GENESIS OF A PODZOL SEQUENCE ON THE WEST COAST OF VANCOUVER ISLAND
by
SEEWANT BHOOJEDHUR
B.S.A., The University of British Columbia, 1968
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE
in the Department
of
SOIL SCIENCE
We accept this thesis as conforming to the
required standard.
THE UNIVERSITY OF BRITISH COLUMBIA
September 1969 ii
ABSTRACT
A study was undertaken on the pedogenesis of a Podzol sequence of soils on the West Coast of Vancouver Island. The area is one of abundant rainfall and rather luxuriant vegetation. The soils occur on relatively level topography (glacial fluvial deposits) and have varying degrees of development of placic (pan) horizons. The objectives of the study included characterization, classification and genesis of the soils, based on physical, chemical and mineralogical investigations.
Four soils were chosen for the study. Three of the soils comprisedfhe Ucluelet soil series, while one soil was a member of the
Wreck Bay soil series. The soils were described morphologically, sampled and selected analyses were performed on the major genetic horizons. More detailed analyses, including differential thermal analyses, were conducted on the placic materials.
The soils were classified into the Canadian Classification Scheme as as follows:
Ucluelet I Placic Ferro-Humic Podzol Ucluelet II Orthic Humo-Ferric Podzol Ucluelet III Placic Humo-Ferric Podzol Wreck Bay Gleyed Placic Ferro-Humic Podzol
Analyses of the placic materials indicated, that although the material appeared vitreous in the field, no crystallinity could be deterntined by X-ray diffraction. It appeared that the major component of the placic horizon is composed of iron and organic matter, probably in some intimate association. It was observed that the placic horizon could form in materials of initially low iron contents. iii
From the foregoing observations the following chronosequence of soil development appears to be justified:
Orthic Humo-Ferric Podzol > Placic Humo-Ferric Podzol (Ucluelet II) (Ucluelet III)
> Placic Ferro-Humic Podzol •> Gleyed Placic Ferro- (Ucluelet I) Humic Podzol (Wreck Bay)
The differences in pedogenic age of the three Ucluelet sites can be attributed to degrees of "churning" by the trees at these sites. iv
In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission may be granted by the Head of the Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.
Department of ( cP
The University of British Columbia, Vancouver 168, B.C, Canada.
Date 3vA /9i? V
ACKNOWliBGMENTS
The study was made possible by a scholarship awarded by the
Canadian International Development Agency. Particular acknowledgment is offered to Dr. L.M. Lavkulich, Assistant Professor, Department of
Soil Science for suggesting the nature of the research, for assistance, encouragement and supervision during its progress.
The author wishes to express his gratitude to the members of the Ctommittee and the members and staff of the Department of Soil
Science. Thanks are extended to members of the Soil Survey Division,
Canada Department of Agriculture, Vancouver. vi
TABLE OF CONTENTS
Page
INTRODUCTION
LITERATURE REVIEW 1
MATERIALS AND METHODS 22
RESULTS AND DISCUSSION 38
CHARACTERIZATION OF PLACIC MATERIAL 77
SUMMARY AND CONCLUSIONS 84
REFERENCES 88 vii
TABLES
TABLE PAGE
I Profile Description of Site I 30
II Profile Description of Site II 31
III Profile Description of Site III 32
IV Profile Description of Site IV 33
V Selected Physical Properties of the Ucluelet
and Wreck Bay Series 40
VI Selected Soil Water Parameters 43
VII Selected Chemical Data 51
VIII (a) Selected Extractable Constituents 54
VIII (b) Selected Extractable Constituents 55
IX Cation Exchange Properties 61
X pH-Dependent Cation Exchange and Lime Potential 63
XI Elemental Analysis on the <2 mm soil 65
XII Elemental Analysis on the <2 u Clay Fraction 66
XIII Mineral Distribution in the Ucluelet I Soil 70
XIV Mineral Distribution in the Ucluelet II Soil 71
XV Mineral Distribution in the Ucluelet III Soil 72
XVI Mineral Distribution in the Wreck Bay soil 73
XVII Selected Chemical Comparisons of the Composition of the Pan to the Soil Matrix 80 viii
FIGURES
FIGURE PAGE
1 Vegetation and Soil at the Ucluelet Site 23
2 Vegetation and Soil at the Wreck Bay
Site 24
3 Water Retention Curves for Ucluelet I 45
4 Water Retention Curves for Ucluelet II 46
5 Water Retention Curves for Ucluelet III 47
6 Water Retention Curves for Wreck Bay 48 7 Total Water Storage Capacity for the Ucluelet (Sites I-III) and Wreck Bay (Site IV) 49
8 Photographs of Placic Material at a Ucluelet Site 79
9 Differential Thermal Curves of (1) Ucluelet Pan and (2) Wreck Bay Pan 82 i INTRODUCTION
Research in pedology facilitates an understanding of soil properties and therefore is important in developing sound land use practices.
Many pedological studies of Podzol soils have been made, particularly in coastal regions of Eastern and Western Canada, and some of these have had iron pans present. On the. west coast of
Vancouver Island, there are extensive areas of Podzol soils that have not been studied in any detail. These Soils are heavily forested and some have iron pans present which are known to affect land use and plant growth. This study is concerned with several of these soils.
The soils studied occur on the Ucluelet lowland and the objectives of the work were:
1. To determine selected physical, chemical
and mineralogical properties of four soils.
2. To classify the soils in the Canadian System
3. To correlate the above results with develop•
ment of these soils.
U. Attempt to relate the soil properties to
plant growth. LITERATURE REVIEW
The modern concept of soil as a natural body was not recognized until 1879 when Dokuchaev became the first to appreciate the complexity of natural agencies responsible for the processes of soil formation, and when Sibertsev integrated these natural agencies and established their
differential role in soil formation. Prior to Dokuchaev, credit must be
given to pioneer soil scientists like Berzelius, Liebig, Thaer, Davy and Schubler for their views on soil as a medium for plant growth; to the geologists, Sprengel, Hausman, Gotta, Werner and others who though recognizing some of the soil forming agencies, failed to recognize the harmony of these factors in building up the soil; and finally, to
Fallou (1855) who stressed his point of view that soil is a formation by
itself and is not simply unconsolidated rock.
Podzol as a kind of soil
Podzol soils are prevalent under cool and humid conditions with an annual rainfall varying from 50 to 75 cm and a mean annual temperature of about 4°C. Podzols cover the largest habitable area of the earth's surface (Joffe, 1949); extending from the sub-arctic region through the temperate zone, to a few degrees north of the
Mediterranean region in Europe, to about the 50° parallel north latitude in Asia and North America. They are generally freely-drained, acid,
sandy soils with strongly differentiated profiles. They do not seem to develop in soils that are saturated with water throughout the year.
The natural vegetation may be heath, woodland or coniferous forest.
Podzols are not confined to cool temperate regions, but, are also found in the tropics at high elevations, where climatic conditions tend to become similar to temperate regions. - 2 -
The name 'podzol' originated from the Russian word 'Zola" which means ash. Long before the true nature of podzols was characterized, the bleached layer just below the surface of the soil was observed and reported. Sprengel in 1837 gave a description of what is now known as a podzol. Scandinavian and German foresters of that time also noted and described podzols-, but it was Dokuchaev who revealed the genetic relationships of the soil horizons in the profile and introduced the term 'podzol' based on his experiences and comprehensive field and laboratory investigation of virgin and cultivated soils of Russia.
Extracts from the cartography of Russian soils (Dokuchaev, 1879), show that the term 'podzol' was confined to the ashy grey layer without any reference to what was below. These soils were found in areas with abundant rainfall and an abundance of both forests and bogs. In the
second soil classification of Dokuchaev in 1900 (Soil Survey Staff
1960) podzols were classified under normal soils. It was Sibertsev
(1900) who separated the podzols as a special type, equivalent to the U.S.A., 1949 Great Group and sub-types, the latter being:-
"(1) Soddy soils, weakly affected by podzol forming
processes,
(2) Podzolic soils proper, with a podzolic horizon clearly
separated and sharply distinct from the upper horizon
(3) Podzols or soils strongly "podzolized"
While the Russians related their observations to the effects of climate, vegetation and parent material, the Germans diverted most - 3 - of their attention to a special formation, the ortstein. Consequently knowledge from the two schools was not synchronized and thus the
Western world could not characterize the group.
With time, knowledge spread and workers in North America,
Britain, and France started to intensify their contributions. Marbut
(Soil Survey Staff, 1960) classified the podzols under the order of
Pedalfers. During the 1930's, the outlook towards soils changed drastically as soil scientists started to look deeper into the chemical, physical, mineralogical and micromorphological properties of soils. These scientists integrated laboratory data with field observations to differentiate among groups of soils; and, thus in
1938 Baldwin et al. (Soil Survey Staff, 1960) suggested the following Great Soil Groups which comprised the podzols:
Podzol soils
Gray wooded or gray podzolic soils
Brown podzolic soils
Gray brown podzolic soils
Red yellow podzolic soils.
Muir (1961), after reviewing the Russian literature, stated that the Russians recognize about twenty sub-types and varieties of podzolic soils. In his summary, Muir attempted to correlate the main features of the podzols as follows: 4 -
RUSSIA W. EUROPE AND N. AMERICA
Sandy podzolic soils Iron-or iron-humus podzols
Sandy podzolic soils with Iron-humus or humus podzols illuvial humic horizon
Podzolic soils Sols 'lessives' or sol podzoliques
Podzolic soils with Molkenpodzol illuvial humic horizon
Sod-podzolic soils Bleached Parabraunerde, Pseudo Gleys or Gray-wooded soils
In 1960, the Soil Survey Staff of the United States
Department of Agriculture presented a comprehensive soil classification
system based on the degree of development of the soil as affected by external factors. In this classification what formerly were known as ..
soils of the podzolic group fell into three orders. Those with an argillic horizon, i.e. the Gray-brown podzolics and Gray wooded soils are in the order of Alfisols; those with a spodic horizon, namely, the Podzols, Brown-podzolics and Ground-water podzols in the order of
Spodosols; and the Red-yellow podzolics in the order Ultisols.
The French classification (Duchaufour, 1962) (which is based mainly on the intensity of profile development, type of humus and
degree of wetness) is similar to the U.S.D.A. Comprehensive system with regard to the separation of the Gray-brown podzolics and the Gray-
wooded soils from the group of podzols and their insertion under sol
lessives.
The 1968 Canadian Classification is closely linked to that
of the U.S.A. From the report of the sub-committee on the - 5 - classification of podzolic soils, by Stobbe (1968), the podzolic order is divided into Humic, Ferro-Humic and Humo-Ferric Great
Groups. The division is based on the degree of development of the
Bh, Bhf, Bfh or Bf horizon. The Great Groups are again subdivided
into sub-groups predominantly on comparative thicknesses of horizons or degree of development and, any special formations present, for example, pans.
Clayton (1968) made the following taxonomic correlation between the Canadian, American and World systems at the Order,
Great Groups and Sub-group levels. CANADIAN AMERICAN WORLD ORDER Podzolic Spodosols Podzols
GREAT A. Humic Podzol a. Cryohumods Humic and Placic GROUPS: Bh b. Haplohumods Podzols B. Ferro-Humic Podzol a. Humic Cryorthod Humo-Ferric Ae, Bhf b. Humic Haplorthod Podzol C. Humo-Ferric Podzol Cryorthod or Humo-Ferric Bfh or Bf Haplorthod Podzol
SUB• GROUPS:!. Orthic Humic Podzol a. Cryohumod Humic Podzol Bh b. Typic Haplohumod A 2. Placic Humic Podzol Bh, Bf Placohumod Placic Podzol 3. Gleyed Humic Podzol Aquichumod Gleyed Podzol
1. Orthic Ferro Humic a. Humic Cryorthod Humo-Ferric Podzol Ae, Bhf b. Humic Haplorthod Podzol 2. Mini Ferro-Humic Haplic Humic Humo-Ferric Podzol Aej_, Bhf Cryorthod Podzol B 3. Sombric Ferro-Humic Umbric Humic Humo-Ferric Podzol Ah, Aej, Bhf Cryorthod Podzol 4. Placic Ferro-Humic (Humic) Placorthod Podzol Placic podzol Ah, Aej, Bhf, Bf 5. Gleyed Ferro-Humic Aquic Orthod Gleyic Podzol Podzol - 6 -
CANADIAN AMERICAN WORLD
1. Orthic Humo-Ferric Typic Cryorthod Humo-Ferric Podzol or Haplorthod Podzol Ae, Bfh or Bf 2. Mini-Humo-Ferric Haplic Cryorthod Humo-Ferric Podzol Podzol Aej 3. Sombric Humo- Umbric Haplorthod Humo-Ferric Ferric Podzol Podzol Ah C 4. Placic Humo-Ferric Placorthod Placic Podzol Podzol Bfh, Bf, BC 5. Bisequa Humo- Boralfic Cryorthod Humo-Ferric Ferric Podzol or Alfic Haplor- Podzol thod 6. Gleyed Humo- Aquic Orthod Gleyic Podzol Ferric Podzol 7. Cryic Humo-Ferric Pergelic Leptic Humo-Ferric Podzol Cryorthod Podzol
Processes in the Formation of Podzols
Joffe (1949) in his review of the literature prior to 1949 on "podzolization" remarked on the emphasis Russian workers like
Dokuchaev, Sibertsev, Glinka, Williams, Kossovich and others placed on the role of organic and mineral acids in the process of
"podzolization". At that time it was believed that crenic acid
(which has never been .isolated) was the main agent responsible for the formation of podzols. They recognized the decomposition of organic matter, loss of bases, iron, manganese, and aluminium from the surface mineral horizon and the breakdown of mineral components.
Very few of the early scientists recognized the B horizon as an illuvial horizon because their concept of podzol formation was the presence of an eluvial horizon (Ae). - 7 -
Gedroiz theory (1926) on "podzolization" was based on cation exchange reactions between hydrogen ions from soil water and the soil colloids. In his opinion, as soon as the hydrogen ions displaced the bases from the soil complex, that part of the unsaturated soil complex disintegrated; consequently, the humates as well as the silica, iron
and aluminium oxides were carried downwards. Rode (1937) focussed attention mainly on the transformation of the primary and secondary minerals in the "podzolization process". However, no one gave a concrete statement as to what is meant by the term "podzolization". although
Joffe (19U9) described it as:
1. Depletion of bases from the A horizon, followed by sesquioxides'and clay particles entering into circulation and moving downward to accumulate in the profile forming the B horizon.
2. Retention of some of the alkaline earth bases which in turn enhance the precipitation of sesquioxides by the soil colloids.
In another separate statement, Joffe postulated that conditions due to the depletion of bases and unsaturation of the exchange complex, bring about the breakdown of kaolin with the release of SiCX,. He concluded by suggesting that the balance between the incoming and outgoing of bases, apart from the nature of the parent material and vegetation, determined the degree of "podzolization", and on a morphological basis, the degree of "podzolization" depends on the intensity of the ash-grey colour of the eluvial horizon. - 8 -
Since then many papers have appeared leading to much con• fusion in the literature. Stobbe and Wright (1959) made the point that:
"The terms 'podzolization process' and 'podzolization'
are often used as general terms for the overall reactions
and processes which have resulted in the formation of
podzols. Recently, these terms have been associated by
some workers, more specifically with those reactions which
are involved in the movement and accumulation of
sesquioxides and organic matter, features which are closely
associated with the morphology of podzols".
The term "podzolization process" as described by
Franzmier and White (1953) from their work in Northern Michigan on a podzol from sandy soil may be summarized as:
1. Additions of organic matter begins.
2. Carbonates are dissolved and the reaction
products are removed.
3. Basic cations in the A2 (Ae) horizon are replaced
by hydrogen ions and a pH gradient is established
between the A2 (Ae) and podzol B horizons.
4. The absence of the neutralizing effect of bases in
the A2 (Ae) makes it possible for organic acid
solutions to dissolve primary phosphatic minerals
in this horizon and transport the soluble products
to the B horizon where they are precipitated,
probably as aluminium phosphates. - 9 -
5. Weathering of minerals such as primary or altered
ferromagnesian minerals, altered feldspars and base
containing clay minerals (illite and chlorite) in
the A2 (Ae) horizon releases cations such as Fe, Al,
K and Mg. The sesquioxides are transported to the
B horizon where they are precipitated, probably with
small amounts of silicate clays, on the surface of
sand grains as thin, somewhat crystalline, weakly
birefringent coatings.
6. When there is sufficient concentration of metals in
the B horizon to provide enough active metallic ions
to saturate most or all of the functional .groups of
the percolating humus solutions, the humus is
immobilized as amorphous coatings on the outside of
the slightly crystalline rims around the sand grains.
This results in a marked segregation of organic
carbon into horizons. Aluminium phosphates may be
converted to iron phosphates or other related forms
during this time.
7. The amount of clay in the upper part of the soil
increases and this clay is segregated into horizons
in the podzol sequum. The clay in the B horizon
becomes embedded in the dark, reddish brown, amorphous
coatings around sand grains. - 10 -
8. Coatings on skeletal grains increase in thickness by
additions of sesquioxides, humus and clay. They
eventually flake off the grain to occupy previous
intergranular space as aggregates or pellets of coarse
silt to very fine sand size (0.02 to 0.1 mm in
diameter). The layer in which the pellets are formed
becomes the Bh horizon, a thin layer having a low
bulk density lying beneath the tongued A2 (Ae) horizon.
The development of the Bh horizon causes an increase
in the available water and nutrient supplying power
of the soil, which may be correlated with a change in
vegetation from a pine association to a maple beech
association.
Stobbe and Wright (1959) believed that unsaturation of the upper horizon is a conditioning process for "podzolization". This process takes place relatively rapidly when the parent material is coarse-textured, acidic and of low base status. They postulated that on basic parent materials this unsaturation may be slow and may involve other reactions; namely, the removal of the free lime or salts which brings about dispersion of the clay with consequent downward movement and .eventual flocculation. This latter mechanism may apply in the case of some podzolic soils in which horizons of clay accumulation are the major illuvial horizons and consequently may be the conditioning process of the parent material for "podzolization". - 11 -
Duchaufour's (1965) concept of "podzolization" is a specific process and is a 'climax'. * He contends that "podzolization" results from:
1. Intensive acidification of the humus (Mor), with the
liberation of large quantities of soluble or pseudo-
soluble organic compounds which move downwards. There
are two classes of such compounds: (a) free fulvic
acids which migrate in the podzolic soils and podzols.
(b) humic acid polymers which accumulate in the
horizons of humus and iron-humus podzols.
2. These dispersed or soluble organic compounds not only
reduce the level of free iron in the A horizon, but
also chemically degrade the minerals, with consequent
liberation of free Al and Si. The Fe and Al form
soluble organic complexes which resist microbial
attack are finally carried down.
3. Finally, the A2 (Ae) horizon of a typical podzol
contains a low percentage of clay minerals. The
water soluble silica as well as colloidal silica
migrate into the B horizon. There is the possibility
that oppositely charged colloidal silica and aluminium
co-precipitate and give rise to allophane which may
eventually evolve to micro-crystalline form and then
to a clay mineral of neo-formation. - 12 -
Before dealing with the present opinion that "podzolization" is mainly the sum of the reactions that involve movement and accumulation of sesquioxides and organic matter, it is imperative to review the modern concepts of soil genesis.
Simonson (1961) stated that soil genesis consists of two overlapping steps:
1. The accumulation of parent materials
2. The differentiation of horizons in the profile.
Without imdermining the relative importance of parent material, it is the second step that is more directly involved.
Horizon differentiation can result from four kinds of changes; namely, additions, removals, transfers and transformations in the soil system. These changes occur in all soils. Each change per se is a function of many variables, and, if one thinks in mathematical terms, then there are an infinite number of combinations that can occur. Consequently there would have been an infinite number of soils; but as only a finite number of soils are recognized, one must conclude that only a limited number of combinations, exist and are expressed morphologically by horizon differentiation. The ultimate character of the soil will depend on the combination of variables that , predominate. This concept is important in the study of soils, as one can predict development of a soil if the mechanisms of the pre• dominating reactions are known.
At this stage,therefore, it seems appropriate to look into the theories leading to the movement and accumulation of sesquioxides and organic matter in a typical podzol. T 13 -
Movement and accumulation of organic matter and sesquioxides
There are two main theories for the removal and transfer of sesqui-oxides from the A to the B horizon. The pioneer work on both theories dates as far back as the early 1900's. One theory postulates movement as colloidal sesquioxides, whereas the other suggests movement as organo-metallic complexes. Mattson's theory (1938) states that the sesquioxides move downwards as sols and as complexes; and, when they attain their iso-electric points, get deposited in the B horizon. Stobbe and Wright (1959) argued that this theory cannot be substantiated, owing to the fact that no significant pH gradient exists between the A and B horizons in podzols.
Deb (1949) suggested some possible modes of movement of
Fe and evaluated each of them:-
1. A trivalent inorganic cation.
2. A divalent inorganic cation.
3. A positively charged iron-oxide sol.
4. A negatively charged silica protected iron-
oxide sol.
5. A negatively charged humus protected iron-oxide.
6. A complex organic ion.
The solubility of ferric ion above pH 3.5 is very low.
Under normal conditions in the absence of waterlogging, the ferrous ion in soil is rapidly oxidized to the ferric form and precipitated.
If the soil is saturated with water and under anaerobic conditions ferrous ion may migrate in the soil solution. - 14 -
The movement .as a positive iron-oxide sol associated with alumina and humus cannot be supported as no podzol soils have an A horizon that is positively charged (Deb, 1949).
The movement of iron as silica protected iron-oxide sol was also discounted,because at low pH values there can be little peptization by .silica (Deb, 1949).
Work on the movement of iron as a negative iron-oxide sol protected by humus was first initiated by Aarnio (1913), based on a series of experiments on the role of organic matter in the precipitation of Fe and Al in podzol soils. He investigated what amount of humic extract was needed to coagulate Fe and Al. His work, however, did not entail the study of the effects of concentration, pH and types of humus. Deb (1949) pursued this omission and concluded that:
"The amount of humus required to peptize iron-oxide sol
varies significantly with the source of humus, the
concentration and the pH of the iron-oxide sol".
He could not find evidence to support, (1) the effect of calcium in the precipitation of the humus protected sols in the B horizon; and (2) the chemical precipitation of complex salts of iron and organic acids. He suggested, therefore, a mechanism involving microbial action for precipitation of Fe in the B horizon.
There seems to be growing support for the alternate theory that sesquioxides move as soluble metallo-organic complexes,
(Broadbent, 1957), Levesque and Schnitzer (1967), Schnitzer and
Skinner (1963, 1964, 1967), Levesque and Hanna (1966), Mortensen
(1963), Delong and Schnitzer (1955), Bloomfield (1951, 1952, 1953, 1954)
Atkinson and Wright (1957), Van Schuylenborgh (1962). - 15 -
Bloomfield (1953) found peat to be an ineffective agent in causing dissolution of ferric oxide. Consequently he considered the plant material not remaining in the plant residue. He studied extracts of certain plants which are associated with podzols, and found that leaf extracts solubilized the ferric and aluminium oxides non- biologically; and,that both solution and reduction can take place under neutral and aerobic conditions. From further studies, he suggested that the extent of sorption of ferrous organic complexes may play an important role in the effectiveness of a particular species as a
"podzolizing" agent.
Delong and Schnitzer (1955), also came to the same conclusion that leaf extracts and leachates are able to mobilize Fe and Al from A to the B horizon of podzol soils; and, both the forest canopy and the forest floor contribute active organic agents under favourable conditions. They postulated the following:-
1. An environment predondnating in Na rather than
Ca is more favourable.
2. Ca is more favourable than H-ion.
3. The retention of Fe by these solutions vary with
the environment.
4. The Fe-complexes separated from solution at a critical
iron content which again depends on the environment.
5. No evidence was found to support chelate formation.
6. The organic compounds in solution act as peptizing
agents and as protective colloids.
Wright and Schnitzer (1963) have renewed interest in fulvic 16 -
acid, which was considered by many early Russian workers as the main
active agent in "podzolization". Wright and Schnitzer found that
approximately 85% of the organic matter in the Bh horizon of a podzol consisted of fulvic acid. The latter may be an alteration product of humic acid.
As much as 60% of the fulvic acid contains carboxyl, hydroxyl and carbonyl groups. This acid reacts with Fe and Al to form water
soluble complexes and probably also metal complexes. As these metal complexes move down the profile, they may precipitate by reacting with the same metals or with other ions.
Research is being pursued to study the interaction of
fulvic acid and complexes with metals, such as laboratory studies, where soils are leached with ethylene-diamine-tetra-acetic acid and
its corresponding salts. These studies have been found to produce horizons similar to that of a podzol or podzolic soil (Atkinson and
Wright, 1957), Levesque and Hanna (1966), Wright and Schnitzer (1963).
Ponomareva (1947) found that the precipitation of colloidal compounds of fulvic acid and Fe occurred in the pH range of 5.8 to
5.9, with a fulvic acid iron ratio of about one to fifteen.
Precipitation of Al with fulvic acid took place over a wide pH range, with complete precipitation at pH 4.5 and the precipitate consisted of one part by weight of fulvic acid to 3 parts of aluminium oxide.
Schnitzer and Skinner (1963, 1964), prepared Fe and Al organic matter complexes which varied in composition from 1:1 to 6:1 molar (metal:organic matter). Their solubilities in water decreased - 17 - with increasing molecular weight. They also extracted a metal- organic matter complex from the Bh horizon of a podzol and found that the analytical characteristics of the soil-organic matter
complex were similar to that of a 3:1 metal-organic matter complex.
X-ray diffraction showed no evidence of crystallinity in the com• plexes. With regard to relative stability, the soil complex behaved
similarly to the prepared 1:1 metal-organic matter complex. In 1967,
Schnitzer and Skinner, investigated the stability constants of several metal ions including Fe with fulvic acid prepared from a podzol.
They found that varying the pH, varied the order of the Fe-complex.
They have suggested electrovalent bonding talcing place between negatively charged carboxyl groups of the organic matter and positively
charged partially hydroxylated iron and aluminium compounds. Mortensen
(1963) ascribed the formation of organo-metallic complexes to ion-
exchange, surface absorption and chelation reaction mechanisms.
Kawaguchi and Matsuo (1960), found from leaching experiments
that the ratio of the amount of mobilizing agent to the amount of
iron oxide present, regulated the movement of iron oxide, regardless of the presence of other oxides. This suggests that seasonal peaks
are more important than the total amount over a year. They added that this ratio can explain the accumulation and ascent of Fe in the
B horizon; and downward expansion of the Ae.
As long as no definite organo-metallic complexes are
isolated from the soil and characterized, no existing theory can
be taken for granted. However, continued concerted efforts to
acquire more knowledge on podzol formation will no doubt improve - 18 - our understanding of other genetic processes, for example, iron and humus-iron pan formation.
Genesis of Iron Pan Podzols
Iron pans are commonly associated with the B horizon of podzol soils. A voluminous amount of literature has been dedicated to iron pans, and many date back to the beginning of the nineteenth century. There are many types of pans, namely, duripan, fragipan, plinthite, ortstein,clay-pan, iron-pan, iron-manganese pan and humus-iron pan. They are differentiated on the basis of morphology and genesis. The exact genesis of most of them are not known and research towards this line is in progress.
For the present purpose, the probable genesis of iron pans and humus-iron pans (placic horizons) associated with podzols will be discussed.
Iron pans have been recognized in many parts of the world.
These pans may be black to dark red in colour and often vitreous
in appearance. The thickness may vary from 2 mm to 10 mm. The pan is usually found within the upper 50 cm of the mineral soil, and follows a branching course roughly parallel to the soil surface.
It is only slightly permeable or impermeable to water and roots.
These pans develop generally on moderately well drained slopes with
soils termed, wet iron humus podzols and hydromorphic humus podzols.
Glentworth (1944) found the pans to develop through a wide range of topography, parent material, vegetation and under variations in climate within the humid temperate region. - 19 -
Fritzpatrick (1956) has drawn the broad outlines that are associated with an iron-pan podzol. According to Fritzpatrick the pan is a fossilized permafrost layer. Proudfoot (1958) studied two areas in Northern Ireland. One, covered with peat, contained two layers of pans, the more pronounced layer occurring at a greater depth. He concluded by associating the pans in the peat site to a sub-peat fossil soil; and the other site to be of more recent origin which has not reached the stage of bog association.
According to Hackney (1961) supported by morphological and chemical data, the following events take place in the sequence of iron-humus podzol formation:
1. Translocation of clay.
2. Chemical weathering of the Ae horizon resulting in
an association of iron with organic matter and slight
eluviation of iron; the stage of podzol intergrade.
3. Strong iron eluviation; the stage of iron podzol.
4. Eluviation of organic matter, which rests on or is
incorporated into a previously developed iron B
horizon; the stage of humus-iron podzol.
Muir (1934) gave the following explanation for the origin of iron pan podzols:
Iron exists in the reduced state, immediately below the peaty surface, because of saturated conditions. The iron thus reduced is mobilized and oxidizes below, where there is better aeration; the development of an iron pan produces an impermeable layer holding back water and encourages water logging in the overlying horizons. - 20 -
.Romans (1962) recognized this hard pan layer as a result of pedogenic processes and suggested that it resulted from differential translocation of sesquioxides followed by cementation; and that the intensity of induration was a function of the length of time that this process had been active.
Crampton (1963, 1965) did not agree with the views of
Romans but rather with that of Fritzpatrick (1956). Crampton (1965) found very little translocation of iron to form the pan. He observed clay illuviation within the indurated horizon. Where there had been no clay illuviation, no pronounced morphological discontinuity was noted. He ascribed segregation of iron within lenticular zones in the indurated horizon to reduction brought about by lack of aeration. His alternate explanation coincided with that of Fritzpatrick, that is that pressure once exerted by lenticular ice in the soil had compacted the fabric and severely restricted pore space.
Daman (1965) elaborated on the hypothesis of reducing and oxidizing conditions above and below the iron pan as suggested by Crampton (1952). Daman postulated that:
1. Precipitation at the air-water interface explains
why the iron is concentrated in such a thin and well
defined layer.
2. Fe removal appears to have occurred under imperfectly
drained conditions; vertical translocation of iron
and humus colloids is not possible under permanently
wet conditions. - 21 -
3. The position of the pan depends primarily on the
location of the lower part of the saturated zone; this
explains why the pan can occur in such a variety of
horizons and why it is almost independent of textural
changes.
Mckeague et al. (1967) found that the differential thermal gravimetric curves for a pan of an iron-pan Humic Podzol was similar to that of a 6:1 Fe-fulvic acid preparation and that the pan con• tained a high content of functional groups capable of forming co-ordination complexes. Owing to the high organic matter content and high extractable Fe, Mckeague et al. suggested the pan to be probably an iron-fulvic acid complex. From thin section observations of the pan, they found the intergrain spaces filled with isotropic plasma which followed a branching course between the skeletal grains.
Valentine (1969) reported on a moderately well drained
Orthic Ferro-Humic Podzol developed on gentle slopes grading to an imperfectly Gleyed Orthic-Ferro-Humic Podzol on the west coast of Vancouver Island. He too suggests from his data of organic matter and Fe contents that the cementing agent of the pan is Fe and organic matter. However, the exact mechanism of formation of thin iron pans (placic horizons) is still in doubt. - 22 -
MATERIALS AND METHODS
Description of the Sample Area
The samples under study were collected from the Ucluelet lowland on the west coast of Vancouver Island. This area lies between thirty and one hundred meters above sea-level. The geological formations comprise Permian altered volcanics and sediments, basic and ultrabasic intrusives and Tertiary granitic rocks. The last glaciation deposited marine clay; when the ice melted, outwash sands and gravels accumulated on the clay plain (Valentine, 1969).
The soils in this region are found under a maritime climate with mild winters, cool summers, a maximum rainfall during the winter season and very little snow. The annual rainfall recorded is 345 cm and potential evapotranspiration, 61 cm. The relative humidity is high all year and the mean annual temperature is 9°C
(Anomymous, 1967). Light winds blow from the south-east during
October to April and from the north-west during the rest of the year; however, windstorms of more than 50 kilometers per hour are common in winter (Valentine, 1969).
Four sites were chosen for this study, three of them from the Ucluelet series and the last one from the Wreck Bay series.
Figures 1 and 2 show the general nature of the vegetation and soils at the Ucluelet and Wreck Bay sites. The soils have been classified in the Canadian classification scheme as Placic Ferro Humic Podzol and Orthic Ferro Humic Podzol (Valentine, 1969). A sequence of soils was sampled in an attempt to determine through physical, Fig. 1(a). Vegetation at the Ucluelet sites - 23a -
Fig. Kb). Soil at the Ucluelet sites - 24 -
Fig. 2(a). Vegetation at the Wreck Bay site - 24a -
g. 2(b). Soil at the Wreck Bay site - 25 - chemical and mineralogical analyses, the nature of development of these soils. Sampling choice was based purely on maximum morphological expression of genetic horizons.
The sites chosen were about a mile inland from the shore and at an elevation of about 33 metres above sea-level. The landscape is undulating with a 2 to 5 per cent slope and a north- north-west aspect. The site index for the trees on the Ucluelet soils is 90+. The hemlock and balsam were more than one hundred feet high with an average diameter of three feet and may be between one hundred and three hundred years old. The tree association on the
Wreck Bay series showed a stunted behaviour and a marked abundance of shrubs and mosses leading towards a bog type association was observed. The litter was of a mor type.
The Ucluelet series is moderately well drained; the Wreck
Bay series is very poorly drained and is found on flat topography.
A few miles away from the above sites, morphological observations from a gravel pit about 50 feet deep, showed the sequence of development of these soils and the manner in which they were associated.
Vegetation
The natural vegetation is composed of a mixed cover of trees, shrubs, ferns and mosses.
At the Wreck Bay soil site the vegetation was:
Trees
Western Hemlock (Tsuga Heterophylla)
Western Red cedar (Thuja plicata)
Lodgepole pine (Pinus contorta) - 26 -
Balsam (Abies amabilis)
Douglas fir (Pseudotsuga menziesii)
Shrubs
Evergreen Huckleberry (Vaccinium oyatum)
Tall Blue Huckleberry (Vaccinium ovalifolium)
Gentian (Gentian spp.)
Wild lily-of-the-valley (Naianthenum dilatatum)
False heather (Phyllodoce spp.)
Labrador tea (Ledum groenlandicum)
Salal (Gaultharia shallon)
Ferns
Deer fern (Struthiopteris spicant)
Mosses
Rhytidiadelphys triquetrus
Hylocomium splendens
Lycopodium annotinum
Sphagnum squarrosum
Others
Skunk cabbage (Lysichiton kamtchateense)
Bunch berry (Cornus cenadensis)
Starflower (Trientalis latifolin)
Agoseria (Agoseria spp.)
In the Ucluelet soil series, the same tree association exists as in the Wreck Bay soil series, but only few shrubs, ferns and mosses are present.
The soil samples were collected in late August, 1968. The - 27 - three Ucluelet soils (Sites I, II, III) were sampled within a radius of about 200 feet; and the Wreck Bay (Site IV) was sampled a few miles away. Sampling was carried out on a horizon basis. The samples were placed immediately in polyethylene bags and brought to the laboratory.
Valentine (1969) described and mapped the Ucluelet lowland and established the Ucluelet and Wreck Bay series. The profile description of the Ucluelet series is as follows:
Orthic Ferro-Humic Podzol
Horizon Depth (cm) Description
L-F (15-8) Undecomposed and partially decomposed needles, leaves and mosses, abundant large and medium roots; pH 3.7
H (8-0) Very dark gray (10 YR 3/1, d) decomposed organic material; pH 3.1
Ae (0-1.3) Light gray (10 YR 7/2, d) silt loam; amorphous; loose; fine roots
Bh - (1-3-5) Dark grayish brown (10 YR 4/2, m) gravelly sandy loam; weak, fine, subangular blocky; friable; fine roots; clear, wavy boundary; 2.5 to 7.5 cm thick; pH 3.6
Bhf (5-19) Dark brown (10 YR 4/3, m) gravelly sandy clay loam; weak, fine, subangular blocky; firm; fine roots; clear, wavy boundary; 7.5 to 17.5 cm thick; pH 4.4
Bfhl (19-41) Yellowish brown (10 YR 5/8, m) gravelly sandy clay loam; weak, fine subangular blocky; firm; occasional fine roots; gradual irregular boundary; 15 to 27.5 cm thick; pH 5.0
Bfh2 (41-61) Dark brown (10 YR 4/3, m) gravelly loamy sand; single grain; common, fine, distinct mottles (10 YR 5/6, m) non-sticky, non- plastic; occasional fine roots; clear,wavy boundary; 15 to 30 cm thick; pH 5.0 - 28 -
Horizon Depth (cm) Description
BC (61-89) Dark brown (10 YR 4/3, m) gravelly loamy sand; single grain; common, fine, distinct mottles (10 YR 5/6, m); non sticky, non plastic; thin iron coatings on sand and gravel particles; slightly cemented; occasional fine roots in clay pockets; abrupt smooth boundary; 17.5 to 37.5 cm thick; pH 5.0
C (89-122) Olive (5 Y 4/4, m) gravelly sand; single grain; non sticky, non plastic; no roots; pH 5.4.
The profile description for the Wreck Bay series was as follows:
Placic Humic Podzol
Horizon Depth (cm) Description
Of-Om (17-2.5) Dark brown (7.5 YR 3/2, W) semi-decomposed mosses, leaves and needles; fibrous, abundant fine, medium and large roots;abrupt smooth boundary; 12.5 to 20 cm thick; pH 3.1
Oh (2.5-0)' Black (10 YR 2/1, W) very.dark gray (10 YR 3/1, d) decomposed organic matter; slightly stickly; abundant, fine, medium and large roots; abrupt, smooth boundary; 1.2 to 5 cm thick; pH 3.2
Bb^ (0-8) Black (10 YR 2/1, W) very dark gray (10 YR 3/1, m) gray (10 YR 5/1, d) sandy loam; weak, very fine,, subangular blocky; non sticky, non plastic; occasional fine to medium con• cretions; abundant, fine and medium roots; abrupt smooth boundary; 5 to 12.5 cm thick; pH 3.1
Bh2 (8-9) Very dark brown (10 YR 2/2/, W) dark gray (10 YR 4/1, d) sandy loam; weak, very fine; subangular blocky; non sticky non plastic; abundant, fine and medium roots; abrupt, smooth boundary; 1.2 to 3.7 cm thick; pH 3.4
Rootmat (9-10) Very dark brown (10 YR 2/2, W) mat of living roots and single loose sand grains; fibrous; very abrupt boundary with iron pan below; 0-12.5 cm thick - 29 -
Horizon Depth (cm) Description
Bfhc (10-10.25) Black (10 YR 2/1, W) dark brown (7.5 YR 3/2, d) amorphous material forming an un• dulating pan that cements the sand grains and fine gravel. The pan varies in depth from 10 to 20 cm and occasionally bifureates. It is completely impervious to roots
Bfc (10.25-18) Very dark grayish brown (10 YR 3/2,W) brown (10 YR 5/3,d) loamy sand, strongly cemented with iron coatings on individual grains; non sticky, non plastic; no roots; clear, wavy boundary; 5 to 10 cm thick; pH 3.8 IIBf (18-146) Dark grayish brown (2.5 Y 4/2, W) light olive brown (2.5 Y 5/4, d) loamy sand single grain; saturated, flowing; no roots; pH 5.2
The soils sampled were representative of the two series outlined above. Although the Wreck Bay soil was sampled at the same site as reported by Valentine (1969), the classification differs.
Descriptions of the soils sampled are given in Tables I to IV.
Thin iron pans were found at a depth of 40 to 100 cm averaging about 1 to 2 cm in thickness. These pans appeared to run parallel to the soil surface with often an involute and branched nature.
At a deep cut some distance from the sampling sites, it was observed that the "pans" could be found to depths of 300 cm in multiple layers approximately paralleling each other. These pans apparently cut across stones and rocks and often branched. The multiple parallel layers were joined occasionally by a pan which TABLE I. Profile description of Site I
Depth Horizon (cm) Colour* Dry Colour* Moist Texture Structure Other Characteristics
F-H 40-0 12.8°C- semi-decomposed and decomposed needles and twigs
Ae 0-10.0 Brown Grayish-brown loam weak platy Wavy boundary, discontinuous 10 YR 5/2 7.5 YR 5.5/2
Bhf 10- Dark brown Very dark-brown loam amorphous 12.2°C; fairly distinct 17.5 10 YR 3/3 10 YR 2/2 to massive boundary-
Bfc 17.5- Yellowish Dark-red sand massive Compact lamellae; presence of 21.5 brown 2/5 YR 3/6 bifurcation of compact lamellae 10 YR 5/4
C 21.5+ Grayish1 Brownish sand single 11.1°C; friable brown yellow grained 10 YR 5/2 10 YR 6/8
Munsell colours TABLE II. Profile description of Site II
Depth Horizon (cm) Colour* Dry Colour* Moist Texture Structure Other characteristics
F-H 30-0 Semi*-decomposed and decomposed needles, leaves and twigs
Ae 0-5 Brown Reddish brown sandy weak platy Boundary wavy clear 7.5 YR 5/2 5 YR 3/3 loam
Bf 5-70 Yellowish Yellowish red sandy single Boundary wavy clear i brown 5 YR 4/6 loam grained 10 YR 5/4
70+ sand single No evidence of pan grained
Munsell colours TABLE III. Profile description of Site III
Depth Horizon (cm) Colour* Dry Colour* Moist Texture Structure Other characteristics
F-H 10-0 Semi-decomposed and decomposed needles, leaves and twigs
Ae 0-7.5 Brown Grayish-brown loam Boundary wavy clear 10 YR 5/3 10 YR 5/2
Bfc 7.5- Yellowish Strong brown sandy Merging into Bf 20.0 brown 7.5 YR 5/6 loam 10 YR 5/6
Bf 20.0- Dark Dark yellowish sandy Gradual boundary 42.5 yellowish brown loam brown 10 YR 4/4 10 YR 4/4
42.5+ Light olive Very dark sand brown grayish brown 2.5 Y 5/4 2.5 Y 3/2
ft Munsell Colours TABLE IV. Profile description of Site IV
Depth Horizon (cm) Colour* Dry Colour* Moist Texture Structure Other characteristics
F-H 47.5-0 12.8 C, decomposed organic remains; boundary clear
Ahe 0-25 Dark-brown Black sandy weak platy Boundary clear; variable 7.5 YR 3/2 5 YR 2/1 loam to thickness of Ahe range structure• from 0-4 to 0-16 less CO CO Bhfe 25- Dark Dark-reddish sand massive Presence of a compact band 42.5 yellowish brown about half-inch thick con• brown 5 YR 3/2 taining decayed roots; 10 YR 4/4 bifurcation of band
Bf(BC) 42.5- Grayish-brown Dark-grayish sand single 102.5 2.5 Y 5/2 brown grained 2.5 Y 4/2
102.5+ Grayish Very dark sand single brown grayish brown grained 2.5 Y 5/2 2.5 Y 3/2
Munsell Colours - 34 -
had formed vertically. At this site, it was observed that soil water did not penetrate these pans but rather flowed laterally above them. These pans therefore act as barriers to the downward movement of water and consequently prevent leaching of the soils to great depths.
METHODS
Preparation of Sample
In the laboratory, the field samples were air-dried at room temperature, ground with a wooden rolling pin and passed through a 2 mm sieve. The per cent of stones present in the bulk samples were determined. The sieved samples were stored in card• board boxes.
Physical Analyses
A number of physical determinations were carried out on the samples. As soon as the samples reached the laboratory, a portion of each sample was taken immediately to determine field water content by drying the samples for 24 hours at 105°C. Bulk density was determined using the clod method on dried samples (Black,
1965). Particle size analyses of the soil samples were determined by a modified method of Kittrick and Hope (1963), whereby a pretreat• ment for organic matter and iron removal was undertaken, before applying centrifugation, sedimentation and gravimetric techniques for the separation of particle sizes. Water contents at four different negative pressures using the porous plate extractor were determined gravimetrically (Black, 1965). - 35 -
Chemical Analyses
Selected chemical analyses were conducted on the soil samples. The measurement of pH in water and calcium chloride were carried out on the field samples. A soil water ratio of 1 to 2.5 and
1:2 soil to 0.1 M CaCl2 were used. Total carbon and sulphur contents were determined by the dry combustion method using the Leco Induction furnace (Black, 1965). Total nitrogen was determined by the macro
Kjeldahl method as described in Methods of Soil Analysis (Black, 1965).
Available phosphorus was determined colorimetrically by using ammonium fluoride as the extracting solution, chloromolybdic acid as the complexing agent and stannous chloride as reducing agent
(Jackson, 1958).
The three elements, iron, aluminium and silicon, were determined spectrophotometrically by the atomic absorption spectro• photometer, following extraction of the samples with sodium acetate- acetic acid adjusted to pH 3.5 and by sodium dithionite and citric acid in a water-bath set between 75-80°C. Oxalate extractable Fe,
Al, Mn were determined spectrophotometrically by the atomic absorption spectrophotometer after shaking the samples for four hours in the dark with a mixture of ammonium oxalate and oxalic acid adjusted to pH 3.0 (McKeague and Day, 1966).
One normal KC1 was used to extract exchangeable aluminium according to the method described in Methods of Soil Analysis (1965).
The determination was carried out using an atomic absorption spectrophotometer. - 36 -
Amorphous aluminium and silicon were determined on the
less than 2 mm soil as well as on the coarse clay fraction. The
procedure followed for the extraction was pretreatment for removal
of O.M. and Fe before boiling in 0.5 NaOH (Black, 1965). Aluminium
and silicon were determined by the atomic absorption spectrophotometer.
Exchangeable acidity was extracted from the soil samples with 0.5N barium chloride - 0.05 N triethanolamine adjusted to pH
8.0 and titration with 0.2 N HC1 (Black, 1965).
Exchangeable cations were extracted from the samples with normal ammonium acetate adjusted to pH 7.0. Exchangeable K,
Na, Mg, Ca, Fe were determined by the atomic absorption spectro• photometer. The cation exchange capacity was determined by the displacement of the adsorbed ammonium with normal sodium chloride
and distillation of the ammonia extract by the macro-Kjeldahl method (Black, 1965).
For the determination of lime potential and pH dependent
cation exchange capacity the soil samples were equilibrated by
shaking with 0.01 M CaCl2 for five days and then centrifuged. The
supernatant solution was used to determine calcium, magnesium and
aluminium for the calculation of lime potential. The centrifugate was shaken for 24 hours with 2 N NaCl. Calcium, magnesium and
aluminium were determined by the atomic absorption spectrophotometer
for the calculation of pH-dependent cation exchange capacity (Clark,
1965).
Elemental analyses were conducted on the soil samples.
The elements, Fe, Al, Mn, Ca, Mg, Na, K, were determined using the - 37 - atomic absorption spectrophotometer on less than 2 mm soil and on the clay fraction. Silicon was determined by difference. The samples were ignited at 900°C for 2 hours and then digested three times with a mixture of concentrated hydrofluoric, perchloric and hydrochloric acid prior to elemental determinations.
Identification of the clay minerals present in the fine silt, coarse clay and fine clay fractions were made using x-ray diffraction methods. The x-ray unit employed was a Philips x-ray diffractometer with high angle goniometer. The radiation was
CuKa using a nickel filter.
The procedure followed for the initial treatment prior to x-radiation was that described by Kittrick and Hope (1963). The following slides were prepared for the x-ray examination of the clay samples: (1) Mg-saturated, air dried sample; (2) Mg-saturated glycerol solvated sample; (3) K-saturated, air dried sample; and
(4) K-saturated, heated sample 300°C and 500°C.
For the differential thermal analysis the samples were placed in one hole of a specimen holder, and calcined aluminium oxide (ot-A^Og). an inert material was placed in another hole of the specimen holder. One junction of the difference thermocouple was placed in the middle of the sample and the other junction in that of the inert material.
Both holder and thermocouples were placed in a furnace which produced a uniform rate of increase in temperature. The sample was heated at a rate of 20°C per minute, up to a temperature of 1200°C. The pattern of the thermal reaction was recorded on a chart as a function of temperature. - 38 -
RESULTS AMD DISCUSSION
Characterization through physical, chemical and mineralogical analyses were carried out in order to study the nature of profile development. The results of these analyses are presented in the form of tables and graphs. Tables V-VI are concerned with particle size distribution, bulk-density, total porosity, field water and water-retention properties. Water retention curves are shown in Figures 3-6 (pages 45-48 ) and water storage in Figure
7 (page 49 ). Some selected chemical analyses for the four sites are presented in Tables VII to XII and Table XVII. Table VII contains data for pH, total organic carbon, organic matter (O.M.), total nitrogen, available phosphorus, total sulphur, C/N and C/N/S ratios. Table VIII contains data for KCl-extractable Al, dithionite extractable Al, Fe and Si, oxalate-extractable Al, Fe and Mn, amorphous Al and Si in the <2 mm soil and total clay fraction;
A (Fe + Al) values and O.M. to Fe ratios. Table IX deals with exchange capacity and per cent base saturation values. In Table X, data are presented for lime potential and pH dependent cation- exchange capacity. Tables XI-XII show values for elemental analysis on the <2 mm soil and the total clay fraction, together with weathering indexes. In Tables XIII-XVI, the mineralogical composition of the fine clay, coarse clay and silt fractions of each horizon are presented. Table XVII deals with some selected chemical properties of the pans compared to soil matrix. - 39 -
Particle-Size Distribution
Particle size distribution in soils is an indication of
the intensity of pedogenic processes, in breaking down coarse
fragments to fine, and also an indication of the uniformity of the
parent material.
Sandy loam and sand were the predominant textural classes in
all except two horizons, namely, Site I-Ae and Site III-Ae. The sand
size fraction increased with depth in all the four soils. The silt
fractions in the surface horizons were much above the values observed
for the lower horizons. Franzmeier and VJhiteside (1963) state that the amount of silt present in the upper horizons increases with age
of the soil. However, for Site III, the Bf horizon contained more
silt than the overlying horizon. This seems to indicate that at
some stage, there has been a discontinuity in the pattern of intensity
of physical weathering, which may be due, either to different sequence
of events taking place in the overlying horizon, or an in situ
weathering of the .sand to silt. The other explanation may be dis•
continuous deposition of the parent material prior to soil formation.
The total clay fractions in the horizons ranged from 1.3
to 13.6%. There was a general decrease in clay content in the soils,
going from Sites I, III and IV; however, the decrease was very marked
for Site IV. This latter fact may be the result of either poor
translocation of clay down the profile because of the very wet
conditions or complete breakdown of the clay as it moved downwards.
The clay data for Site II showed an increase in the Bf and this seemed
to indicate that this is a younger soil and is still in an earlier TABLE V. Selected Physical Properties of the Ucluelet and Wreck Bay Series
Particle-size distribution
based on less than 2 ramsoil ? wt %
Soil and Depth BD Total 0.2 2- 5- 20- 50u- wt % Horizon (cm) g/cc Porosity <0.2u -2u 5u 20u 50u 2mm 2mm Texture class
Ucluelet I F-H 10-0 Ae 0-10 1.17 55.8 2.0 11.6 5.0 23.0 8.0 50.0 82.6 Loam Bhf 10-17.5 1.40 47.2 3.0 8.0 3.0 8.0 5.0 73.0 50.0 Sandy Loam Bfc 17.5-21.2 1.63 38.5 4.0 4:0 0.1 2.0 2.0 88.0 53.0 Sand C 21.2+ 1.60 39.6 2.0 3*.0 0.5 1.0 1.0 93.0 55.7 Sand
Ucluelet II F-H 30-0 Ae 0-5 1.32 50.0 2 9 3 20 12 52 20.0 Sandy Loam Bf 5-80+ 1.00 62.3 4 9 4 14 9 61 29.4 Sandy Loam
Ucluelet III F-H 10-0 Ae 0-7.5 1.08 59.2 2 11 6 24 14 43 40.0 Loam Bfc 7.5-2.0 1.46 44.9 4 6 1 4 4 79 56.5 Sandy Loam Bf 20-42 1.39 47.5 3 7 5 5 4 76 58.3 Sandy Loam C 42+ 1.96 26.0 2 2 1 2 2 92 54.2 Sand
Wreck Bay F-H 48-0 Ahe 0-25 0.96 63.8 2.0 8.0 7.0 12.0 10.0 61.0 N.D. Sandy Loam Bhfc 25-42 1.59 40.0 1.0 1.0 1.0 2.0 2.0 92.0 26.1 Sand Bf(BC) 42-102 1.66 37.4 2.0 0.4 0.3 0.7 0.9 96.0 5.4 Sand C 102+ 1.65 37.7 0.9 0.4 0.3 0.6 1.0 97.0 9.0 Sand - 41 -
stage of development. The ratio of coarse clay to fine clay in the profile was a little more than 2.0 for Sites I, III and IV; and for
Site II, the ratio was 3.0. The fine clay content increased with depth and then decreased in the C horizons. With the coarse clay fraction, the reverse took place except for Site II where it was constant. This indicated that there has not been translocation of coarse clay material. Rather through pedogenic action the coarse- clay fraction was broken down in the upper horizons to fine clay, which is consequently translocated either as clay minerals or colloidal sesquioxides. The sand plus silt to clay ratio increased with depth in Sites III and IV. In Site I, the ratio increased and then decreased in the C horizon, whereas in Site II, there was a decrease in the ratio, indicating a translocation of clay.
Bulk-Density
Bulk-density is related to packing and varies therefore with the structural condition of the soil. Bulk-density values for these soils ranged from 0.96 to 1.66, (Table V). Values for Sites
I and IV increased with depth and then decreased slightly in the
C horizon. For Site II, the bulk-density values decreased with depth; at Site IV, there was an increase, then a decrease, and finally an increase with depth. Comparing the organic matter distribution with bulk-density, only for Sites III and IV, an inverse relationship between the organic matter content, and the bulk-density was found.
No regular relationship with depth could be found between amorphous
Al and Si, oxalate extractable sesquioxides, or va^ues from elemental analysis and bulk-density values. - 42 -
Total Porosity
Total porosity is a dynamic property that changes with soil structure. It is therefore an important property in the study of soil structure and is concerned with the storage and movement of water and gases, soil strength and heat flow.
The total porosity values found, varied from a minimum of
26% in the C horizon to a maximum of 64% in the A horizon. For
Sites I and IV, the total porosity decreased with depth up to the
B horizon followed by a slight increase in the C horizon; for Site
III, there was a decrease followed by an increase in the Bf, and decreased again in the C horizon. For Site II, the total porosity increased in the Bf. No relationship could be observed between organic matter, clay and silt distribution and porosity values.
Field Water Content
Generally, the water content in the field was found to increase with clay content and amount of organic matter in the mineral horizons under study. The organic horizons as expected were found to contain the highest amount of water.
Water Retention and Available Water Storage Capacity
The tension at which water is held in a soil is a function of the soil water. The former is a primary factor in the transport of water in the soil-plant-atmosphere system. Each soil has a characteristic water retention curve and the variation is due to the effects of the distribution of organic matter, mineral colloids, type of clay minerals and pore size distribution. TABLE VI. Selected soil water parameters
Water Retention % by wt.* A.W.S.C. gm/100 gm« Soil and Depth % Field Bars (0.33-15.0 bars)
Horizon (cm) H20 0.10 0.33 1.0 15.0 O.D. Soil
Ucluelet I F-H 40-0 459 Ae 0-10 59 72.9 33.3 27.4 15.2 18.1 Bhf 10-17.5 81 79.3 26.2 23.3 18.1 8.2 Bfc 17.5-21.2 23 40.9 11.0 9.5 7.4 3.6 C 21.2+ 9 22.6 5.5 4.8 3.8 1.7
Ucluelet II F-H 30-0 390 Ae 0-5 40 72.1 27.8 25.3 15.5 12.4 Bf 5-80+ 68 83.0 34.4 26.3 18.3 16.2 Ocluelet III F-H 10-0 387 Ae 0-7.5 75 74.9 35.4 31.6 18.1 17.3 Bfc 7.5-20 34 21.5 18.9 15.6 12.5 6.4 Bf 20-42 53 22.7 20.4 15.7 13.4 7.0 C - 42+ 16 10.2 7.2 6,2 5.1 2.0 Wreck Bay F-H 48-0 Ahe 0-25 N.D. 48.9 34.7 33.7 20.3 11.5 Bhfc 25-42 23 27.4 21.5 19.4 13.3 8.2 Bf(BC) 42-102 16 8.5 7.7 7.0 5.0 2.6 C 102+ 3 4.6 4.0 3.8 2.6 1.4 Bulk density was determined on an undisturbed soil ped, while water retention properties were conducted on the 2 mm soil; thus the retention values and A.W.S.C. are higher than expected and are therefore only relative. - 44 -
For each soil water tension under study the water content decreased with depth in each soil. This observation coincided with the fact that the plants growing on these soils are shallow rooted and are able to remove enough water for growth from the surface horizons especially the organic horizons. Kbhnke (1968) stated that at 1/3 bar percentage, a value of 20% is a well supplied situation.
From the data, (Table VI), it can be observed that within a depth of 42 cm and at 1/3 bar tension, the values for Sites II, III and
IV ranged above 18.9%; for Site I, after a depth of 18 cm (Bhf), there was a sharp decrease from 26.2% to 11.0% at 21 cm (Bfc).
This coincided with sharp drops in organic matter and clay contents from the Bhf to the Bfc. At 15 bars tension, the upper finer textured horizons were still fairly well supplied with water, ranging from 12.5 to 18.0%; this can be attributed to the fairly high amount of organic matter present and the loamy to sandy loam texture of these horizons. In the lower sandy horizons, the values ranged from
2.6% to 13.4%.
The available water storage capacity has been considered in Table VI as the difference in weight percentage between the water content at 0.33 bar and 15 bar tensions. The available water storage capacity in the profiles decreased with depth, with the exception of Site II. The decrease with depth can be explained by the increase in coarse-textured material. From the bar graph in
Figure 7 showing the available water storage capacity to a depth of 40 cm from the surface, it is observed that Sites I-IV contained
3.70, 6.49, 4.51 and 4.71 cm of water respectively. For Site I it has been assumed that in the C horizon, the available water storage capacity at 40 cm depth is the same as at 21 cm depth. - 145 - - 46 -
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 I.I
Volumetric water content - 47 - - 48 -
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 - - Volumetric water content - 49 -
Fig. 7. Total Water Storage Capacity for the Ucluelet (Sites I-III) and Wreck Bay (Site IV)
0 bfl u 4 o +-» ~ co 6 o oi o e
S o H «d o
m 12
Sites - 50 -
CHEMICAL ANALYSES
pH in H20 and CaCl2
The pH values in both water and calcium chloride increased
with depth for the four soils (Table VII). The range of pH in water
fluctuated between 4.2 and 5.7; in 0.1 M CaCl2, the values were
between 3.4 and 5.4.Clark (1965) stated that shaking the soil with
0.01 M CaCl2 under aerated conditions for 5 days would give values
nearer to natural conditions. Values for the latter study are
reported in Table X. In this case, the pH values were about 5% lower
than they were without equilibration in 0.1 M CaCl2-
Nitrogen, Phosphorus and Sulphur
The nitrogen values were highest in the organic horizons
and decreased markedly with depth in all the four profiles studied.
No definite relationship with depth could be found for phosphorus
values; however, Site IV was richer in phosphorus than the other
soils studied. The values for Site IV ranged from 102 ppm to 32 ppm,
followed by Site I (75 to 0.7 ppm). There was a general decrease in
the sulphur content with depth in all the four profiles, values
ranging from 0.01% to 0.14% (Table VII).
Organic Carbon, C:N and C:N:S Ratios
The organic carbon contents were highest in the organic
horizons and decreased sharply with depth. It should be noted that
the organic carbon content of the Ahe of Site IV did not reflect the
morphological observations, because in the field, it appeared to be
an Ah or Bh. The C:N ratios ranged from a minimum of 12.0 in the C TABLE VII. Selected chemical data
Organic Soil and PH pH C O/M N P S
Horizon H20 CaCl2 % % % ppm % C/l C/N/S
Ucluelet I F-H 4.2 3.4 48.7 84.3 0.95 75.0 0.08 51 608:12:1 Ae 4.9 3.8 4.5 7.8 0.16 0.7 0.02 28 226:8:1 Bhf 5.2 4.4 7.5 13.0 0.22 12.0 0.04 34 188:5:1 Bfc 5.2 4.6 2.3 4.0 0.05 25.0 0.02 46 115:2:1 C 5.3 5.4 ' 0.4 0.7 0.03 42.0 0.01 14 41:3:1
Ucluelet II F-H 4.3 3.4 43.2 74.9 0.91 62.0 0.07 47 618:13:1 Ae 4.6 3.4 5.8 10.3 0.18 12.0 0.02 32 292:9:1 Bf 4.9 . 4.7 4.0 6.9 0.12 0.2 0.06 33 66:2:1
Ucluelet III F-H 4.9 3.7 37.9 65.7 1.57 16.0 0.14 24 271:11:1 Ae 5.1 4.3 5.7 9.9 0.15 16.0 Q.03 38 190:5:1 Bfc 5.3 5.3 2.3 4.0 0.08 2.0 0.05 29 47:2:1 Bf 5.3 5.4 3.5 6.0 0.13 0.3 0.05 27 70:3:1 C 5.7 5.4 0.5 0.8 0.04 16.0 0.02 12 24:2:1
Wreck Bay IV F-H 4.3 3.4 44.2 76.5 1.12 68.0 0.13 39 340:9:1 Ahe 4.6 4.0 6.8 11.7 0.33 102.0 0.08 20 85:4:1 Bhfc 5.1 4.4 5.0 8.6 0.12 75.0 0.07 41 71:2:1 Bf(BC) 5.3 4.7 1.0 1.7 0.02 32.0 0.01 50 100:2:1 C 5.5 4.8 0.4 0.7 0.01 40.0 0.01 41 41:1:1 -r 52 -
horizon to a maximum of 51.0 in the organic horizon (Table VII).
Mackney and Burnham (1964) reported a C:N of 12 in the Ae, 19 in the
B horizon and 13 in the C horizon for a Humic-Iron-Podzol. Van
Schuylenborgh (1962) found the C:N ratio to range between 16 to
55 for Iron Humus Podzols. There was a wide variation in the C:N ratio throughout the sola; this may be due to the fact that very little nitrogen is being retained in the lower horizons where the materials are coarser-textured. The C:N:S ratios were very high in the organic and eluvial horizons, values ranging from 608:12:1 to
85:4:1 (Table VII), indicating that optional conditions do not exist for rapid microbial degradation.
Iron-Oxides
A substantial amount of the iron in soils is in the form of iron oxides. These oxides may exist as individual particles, as coatings on soil minerals and as cement between mineral particles.
A method for the removal of these iron-oxides should be such that the layer silicate minerals and other minerals like allophane, magnetite and ilmenite are not attacked.
In this study, two such methods have been used, namely the oxalate and dithionite methods. The oxalate method is assumed to remove only the amorphous oxides and amorphous coatings; the dithionite method removes amorphous iron and much of the inter-
stratified iron in the silicate layer minerals. However, with regard to the oxalate method, Baril and Bitton (1969) found that the method attacks magnetite and recommended that the latter should be removed if more accurate results are to be envisaged. - 53 -
From Table VIII, it was found that the values obtained by the dithionite method were generally higher than those by the oxalate method. The values for Sites I, II and III ranged from
0.62% in the C horizon to 1.8% in the B horizon, by the oxalate method. With the dithionite method, values ranged from 0.88% to
2.85%. Clark et al. (1966) reported oxalate Fe values for Bf, Bhf and Bh horizons of Podzols and Humic Podzols to be between 0.02 to
2.1%. McKeague and Day (1966) found 0.04% oxalate Fe and 0.14% dithionite Fe for the Bh of a Humus Podzol. McKeague et al.
(1967) reported, for the Bf j and Bf horizons of an Iron Pan Humic
Podzol, values of 1.76 and 0.52% oxalate Fe, respectively. These values are well within the range found in this study. Values for
Site IV were much lower than for the other sites. Generally, an increase followed by a decrease with depth was observed by both methods. No consistent relationship with depth could be found for per cent oxalate extractable Fe in the total clay fraction (Table
VIII). However, there is a relationship in all the profiles between oxalate extractable Fe and Fe from total elemental analysis (Table XI).
Extractable Aluminium
Extractable aluminium may include exchangeable Al, plus soluble Al (OH)g and probably some hydroxy-Al monomers or polymers which may be strongly adsorbed by the silicate minerals. Black
(1965) states that extractable Al may be useful as an index of the weathering status of soil. In the Canadian classification scheme
(1968) , oxalate-Al and Fe values are used to differentiate podzolic
B horizons. Data obtained for aluminium by the oxalate method were higher than that extracted by dithionite and 1 N KC1 (Table VIII). TABLE VIII (a) Selected extractable constituents
% Soil and Dithionite Oxalate Oxalate Fe P.M. Horizon Al% • Fe% Si% ALl Fe%" Mn Clay A(Fe+Al)» Fe (ppm)
Ucluelet I F-H Ae 0.14 1.74 0.75 0.6 0.90 20.0 6.6 8.7 Bhf 0.57 1.61 0.16 3.0 1.20 120.0 10.9 1.78 10.8 Bfc 0.55 1.22 0.27 1.2 0.90 310.8 11.2 4.4 C 0.53 1.08 0.43 1.3 1.12 22.0 0.6
Ucluelet II F-H Ae 0.30 2.62 0.10 0.9 1.72 40.0 15.6 6.0 Bf 1.26 2.85 0.40 2.4 1.93 14.8 14.8 2.41 3.5
Ucluelet III F-H Ae 0.55 2.20 0.12 1.0 1.28 44.0 9.8 7.7 Bfc 1.20 2.06 0.60 3.1 1.80 108.4 18.0 2.98 2.2 Bf 1.18 2.16 0.43 3.8 1.57 116.0 15.7 3.45 3.8 C 0.42 0.88 0.26 1.3 0.62 124.8 15.5 1.3 Wreck Bay IV F-H Ahe 0.10 0.10 0.05 1.7 0.10 10.0 1.0 117.0 Bhfc 0.58 0.74 0.31 1.8 0.77 80.0 38.0 1.48 11.2 Bf(BC) 0.42 0.54 0.27 0.8 0.41 56.0 17.0 0.12 4.3 C 0.27 0.32 0.23 0.7 0.39 44.0 30.0 1.8
(Fe+Al) = % oxalate-extractable Fe+Al in B - % oxalate-extractable Fe+Al in C. The C horizon of Sites II and III were considered similar TABLE VIII (b) Selected extractable constituents
HC1+400°C+ NaOH NaOH NaOH Amorphous Amorphous Amorphous Soil and KC1 (on <2mm) (on < 2mm) (on < 2 u) Horizon Al% Si% Al% Si% Al% Si%
Ucluelet I • F-H Ae 0.155 0.36 0.75 0.32 1.08 0.95 1.98 Bhf 0.062 1.89 0.98 0.60 0.86 8.52 7.70 Bfc 0.007 1.36 1.50 0.74 1.19 16.37 12.28 C 0.001 0.82 2.20 0.58 2.51 14.03 13.61
Ucluelet II F-H Ae 0.146 0.60 0.81 0.51 1.17 2.69 2.95 Bf 0.032 1.65 1.79 1.75 1.93 12.19 7.47
Ucluelet III F-H Ae 0.079 1.14 0.71 1.11 1.50 4.10 2.46 Bfc 0.003 1.83 2.83 1.11 2.29 18.80 12.03 Bf 0.002 2.63: 3.27 2.50 3.61 17.28 10.60 C 0.001 1.00 1.50 0.43 1.03 13.92 10.83
Wreck Bay IV F-H Ahe 0.167 1.10 0.56 0.38 1.24 1.25 2.50 Bhfc 0.044 1.19 1.98 0.72 2.29 9.40 9.61 Bf(BC) 0.005 0.86 1.90 0.44 1.80 15.00 16.24 C 0.002 0.52 1.48 0.39 1.82 18.59 15.70 - 56 -
Both oxalate and dithionite values were found to increase in the B horizon and decrease in the C horizon. Oxalate values ranged from
0.6% to 3.8% and dithionite values from 0.14 to 1.20% for Sites I-III.
For Site IV, the data ranged from 0.1% in the Ahe to 0.58% in the
Bhfc by the dithionite method; and 0.7% in the C horizon to 1.8% in the Bhfc by the oxalate method.
Some values that have been reported in the literature are:
Clark et al. (1966)0.31-2.86% oxalate-Al for Bf, Bfh and Bhf of
Podzols and Humic Podzols; McKeague and Cay (1966) 0.66% oxalate-Al and 0.79% dithionite Al for the Bh of a Humus Podzol; and McKeague et al. (1967) 0.94% and 1.13% Al respectively for the Bhf and Bf of an Iron Pan Humic Podzol. The values found in this study therefore fall within the range quoted from the literature.
KC1 extractable-Al showed a consistent decrease with depth in all the four profiles studied, with a maximum of 0.17% in the eluvial horizon and a minimum of 0.001% in the C horizon.
P.M. :Fe Ratio and A(Fe + Al)
The Canadian Classification (1968) makes use of the O.M.:Fe ratio and A(Fe + Al) values for horizon designation of the master
B horizon of Podzols. From Tables VII and VIII, it is observed that for Site I, the horizon below the Ae had an organic matter content of 13%, A (Fe + Al) of 1.78% and an O.M. to Fe ratio of 10.8.
These would designate that horizon as a Bhf. The term A(Fe + Al) cannot be applied to the horizon below the Bhf as the sum of Fe and
Al is greater for the C horizon. However, as that horizon was cemented and had an O.M. to Fe ratio of less than 5, it has been denoted as a Bfc, - 57 -
For Site II, the layer below the Ae, had an organic-matter content of 6.86%, a A(Fe + Al) of 2.41% and an O.M. to Fe ratio of 3.5. The high A(Fe + Al) value and lotv O.M. to Fe ratio would favour a Bf instead of a Bfh horizon.
For Site III, the upper B horizon had an O.M. content of
4.05%, a A(Fe + Al) of 2.98 and an O.M. to Fe ratio of 2.2 This horizon from morphological observations was cemented and is therefore designated as Bfc. The lower B horizon had an organic matter content of 6.04%, a A(Fe + Al) of 3.45 and an O.M. to Fe ratio of 3.8 This horizon would be better designated as a Bf instead of a BC.
For Site IV, the upper B horizon contained 8.62% O.M., a A(Fe + Al) of 1.48 and an O.M. to Fe ratio of 11.2; and would be called a Bhfc due to the presence of a weakly cemented lamella. It seems hard to designate the horizon above the C horizon as the
A(Fe + Al) value is less than 0.8% oxalate Fe. Due to its low O.M. to Fe ratio of 4.3, it can be designated as a Bf or BC. McKeague and Day (1966) have reported A(Fe + Al) values of 2.26% for a Podzol and 0.24% for a Humus Podzol. Clark et al.(1966) found A(Fe + Al) values of 0.16-3.36 for Podzols and Humic Podzols.
Recently, McKeague and Day (1969) suggested oxalate- extractable Al as the most useful single criterion for characterizing podzol B horizons, if the latter has a minimum value of 0.6% Al.
Following their statement, values from this study would place all the mineral horizons in all the soils as podzolic (spodic) horizons.
This suggested limit does not seem to correspond either in the case of dithionite or oxalate extractable Al. - 58 -
Soil samples were heated at 550 C in an attempt to see how colours relate to the loss on ignition and amount of staining
by organic matter and iron-oxides and whether characteristic colours
develop for Bhf and Bf horizons.
The following colours were obtained:
Soil and Horizon Air=dry 550°C
Ucluelet Ae 10 YR 5/2 Brown 7.5 YR 7/4 Pink Site I Bhf 10 YR 3/3 Dark brown 7.5 YR 6/4 Light brown Bfc 10 YR 5/4 Yellowish brown 10 YR 6/4 Light yellowish brown C 10 YR 5/2 Grayish-brown 10 YR 5/2 Grayish-brown
Ucluelet Ae 7.5 YR 5/2 Brown 5 YR 5.5/6 Reddish yellow Site II to yellowish red Bf 10 YR 5/4 Yellowish brown 5 YR 6/6 Reddish yellow
Ucluelet Ae 10 YR 5/3 Brown 7.5 YR 7/4 Pink Site III Bfc 10 YR 5/6 Yellowish brown 5 YR 6/6 Reddish yellow Bf 10 YR 4/4 Dark-Yellowish 5 YR 5/4 Reddish-brown brown C 2.5 Y 5/4 Light olive 7.5 YR 5/4 Brown brown
Wreck Bay Ae 7.5 YR 3/2 Dark brown 10 YR 7/1 Light gray Site IV Bhfe 10 YR 4/4 Dark yellowish 10 YR 6/1 Gray brown Bf(BC) 2.5 Y 5/2 Grayish-brown 10 YR 6/1 Light gray to gray C 2.5 Y 5/2 Grayish brown 10 YR 5/1 Gray
The change in colours from air-dry to that at 550°C in Site
IV reflect staining mainly by organic matter as colours changed from
brown to gray throughout the profile and confirm the low oxalate-Fe
values found and the aluminium values are similar to the Ucluelet
soils. The change in colours for the Ucluelet soils tends towards
a redder hue on ignition. This is attributed to coloration due to
iron. No definite hue seems to be associated with the Bhf and Bf
horizons when heated at 550°C. - 59 -
The C horizons remained gray or became grayer on heating, indicating the probability of Al contributing to the podzolic character, namely high sesquioxides. Therefore, in the B horizons in the Ucluelet soils the coloration is probably the result of Fe, since
Al does not have a marked coloration change on heating.
Dithionite Silicon and Oxalate-Extractable-Manganese
Estimations of extractable silicon and manganese in soils may give an indication of the intensity of profile development.
Dithionite extractable-silicon values ranged from 0.05% to 0.75%
(Table VIII). For Sites II, III and IV, the silicon values increased in the B horizon; for Site I, the highest reported value was in the
Ae. The oxalate-extractable-manganese also generally increased in the B horizons and values ranged from 10.0 ppm to 310.8 ppm.
Amorphous Alunrinium and Silicon
Values for amorphous aluminium and silicon are reported in
Table VIII. Heating the sample to 100°C followed by extraction with
0.5 N NaOH dissolves some interlayer alumina, which frequently occurs in expanded layer silicates of soils (Dickson and Jackson, 1959,1962,
Jackson 1963). Some authors state that an increment of alumina, silica and iron oxide often becomes soluble as a result of heating to 400^, suggesting that an allophane-like inter layer precipitate may be characteristic of expanded layer silicates of some soils.
From values reported in Table VIII for the <2 mm soil, the 400°C treatment did not remove an increment of Al, but, rather a decrease was observed. However, the silica values for the U00°C treatment were generally higher than for the untreated samples. The amorphous - 60 -
aluminium and silicon generally increased in the B horizons, and
decreased in the C, in all the four profiles. Site III had the
greatest accumulation of amorphous Al and Si. Values for Al ranged
from 0.36% to 2.63%; and for Si, 0.56 to 3.27%.
The analysis of the less than 2 JJ clay fraction showed that
the Al values increased in the B horizons for Sites I-III, followed
by a decrease in the C horizon; for Site IV, the highest content
was in the C horizon. With regard to silicon, a maximum concentration
existed in the C horizon for Site I, and, for the other sites, the maximum occurred in the B horizon. Values for Al ranged from 0.95
to 18.8% arid for silicon, 1.98 to 16.24%.
The distribution of Al throughout the profiles as found by
the oxalate, NaOH and elamental analysis procedures bore a common
relationship. The increase in Al and Fe in the B horizons is there•
fore due to the accumulation of amorphous sesquioxides. Observations
from X-ray mineralogical analysis give supporting evidence for the
latter statement. The accumulation of these amorphous constituents may have occurred either as individual particles or as organo-complexes.
Exchangeable Cations, Cation-Exchange Capacity and Base Saturation
The exchangeable calcium values ranged from 0.02 to 0.86 m.eq/100 gm. Site IV had more calcium with a maximum in the Bhfc
in the profile than the other sites. Exchangeable Mg, Na, K
generally decreased with depth throughout the sola in all the four
profiles. Exchangeable Al reached a maximum of 0.74 m.eq/100 gm
in Bhf of Site I; increased with depth in Site II and decreased with
depth in Sites III and IV. Exchangeable Fe was at least ten times TABLE IX. Cation exchange properties
Exchangeable cations Soil and Exchange Horizon acidity Ca Mg K Na Al Fe %B.S. m.eq/100 gm Ucluelet I F-H Ae 25.2 0.40 0.41 0.04 0.20 0.14 0.050 16.9 6.2 Bhf 36.7 0.04 0.20 0.06 0.17 0.74 0.080 27.0 1.7 Bfc 16.8 0.09 0.04 0.02 0.005 0.05 0.004 4.6 3.4 C •+.2 0.05 0.01 0.01 - - 0.004 1.7 4.1 I Ucluelet II F-H CD Ae 32.5 0.86 0.65 0.06 0.25 0.18 0.110 14.9 12.2 Bf 29.4 - 0.04 0.02 0.07 0.92 0.070 11.3 2.1
Ucluelet III F-H Ae 31.5 - 0.08 0.04 0.09 0.74 0.160 18.9 1.1 Bfc 23.1 0.12 - 0.03 0.03 0.02 0.05 0.004 6.1 3.3 Bf 26.2 0.02 0.03 0.04 0.05 0.05 0.004 8.0 1.9 C 8.4 0.50 0.08 0.03 0.02 - 0.004 5.2 1.2
Wreck Bay IV F-H Ahe 46.2 0.15 0.20 0.03 0.06 3.70 0.004 36.7 1.2 Bhfc 34.6 0.60 0.04 0.01 - 0.05 0.004 18.6 3.5 BKBC) 10.5 0.20 0.01 0.01 - - 0.004 4.6 4.8 C 4.2 0.07 0.01 0.02 0.02 - 0.004 1.7 7.0 - 62 -
lower than the other exchangeable cations with a maximum of 0.16 m.eq/100 gm in the Ae of Site III; and 0.004 m.eq/100 gm throughout the profile for Site IV (Table IX).
Cation-exchange capacity (C.E.C.) values ranged from 1.7 to 36.7 meq/100 gm. For Site I, the Bhf had a maximum of 27.0 meq/100 gm. For Sites II, III and IV, the C.E.C. decreased with depth.
Percent base saturation values have been reported by con• sidering the sum of exchangeable Ca, Mg, K and Na. Highest values for Site I and II were in the Ae; for Site III, the maximum was in the upper B horizon. For Site IV, the base-saturation increased with depth.
Exchange Acidity
Exchange acidity by the barium-chloride tri-ethanolamine method results from the neutralization of H*, Al+++ ions, and, dissociable acidic groups from the clay surface. The exchange acidity ranged from 4.2 to 46.2 meq/100 gm (Table IX). For Site I, the Bhf had a maximum of 36.7 meq/100 gm; for Site II and IV, it decreased with depth; for Site III, it decreased in the upper B, increased and decreased again in the C horizon. pH-dependent Cation-Exchange-Capacity and Lime Potential
The lime potential for the four profiles increased with depth (Table X). When ionic activities of hydroxylated aluminium present in solution were taken into account, the corrected lime potential values for the horizons having pKsp values greater than
33.8, were found to be higher than the lime potential values and these horizons were the eluvial horizons with lowest base-saturation. TABLE X. pH Dependent cation exchange and line potential Solution Exchange Ca Mg Al Soil and Ca+Mg Al pH-^P m.eq/ m.eq/ m.eq/ Ca+Mg x 100 Horizon £H M/lxlO3 M/lxlO5 (Ca+Mg) pAl+3pOH C.L.P* lOOgm lOOgm lOOgm Ca+Mg+Al
Ucluelet I Ae 3.59 7.40 59.30 2.40 34.70 2.70 1.60 0.16 3.16 35.77 Bhf 4.08 8.15 66.72 2.91 33.19 2.71 3.22 0.05 1.15 73.98 Bfc 4.52 8.70 1.85 3.36 33.43 3.24 2.07 0.05 0.08 96.36 C 5.30 8.72 - 4.14 — — 1.69 0.05 0.17 91.09 II Ae 3.45 7.62 8.15 2.27 35.99 3.00 1.86 0.21 3.14 39.73 Bf 4.46 9.12 12.97 3.31 32.77 2.96 3.47 0.05 0.43 89.11
Ucluelet III cn Ae 4.11 7.62 51.89 2.93 33.20 2.73 2.13 0.05 1.58 57.97 CO Bfc 4.75 8.70 - 3,59 - - 2.90 0.05 0.02 99.32 Bf 4.80 8.55 - 3.64 - - 2.62 0.05 0.04 98.52 C 5.02 9.30 — 3.87 — — 2.61 0.10 0.08 97.13
Wreck Bay Ahe 3.56 7.57 114.90 2.38 34.51 2.61 1.89 0.10 3.21 38.27 Bhfc 3.95 9.30 51.89 2.80 33.70 2.77 2.89 0.05 0.82 78.19 Bf(BC)4.67 10.02 3.71 3.53 32.70 3.17 1.86 0.05 0.19 90.95 C 4.71 9.90 - 3.57 - - 2.07 0.05 0.16 92.98
C.L.P. = pH - 5§(P(Ca + Mg) - 1/3 (33.8 - 3pOH) - 64 -
For the remaining horizons, the corrected lime potential values were about 4-11% lower than the lime potential values- The pAl + 3pOH values ranged between 32.70 and 35.99.
The pH-dependent C.E.C, values decreased with depth through• out the four profiles. These values were found to be much lower than those determined by the ammonium acetate method. On the other hand, a consistent relationship with depth for per cent base saturation was obtained with values ranging from approximately 40% to 95%.
The corrected lime potential and per cent base saturation values
showed a significant relationship in the same manner as found by
Clark.
Elemental Analysis ( <2 mm soil)
Values for the oxides of Fe, Mn, Mg, Ca, Na, K, Al and Si are reported in Table XI. For Site I, Fe and Al reached a maximum
in the Bhf; Mn, Mg, Ca, Na, K in the C horizon. For Site II, Fe,
Mg, K and Al were higher in the Bf. For Site III, Fe and Al were highest in Bf and a maximum of Mn, Mg, Ca, Na, K in the C horizon.
For Site IV, Fe, Mg and Al were highest in the Bhfc, Ca and Ma highest in the C; K in the Ahe, and Mn in Bf.
For Sites, I, II and III, the silica content decreased with depth. For Site IV, the silica decreased in the Bhfc to
increase with depth. The maximum values in the profiles were:
Bhf of Site I (26.41%); Bf of Site II (28.07%); Bf of Site III
(29.2%); and Bhfc of Site IV 24.99%.
SXO2 to ^2^3 ratl° ^rtas been used as an index of weathering.
The lowest value observed was 2.11 in the Bf of Site III, followed
by 2.27 for the Bf of Site II; 2.49 for Bhf of Site I and 2.57 for
Bhfc of Site IV. TABLE XI. Elemental analysis on the < 2 mm soil*
Si02 Si02 Soil and Loss on
Fe203 Mn02 MgO CaO Na20 K20 A1203 Si02 R R A120; ignition* Horizon 2°3 2°3
Ucluelet I Ae 5.65 0.09 0.98 0.20 3.00 0.83 16.00 73.25 19.62 3.73 4.57 11.5 Bhf 8.82 0.13 1.67 0.45 2.18 0.91 19.93 65.85 26.41 2.49 3.30 23.0 Bfc 7.03 0.17 1.65 0.59 3.72 1.08 19.37 66.35 23.96 2.77 3.42 8.5 C 6.78 0.17 1.89 1.09 5.21 1.11 18.65 65.00 23.08 2.82 3.48 5.0
Ucluelet II Ae 8.33 0.08 0.86 0.69 3.95 0.72 14.49 70.78 21.32 3.32 4.89 18.5 Bf 9.26 0.08 0.91 0.41 3.35 0.34 21.33 63.80 28.07 2.27 2.99 17.0
Ucluelet III Ae 7.28 0.11 1.20 1.06 3.34 0.84 19.80 66.37 24.59 2.70 3.35 16.5 Bfc 9.13 0.14 1.70 0.39 3.49 0.90 20.12 64.19 26.91 2.38 3.19 12.0 Bf 9.52 0.13 1.68 0.42 3.49 0.90 22.35 61.51 29.20 2.11 2.75 15.5 C 8.26 0.17 1.73 0.76 3.96 . 1.07 19.05 64.86 25.05 2.59 3.41 7.0
Wreck Bay IV Ahe 2.84 0.06 0.71 0.38 3.14 1.42 15.40 75.85 16.02 4.74 4.93 31.0 Bhfc 6.76 0.11 1.88 0.63 4.22 1.18 20.95 64.23 24.99 2.57 3.07 15,5 Bf(BC) 6.09 0.13 1.73 0.92 4.19 0.94 18.84 67.32 22.48 2.99 3.57 6.0 C 4.85 0.08 1.45 1.08 4.35 1.25 18.46 68.36 20.79 3.29 3.70 4.0
* o Based on oven-dry weights (110 C) it it Loss on ignition at 900°C for 2 hrs. TABLE XII. Elemental analysis on the<2 u clay fraction*
„ . % SiO. SiO„ Soil and 2 2_ Loss on
Horizon Fe203 Mn02 MgO CaO Na20 K?0 A1203 Si02 R203 R203 A1203 ignition**
Ucluelet I Ae 4.00 0.13 1.33 0.11 1.14 3.53 34.81 54.95 33.60 1.63 1.58 21.5 Bhf 5.39 0.16 1.83 1.39 2.00 48.12 40.11 47.38 0.85 0.83 30.9 Bfc 4.90 0.19 1.30 1.22 1.08 48.50 42.81 46.06 0.93 0.88 33.7 BC 5.66 0.22 1.60 1.17 1.24 48.00 42.11 46.48 0.91 0.88 0.0
Ucluelet II Ae 3.86 0.13 1.22 0.06 1.20 2.01 33.53 57.99 32.36 1. 79 1.73 18.5 Bf 4.42 0.09 0.90 1.34 1.65 42.35 49.25 40.37 1. 22 1.16 28.8
Ucluelet III Ae 4.67 0.11 1.21 0.02 1.59 1.79 33.12 57.49 32.92 1.75 1.73 17.5 Bfc 3.80 0.11 0.82 0.03 1.18 1.06 53.30 39.7 44.68 0.89 0.74 39.9 Bf 3.70 0.13 0.71 0.15 0.99 0.91 54.90 38.51 50.10 0.77 0.70 38.2 CD C 5.93 0.24 1.77 0.93 2.08 48.01 41.04 46.78 0.88 0.85 32.9
Wreck Bay IV Ahe 3.95 0.16 1.72 0.13 0.99 4.61 29.98 59.46 28.59 2.08 2.05 34.8 Bhfc 3.09 0.13 0.92 0.09 2.37 11.28 39.06 43.06 36.06 1.19 1.10 43.5 Ef(BC) 0.87 0.05 0.29 0.25 4.88 11.36 48.00 34.30 41.09 0.83 0.71 39.0 C 3.09 0.14 1.01 0.77 2.01 4.66 51.00 37.32 46.06 0.81 0.73 38.3
Based on oven-dry weights (110 C) Loss on ignition at 900 C for 2 hrs. - 67 -
The SiO^ to A^O^ ratio decreased with depth in the sola and increased in the C horizon in all the four profiles.
Elemental Analysis (Total Clay Fraction)
The values have been reported in Table XII. For Site I,
Fe, Mg and Na reached a maximum in the Bhf, Mn in the C, Al in the
Bfc and Ca was present only in the Ae. For Site II, Fe, Na and Al increased with depth. For Site III, Fe, Mn, Mg and K were highest in the C horizon; Na highest in the Ae; Al and Ca highest in the
Bf, with no detectable Ca in the C. For Site IV, Fe, Mg and Mn were highest in the Ae; Ca, K and Al highest in the C; and Na highest in the Bf.
The Si02 values generally decreased with depth in all the four profiles, with a maximum of 59.46% and a minimum of 37.32%.
The R203 in the profiles was highest in the Bf of Site III (50.10%);
Bhf of Site I (47.38%); C of Site IV (46.06%) and Bf of Site II
(40.37%).
The Si02 to R,,03 ratio in the profiles was lowest for Bf of Site III (0.77); 0.81% for the C horizon of Site IV; 0.85 for
Bhf of Site I and 1.22 for Bf of Site II. The Si02 to A1203 ratio decreased with depth to increase in the C horizon for the four profiles.
Van Schuylenborgh (1962) from a study of some Iron Humus
Podzols in Indonesia, Germany and Holland found the Si02:R203 ratios on the<^2 mm soil to be between 58-240 in the eluvial horizons;
25-71 in the Bh and 19-111 in the Bf horizons. On the clay separates, he found very low sesquioxide ratios, ranging from 2.6 to 8.2 in - 68 -
the Ae:, 0.6 to 5.1 in the Bh and 1.2 to 4.1 in the Bf. In the podzols under study, there is a decrease in the sesquioxide ratio between the< 2 mm soil and the clay separates of only about 50% and not as high, as found by Van Schuylenborgh. - 69 -
MINERALOGICAL ANALYSES
In the soils under study, the more frequent minerals de• tected were vermiculite, kaolinite, chlorite, mixed-layered minerals, quartz and feldspars. The variations among the soils with respect to mineralogy were in the amounts and distribution of these minerals through the profiles (Tables XIII-XVI).
Fine Clay Fraction
The fine clay fraction for the Ae of the Ucluelet soils contained mainly vermiculite and mixed layered minerals, whereas the Ahe of the Wreck Bay soil contained in addition chlorite and quartz in trace elements. The fine clay fraction of the Bfc horizon for Ucluelet I had mainly kaolinite and that for Ucluelet III mainly chlorite and mixed-layered minerals. The Bhf horizon of Ucluelet I had trace to minor amounts of vermiculite, kaolinite, chlorite and mixed-layered minerals. The Bhfc horizon of the Wreck Bay soil had minor amounts of chlorite and traces of vermiculite and mixed layer minerals. The Bf horizon of Ucluelet II contained only feldspars and kaolinite; that of Ucluelet III traces of kaolinite, chlorite, mixed-layered minerals and feldspars. Only traces of kaolinite, vermiculite and chlorite could be detected in the Bf horizon of the Wreck Bay soil. The C horizon of the latter had minor to major amounts of kaolinite and traces of vermiculite. The C horizon of
Ucluelet III had minor amount of kaolinite and traces of chlorite; whereas that of Ucluelet I had kaolinite in major amount and traces of feldspars. It must be pointed out that the x-ray patterns for most of the horizons showed a significant amount of amorphous clays to be present. o ca i? 5» 8* A A Hi A 3. •o •o N •o •o o o ro ro ro ro ro ro s N M M I I o o I I I I cn ro~c; • • cn ro~C ro to I I cn ro~C Cn tO~C h-1 M 1 I I Montmorillonite* O fO I I I I I I
I I I i i i i i i ro ro ro rIo ro ro Vermiculite*
ro ro CO CO -P I ro I i ro h-> Kaolinite* CO CO -P H co -P H 31 s; ro ro co ro -J' g (6 CD CO M OJ I co \-> I I I 0) cn cn H co , V Chlorite Fe-Mg* 3 cn CD CO -P CO G rt -Pv» M o 28 ro H I o I I ro H co I I I I I I I co i j_ co Mixed Layer* cn H 3
»ii III III £ i ! Illite*
< i f t cn
6
- oz. - 03 s a> 8 A A o O O o 3 rO ro ro ro ro I 1 1 1 Ol rO cn ro "C
I Montmorillonite* o
CO ! I Vermiculite* -P ro
H to M M i Kaolinite* K x M i i i i i i Chlorite Fe-Mg* < o
ro I Mixed Layer* CD ro I ro co I I ro co Quartz* H- Ui ct
ro ro t—1 ro l ro Plagioclase co feldspar* I 3 I ro Amphibole* l-> $ I ro Olivine* S s 1 1 1 1 1 h- ro ' Magnetite (D f+ M M I I I co i 10°A Mica* 8
I I I r—1 I Illite*
I f 1? H O H« r+ £ r+ fO M CD
- U - TABLE XV. Mineral distribution in the Ucluelet III soil
cu •p s rH •H rH Q) rH D, rH •H H .ti 3 O W •H U r8 1 o til cu .5 bC Q) I rH rd
Ucluelet III Ae < 0.2 }i 14 3 1 Intergradient Mont- 0.2-2 )X 4 1 1 1 Vm-Cht 2-5 ji 3 2 1 1
Bfc <0.2 u 2 1 1 High amorphous content 0.2-2 >i 4 1-2 1 1 2-5 >i 3 3 1 2 Bf <0.2 _u 1- 2 Vm-Mont-Cht; 1- 2 High amorphous 0.2-2 ji 2 3 1-2 High amorphous 2-5 yx 2- 3 2-3 3-4 1 1-2 1-0 1-0 - 2- 3 C < 0- 2 ja 2-3 2 1 High amorphous 0.2-2 ja 2 3 1-2 1 1 - 1-2 2-5 ii 2 3 4 1-2 1-2
''Expressed as relative quantities in the following series progression: 1. Present, 0-10%, 2. Trace, 10-25%, 3. Minor, 25-40%, 4. Major, 40-65%, 5. Eominant, 65-100%. \
o W Hi CD f ro O O CM A O O 03 s A A A • • OJ ro ro ro o o o o I I • o o ro ro ro • • ro ro cn ro -p ro ro ro I I I I ro cn ro "£ I I cn ro cn rot •v 1= -c I I I M i I I I I I I I I I Montmorillonite* O
ro H ro CO I I ro co ro ro I I ro I I Vermi culite* ro co -P 3 CD cn ro cn co n> co 3 a r+ co co co I ro I ro Kaolinite* -P ro o CD I M cnHdi I O H ro H r-* of OJ ro co I I co 1 co -P ro co ro Chlorite Fe-Mg* O- rt co ro O H- of < • NO (D ro x I I I I I I I I I I Mixed Layer* < ro ro CO ft rt Cf> H* x rr M CD co t~> Co H J Q CO I I H CO t r- CO i-> J_ to 1 Quartz* CD I -p ro ro ro cn 5 of - rt V ro ro ro CD ro I )-> I I Plagioclase CO co ro CO CO CO feldspar* rt L8» Araphibole* I 5 S* OP
ro 1 cn co I I I H- I I Olivine* I CD -P H O H- of CD - CO I I I I I I Magnetite o o •i -P co I 10°A Mica* art ro CO 0 cn CO o 4 H- I I I I I I Illite* p. -8 o I •rt cn 'TJ cn CD CO T rt- T of CO CO H- CD H- H 4 H H Si H !&• O Hi I H« rt- H* rt H" r+ rt r+ CD CD {B CD 1 a i rt- H- " 5* Pi ft CD CD rt .a CD
- 8Z. - - 74 -
Coarse Clay Fraction
The x-ray patterns for the Ae of Ucluelet I showed traces of vermiculite, kaolinite, chlorite, quartz, feldspars and minor to major amount of mixed-layered minerals. The Ae of
Ucluelet II had major amounts of vermiculite, followed by traces of quartz, feldspars and mixed-layered minerals. Traces of mixed
layers and vermiculite in major amount were present in the Ae of
Ucluelet III. The Ahe of Wreck Bay had minor amounts of 10°
A mica, chlorite and vermiculite, followed by traces of quartz and mixed-layered minerals. The Bhf of Ucluelet I had most of the minerals encountered, from trace to minor amounts. In the Bhfc of
Wreck Bay, chlorite was found in major amount together with traces of vermiculite and mica. The x-ray patterns for the Bfc horizon of
Ucluelet I showed minor amounts of kaolinite and chlorite with traces of quartz and feldspars; whereas that of Ucluelet III showed chlorite in major amount and traces of vermiculite and quartz.
The Bf horizon of Ucluelet II had vermiculite in major amount followed by traces of quartz, kaolinite and vermiculite; that of
Wreck Bay mainly chlorite and vermiculite in minor amounts and traces of kaolinite and quartz. The C horizon of Ucluelet III contained chlorite in minor amount and traces of vermiculite, kaolinite, feldspars and 10°A mica; that of Ucluelet I, chlorite and kaolinite in minor amounts with traces of quartz and feldspars.
The C horizon for Wreck Bay contained chlorite and vermiculite in minor amount together with traces of quartz and feldspars. - 75 -
Fine Silt Fraction
The x-ray pattern for the Ae horizon of Ucluelet I showed illite and quartz to be present in major amounts together with traces of vermiculite; whereas that for Ucluelet III showed minor amounts of vermiculite, chlorite, and traces of quartz. The Ae of Ucluelet
II contained minor amounts of 10°A mica, quartz and feldspars with trace of vermiculite; and that of the Wreck Bay, major amounts of quartz and 10°A mica together with traces of chlorite and vermiculite.
The Bhf of Ucluelet I comprised quartz in major amount followed by traces of vermiculite, kaolinite, chlorite and feldspars; the Bhfc of Wreck Bay, minor amounts of chlorite, quartz, feldspars and traces of vermiculite. The Bfc of Ucluelet I had minor amounts of kaolinite, chlorite, quartz, with traces of feldspar. Evidence from x-ray patterns showed the Bf of Ucluelet II to contain vermiculite in minor amount and traces of the primary minerals quartz, feldspars, amphibole, olivine and quartz in minor amount. The Bf of Ucluelet
III had traces of kaolinite, chlorite, feldspars, and quartz in minor amount; whereas that of Wreck Bay contained traces of vermiculite, kaolinite, chlorite, feldspars, together with quartz in minor amount. The C horizon of Ucluelet I comprised mainly, minor amounts of kaolinite and quartz with traces of chlorite, feldspars and amphibole; that of Ucluelet III quartz in major amount, chlorite in minor amount and traces of kaolinite, feldspars and amphibole. The C horizon of Wreck Bay had feldspars and kaolinite in minor amount and traces of chlorite and feldspars. - 76 -
The distribution of each mineral with depth was not similar in all the four profiles under study. For instance, vermiculite appeared mainly in the Ae of Ucluelet III in major amount; in the Ae and Bhf of Ucluelet I in trace amount-, in major amount in the
Ucluelet II soil; from trace to minor amount in the A and B horizons of Wreck Bay and absent in the C horizon. Kaolinite increased with depth in the Ucluelet I, III and Wreck Bay soils from none to minor amounts. In Ucluelet II, kaolinite was still present in the
Ae. Chlorite stayed ahrost constant with depth in the soils of
Wreck Bay, Ucluelet I and III, and was absent in Ucluelet II. The mixed-1 layered minerals were generally present only in the upper textured horizons of the four soils. Quartz and plagioclase feldspars had the same pattern of distribution with depth in all the four profiles. The more easily weatherable mineral like amphibole, olivine and ferromagnesian mica were generally absent in all the four profiles. - 77 -
CHARACTERIZATION OF PLACIC MATERIAL
During field sampling of the soils, cemented material in the master B horizons was observed. The Wreck Bay soil which is poorly drained, had a thin pan which occurred about 30 cm from the surface. This pan followed a branching course parallel to the soil surface. In the field it appeared "rusty" black and was about 5 mm thick. A bulk sample of the Bhfc horizon was brought to the laboratory. The bulk layer was allowed to dry and that layer con• taining the placic horizon was scraped and ground for chemical analyses.
In the field, the pan did not seem to allow water to permeate through, as the layer below it was dry. Morphology of the pan with time was found to change in the laboratory. The "rustiness" started to become less apparent. The material became permeable to water; turned softer to the touch and could be easily broken by hand. Decayed wood was frequently found in the pan itself and also as black spots in the surrounding matrix.
The Ucluelet soil (Site III) is moderately well drained.
The pan present here was observed to be 2 mm thick, had a vitreous appearance and was black in colour. The pan followed an irregular course, leaving its marks on cobbles and gravels, and apparently penetrating these coarse fragments. It was surrounded by a matrix which was dusky-red and scattered tiny black spots were present.
When the pan and matrix were broken, it was frequently found to have a concentration of a red powder, surrounded by a black one. Most of the material forming the matrix was coarse-textured ranging from
2 to 10 mm in size; these, together with the sand grains,were cemented by iron-oxide coatings. This pan could also be broken by - 78 - hand, but less easily than the one at Wreck Bay.
Observations at a gravel pit, a few miJ.es away from the
Ucluelet sites, showed a pan having the same morphological characteristics as the one described for Ucluelet (Site III). This is shown in Figure 8. The extent of this placic material is not known exactly.
Results and Discussion
Some selected chemical analyses were carried out to determine the nature of these placic horizons, namely, elemental analysis, oxalate-extractable Al, Fe and Mn; dithionite-extractable Al, Fe and Mn; amorphous Al and Si; and organic matter. The data are presented in Table XVII. The sample from the Wreck Bay soil con• tained about 50% of the. < 2 mm material. The pan from the Ucluelet soil had a bulk density of 2.64 and a total porosity of, 0.38%; its matrix had a bulk density of 2.47 and a total porosity of
6.79%.
The results of the elemental analysis on the <2 mm fraction for the Wreck Bay pan, were not very different from those of the Bhfc horizon (Tables XI and XVII). The main difference was the higher organic matter content in the pan. Sesquioxide values were higher than those for the BC horizon. Comparing the clay fraction data, the sesquioxide values for the pan were slightly higher than that for the Bhfc horizon, but lower than that for the BC horizon. Fe and Al values extracted by dithionite and oxalate were higher than in the Bhfc and BC horizons.
Amorphous Al was also higher than in the Bhfc and BC horizons. Fig. 8(a). Photograph of placic material at a Ucluelet site - 79a -
Fig. 8(b). Photograph of placic material at a Ucluelet site TABLE XVII. Selected chemical comparisons of the composition of the pan to the soil matrix
Dithionite Oxalate Amorphous O.M. Al Fe Si Al Fe Mn Al Al % % % % ppm
Pan (Wreck Bay) 14.30 0.8-5.8 1.1-4.1 0.22 2.9 1.3 16.0 1.71 1.39 Pan (Ucluelet III) 8.63 0.60 15.6 0.25 0.80 16.0 176 N.D. N.D. Matric (Ucluelet III) 1.38 0.30 4.9 0.21 0.53 4.6 44.0 N.D. N.D.
Elemental Analyses T
Si02 SiO„ Loss on CO o Fe203 MnOr MgO CaO 2 2 Ma 0 K 0 M SiO, R A1203 Ignition 2°3 2°3 *2°3 Par (Wreck Bay) <2 mm 7.25 0.24 1.55 1.11 3.35 0.99 20.75 64.58 23.35 2.55 3.12 26.00 Fan (Wreck Bay) 2_u clay fraction 7.06 0.33 2.75 1.23 2.05 2.06 36.33 48.19 38.18 1.26 1.30 27.20 Pan (Ucluelet III) 73.10 2.05 1.14 0.53 1.87 0.51 8.59 12.20 87.96 0.14 1.42 31.56 ^trix (Ucluelet III) 19.91 0.71 1.71 0.76 5.27 1.07 12.19 58.38 32.18 1.81 4.79 8.70 - 81 -
Chemical data for the Ucluelet pan showed a very high concentration of iron in comparison to that found in the matrix and the underlying horizons. The sesquioxide value by elemental analysis was 87.96% (Table XVII) and dithionite-extractable Fe and oxalate extractable Fe were about 16%. Here again a higher organic matter content was noted in comparison to the matrix and underlying horizons. The high content of Fe20gConfirmed the high bulk density found.
From the study of an Iron Pan Humic Podzol; McKeague et al.
(1967) found the pan to contain 13.4% oxalate-Fe and 1.9% oxalate Al. The loss on ignition was 26-32% and total iron and alurninium to be about 16 and 6% respectively. In 1968, McKeague et al. studied several podzols and found that the oxalate extract- able Al and Fe values for the pan ranged between 0.4 to 2.6% Al and 1.4 to 11% Fe. The total iron as elemental Fe reached a maximum of 25%. In this study the maximum total iron content observed was 51%.
Differential thermal analysis gave two exothermic peaks at 257°C and 273°C for the Ucluelet pan and 273°C and 326°C for the Wreck Bay pan. These curves are reported in Figure 9.
Characterization of these peaks failed to approach the patterns obtained during the analysis of the clay minerals. They faintly approached the patterns for iron oxide gels. Interpretation of these two curves seems to favour presence of an unidentified metal-
O.M. complex, in the same manner as reported by Schnitzer and
Skinner (1964). They found exothermic peaks of prepared metallo- organic complexes and a complex extracted from the soil, to fall 200 400
Temperature °C
9. Differential thermal curves (1) Ucluelet pan and (2) Wreck Bay pan - 83 - at about 280°C. X-ray analysis failed to show evidence of crystallinity in both pans.
It can be suggested that the formation of these placic horizons may be due to different heat energy changes and rates of reactions taking place, in comparison to the formation of a podzolic horizon. The types of functional groups, the number of charges" on the low and high molecular weight polymers present in the organic matter, together with the stability constants of the complexes may play very important roles in controlling the amount of iron translocated and deposited. One must not rule out the possibility of the organic portion of the complex leading to pan formation to be different in chemical properties than that leading to the
Bf horizon, because data show higher organic matter content in the pans than in the podzolic horizons: - 84 -
SUMMARY AND CONCLUSIONS
The purpose of this study was to assess the soils through selected physical, chemical and niineralogical properties in order to relate the data with morphological observations, the landscape and soil development.
The soils investigated were acid, sandy and gravelly textured, with bulk density values greater than one. The organic carbon content of the Ahe of the Wreck Bay soil did not reflect the morphological observations. Due to the high precipitation in the region, the field water contents were high. Water retention curves showed that even at 15 bars tension, the upper finer textured horizons had significant amounts of soil water. The base status of these soils was generally low and the C/N and C/N/S ratios were very wide, indicating microbial action and recycling of nutrients to be slow. The Wreck Bay soil had less available Mg, K and total
N than the Ucluelet soils. It is suggested that the effects of these elements, coupled with less favourable physical properties led to the establishment of a "bush type" vegetation and stunted growth of the lodgepole pine at the Wreck Bay site when compared with that of the Ucluelet sites. Determination of base saturation with calcium chloride gave a more meaningful relationship with depth than that found by using ammonium acetate. The relationship found was that base saturation increased consistently with depth.
A common relationship with depth was found between lime potential
and base saturation. Dithionite extractable aluminium values were - 85 -
generally less than those found by oxalate; but iron values were higher by the dithionite method. Values for aluminium and iron by oxalate and aluminium by NaOH treatment paralled values from elemental analysis. Mineralogical analysis indicated the presence of vermiculite, kaolinite, quartz, feldspars, chlorite and mixed- layered minerals in significant amounts.
These soils have been found to have podzolic (spodic) horizons, that is Bhf and/or Bf. In the Ucluelet soils, it appeared that both iron and aluminium have been significant in the processes leading to podzol formation. In the Wreck Bay soil, the dominant metal ion seems to have been aluminium. Out of these four soils, three contained placic horizons. Iron and organic matter were the major components and contributed most to the formation of the pan in the Ucluelet soils. This is best exemplified by
Ucluelet III. However, in the case of the Wreck Bay soil, it has been found that the pan can form with amorphous iron values of less than 2%. Crystallinity could not be detected by x-ray analysis in the pan samples.
Differential thermal curves did not confirm the presence of any mineral or compound that could be identified; there was however, evidence of some constituent present which gave an exothermic peak between 250-350°C. This was attributed to either iron-oxide gels or iron-organic matter complexes. The vitreous nature requires further elucidation.
The Wreck Bay soil is a poorly drained soil having a flat topography, whereas the Ucluelet soils are moderately well drained - 86 - and occur on gentle slopes. It was observed that topography played a significant role in changing the course of profile development of these soils. In the Wreck Bay soil, the pan has caused an impervious barrier to movement of materials downwards and there is indication that with time, there will, be a build-up of organic material leading to a bog type plant association. The situation may stay the same in Ucluelet if the rate of lateral drainage exceeds the rate of precipitation; however, with time, it is to be expected that the fertility status of the upper horizons will be impoverished to a point that plant growth will be impaired and the present plant association will give place to the type of association now existing at Wreck Bay.
Classification of the soils into the Canadian, U.S.A. and World systems would be as follows:
Taxonomic Correlation
Canadian American World
Ucluelet I Placic-Ferro Humic Placorthod Placic Podzol Humic Podzol
Ucluelet II Orthic Humo-Ferric Cryorthod or Humo-Ferric Podzol Haplorthod Podzol
Ucluelet III Placic Humo- Placorthod Placic Podzol Ferric Podzol
Wreck Bay Placic Ferro- Humic Placic Podzol Humic Podzol Placorthod
In an attempt to summarize the results from the preceding discussion the following sequence of soil development may be postulated: - 87 -
Regosol ^ Orthic Humo-Ferric Podzol > Placic Humo-Ferric (Ucluelet II) Podzol (Ucluelet III)
Gleyed Placic Ferro-Humic Placic Ferro-Humic Podzol -f- Podzol (Wreck Bay) (Ucluelet I)
The genesis of iron pans is still not well understood. The pans may form under alternating conditions of oxidation and reduction; i.e. the Ucluelet stage. It is after the formation of the placic horizon (Ucluelet III and I) that more reducing conditions may be present above the pan. Since oxidizing conditions probably occur below the pan, the latter once formed does not thicken-.
Inorganic iron mobilization and reprecipitation does not appear to explain the concentration of iron in the pan. One of the modern concepts of the formation of the Bf horizon is movement of organic matter metal complexes and deposition of sesquioxides. This could mean that these complexes are broken down at various depths and, most of the organic portion with some sesquioxides are leached resulting in a net sesquioxide accumulation. In the case of the iron pan, translocation may have taken place in the same manner, but deposition may have been different due to chemical changes taking place such as changes in oxidation-reduction potentials. - 88 -
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