferrous-ferric couple to have been operating. Therefore
some other couples would have to be active. The oxidation-

reduction couple (38)

Fe(OH)2 + OH' : Fe(OH)3+ s
has an litc of 271. nv. at pH 5.0, or the couple

a 25'. 2 +608. : zre(on)3(s)

which has an Ec of 80 millivolts at pH 5.0 could have been operative
at lower soil redox potentials.

Under the aerobic conditions observed in the soil at the Kelkaske
and Saugatuck sites the Fe 22‘:- Fe(OH)3 couple cited above does
not detenine the Ec of the soil. In the presence of sufficient
twdroxyl ion, the ferrous iron content of the soil would be very
snall since it would tend to be converted quickly to ferric hydroxide.
According to the literature (51) this process could be inportmt at
pH values higher than 5.0. Under the conditions observed in the
soil at the Rosconon site the couple could be active in the week GB-l hen-
ison found there and this reaction any help to emlain the highly
mottled zone observed in many poorly drained soils. It also suggests
that soil redox potentials should be lower than 80 nv before the

gley process becomes strongly active.

 

*Calculated from the solubility products of Fe 2 and Fe(OH)3
using Latiner's convention.

84

According to Lattler (38) the ferrous-ferric couple tends to
go spontaneously in the direction of the ferrous ion. That is the
ferrous-ferric couple tends to be oxidizing under acid conditions. In
order for the couple to be reversed so that ferrous iron is converted
to the ferric state, a strong oxidizing force is necessary. 0n
the other hand, Mbrkle's (50) discussion indicates that the ferrous-
ferric couple could contribute to the Ec of the soil. In fact, at.
potentials approaching 600 millivolts, it indicates that the iron
would be 99% or better in the ferric state at pH 5.0. Under
conditions of good aeration in the soils at the Kalkaska and Saugatuck
sites such potentials were observed.

The strong oxidizing force required to drive the ferrous-
ferric couple to the ferric side could be provided by oxygen in
well aerated soils and also by the iron oxidizing organisms found
to be present in the Bir horizons of both soils in this study.

Manganese is commonly present in soils and is strongly oxidizing.
Manganese dioxide (MnOZ) is a common form of manganese in soils.

1'

Therefore, one fi-‘o‘fld e:-:pcct the -ollm'ing couple to be fictive.

Mnc2 + u~z++2e221~m 2 + rang-c
Compared with the calomel electrode and adjusted to pH 5.0, the
EC of this cell is ASS millivolts. This means that manganese is
also an important contributor to the redox potential in soils, and
since it is oxidizing by nature, it may determine the redox
potential of the soil at times and could provide an oxidizing force

£01“ irone

85
According to the results of the redox potential studies in the
soils at the Kalkaska and Saugatuck sites, the degree of aeration
is also important in determining the redox potential of the soil.
The effects of variations in aeration are also well demonstrated at
iho Tosconnon site. Tince oxygen is the important element concerned

all.

with aeration of soils, an oxygen couple may be important. The

following couple:
$02 + 2H+ + 2e ‘1‘ H20

has an Ec of 689 millivolts at pH 5.0.

This oxygen couple therefore falls within the range of the
redox potentials observed in soils and suggests that oxygen is also
an important contributor to the redox potential of the soil. Since
the omgen content of the soil varies widely as affected by the amount
of water present in the soil and the amount of carbon dioxide in the
soil atmosphere, this couple could be responsible for the high
potential: ohseyvcd in the soils during the period; of good aeration
and could accrunt for the wide changes ohnorved in the redox
potentials. This type of variability is closely related to climate
and microorganisms which are the active factors of soil formation
(32). The effects of these factors have been shown in Figure 11 and 12.

In this soil study, the redox potentials observed ranged from
aPPrOJdnately 750 millivolts on the positive side to --300 millivolts
on the negative side. According to Merkle (38) this is about the
normal range in soils. Oxidation-reduction couples which operate

outside of this range may not be operative in soils.

86

Therefore, the study of redox potentials can be useful in
serving as an aid to point out certain reactions which may be
operative in soils and which may determine the redox potential of
the soil at times. The evidence discussed here is inconclusive
and further studies should be carried out to determine the effects
of the oxidation-reduction processes that go on in soils and to
clarify the mechanics of the weathering processes involved in soil
genesis. They may be useful in soil fertility studies also.

In the soil profile, redox potentials are a measure of the inten-
sity of the oxidizing or reducing tendencies. The amount of material
in the soil that is oxidized or reduced depends on the magnitude of
the oxidizing or reducing force and the length of time that the
force is operative. It also depends on the amounts and kinds of
materials available, their chemical nature and the rate at which the .
redox reaction proceeds once it is initiated. This serves to explain
wl'w low redox potentials may be observed in a soil for a short time
with little effect on the soil characteristics as in the Saugatuck
and Kalkaska while low potentials present for long periods are
observed in soil profile characteristics as in the Roscomon site.
The amount of material oxidized or reduced can be measured with
a strong oxidizing or reducing agent. Since ondizabls and reduce-
:able materials are continually being added to the soil through
additions of organic matter and inorganic materials, and at the
same time other materials are being removed by leaching processes,
the measurement of the total amount of oxidizable or reduceahle

material by simple titration cannot be of much use. Rather, effects

on specific materials should be studied and measured periodically
to follow changes that occur. The change in redox potential as it
varies with changes in soil tenerature, moisture content of the
soil, aeration of the soil, and microorganisms can serve as a guide
to point out suitable dates for sampling.

Examination of Figure 13 shows that temperature affects the
redox potential of the soil. The absolute temperature factor in the
Nernst equation determines the effect of temperature on redox systems
being measured. According to mohaelis (52) this factor amounts
to about one millivolt per degree over the range of temperatures in
which this study was carried out and that it varies directly as the
temperature. In this study the temperature ranged from about 0°C to
30°C which would amount to about 30 millivolts and would tend to
overemphasise the redox potentials observed in the, soil at the
higher temperatures. This variation is within the limits of the
error term in the statistical analysis. The more important
effects of temperature is the indirect effect on the redox potential
through microorganisms and vegetation.

Exsmimtion of Figures 1. and 5 shows that the redox potential
of the A1 horizon of the soil at the Kalhaska site was significantly
lower than that of the underlying horizons. In addition, the redox
potential of the Bhir horizon was lower than the overlying A2
horizon and the underlying Bir horison. These results are due to
the effect of the organic matter in those horizons. The result could
be due to the activity of microorganisms (27) or to the formation
of ferrous or ferric complexes with organic complex forming

88
materials (51). According to Bloomfield (5, la) a large part of
the ferric iron was reduced to ferrous iron during the process of
caplex formation. If the ferrous-ferric couple was determining
the redox potential of the soil, one would expect the redox potential
to be lowered under such conditions.

If the reducing effect of the organic matter in the A1 horizon
was strong enough to cause reduction in the presence of oxygen to
account for the low potentials observed there, the mechanism could
operate in the B horizon under aerobic conditions and give rise
to high potentials. The thickness of the A2 horizon would then be
a measure of the intensity of reducing conditions in the A1 horizon,
and would vary with the kind of organic matter in the A1 horizon,
the activities of microorganim present in the A1 horizon, and the
effect of moisture which would be related to the micro relief. This
agrees with the observations of Lag and Einevoll (37). The degree
of development of the B horizon would be a function of the reducing
intensity in the A1 and A2 horizons, the amount of leaching, and
the amount of the sesquioxides present in the A horizons that were
susceptible to the mobilization process. Such a process would
lead to the developeent of an incipient A2 and 32 horizon in a
youthful soil; and a gradual developsent of both horizons downward
until equilibriun with the enviroment was reached. The soil
profile would then have reached maturity. This also agrees with
observation in the field (68).

The redox profile at the Saugatuck site is the reverse of the
one at the Kalkaska site. The observed potentials in the A1

89

horizon of the Saugatuck site are highest from April through August.
This correlates with the period of maximum growth of the vegetation.

In this site, the aspen feeding roots were concentrated in the A

horizon due to the impervious nature of the "ortstein", and the

presence of a high water table. In the Kalkaska site there was no

concentration of tree roots in the A horizon. This suggests that

the plant roots, by removing the water from the soil through

transpiration, were improving the aeration of the A1 horizon.
aeration caused oxidation of the reduced substances there and

The low potentials observed in the

Improved

raised the redox potential.
Biz- horizon were due to the high water table. Because of the
hardness of the ortstein in the Saugatuck profile, it was not poss-

ible to put electrodes into the C horizon. No results were therefore

obtained for the C horizon of the Saugatuck site. The low potentials
obsemd during the winter of 1951. and 1955 were probably due to
the cancess moisture, and during this time the redox potential of
A2 and BM, horizons dropped below that of the 31, horizon.

The characteristics of the soil profile at the Saugatuck site,
"‘1‘ such that they suggested a soil forming process similar to the
one at, the Kalkaska site. The redox potentials in the A1 horizon of
th’ Saugatuck were the highest observed in the profile. web
results suggest that the process of mobilization of sesquioxides
is "‘9 which can operate even under strongly oxidizing conditions.
“1° Process of iron-organic matter complex fomation could have
been in operation however and microorganisms were also active as

is
indicated by the experiment on citrate oxidizing organisms in

90
both the A1 and Bhir horizons. The degree of development of the Bhir
and Bir horizons suggest that more materials had been deposited
there than could be accounted for by the normal downward leaching
process.

In the spring of 1956, when the site was sampled for the study
of microorganisms there was lateral.movement of water through the
Bir horizon along a moisture gradient. This movement no doubt
occurred whenever the water table was high and could have contributed
to the accumulation of sesquioxides deposited in the B1, horizon.
Although the redox.potentials of the Bir horizon were lower than
those in the horizons above, conditions were still suitable for the
deposition of sesquioxides, since an ortstein had developed there.
The iron oxidizing bacteria may have been a contributing ‘
factor.

The analysis of variance of the results from.the Roscommon site
indicate that only the C and 862 horizons were significantly
different from.the other horizons. Since these horizons were the
deepest in the profile, they were probably affected longest by the
.high water table. The upper horizons were affected'hy oxidizing
conditions for some of the time during the sulmner months. The
higher potentials observed during the winter of 1953 and 1954 were due
to the lack of exeess moisture which was pointed out in the discussion
on rainfall. In both summer seasons the potentials tended to rise
as the soil aeration improved. The lowest potentials were observed
during the month of June. This time corresponds to the season when

'the temperature and moisture conditions favored the activities of

a ‘ ‘5'.._.'n.

91

microorganisms. In the case of the Rosconmon site anaerobic
conditions were dominant and strong reduction occurred, while at
the Saugatuck and Kalkaska sites, aerobic conditions prevailed and

the redox potentials rose.

The oxidation-reduction systems in the soil which are dependent

on the aeration status of the soil and are important in soil ; 3

fertility, must change their oxidation state as the redox potential
of the soil changes with conditions of climate and drainage. The
use of drainage, irrigation and other management practices which help i j
to control the redox potential of the soil are thus important in .-_-_-
soil fertility. The importance of organic matter in changing the

oxidation state of the soil constituents has been established.

However, very little is known about the organic redox couples that

may be important in affecting the redox state of the soil. An

effort should be made to discover the nature of such couples.

92
SUMMARY AND CONCLUSION

A technique was devised for the measurement of redox potentials
in the soil in all seasons of the year. Using this technique the
change in oxidation-reduction status of Kalkaska, Saugatuck and
Roscomon series, a hydrosequence of soils, was followed for a
period of two years extending from September 1953 to August 1955.

It was established that the variation in redox potential with time
correlates with the moisture content of the soil and with the
prevailing air temperature prior to the tile of the measurements.

A more exact comparison would no doubt be obtained by measurement

of soil temperature. It was also established that there is a redox
profile in the soil which is related to the soil horizons. Conditions
were oxidising for iron in the B horizons of Kalkaska and Saugatuck
in all seasons, but were not for the Rosco-Ion series. A study

of the distribution of citrate oxidizing microorganisms in the
profile of the Kalkaeka and Saugatuck series was carried out.

Mic reorganisls capable of oxidizing ferrous iron to ferric hydroxide
have been isolated from the Eu horizons of the Kalkaska and
Saugatuck series. The data suggest that iron oxides may be mobilized
by reduction and the formation of organs-metallic couplers in the

A horizons of podsols and that the complexes may be decomposed by
microorganisms there, releasing the ferrous or ferric iron into
solution. The presence of the redox profile indicates that the
ferrous iron was oxidized in the B horizon and there precipitated

or adsorbed by the ferric hydroxide already present and then
oxidized by the process of valence induction as suggested by

93
Bloomfield (12). These results do not eliminate the possibility

that movement of sesquioxides in colloidal form such as clay
hunates, or as clay iron complexes, takes place and that they can
be precipitated at the isoelectric point of the colloids. It is
concluded that several processes including the washing of dispersed
clay particles downwards by percolating waters may be active in the

developent of podzol B horizons.

 

 

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(2)

(3)

(A)

(5)

(6)

(7)

(8)

(9)

(10)

94
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SChnitzer, Me am Debug, We A.
Investigations on the mobilization and transport
of iron in forested soils II The nature of the
reaction of leaf extracts and leachates with iron.
Soil Sci. Soc. Am. Proc. 19 (No.3): 363-368 (1955).

SChflitvzer, I'Ie and Wright, Je Re
Note on.the extraction of organic matter from
the B horizon of a Podzol soil.
Can. Jour. of Agr. Sci. 36: 511-512 (Nov. 1956).

Selwood, P.w.
Valence Inductivity
Jour. Am. Chem. Soc. 70: 883 (1948).

(72)

(73)

(7h)

(75)

(76)

(77)

(78)

(79)

(80)

101

311571318, CeVe .
The mechanism of iron catalysis in certain

oxidations.
Jour. of Bio. Chem. 90: 251-265 (1931).

Smythe, C.V. and Schmidt, C.L.A.
Studies on the mode of combination of iron

'with certain proteins, amino acids and relative

compounds.
Jour. Bio. Chem. 88: 241-269 (1930).

Sowden, Fe Je
Estimation of amino acids in soil hydrolysates
by the Moore and Stein method.
Soil Sci. Vol. so (No. 3): 181-187 (1955).

Starkey, R.L.
Transformations of iron by bacteria in water. i
Jour. of Am. Waterworks Assoc. 37 (No. 10: 963-984 (1945).

Starkey, R.L. and Halvorson, 3.0.
Studies on the transformations of iron in
nature. II Concerning the importance of
microorganisms in the solution and precipitation of
iron.
Soil Sci. 24: 381-AC2 (1927).

Starkey, R.L. and Wight, K.M.
Anaerobic corrosion of iron in the soil. Final
report of the American Gas Association iron
corrosion research fellowship.
New Jersey Agr. Exp. Sta. New Brunswick, N. J.

Stevenson, R.E. et a1
Oxidationpreducticn potentials in Oregon Orchard
soils.
Jour. Am. Soc. of Agron. 30: 91,96 (1938).

Sturgis, M.B.
Changes in redox.equilibrium in soils as related to the
physical properties of the soil and the growth of rice.
Lae Agr. Exp. Stae 311.13th 271 (1936)e

Tenney, F.C. and waksman, S.A.
Composition of natural organic materials and their
decomposition in the soil: V. Decomposition of
various chemical constituents in plant materials
under anaerobic conditions.

Soil Sci. 30: 113-160 (1930).

(81)

(82)

(83)

(81:)

(85)

(86)

(87)

(88)

(89)

(90)

102

Volk, N.J.

The oxidation— reduction potentials of Alabama
soils as affected by soil types, soil moisture,
cultivation, and vegetation.

Joure Alfie $Ce Agrone 31: 577‘589 (1939)e

The effect of oxidation-reduction on plant growth.
Joure Alfie &Ce Agron. 31: 665-670 (1939)e

The determination of redox potentials of soils.
Jour. Am. Soc. Agron. 31: BAA-351 (1939).

Whiteside, E.P., Schneider, I.F., and Cook, R.L.

Soils of Michigan.
Michigan Agr. Exp. Sta. Special 3111. 1.02 (1956).

Wilde, S.A., Trach, J. and Peterson, S.F.

Willis,

Electro chemical properties of ground water
in major types of organic soils.
Soil SCie &Ce Amp PrOCe 1‘}: 279-281 (19h9)e

LOGO

Evidences of the significance of oxidation-
reduction equilibrium in soils.

Sci1 Sci. Soc. Am. Proc. 1: 291-297 (1936).

(bridation- reduction potentials and the hydrogen ion
concentration of a soil.
Joure Of Agre R88. 1&5: 571‘575 (1932)e

Winters, E.

Wright ,

Ferro manganiferous concretions from some podzol soils.

Soil Sci. 1.6: 33-40 (1938).

JeRe m LOViCk, Re

Developnent of a profile in a soil column leached
with a chelating agent.

Sixieme Congress de la Science du Sol Paris 1956.

Bromfield, 8.1!.

The reduction of iron oxide by bacteria.
Jour. of Soil Sci. 5 (so. 1): 129-139 (1954).

APPENDIX

pH

 

 

 

 

{I ..

I00 200 300 400 500
Eh(mv)
7° KALKASKA SAND '

 

Ilr

8.0 ——

 

 

 

 

0 AI
4.0-.— 0 AG __
A 83
O C
l l 1
IOO zoo soo soo soo
Eh (mv)

ROSCOMMON SAND

7.0

 

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a ‘3
0A.
0A2
4.0)— A BHIR 1 __
As":
e c
{ l 1 1
too zoo see coo goo
Eh(mv)

SAUGATUCK SAND

FIGURE l4
Eh-pH CURVES
FOR
KALKASKA,SAUGATUCK
AND ROSCOMMON SAND
BY HORIZONS'

105

 

 

 

 

 

 

Table 9 Mechanical Anaxysis
Percent Composition by Separates
Soil Series Horizon 2- 1.0— 0.5- 0.25- .105. .05- Total
1.0 0.5 0.25 .105 .05 .002 .002
KaIkESka A1 0e26 10e12 33ell§ h2e18 #69 6eh2 3.19 100
A2 0.26 9.66 34.96 49.83 2.70 1.49 1.10 100
Bhir 0.27 6.46 30.75 58.20 1.57 2.75 100
Bir 0.14 4.55 30.30 61.40 2.41 1.31 100
C 0.20 3.23 18.8 73.0 4.17 0.42 100
Saugatuck 0e13 6e]. 190165 “060 6e95 18e% 4.0 100.13
A2 0.32 3.55 26.0 58.80 7.19 3.69 0.46 100
Bhir 0.25 12.13 40.5 37.12 2.66 4.08 3.30 100
Bir 0.04 0.84 2.97 49.80 38.30 7.35 0.69 100
C 0.02 0.62 12.72 82.4 3.15 1.11 0.03 100.1
Roscommon A 0.23 5.46 16.05 49.20 9.18 6.13 3.87 100.1
GA-1 0.58 11.50 25.10 54.80 3.55 3.21 0.94 99.7
GB_1 0.77 13.10 32.80 43.70 4.49 3.75 1.12 99.7
GA_ 0.17 8.20 33.10 55.40 1.74 1.23 0.43 100.3
GB__~ 0.04 1.50 3.18 53.70 36.75 4.20 0.52 100
GB_3 0e06 3e27 13e20 69e50 9.4.0 2e86 le52 99e8
C 0.07 16.0 50.0 33.0 0.51 0.57 0.26 100.4

 

 

 

 

 

 

 

 

 

 

 

 

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109

 

 

 

Type of Block Moisture by Dates (Ohms x 1000)*
and Inches

Soil Series Horizon Depth 1-16 3-6 4-10 5-1 6-28 8-20 11-20 12-31
Kalkaska A1 5 -- 1.59 1.52 1.05 0.97 2.07 - 1.74
A2 12 -- 1060 1056 1022 lo08 1054 -" 1074
(Plaster of Bhir 18 -- 1.44 1.50 1.27 1.10 3.65 -- 1.88
PariS) 811' 28 -- 1052 1055 1036 1016 1033 "‘ 3400
C 44 -~ 1.56 1.68 1.50 1.27 1.26 1.52 1.70
Saugatuck A1 5 120.0 350.0 6.43 4.05 4.70 80.00 2.92 6.75
A2 8 84.0 8.55 5.46 4.01 5.00 8850 3.67 5.20
(Nylon) Bhir 12 79.0 14.112.90 9.05 6.71 90.00 5.54 550.0
Bir 20 6403 3099 1075 6003 4015 32.40 3056 3090
C 42 34.5 1.56 1.81 1.29 3.15 7.90 1.26 1.48
Roscomnon A1 3 6.22 0.84 1.18 0.92 0.97 20.0 1.22 1.58
GA__1 9 lulu-0 0.81 1.02 0.87 1.08 21.6 0.99 1.38
(Nylon) GB_]_ 15 3.26 1.50 1.95 1.11 1.10 4.20 1.78 2.14
C 36 0.56 0.77 1.26 1.06 1.27 1.11 1.11 1.50

 

 

 

 

* For nylon blocks these readings have approximately the follow-
ing meaning:

1.

2.

3.

Dry 3 over ten thousand ohms (less than 2% moisture
by weight.)
Moist = under ten thousand and over twelves hundred
ohms (2 - 7% moisture by weight)
Wet :- less than twelve hundred ohms (saturated with
water)

Table 13 Change in Resistance of Bouyouoos

Moisture Blocks with Dates in Kalkaska ,

Saugatuck and Roscommon Sands

 

110

 

 

 

Ec (Volts)

Element Redox Couple at pH 5.0
Iron 22.3 1 23g v 201'.“ 2: 23.2.4- 332012 .526
2Fe(OH)2+ 2014- + ngmzf,‘ Fe(OH) + 2H3 4—201- .271.
2Fe 2+ 60H” + 11320125 , Fe(OH)3 4 2H3 4 201- .080
Manganese 233 + 201‘ '-;- 141102 + an“ r ,4 \In 2+ 2H20 + 1132012 .495
Omgen 23.3 4 201' 4— $02 + 211* t @2012 + H20 .689

 

 

 

 

Table 11,; En! of Spontaneous Oxidation
or Reduction Reactions with the
Saturated Calomel Electrode at pH 5.0
from Latimer and De Vries

Table 15 Weather Data from Cadillac Weather Station

 

 

 

 

Mbnth Date of Redox Mean Temp. Rainfall Dep. from Nbrmal
Determination 2 Wke. before (Inches)
Reading
September 11 65 3.16 ~0.5h
October -- -— 1.20 -1.56
November 5 22 1.26 -1.43
December 1h 28 1.55 -0.12
February -- -- lo 86 0. 27
M‘I’Ch 6 16 1. 62 “‘00 30
April 10 50 5.13 2.68
MEy 1 65 3.00 ~0.02
June 28 61 7o 23 [#013
Juxy -- -- 2.99 0.32
August 20 59 0.65 -2.25
September -- -- 4.27 0.57
OCtObel' -~ -- 6.158 30 72
November 20 35 1.46 -l.23
December 31 23 1.53 -0.lh
January -- -- 1.18 -0.52
February 19 28 0.98 -O.6l
March ~- -- 1.36 0.56
May —- -- 2. M -0. ‘58
June I. 68 1. 67 4.1.).
July -- -- 4.63 1.96
August 10 . 68 1.29 -l.6l

 

 

 

 

 

 

 

 

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