PHYSICO-CHEMICAL INVESTIGATIONS OF CLAY-ADSORBED ORGANIC COLLOIDS

95 Pages·4.559 MB·English

by  STEVENSON, FRANK JAY

PHYSICO-CHEMICAL INVESTIGATIONS OF CLAY-ADSORBED
ORGANIC COLLOIDS
DISSERTATION
Presented in Partial Fulfillment of the Requirements
for the Degree Doctor of - Philosophy in the
Graduate School of the Ohio
State University
By
Frarifc Jay Stevenson,. B* S.
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The Ohio State University
1952
Approved by*
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ACKNOWLEDGMEWTS
The author wishes to express his appreciation to
the f'e.cuity end grg.due.te students of the Department of
Agronomy of the Ohio State University for their interest
gnd guidance during the course of this investigation.
Special appreciation is expressed to Dr. W. P. Martin,
who supervised this study.
The author is indebted to Dr. Quentin Van Winkle
of the Chemistry Department for his help in planning the
experiments and interpreting the results. Mention should
also be made of Dr. D. 0. Robinson, now of Arizona State
College, who- initiated the electrophoresis study, gnd of
Kenneth Pox, graduate student in Dairy Technology, who
helped the author master the mechanical operation of the
electrophoresis and ultracentrifuge apparatus.
Sincere gratitude is expressed to the author1s wife,
Leda Jensen Stevenson, for her encouragement and inspira­
tion, and for typing the manuscript.
r
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TABLE OF CONTENTS
Page
I. Introduction ........ 1
II. Review of Literature .................. 3
III. Experimental .................. 13
Ultraviolet and Infrared Absorp­
tion Analysis ........ 17
Results....................... 18
Electrophoresis .................... 22
Electrophoretic Mobility ..... 31
Boundary Anomalies........... 32
Procedure ..................... 33
Results ..... 34
Determination of Molecular Weight • . 42
Molecular Weight of Poly-
disperse Systems.......... 44
Sedimentation Velocity ............ 46
The Light Absorption Method ... 47
Procedure ............ • 49
Results .............. 53
Diffusion......................... 58
Polydisperse Systems 61
Procedure ........ 63
Results ....... . 65
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Page
Partial Specific Volume . ...........• • 67
Procedure ..... 69
Results: ................ 70
XV. Calculations ............ 71
V.. Discussion............................. 72
VI. Summary .............................. 78
Bibliography ......... 80
Autobiography ...... 91
I. INTRODUCTION
Soil organic matter, although marring up hut a small
fraction of the soil mass, is. a characteristic and essen­
tial component of the soil, and as such, an understanding
of the role it plays is of fundamental importance. At the
present time there are still a large number of practical
problems in soil organic matter management which need to
be solved, and the final solutions to many of them await a
better understanding of the chemical nature and composition
of soil organic matter.
Progress towards the elucidation of soil organic matter
has been unusually slow; both because of the complex nature
of soil organic matter and because, in general, soil chem­
ists have attempted to characterize soil organic matter
using simple analytical procedures, while if we are to
judge by its complexity, the more specialized methods and
techniques should have been applied.
In recent years, physico-chemical methods, such as
electrophoresis, ultracentrifugation, diffusion, light
scattering, osmotic pressure, electron diffraction, and
others have contributed considerably to the characterization
of complex organic colloids occurring in biological systems.
It was the purpose of this investigation to apply some of
these methods to a study of the organic colloids extracted
from clays, with the object in view of evaluating the
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applicability of* these methods for the chsrg.cterizg.tion of
some of the more complex components of soil organic matter*
The clay fraction of the soil was chosen for study for
the following reasons:
1. The organic matter associated with clays is prob­
ably similar in composition to the substances which have
become known as humus. Thus, the data obtained would refer
to true products of microbial decomposition and not to
compounds extracted from the unaltered plant residues*
2. The degree of soil aggregation and stability of
aggregates appears to be a function of the organo—clay
complex*
3. Evidence is accumulating that certain compounds
like the proteins and polyuronides when adsorbed on the
clays are less susceptible to microbial attack and persist
for longer periods of time in the soil.
The investigation consisted of an electrophoresis exam­
ination to determine the number of electrically separable
colloids extracted from Brookston, Crosby, and Miami clay
with neutral sodium pyrophosphate solution, and of a sedi­
mentation velocity and free diffusion stuidy to determine
the size and shape properties of humic acid. In addition,
ultraviolet and infrared absorption analyses were made of
the humic acid colloid.
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II. REVIEW OF LITERATURE
Wgksman (119) (121) has written an excellent histor­
ical account of soil organic matter, and Norman (77) (79),
Bremner (14), gnd Russell (100) have outlined some of the
recent developments. This review will deal only with some
of the more recent researches in the field.
Considerable confusion has existed in the literature
with respect to the terminology used to designate the
various organic matter fractions. In this discussion the
following definitions will apply: humin for the portion
of the organic matter insoluble in alkali, humic acid for
the alkali-soluble acid-precipitated fraction, and fulvie
acid for the fraction soluble in both alkali and acid.
In addition, the terms soil organic matter and humus
require clarification.. They will be used as defined by
Russell (100)t i.e. soil organic matter to denote the total
of the humified and non-humified material, and humus, the
“matiere noire“ of Grandeau, to designate the humified
material, the end product resulting from the microbial
breakdown of organic residues in the soil.
Fractionation of Organic Matter
The classical method of fractionating soil organic matter
was based on the separation of humin, humic acid, and fulvic
acid from an alkali extract of the soil and determining the
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relative proportions of carbon and nitrogen in the fractions
thus obtained. The data served as an index for determining
the differences or similarities of the organic matter in
various soil types but contributed very little to our under­
standing of the chemical nature of soil organic matter.
Waksman (119) (123) made a study of soil organic matter
using a method of fractionation suitable for the identifica­
tion of organic constituents found in plant materials* The
groups separated were fats and waxes, resins, hemicellulose,
cellulose, soil proteins, and ligno-humus., A severe limita­
tion with this method was that the so-called soil proteins
and ligno-humus groups were not determined directly but were
estimated by differences.
Recently,, a method of. fractionating the fulvic acid
fraction was introduced by Forsyth (31) using a selective
adsorption technique. One fraction contained water soluble
organic compounds, such as sugars and amino acids, a second
phenolic glycosides or tannins, a third polyuronides, and a
fourth pentose sugars and organic phosphates., Bremner (100,
p. 264) carried out a similar fractionation using sodium
pyrophosphate solution to extract the organic matter instead
of the usual harsh alkalies. He found that the same general
groups were present but in different proportions, indicating
that harsh alkalies may alter some of the organic complexes.
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Lignin and Protein Content
The opinion is now quite generally held that a con­
siderable portion of humus is made up of lignin or lignin-
derived materials. This is based on the fact that lignin
is the least readily attacked of all plant constituents,
with the result that the lignin content of decomposing
plant materials is increased, thus contributing to humus.
Hebert and Deherian (119, p. 186) postulated that humus
consisted of lignin derived from plant tissues and of pro­
teins formed by microbial synthesis. Waksman and lyre (126)
prepared a synthetic lignin-protein complex in the labora­
tory which had many properties in common with humic acid*.
They attributed the stability of soil proteins to a union
with lignin, as indicated by the fact that the proteins so
prepared appeared to be resistant to microbial attack.
Little is known of the chemical changes involved in
the conversion of plant lignin to form humic acid. The
studies of Gillam (39) indicated that the transformation
involved a gain in carboxyl groups, as; shown by base ex­
change studies. Gottlieb and Hendricks (4-5). found that
material in the soil derived from plant material was dras­
tically altered in the kind and position of the peripheral
groupings on the aromatic ring. They suggested that plant
lignin undergoes a type of change similar to that obtained
when lignin is treated with alkali. Essentially the change
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consists of g condensgtion of demethoxylgted lignin molecules
with the production of g fused ring structure*. Wgksmgn gnd
Smith (127) found thgt under gerobic decomposition lignin
is gttgcked gs g whole gnd the methoxy content of the re-
sidugl lignin remgins unchgnged; but under gnerobic condi­
tions lignin is modified gnd its methoxy content reduced*.
The grgdugl trgnsformgtion of lignin into dgrk colored
humic substgnces is chgrgcterized by g reduction in methoxy
content (127).
Evidence for the production of humic gcid from lignin
is glmost overwhelming, but nevertheless presumptive*. Pinck
gnd Allison (89) found thgt blgck gnd brown species of fungi
isolgted from the soil contgined up to 29 per cent lignin-
like complexes hgving' properties similgr to soil humus*
These workers do not exclude the possibility thgt lignin
is converted to humic gcid, but suggest thgt g considergble
gmount of lignin-like mgterigl could be formed by lignin-
synthesizing orggnisms* Mgrtin et gl* (70) found thgt g
relationship existed between the type of molds thgt develop
during decomposition gnd the chgnges in the properties of
the vgrious constituents of soil orggnic mgtter during the
decomposition process*. According to Geltzer (38) soil
orggnic mgtter is first gttgcked by fungi, gnd humus is
produced by bgcterig which in turn gttgck the funggl mycelig.
The chemicgl ngture of humic gcid is one of the unsolved
mysteries of ggriculture. A survey of the litergture (30)