Table Of ContentCROAVO-CLAT HVLATIOBSVIPS IV SOIL AOGRBGATS FORMATION
DISSERTATION
Presented in Partial Fulf iHjaent of the Requi remote far the
Degree Doctor of Philosophy In the Graduate School of
the Ohio State University
By
Jams John Doyle, B. S., M. 3,
The Ohio State University
1952
Approved by: /
Adviser
ACKNOWLEDGMENT
The author wishes to express his sincere appreciation to
Dr. G. V. Yolk, Dr. V. P. Martin and to other members of
staff of the Agronomy Department of Ohio State University,
and to Dr. R . A. Ruerhweln of the Monsanto Chemical Company
and to Dr. L. Y. Burt of the Hercules Powder Company for their
assistance and information.
The writer la grateful for the financial assistance pro
vided by the Ohio State University through an asslstantshlp In
the Agronomy Department.
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TABLE OF CONTENTS
Page
Introduction ............................................. 1
Berlev of LI terature.................. .................. 3
(a) Types of aggregates ........................... 3
<*> Causes of stability ........................... U
(c) Stabilizing agents ............................. 5
(d) Organic-inorganic bonding ...................... 8
(e) Properties of cementing material .............. 11
Purpose of This Investigation ............................. 12
Materials Used........ . . .............................. 13
Experimental ............................................. 16
(a) Screening of aggregating materials ............ 16
(b) Determination of relative aggregating powers of
aggregating materials ........................ 20
(c) Adsorption of polymers on clays ................ 26
(d) Cation exchange vs adsorption .................. 26
(e) Anion surface vs adsorption .................... 26
(f) Specific surface vs adsorption ................ 30
(g) Functional groups vs adsorption and aggregation . 33
(b) Viscosity vs aggregating power ................ 31*
(1) Response of different clays to polymers . . . . 39
(J) Effect of cations on aggregation .............. 1+1
(k> Effect of polymers on cation exchange capacity . 16
(1) Effect of polymers on moisture holding capacity. U6
(m) Resistance of polymers to microbial attack . . . 1*9
General Discussion ....................................... 51
Suaanary . 53
List of References . . ................................. 51+
Autoblography ........................................... 57
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ORGAJIO-CLAY RELATIOHSHIP8 DC SOIL AGGREGATE FORMATIOH
ihtroduction
In the attempts to increase or even maintain crop yields the
problem soon resolves Itself Into one of the detection and cor
rection of Halting factors. The Halting factor aay be an
obvious one such as a deficiency of certain major elements or
minor elements, lov rainfall or soil acidity. However, after
the correction of all the known deficiencies many soils still
fall to produce Increased yields or even to maintain yields. Al
though It was realised in the early days of agriculture that the
soil should be in good tilth, the emphasis has always been on the
chemical phase of soil plant relations, therefore as long as yields
could be increased through the use of larger quantities of better
balanced fertilisers, the physical aspect of soil plant relations
was pretty well overlooked.
Although all the limiting factors In the chemistry of soils
have not been discovered and corrected, it Is being realised more
and more that the physical condition of the soil may be the largest
single factor.
With this new Interest in soil structure there arises an Inter
est In the materials capable of aggregating soils as well as In the
me chanisms by which aggregation Is brought about. An Increased know
ledge of natural organic aggregating materials, as well as the devel-
opment of a large number of synthetic polymers capable of aggregating
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■ olle hare provided toole which are extremely valuable Id Baking
a fundamental study of aggregation and the oechanlaia of
aggregation.
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REVTEW OF LITERATURE
Type* of Aggregate*
Soil* are casq>osed of particles of different sites possessing
a tendency to cluster together and f a n larger aggregates. These
aggregates are classified bj Russel (3!*, p. 71) as
" clods which are large and can be broken down by
neebanleal neane; crumbs and granules which are snaller
but in which the particles are held more tenaciously, so
that same gentle chemical treatment is necessary to
separate them; and coocretloos in which fine material is
bound still more firmly by a cement containing inorganic
colloids"........"Deflocculated (dispersed) clay pastes
dry to hard uniform and usually large clods, possessing
▼ery few cracks, while flocculated pastes dry to smaller
more crumbly clods, usually full of cracks Clods
formed by drying a deflocculated clay paste differ In
another fundamental respect from these formed from a
flocculated paste; on wetting, the former typically re-
disperse into a paste; whereas the latter may swell in
water but they retain their shape, and do not reddsperse.
Clods showing the farmer behavior are called water-
unstable and the latter water-stable, crumb formation is
thus seen to be a characteristic of a flocculated and hard
clod formation of a deflocculated clay."
Although, as Russel points out there are at least three types
of aggregates, most interest is centered around the crumb type,
because it la the desirable type of aggregate from the standpoint
of soil stability and porosity. This crumb type of aggregate,
however, must be water stable to be of any lasting value.
The cause of water stability or instability in clay crumbs is
not known, but Russel (3*», p. U13) suggests that in a deflocculated
paste there is a mutual orientation of the clay particles, and if
more water is added, it can penetrate freely between the clay
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particle*, whereas the mare random orientation of the particles In
the flocculated suspension does not allow the penetration of
additional water. He states further that
"The mechanism of the intraparticle hoods that hold them
together in these stable coofIguratloos Is not known ....
hut their existence Implies that the large volumes occu
pied by floes In dilute suspension must he due to these
bonds holding clay particles together In chains enclosing
large volumes of solution.1*
To sum up, stable aggregates are built up from floccules In which
the random orientation of the clay particles does not permit the
penetration of additional water.
Causes of Stability
Many of the early workers considered cations, especially cal
cium, as being the principal flocculating agents which bring about
stable aggregate formation. Although the effect of catloos,
especially divalent cations Is not to be Ignored, it Is pretty
well realised that most of the effect of calcium In Improving
soil structure Is Indirect, In that addition of calcium to an acid
soil gives rise to Increased production of plant material and to
Intensified biological activity. Bradfleld (2) describes aggregate
stability as being brought about through a coating of clusters of
particles with organic material. The work by Kroth and Page (19)
however Indicates that instead of a coating of organic material on
the surface of aggregates there Is a uniform distribution of organic
materials throughout all parts of the aggregates, with the possible
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exceptlon of the centers. Recent experimental work by Jones
(17) on methods of applying synthetic conditioning materials
demonstrates that stable aggregates can be farmed by stabilizing
the exterior of unstable clods . Whatever the distribution of ag
gregating agents, or the mechanism by which clay particles assume
stable configurations, It is known that certain materials when
added to clay or soil, effect stable aggregation.
Stabilizing Agents
The difficulty of Isolating cementing substances from
naturally aggregated soils, without destruction or modification of
these substances led to an Indirect approach In the search for
aggregating agents. Thus, Lutz (21) concludes that free Iron is
an Important factor In Influencing the granulation of semi -
laterltic and lateritic soils. He postulates that the free Iron
serves a dual purpose, the part vhlch is In solution functioning
as a flocculating agent and the other as a cementing agent. Dutt
(7) Increased aggregation In Icrollnite by using silicates, he
ooncludes that it Is the silicon vhlch does the aggregating.
Van fiavel (39) found that Hthe aggregation of widely different
soils vas Increased from 50 to 100 percent when exposed to the
fumes of methylchlar os Hones**. Russel (3H, p. UI3) lists clay
Itself as one of the principal agents responsible for crumb forma
tion. He points out that in most soils the clay forms a continuous
network that enmeshes the silt and sand particles; but that the
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clay may actually bind the sand and silt par tic lea together
(through bonding). The theory of a bond between clay and aand la
also advanced by Slderl (36) who prepared aggregates front sodium
clay and quartz sand "which showed a very remarkable resistance to
water".
It has long been recognized however, that organic matter,
including products of* microbial activity Is the most Important
single agency responsible for the development of stable aggregates
In soils. Studies of the effects of various types of organic matter
on soil structure soon led to the very Important observation that
the condition of the organic matter Is a factor. Russel (3**,
p. U09) states "the role of organic matter In soil structure depends
on the type of organic matter present, mere organic remains, such as
sone types of peat have no effect on structure Itself - although
they may assist the aeration or the water-holding power of the soil -
nor is the effect of old stable humlc colloidal material very great."
Martin (26) about the same time observed that compost# have less
effect on soil aggregation than less well-rotted material. On the
same observation, Bradfleld (2) notes that prairie soils when bad
ly farmed have a high organic matter content but poor aggregation.
It was further observed by Browning and Milan (3) that organic mat
ter, decomposing rapidly, produces an increase In aggregation with
in a few days and that a maximum of aggregation Is reached within
20 to 30 days, followed by a decline. This increase and decline
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ln aggregation parallels or lags slightly behind the corresponding
microbial activity. It appears then, that aggregation is brought
about by decomposition products of organic matter or by synthesis
products of bacteria. That the aggregation produced by microbial
activity Is temporary In nature vas observed by McCalla (22). The
temporary nature of this aggregation suggests that the aggregating
materials are themselves further decomposed by organisms. Stable
aggregation under natural conditions Is therefore seen as a
dynamic process In vhlch continuous turnover of organic matter
Is required for the maintenance of stability.
It le clear then that organic matter as suggested by Russel
"seems to Improve the structure more by Its decomposition than by
its presence”. What then is the nature of the decomposition or
synthesis products vhlch act as stabilizing agents? Martin (27)
concludes from his experimental vork that Increased aggregation Is
brought about by one or more of the following:
1. Cells and filaments of the numerous microorganisms that
decompose organic residues.
2. Products of microbial synthesis.
3. Decomposition products of microbial metabolism.
U. Water soluble aggregating substances contained In the
original material. McNamara (25) divides these organic binding
materials Into tvo general classes, the proteins and the carbo
hydrates .
Although there Is no direct evidence that proteins as such
