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CHAPTER VI
INFILTRATION RATES OF SOILS FOR WATERS OF DIFFERENT
SAR WITH DIFFERENT SALINITY LEVELS
The downward entry of water into soils is referred as
infiltration. The study of infiltration rates has special
significance in soil studies as it is influenced by many
factors such as chemical and physical status of the soil,
nature of the soil surface and profile. Infiltration rate
is defined as the volume of water passing into the soil per
unit of area per unit of time. It has the dimension of
-1 velocity (LT ).
When water, either from rain or irrigation,enters the
soil it immediately fills the uppermost layer of micropores.
At the same time some of the water is filled into the
continuous micropores by capillarity. Thus two types of
water movement, percolation (gravity flow) and capillarity,
work together in facilitating the irregular downward
penetration of water (67). If the infiltration is high the
soil interstices, both micro and macro,ultimately become
saturated to the full length of the profile until some
impervious layer is encountered. Under such circumstances,
the necessity of clearing off the micropores by drainage is
essential, otherwise the aeration conditions may
deteriorates. Certain factors further complicate the
percolation of water through soils,especially in the case
147
of saline-alkali and non-saline alkali soils. Clay
colloidal matter may clog not only the connecting channel,
but even the macropores, ultimately closing the smaller
pores. Secondly, entrapped air also impede the rate of
percolation.
In general, the finer the texture of the soil,slower
will be the rate of gravitational water flow. In sandy
soils the pores are large,amount of colloidal matter low
and flow will be easier. In heavy soils the pore spaces are
small and clogged with colloidal materials and the
contraction are many (34). The situation is further
aggravated in the case of a saline-alkali soil due to the
dispersion of the clay resulting from the hydrolysis of
exchangeable sodium in the soil matrix. Unless granulation
is encouraged by organic matter and other means,drainage in
such case will be slow and often ineffective.
According to Russell (61),plant growth on soils depends
directly on the presence of air,water and nutrients as well
as on suitable conditions of temperature and light. Under
normal circumstances, the soil complex contains sufficient
amount of nutrients which are released to the ·plant
gradually. The interspace between particles provides
sufficient water storage and at the same time permits
necessary aeration to the plant roots. When all conditions
are favourable the soil is known as a fertile soil. Wollny
(69) considered
physical properties
large
of
number
the soil.
of factors
According
influencing
to him, in
compact soil,the soil behaviour with regard to aeration and
148
availability of the air and water to the plants can be
considered poor. King (27) attempted to determine the
effective diameter of the pores by means of rate of flow of
air into a column of a soil. He also concluded from his
experiments
properties
colloidal
that clay and humus controlled the physical
of the soil due to high surface activity of clay
materials. The soil colloids will suffer either
dispersion
will form
due to the presence of high amounts of sodium or
large aggregates in presence of calcium or
organic matter. It is known that the stability of the clay
suspension is decided by the magnitude of the electric
charge (electric potential).
Wiegner (68),was the first to point out that the degree
of dispersion or stability of clay is determined by the
nature of the adsorbed cation. He showed that the stability
of the clay particles saturated with different cations
follows the Hofmester ion series:
L i > Na > K > Rb > Cs
In order to understand the factors influencing the
infiltration
the meaning
and allied
terminology
of America
rate and permeability,it is important to know
of the terms and the difference between these
terms. The report of the sub-committee on
has been published by the Soil Science Society
(55) in 1952. The downward entry of water into
the soil is known as infiltration. The infiltration rate
depends upon
of water in
physical condition of the soil and hydraulics
the profile,both of which may change rapidly
149
with time. The term infiltration velocity is the volume of
water moving downward into the soil surface per unit area
per unit time. The term infiltration velocity is close to
infiltration rate. However,infiltration velocities measured
with
the
small cylindrical infiltrometers will usually exceed
unless an adequate guard-ring infiltration rate
arrangement is used to control divergent flows in the soil
below the cylinder. Also,infiltration velocities measured
in water spreading
rate for the soil
operations may exceed the infiltration
if a considerable depth of water is
impounded. But if suitable controlled conditions are
maintained, infiltration rate and infiltration velocity will
have identical values.
The Darcy flow equation
V = K i2
expresses the proportionality between the flow velocity and
the
I K I
driving
in this
force in terms of the hydraulic gradient. The
practical unit
equation (the Darcy K) is commonly used as a
for expressing the permeability of soil to
water by soil scientists and engineers. The value of 1 K1
for a porous medium depends both on the nature of the
medium and the physical properties of water. The early
workers thought permeability as a property of medium alone.
A lot of confusion has been made regarding permeability and
its dependence or non-dependence on the fluid medium.There
are so many physical mechanisms and processes involved in
the flow of water in soil that,it is not clear as to how to
150
take into account all the variables in the fundamental
equation for soil permeability. For example,a change of a
few hundred parts per million in soluble electrolytes can
change the water flow rate in some agriculture soil by a
factor of 300. For media which have stable pore structure,
the permeability (intrinsic permeability) is the same for
liquid and gases.
Experience indicates that the infiltration rate of a
given soil can be high or low,depending on physical status
and management history. Infiltration rate is often
critically influenced by surface soil conditions, but
subsurface layers also are sometimes limiting. Water
distribution in the profile and depth of water applied are
modifying
high or
factors. The infiltration rate can be undesirably
undesirably low. It is the low end of the range
that may be a critical limiting factor in the agricultural
use of alkali soils. It is difficult to specify a boundary
limit between satisfactory and unsatisfactory infiltration
rates at the low end of the range,because so many factors
are involved,including the patience and skill of the farmer.
However, if the infiltration rate is less than 0.25 cm/hr
special water-management problems are involved that may
make an irrigation enterprise unprofitable for average
farmers.
~ow the chief problem of study by various soil
scientists has been the improvement of the saline alkali
soils. Alkali soils often have a dense block single grain
structure; they are hard to tili when dry and have low
151
hydraulic conductivity when wet. Reeve and co-workers (51)
have shown that, the ratio of air permeability to water
permeability for soils is an useful index of stability of
soil structure.Hendrick and co-workers (23) have shown that
dispersed soils may be effectively improved by synthetic
polyelectrolytes applied at the rate of 0.1 percent on the
dry soil basis.
The external surface area of most soils lie in the
range of 10-15 2 m l&m, whereas the internal surface area
varies to a greater extent. It is nil in soils that contain
inter-layer swelling mineral dnd as high as 1500 m2/gm no
or more in soils containing minerals of expanding-lattice
type. It is also known that the soils of arid region
contain clay fraction which contain higher proportion of
montmorillonite and illite and lower proportion of
kaolinite.
The leaching requirement is a ratio of the equivalent
depth of the drainage water to the depth of irrigation
water.
Leaching requirement = Dd /D. W lW
( 1,. R. )
Under the conditions of aerial application of
irrigation water, when no rainfall movement of salt in the
harvested crop and no precipitation of soluble constituents
in the soil takes place,then the leaching requirement can
be correlated as follows:
152
L.R. = Dd /0. = ECd /EC. W lW W lW
Where EC = electrical conductivity of the
respective waters
For irrigation waters with conductivity of 1,2 and 3
mrnhos/cm respectively,the leaching requirements will be 13,
25 and 38 percent·when EC . ' dw = 8 mhos/em for food crops,1s
the tolerable limit. In addition,rainfall,removal of salts
by the crops and precipitation of salts like caco3
or
gypsum will be the additional factors which will reduce the
value of leaching requirement. Leaching practice may vary
from region to region and hence different methods of
leaching may be required for different areas.
It has been found that the curves for a soil,relating
vapour pressure to moisture content, are affected by the
amount and nature of the colloids and the type of the
exchangeable cations on the surface of the clay. At a
relative humidity of 99.8 per cent hygroscopicity increases
according to the series.
L i > Na > H > Ba > Ca > K
At a relative humidity of 74.9%, this order is -
H > Ca > Li > Na > Ba > K
Kuron ( 2 9 ) has obtained similar data for clay from
Gabersdorf.At low vapour pressures,the adsorption series is
H > Mg > Ba > Ca > Na > K
At higher vapour pressures, the sodium saturated clay
adsorbs maximum water. Kuron (29) attributes such a
153
behaviour to the hydration of exchangeable cations. The
peculiar
that at
contains
entrance
behaviour of sodium ions is explained on the basis
low vapour pressure, the dehydrated sodium clay
a large number of pores that are too small for the
of water molecule;calcium clay,on the other hand,
is more open and is able to adsorb more water.
Jenny (26) considers that relative size of the ion is a
contributing factor in the hydration of alumino-silicates.
According to Jenny (26),different clays would be hydrated
according to the following scheme:
Li > Na > K
H >
Mg > Ca > Ba
Since Mg and Li ions are of the same size,Mg-system should
be more highly hydrated because there will be one half as
many ions
Ca-system
found that
present in the Mg as in the Li-system. Similarly
should be more hydrated than Na-system. It was
for Putnam clays (Beidellite),swelling varies
with the nature of the adsorbed cations as follows:
Li > Na > Ca > Ba > H > K
On the other hand, the order of swellingfor bentonite is:
Na > Li > K > Ca = Ba > H
Lutz ( 32) has found that lateritic colloids
(halloysite) do not swell,irrespective of the nature of the
adsorbed ion on the complex. The swelling of Li and Na
clays increases with increase in concentration of these
154
ions on the complex. Maximum swelling is reached at about
60% saturation of the exchange complex with Li ions. On the
other hand there is a continuous decrease in swelling as
the percentage of K-ions in the system increases.
Difference in strength with which these ions are held on
the surface, is not sufficient to explain a high degree of
variation in the swelling. Again the differences can not be
interpreted directly in terms of hydration of ions. The
Li-colloid attracts water molecules very strongly even to
the point of complete dispersion of aggregated system. The
K ions appear to hold the sheet like particles with much
energy than Li or Na ions. Hand Ca-clays do not swell much.
The relative swelling for the various systems is 1,1.7,1.8,
8 and 10 percent for K,Ba,Ca,Na and Li respectively.
The high swelling of bentonites suggests that the
bentonites attract large amount of water as a result of
forces associated with an inner layer of the colloidal
surface. Thus i t seems possible to interpret the
differences in swelling and hydration to variations in the
a t t r a c t i v e f or c e s o f t he 1 aye r a n d t he r e s u 1 t i n g i n c•r e a sed
mobility of the adsorbed ions, which causes measurable
osmotic type of swelling.
Terzaghi (64) has studied the swelling of elastic
systems with soil (porous structure). He has interpreted
that the swelling in this system is due to the combined
action of the surface tension of water in this system and
the elasticity of the solid component.
The flocculating power of active ions increases with
155
valency. Jenny and Reitemeir (26),have studied in detail
the significance of exchange reactions on the stability of
the clay systems, and have helped to clarify relations
between flocculating potential and ionic exchange. When KCl
is added as an electrolyte to a sodium clay,ion exchange
will take place and the lowering of potential is obtained
through exchange; while if KCl is added to K-clay,then
potential is lowered through repression as well as ion
exchange. In both the situations flocculation results.
It has been found by Myres (40),that H-humate forms
more stable aggregates with clays than Ca-saturated humus.
This result brings out the fact that flocculation is not
the same as granulation. In order to have stable
granulation there must be cementation of the flocculated
particles. It is obvious that adsorbed calcium is n~ cementing agent. Most of the cementing agents in the soil
are irreversible or slowly reversible inorganic and organic
colloids. Stable aggregate formation cannot take place
sands or silts in absence of colloids. The soil colloid
material may be divided into atleast three distinct groups
as far as its cementation effects are concerned.
1. Clay particles themselves
2. Irreversible or slowly reversible inorganic colloids
such as oxides of iron and aluminium
3. Organic colloids.
Russell (60),has suggested that the aggregate formation
is dependent on an interaction between exchangeable cations
on the clay particles and the dispersion liquid. According
- --- --------------------------------------------------------------------------------------
156
to him, formation of aggregates is limited to particles
smaller than 1 \.l in diameter and it is a property of those
clays which have a relatively high base exchange capacity
and is brought about only by those liquids whose molecules
have an appreciable dipole moment. Russell (60) presents
the following theory about the mechanism of aggregate
formation. Each particle is surrounded by electrical double
layer, the outer one being diffused and consisting of
cations, while the inner layer consists of negative charges
presumably adsorbed on the surface of the particles. The
cations in the diffused layer move about in the water in
the same way as they do around a complex anion,as in the
Debye-Huckel theory of strong electrolytes. Since water
molecules possess dipole moment they tend to be oriented
along the lines of electric force,radiating from each ion
into the diffused layer and from each free charge on the
surface of the clay particle. A linking system is thus set
up consisting of: particle-oriented molecules cation
oriented wetting molecules particle.
As removal of water proceeds,an increasing proportion
of cations share their water envelope with the clay
particles and so the number of links increases. The links
also become stronger because they become shorter. In
consequence, the cohesion of the clay particles i.e. the
hardness of the crumb,increases. The main weakness in the
Russell hypothesis is the emphasis that is placed upon the
cation as the connecting link between the particles. The
same phenomenon can be explained on the basis of the
157
orientation of liquid molecules on colloidal surface as
developed by Langmuir and Harkins. The tenacity of the
bonds between clay and sand increases with decreasing
particle size. Sideri (63) considers that the tenacity does
not depend upon the naure of the adsorbed bases. Water is
considered to be bonded between the oriented particles.
Organic colloids cause a high degree of aggregation of
clay particles. Experience in the chemistry of Fe (OH) 3 has
shown that this hydrated colloid becomes almost completely
irreversible upon dehydration. There is sufficient evidence
to suggest that this irreversibility of colloidal Fe (OH) 3
is an important factor in the production of stable
aggregates in certain soils. Aggregation depends on the
climatic conditions e.g. the percentage aggregation in
Canada is 73% while it is only 25% in Texas. This is due to
the fact that there is a high percentage of organic matter
in Canada and a lower percentage in Texas. It may be
concluded that the aggregate formation in soils in
reclamation of saline-alkali soils depends upon:
1. The ·coagulation of flocculation of the colloidal
particles
2. The presence. of small primary particles that may be
aggregated
3. The cementation of the coagulated material into stable
aggregates.
The movement of soil water,through a given volume of
soil, must take place through the soil pore-space. Movement
of water through these pores is brought about by the action
158
of gravity or capillary pull,either alone or in combination.
According to the dominance of the moving force,the type of
water movement may be discussed from two points of view:
1. Water which moves in the larger pores primarily
through the action of gravity or movement in a
saturated soil, and
2. Water,which moves thorugh the action of capillary
forces from surface to surface, or in small pores
in the presence of numerous air-water interfaces
or movement in an unsaturated soil.
Soil moisture movement under unsaturated soil
conditions are compared with older concepts of capillarity
and the more recent analogies to the flow of heat or
electricity.
The flow of water in a soil may be expressed according
to Darcy•s equation:
V = - K Grad ¢
where Grad ¢ represents the change in the total water
moving forces per unit distance and K is the specific
conductivity or the amount of water which will flow in one
second across a unit cross-sectional area of soil
perpendicular to the direction of flow,when the value of <I>
changes at the rate of one unit per· centimeter.
The texture and the structure of the soil affect
capillary conductivity, as they influence the number,size
and continuity of the pores.
The capillary conductivity depends upon the kind of
159
soil, its state of packing and the moisture content. Those
particular soil properties that affect capillary movement
are included in the evaluation of K.
In general, the capillary permeability of different
textured groups are:
Sand < fine sand < loam < light clay < clay
For saturated flow the order of permeability is
reversed. These results point out that the water films in
sands become discontinuous of much lower tensions or
moisture contents than in clays. This is due to the fact
that clays possess a larger number of (larger) pores than
in sands.
The movement of capillary water downward takes place
under the combined influences of the gravitational
potential gradient (Grad$ and the capillary potential
gradient (Grad IV).
Philip ( 44) developed a method to calculate the
cumulative infiltration I in terms of power series.
00
I(t) = l: Jn ( e ) t n/2 ( 1 ) n=l
in which the coefficient Jn (0) are,again,calculated from
K(O) and 0(0), and coefficientS is called the sorptivity.
Differentiating above equation with respect to t,we get the
series for the infiltration rate i(t);
( 2 )
160
In practice, it is generally sufficient for an approximate
description of infiltration to replace equations (1) and
(2) by two parameter equations of the type
I(t) = St~ +At
I ( t ) = 1 St-~ + A 2 ( 3 )
where t is not too large. In the limit,as t approaches
infinity, the infiltration rate decreases monotonically to
its final asymptotic value i( <1> ).
However, at very large times,it is possible to represent
above equation (3) as:
~ . 1 St-~ + k I = St + Kt, l = 2 ( 4 )
where 'K' is the hydraulic conductivity of soil's upper
layer which in a uniform soil under ponding, is
approximately equal to the saturated conductivity Ks.
The effect of profile st~atification on infiltration
has been studied by Hanks and Bower (22),Miller and Gardner
(39). Hillel and Gardner (24) recognized three _stages
during transient infiltration into crust-capped profile.
The process of infiltration under rain sprinkler
irrigation was studied by Rubin (58, 59). The exact
relationship between porosity and soil permeability is yet
in the experimental stage. There are sufficient evidences
l
161
that the size, density of packing and hydration of the
particles have great effects upon permeability. Lutz (33)
has demonstrated that the permeability of clays increases
as hydration of the particles decreases. The relative
permeability of Davidson, Iredell, putnum and bentonite
colloids were found to be approximately 100,50,32 and 2
respectively. The relative degrees of hydration of these
systems were 0, 10, 35 and 100 respectively. These
differences are due to the nature of colloids since the
silica-sesquioxide ratio of these systems increases in the
same manner as the hydration. Basically,non-saline alkali,
saline-alkali, and saline non-alkali soils have different
physical properties. Soils differ in texture, levels of
salinity, amount of Caco 3 ~ amount of gypsum,type of clay
minerals as well as availability of different types of
waters in nature: hence there is a need for studying
infiltration rates and permeability of different types of
soils.
In the last twenty years ~normous development has taken
place in the field of study of infiltration,permeability
and the physical and chemical properties of the soil.
Studies on soil structure and the physical properties
of soil have been carried out by McGeorge and Breazeale
(36) and Reeve (52). The behaviour of soil in relation to
the percolating solution and its electrolyte content has
been critically observed by a large number of workers
including McNeal and co-workers (37,Reeve and Doering (53),
Gardner, Bower and co-workers (18),Elirc (13),Philips and
162
Farrell (48), Pack and his co-workers (43),Philip (44,45),
Reeve and Tamoddoni (54),Quirk (50),Brooks and Goertzen (8),
Agassi, Shainberg and Morin (1),Shainberg and Singer (62).
The infiltration behaviour of soils in relation to the
clay type and the associated swelling has been studied by
Klages (28), Gill and Sherman (19),Dettman (10),Aylmore and
Quirk (6), Norrish and Quirk (42),Michaels and Lin (38),
Norrish (41), Quirk (49), Agrawal et. al. (3),Ambergaonkar
(5). The problem of dispersion of soil and the role of
exchangeable sodium in relation to infiltration has been
brought out by Leland (30),Demnead (9),Reeve and Brook (51),
Richards (56) and Eaton and Horton (12).
be
According
hindered
to Agassi et. al. (1,2) infiltration may also
by aggregate destruction from rain drop impact
and resultant crust formation. In many areas of the world
which are characterized by high intensity rains and sodium
affected soils, both mechanisms, which are interrelated
operate to reduce soil water intake.
Agrawal and Ramamoorthy (4) have studied the effect of
saline irrigation water (Ec = 2250 umhos/cm,SAR = 14) on
soils of varying texture and observed that heavy textured
soils (montmorillonitic) showed more of salinity hazard as
compared (to Kaolinitic and Illitic) light textured soils,
whereas the reverse was the case for sodium hazard.
Phillip
concept of
has given a purely mathmatical
infiltration. It can be
treatment to the
said that the
infiltration theory incorporating the various aspects of
soil moisture, water movement and water depth have been
163
fully treated by Phillip (45, 46,47). The improvement in
infiltration rate on application of amendments and the
aggregation of soil particles has also been studied
extensively by Hendricks and co-workers (23), Letey and
co-workers (31), Bower (7),Marshell (35). Side by side the
techniques of measuring infiltration rate,permeability and
hydraulic conductivity have been revised from time to time.
This includes the work of Richards (55),Vries (65,66),Peck
an~ Talsma (43), Fireman (14), and Gardner (15, 16). In
addition some important applications have also been studied;
e.g .. the engineering aspects of the reclamation of sadie
soils with high salt waters has been critically studied by
Doering and Reeve (11). The application of the infiltration
theory to hydrology has been made by Gardner (17).
The Sodium Adsoption Ratio (SAR) is given by,
SAR
+ Na
This equation is used for evaluating the Exchangeable
Sodium Percentage (ESP) in the soil:
ESP = 10 ESF = 100 (Na)/CEC
Where ESF is the exchangeable sodium fraction. The
equilibrium exchangeable sodium fraction of soil that has
been equilibrated with water having a given SAR may be
approximated as:
164
ESF = SAR/(1/K + SAR)
However, on
depending
both SAR
upon
and
diluting
the SAR
the
a water the ESF will change,
and the extent of dilution. Thus,
salinity level will govern the
infiltration rates in soils.
In the present work, soil samples of different clay
types from Ahmedabad (CLAY TYPE:Kaolinite-Montmorillonite),
Amreli (CLAY TYPE: Montmorillonite) and Kutch (CLAY TYPE:
Kaolinite-Illite) district of Gujarat State were used
for infiltration studies. Waters with different SAR and
different salinity levels were used for infiltration study.
Infiltration rates were measured by using the modified
Dettman Emersion technique.
Table 6.1 shows composition of different SAR waters
varying in concentration.
Results for infiltration cates are presented in Table
No.6.2-6.6.
l
165
TABLE 6.1
COMPOSITION OF DIFFERENT SAR WATERS VARYING IN SALINITY LEVELS
SALT CONCENTRATION (Meq/Litre) TOTAL
SAR SALINITY NaCl CaCl 2 MgC1 2
(PPM)
15 75 25 25 9518
15 60 16 16 6793
15 30 4 4 2575
15 20 1. 7 5 1. 7 5 1529
30 150 25 25 13906
30 120 16 16 10303
30 90 9 9 7112
30 60 4 4 4330
45 200 19.79 19.79 15761
45 180 16 16 13813
45 90 4 4 6085
45 50 1. 23 1. 23 3177
60 240 16 16 17323
60 180 9 9 12377
60 120 4 4 7840
60 60 1 1 3715
75 225 9 9 15009
75 150 4 4 9595
75 90 1.44 1. 44 5560
75 50 0.44 0.44 3015
TABLE 6.2
INFILTRATION RATE (Cm/Hr) OF DIFFERENT SOILS OF DIFFERENT CLAY TYPES WITH DIFFERENT SAR WATER
SOIL : NORMAL SAR WATER 15
TOTAL SALINITY LEVEL (PPM)
TIME 9518 6793 2575 1529 (MIN. ) K-M M K-I K-M M K-1 K-M M K-1 K-M M K-1
1 318 96 132 420 132 138 252 96 96 294 108 84
2 84 42 30 180 48 54 156 24 24 78 24 36
3 108 36 30 - 24 12 60 36 24 90 18 30
4 48 36 30 24 12 60 12 18 36 1 8 1 8
5 - 30 12 24 6 - 18 12 - 12 12
6 18 18 12 18 12 12 12 6
7 18 6 36 6 18 12 18 12
8 12 18 18 12 12 6 24 6
9 12 24 18 12 12 12 18 G
10 12 24 12 12 6 24 18 6 ..... O'l O'l
TABLE 6.3
INI•'II.TR/\TION RATE {Cm/Hr) OF DIFFERENT SOILS OF DIFFERENT CLAY TYPES WITH DIFFERENT SAR WATER
SOIL : NORMAL SAR WATER 30
TOTAL SALINITY LEVEL (PPM) TIME
13906 10303 7112 4330 (MIN. ) K-m M K-I K-M M K-I K-M M K-I K-M M K-I
1 276 72 144 300 138 108 252 108 96 240 102 120
2 132 36 18 196 72 12 126 36 18 172 42 18
3 60 18 18 114 30 24 84 24 30 102 30 6
4 90 18 12 66 18 18 72 18 18 106 24 12
5 30 24 12 30 24 18 60 6 12 liO 18 12
6 18 30 18 18 12 6 12 12
7 12 24 18 12 12 12 12 12
8 6 18 12 12 12 6 18 12
9 6 18 18 12 - 6 18 6 .....
10 6 18 12 6 12 - 12 12 0)
-..:)
----------------------- I
TABLE 6.4
INFILTRATION RATE (Cm/Hr) OF DIFFERENT SOILS OF DIFFERENT CLAY TYPES WITH DIFFERENT SAR WATER
SOIL : NORMAL SAR WATER 45
TOTAL SALINITY LEVEL (PPM) TIME
(MIN. ) 15761 13813 6085 3177
K-M M K-I K-M M K-I K-M M K-I K-M M K-I
1 300 126 102 264 102 66 240 96 142 204 120 144
2 184 36 30 96 54 48 120 42 124 196 112 42
J 96 36 24 50 30 44 60 30 36 120 74 34
4 48 30 12 60 24 36 48 36 18 48 36 32
5 72 18 12 40 24 24 42 24 18 42 42 24
6 36 12 24 24 18 36 24 24 30 24 6
7 24 30 30 24 12 30 12 12 18 24 6
8 24 18 30 24 18 18 16 18 6
9 18 12 30 18 6 18 12 18 6
10 12 12 12 12 18 6 12 6
~
O'l 00
TABLE 6.5
INFILTRATION RATE (Cm/Hr) OF DIFFERENT SOILS OF DIFFERENT CLAY TYPES WITH DIFFERENT SAR WATER
SOIL : NORMAL SAR WATER 60
TOTAL SALINITY LEVEL (PPM)
TIME 17323 12377 7840 3715 (MIN. )
K-M M K-I K-M M K-I K-M M K-I K-M M K-I
1 336 102 78 318 96 120 258 90 102 240 96 96
2 90 42 30 160 36 24 90 36 42 84 30 24
3 96 30 24 102 24 24 90 42 24 84 30 12
4 90 30 18 90 24 12 60 30 24 72 24 12
5 18 18 18 24 12 48 30 18 GO 24 12
6 12 18 18 12 12 12 60 18 12
7 12 24 18 6 12 12 18 12
8 12 6 12 6 12 18 18 12
9 12 18 12 12 18 12 12 12
10 12 18 12 6 12 12 12 12 ...... en c.o
TAULE 6.6
INFILTRATION RATE (Cm/Hr) OF DIFFERENT SOILS OF DIFFERENT CLAY TYPES WITH DIFFERENT SAR WATER
SOIL : NORMAL SAR WATER 75
TOTAL SALINITY LEVEL (PPM)
TIME 15009 9595 5560 3015 (MIN. ) K-M M K-I K-M M K-I K-M M K-I K-M M K-I
1 240 96 72 246 84 72 240 60 96 246 108 78
2 120 76 30 90 24 30 102 30 30 108 24 18
3 78 48 24 84 18 24 78 30 24 90 24 18
4 no 24 18 60 18 24 90 18 18 72 12 24
5 78 24 12 54 6 1 2 60 18 18 48 12 18
6 12 12 54 6 12 60 18 24 1 8 1 8 18
7 12 18 6 12 18 1 2 18 12
8 18 12 12 6 12 6 18 6
9 12 12 6 6 12 6 6 12
10 12 12 6 6 12 6 12 12 f-lo
-...J 0
I lnfi!tr!l1101'l r!IIEO [ Qn!Hr I ~r----------------------
Clay Type K-M
SA A 15 300
:t i 0~'------~----~------~------~----~
2 3
Trme rn mnts. 4 0
ll 0- 96l8 pam -+- e 1 oo pam -+- Zfl 1 f> pam
Grapn No - 6.1
lnfil1r!11i0n r111e [ On/Hr ]
1001
:t ... -........ . __ .Clay _ _Type SA A 15
Ml
~~- --
:r ·-· oL-----L-----~----L-----~------~~--~ o z • e a 10
T rme rn mnts.
- Q61S ppm -+- 67QG pgm ..... ?576 pnwn -- 162Q pgm
Grap> No. - 6.2
lntll1r!l110f"l r!lle [ On/Hr I '200~--------------------------------~
4 6
Clay Type K-1
SA A 15
8 10
Trme rn mnts
~ W61B pgm -+- S7Qu pnwn ~ ~676 ppm ~ 162Q pgm
Grap> No. - 6.3
I I
171
:('"""'~·:tow~--.. ~Clay Type K-M I
l ~""' S A R 3 0
'Q .:.""
~I ~~-~~-- ·-. ............ '·
I] ~~~
l 0 2
l1me ~~ rnnts. 4 6
- 1SGO!I ppm -+- 10000 ppm --¥- 7112 ppm -- • 330 ppm
8llh NO. - C.•
r------------------------------------------------. I
lnliltreiiOn rille I On/Hr J 200,.--------------------------------------, Clay Type M
SA R 3 0
0 8 10
11me 1n ITI1tS.
~ 16006 ppm -+- 10606 ppm --¥- 7112 ppm -- •680 ppm
Gra!'fl No. - C-6
lnloltrelion rete I On/Hr l ~---------------------------------------.
160
100
Clay Type K-1 SA R 3 0
oi~----~----L-----~-
-. -i I
o • 0 0 •o 1unc 1n rnnts.
- 16006 ppm -+- 10000 ppm --¥- 7112 ppm -Q... •330 ppm
Grapn No. - C.O
172
r-1
lnfiltrctlon r!llg I On/Hr I
<00[ ---·-··----
Clay Type K-M 300 '
·~··· SAR 45
200
100 "~ '··
--+-0
0 2 4 6 a 10 12
T1me 1n mnts.
Gtepn NO - !I 7
lnfiltrctKJn rille I On/Hr ] 1~.---------------------------------------~
-- C~y TYf?e M SA R 4 5
00
()L------L---~-----~-
0 6 8 10
T 1me 1n mnts.
~ 16761 ppm -+- IS81S ppm ....,.._ 6086 ppm -- Sin ppm
Grat:n NO. - 6 8
"''('""•'~ <do I On!H• I
1.')0 r a
100
00
Clay Type K -I
SA R 4 5
12
ol_--~~-~~~~~~-~-~~~--__j o 2 4 e 8 10 12 1
L..G_r_a., __ N0 __ -_"-_~~ __ ~_6_76_1_"""' ___ -+-__ I_~_:_:oo_"""'_'_n_mr_..,._~~_:_· ·_86_ppm ____ -__ :._•7_7_"""'_j
173
\ I
I
- 17::123 epm
Gr•pn No - 6.10
: ('"''"'~ ·~• I ""'"' I
00~ 60
Clay Type K-M I I
SA R 6 0
QL-----~----~------~----~------~----~ 0 2 4 0 8 10
Time 1n mnts.
- 171!128 epm -+- 12877 epm -+- nwo ppm -a-- s 7\6 ppn
Gr•pn No. - a 11
lnftlt<llltQn rille ( On/Hr I ~~----------------------------------------~
9lay _Type K -I SA R 6 0
100
80
4 6 a 10
T 1rne 1n mnts.
I ~ 1rS2S ppm ~ 9716 ppn
L Grapn No.- al:!
174
175 r------------------------------------------------~
lnflltr11tkJn rllte ( On/Hr I ~-------------------------------~ Clay Type K-M :260
SA A 7 5 200
'o ol____----~--------~------~~------~
0 2 .. 0 8
T1me tn mnts - I600G ppm -+- Q6Q6 ppm ..... 66CO ppm -- 3016 ppm
Gralll'l No - CI.IS
lnflltr~tllan rl!le ( On!Hr I 1ror---------------------------------------~
Clay Type M 100
SA A 7 5 ao
20
OL'----~~----J------J------~----~----~
0 2 4 0 8 10
Time m mnts. - liSOOII ppm -+- gcjQC ppm ....... !lOGO ppm -- !10l6 ppm
Gr~ No.- Cl.14
lnflllr~tlian rl!le I On/Hr }
~----------------------------------------~
100 Clay Type K -I
SA R 7 5 ao
60
40 --
20 --- .. . 0
0 2 .. 0 8 10 12
L Gr~_N_o_. --_e -_,; __ •60<_JO_ppm __ -+-___ Q6_Til6_,rr_:n :'~ ----~-~·:_J
DISCUSSION
At the first sight it appears that Sodium Adsorption
Ratio (SAR) will be directly reflected as the base
saturation of a soil with Na+ with respect to Ca++ and Mg++
and we use the SARin the same context. But infiltration
rate studies indicates that the built up ratio ++ ++
"' +JCa + Mg answered as ESP is different for differer,t l' a , 2
type of clay soils. For example,in the present study it is
noted that the infiltration rate for the
Kaolinite-Montmorillonitic Ahmedabad soil is distinctly
very high for all the SAR ratio waters (15,30,45,60 and 75),
compared to Montmorillonitic Amreli soil and
Kaolinite-Illite Kutch soil. Thus the built up Na controls
the infiltration rate. Electrolyte concentrations also
somewhat affects infiltration rate, yet the pronounced
effect is from the clay mineralogy of the soil.
In the case of Kaolinite-Illite soils the infiltration
rates are not very high for SAR 15 and 30, but are
definitely higher for SAR 45 and again lower infiltration
rate for SAR 60 and 75. It is inferred from these results
that with SAR 15 and 30 waters there is going to be base
saturation + by Na ion. With SAR 45 water electrolyte effect
is slightly prominent. Again with SAR 60 and 75 waters the
base saturation with + respect to Na is higher,which lower
down the infiltration rates.
In the case of Montmorillonitic soil infiltration rates
177
are not very high for SAR 15 waters,but definitely higher
for SAR 30 and SAR 45 water. Again for SAR 60 and SAR 75
infiltration rates decreases. I~ is inferred that high SAR
leads to higher ESP. Higher build up ESP will decrease the
infiltration rates. Higher salt concentration will lead to
increase in infiltration rates due to electrolyte effect.
For this reason even sea-water can be used to reclaim
(saline-alkali) soils.
Considering the results in Table 6.2 to 6.6 we find
that with increasing SAR there is decrease in infiltration
rates, which is more so after the 3rd and 4th minute,because
the 1st and 2nd minute reading are of the uppar part of
column which might contain small amounts of air,the lower
part being filled intact and would have less amounts of atr
vojds.
On comparing the infiltrat1on rates of all three sails
it is concluded that infiltration rates of:
K-M > M > K-I
1. Ag ass i , M. , I .
electrolyte
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