Significance of clay minerals in development of alluvial soils of...
Transcript of Significance of clay minerals in development of alluvial soils of...
Indian Journal of Geo Marine Sciences
Vol. 48 (11), November 2019, pp. 1783-1795
Significance of clay minerals in development of alluvial soils of Aravalli range
R P Sharma1*
, R S Singh2 & S K Singh
1
1ICAR-National Bureau of Soil Survey and Land Use Planning, Amravati Road, Nagpur-440033 2ICAR-National Bureau of Soil Survey and Land Use Planning,
Regional Centre, Bohara Ganesh ji Road, University Campus, Udaipur-313001
*[E-mail address: [email protected]]
Received 27 April 2018; revised 20 June 2018
Fertile lands of eastern Rajasthan uplands are gradually declining their inherent capacity to the produce crops. A study
has been conducted on alluvial soils; surrounded by Aravalli hills and deposited by Banas river. Different soils located over
landforms with varied slopes and rainfall density and annual average rainfall were sampled for morphological, physico-
chemical and mineralogical investigations. Present study is aimed to link the mineralogy of various size fractions and other
physico-chemical characteristics as an evidence of pedogenetic process in development of alluvial soils. Our study indicates
that the soils are coarser (sandy or sandy loam) in texture, consisting predominantly of quartz followed by feldspars and
mica. Specific trend was not observed in minerals present in the clay matrix. Presence of unstable talc mineral in the clay
fraction of soil over upper rolling plain indicates juvenile nature of soils.
[Keywords: Alluvial soils; Aravalli range; Clay minerals; Physico-chemical characteristics; Pedology]
Introduction
The Aravalli hills, extending in north-east and
south-west direction is one of the oldest hill systems
of the world. The system is spreading in Gujarat,
Rajasthan, Haryana and Delhi states. The Aravalli
range breaks at some locations and these active gaps
caused sand drifting from western Thar desert to
eastern fertile lands consisting of eastern Rajasthan,
western Uttar Pradesh, Punjab, Haryana and national
capital Delhi. These active gaps are more vulnerable
if natural forest cover is degraded in climate changing
scenario.
The Aravalli range is very rich in nonmetallic
minerals such as dolomite, calcite, emerald, feldspars,
garnet, mica, rock phosphate, magnesite etc. The
alarming rate of deforestation, declining and erratic
rainfall, mining of natural resources, increased
number of brick kilns, increased soil erosion and
transportation and population pressure on natural
resources are the important factors affecting the agro-
ecosystem of Aravalli hills. All these factors
adversely affect the productivity of eastern Rajasthan
uplands. To understand the behavior and resilient
characteristics of alluvial soils of Aravalli range; the
clay minerals play a very important role1. They are
hydrous aluminium phyllosilicates with variable
amounts of alkaline earth metals, iron and other
cations. Topographical features and drainage network
play a crucial role in the transformation and
redistribution of clay minerals which play a
significant role in holding plant nutrients and water2.
Genesis clay minerals such as 1:1 type clay minerals
(kaolinite and serpentine), 2:1 type clay minerals
(talc, vermiculite montmorillonite and micas) and
interlayered minerals or interstratified minerals are
the major source to evaluate the inherent
characteristics of soils3. Crop productivity potential of
the soil depends on its physico-chemical and
mineralogical characteristics.
Soils of Indo-Gangetic alluvial plains contains
significant amount of silt fractions with clay as major
potion are highly fertile and has the capability to hold
high water and nutrients4. Pedogenic development can
be better understood by studying the mineralogical
composition of various soil size fractions in recent
alluvium. Therefore, the present study was under
taken to investigate the soil mineralogy in various soil
size fractions and to evaluate the variation in soil
morphological, physical, chemical and mineralogical
properties along the climo-topo-sequence. These data
can support to understand nutrient status in soils, their
availability to plants, soil moisture retention and
release and other pedo-transfer and edaphalogical
functions. The information derived from the present
study is useful to understand the soil-plant-nutrient
relationship for agricultural land use planning.
INDIAN J. MAR. SCI., VOL. 48, NO. 11, NOVEMBER 2019
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Materials and Methods
Study area
The study was carried out in Bhilwara district of
Rajasthan. The Geology of the area is of Aravalli
system comprised mainly of quartzite, conglomerates,
shale, slate, phyllite and composite gneisses which are
highly metamorphosed at certain places1. The soils of
this area are mostly underlain by Precambrian rocks.
Alluvial soils of the present study area are possibly
derived upon weathering of Precambrian rocks of
Aravalli range, and was transported by Kothari River,
a tributary of Banas. It got deposited in the form of
successive layers intermixed with gravels and
pebbles. These alluvial soils are highly fertile and
have high crop productivity potential.
Alluvial plains of Aravalli system situated near the
Kothari river in Bhilwara district of Rajasthan were
selected for present investigation. It has three rainfall
zones viz., upper rolling plains with < 600 mm (P1 to
P4), middle sloping plains 600 to 700 mm (P5 to P8)
and lower plains 700 to 800 mm (P9 to P12). The
location map of area is presented in Figure 1 which is
situated between 2501′ and 2558'N latitude and
7401'and 75 28' E longitudes. Soil samples were
collected from each horizon from 12 representative
profiles (P1-P12) to study the morphological,
physical, chemical and mineralogical properties. Point
of observations were located at a distance of 50 km to
each other. Observation were taken on both the side
of river channel at a distance of 250 m and 500 m.
Soil-site characteristics and morphological properties
were recorded in standard format for the interpretation
of pedogenic processes. The samples were brought to
laboratory, dried in air and crushed with wooden
roller and sieved with 2 mm size openings for study
the physical, chemical and mineralogical properties5.
Fractionation of soil separates
Mechanical composition of soils (texture) were
determined by the International pipette method6.
Fig. 1— Location map of study area representing the sampling site of pedons from upper rolling, middle sloping and lower plains
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Results were calculated on oven dry weight basis.
Exactly 10.000 g soil sample was taken in
autoclavable 250 ml centrifuge bottles. Buffer
solution of sodium acetate (1N) pH 5.0 was added to
remove CaCO3. Organic matter was destroyed with
hydrogen peroxide treatments. Free oxides of iron and
aluminum were washed out after citrate-bicarbonate-
dithionite (CBD) treatment. After dispersing the soil
fractions; silt (50-2 m) and total clay (<2m) were
segregated7. Wet sieving technique was deployed for
separating the sand (2000–50 m) fractions. Clay
fraction was separated after multiple centrifugal
processes and coagulated with sodium salt and stored
in 125 ml narrow mouth plastic bottles.
Mineralogical analysis by X-ray diffraction method
(XRD)
Clay and silt fractions were saturated with calcium
and potassium ions and washed with alcohol to
remove excess salts from the exchange sites. One
milliliter suspension of clay or silt was taken and
spread over the glass slides of 4.5x2.5 cm size. Slides
were dried at room temperature before X-ray
diffraction analysis7.
Identification of layer silicate minerals
Qualitative mineralogical framework of sand
fractions was carried out by X-ray diffraction
techniques at room temperature after separating it in
coarse sand (retained on 100 mesh size sieve) and fine
sand (passed through 100 mesh size sieve) fractions.
Parallel oriented samples of silt and clay were
scanned by XRD with Philips diffractometer and Ni-
filtered Cu-K radiation at standard scanning speed
(22/min).
The characteristic peaks were analyzed for
identification and semiquantification of different
minerals by method proposed by Jackson7
supported
by automated mineral identification software. Various
thermal treatments were given before mineral
scanning in XRD, such as K-saturation at room
temperature (K25 C), heating it at 110 ºC (K110
C),
300 ºC (K300 C) and 550 ºC (K550
C), Ca-
saturation (Ca), Ca-saturated and ethylene glycol
solvated (CaEG) for identification and confirmation
of type of clay minerals in silt and clay fractions. The
semi-quantitative estimates of minerals in the silt and
clay fractions were done as per standard procedure8.
Kaolinite: A peak of d (001) reflection is produced
at 0.72 nm which destroyed on dehydroxylation by
heating the mineral at 550 oC for 2 hours.
Smectite: Calcium saturated smectitic minerals if
scanned by XRD in air dry conditions then produce a
peak at 1.4 nm. If such minerals are solvated with
ethylene glycol in closed system, then these organic
molecules are sorbed in the interlayer region of clay
minerals and expand from 1.4 nm to 1.6 nm or 1.8 nm
size depending on layer charge behavior. Higher the
charge lesser the expansion of clay minerals.
Smectites collapsed to 1.0 nm d (001) on saturation
with potassium ions after heating at 110 oC for two
hours. The height of peak indicates the proportion of
smectitic clay minerals. The characteristic swelling on
saturation with polar organic molecule and
contracting on saturation with K confirms the
presence of smectites.
Vermiculite: Calcium saturated and air dried
(temperature 25 o
C) vermiculites shows a
characteristic peak at 1.40 to 1.45 nm and do not shift
on glycolation due to higher layer charge.
Vermiculites act like smectite clay minerals upon K
saturation, collapsing (irreversibly) to d (001) spacing
of 1.0 nm.
Illite: Mica or illite shows peak at 1.0 nm (001 d
spacing) on X-ray scanning of calcium saturated and
CaEG saturated clay slides. Spacing do not alter upon
saturation with various cations, heating or solvation
with ethylene glycol.
Chlorite and Hydroxy-interlayered clay minerals
Calcium saturated chlorite gives a XRD peak at 1.4
nm (001 d spacing) and do not alter on glycolation.
Hydroxyl Aluminum dominated vermiculite and
smectite can produce the XRD peak in the range of
1.4 to 1.7 nm, either they are saturated with glycerol
or not. Water molecules removed on drying of
hydroxy-interlayered minerals at 110 oC. Potassium
ions fit in interlattice space of weakly interlayered
minerals and collapses it to 1.0 nm on 550 oC heating
for >2 hours. The collapsing is relatively incomplete
in Al interlayered minerals even after heating at 550 oC. Resistance towards the collapsing of clay minerals
on severe heat treatments indicates the prominence of
hydroxy-aluminum-interlayered minerals.
Results and discussions
Morphological, physical and chemical characteristics
Munsell colour chart was used to record soil matrix
colour in dry and wet conditions. The difference was
not observed in hue but it varied 2 to 3 units in value
and chroma. Soil colour varied from gray (10YR 5/1)
to very dark brown (10YR 2/2). Arrangement of
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diagnostic horizons in pedons and their pedogenic
development, variations in depth, colour, texture,
structure, size of roots and voids, consistency etc. are
presented in Table 1. Details of morphological
properties for representative pedons are tabulated and
given in Tables 1 to 4. Physical and chemical
properties of representative pedons is given in Table 1.
The soils were moderately deep (75-100 cm), deep
(100-150 cm) and very deep (>150 cm) in upper
rolling plains, middle plains and lower plains,
respectively. All pedons were having A-B-C sequence
of soil horizon except P6 and P10 where B horizon
was absent. Majority of soils were coarse (sandy loam
or loamy sand) textured. Sand is predominant soil
fraction ranged from 37-92 per cent in all landforms.
Average content of sand, silt and clay fractions in
upper rolling plain was 76.9, 15.5 and 7.6 % which
changed to 65.0, 21.9 and 13.1 % in lower plain.
Moderate level of these fractions were found in soils
of middle plain. Clay coating on sand particles or on
pads in sub-surface horizons were observed during
field study. These were confirmed after analyzing the
samples in laboratory. The clay and silt size particles
moved from surface to sub-surface horizons and form
a layer of illuviation (clay enrichment). It was
protuberant in the soils of lower plains. Micro low
topography could have favoured chemical alteration
of primary minerals in the sand fraction to secondary
oxides of silt and clays. Soil reaction (pH) varied
from 7.08-7.87, 8.06-8.15 and 8.49-9.31 and electrical
conductivity ranged from 0.09-0.21, 0.53-089 and
0.31-1.42 dSm-1
in upper, middle and lower plains,
respectively. The secondary accumulation of calcium
carbonate and soluble salts was more pronounced in
lower plain. Electrical conductivity was found with in
safe limits and had no adverse effect on crops. The
soils of all landforms showed the low variability
(CV<15 %) in pH and in case of EC it was high
(CV>35 %).
Mineralogical compositions of sand fractions
For the interpretation of X-ray diffractograms
(XRD), the intensity of peak pattern was considered
which is proportional to the amount of clay minerals
present in soil sample9. Area of peak should be used
for an accurate quantitative analysis rather than height
of peak11
. Under this experiment we have used peak
area as an indicator of specific mineral for sand
fractions12
. Sand was the major part among
the different soil separates in Kothari river basin.
Table 1 — Morphologicala, physical and chemical characteristics of representative pedons
Depth
(cm)
Horizon Soil
colour
Texture Structure
Consistence Porosity Roots Efferv. pH
(2.5:1)
EC
(dS/m)
CaCO3
(%)
O.C.
(%)
Sand
(%)
Silt
(%)
Cla
(%) Moist Wet Size Quantity Size Quantity
Upper rolling plains with a mean annual rainfall <600 mm
P1: Baniyon Ka Khera, 25o 23' 50" N, 74o 03' 00" E, altitude- 592 m , Classification: Coarse-loamy, mixed, hyperthermic Fluventic Haplustepts
0-10 Ap 10YR4/4 ls m 1 sbk l sspo m,f c,m vf, f c nil 7.85 0.21 0.57 0.47 82.1 10.7 7.2
10-26 Bw1 10YR3/4 sl m 1 sbk fr sspo m m m c nil 7.50 0.10 0.95 0.32 74.0 18.5 7.4
26-46 Bw2 10YR3/4 sl m 1 sbk fr sspo m m vf, f m nil 7.08 0.09 0.95 0.26 75.3 16.8 7.9
46-65 Bw3 10YR3/4 sl f 1 sbk fr sspo m m vf m nil 7.12 0.09 1.00 0.34 74.6 18.0 7.4
65-80 Bw4 10YR3/4 ls m 1 sbk fr sspo m m vf f nil 7.87 0.17 0.95 0.18 78.1 14.8 7.1
Middle sloping plains with a mean annual rainfall 600-700 mm
P6: Sarano Ka Kheda, 25o 22' 00" N, 74o 26' 30" E, altitude- 455 m, Classification : Coarse-loamy, mixed, hyperthermic Typic Ustifluvents
0-18 Ap 10YR4/4 ls sg l sopo m,c m vf,f c, f nil 8.15 0.59 0.57 0.15 83.1 6.8 10.2
18-50 A1 10YR3/4 s sg l sopo m m c c nil 8.10 0.89 0.38 0.19 87.3 4.6 8.1
50-100 A2 10YR3/4 ls f 1 sbk fr sopo m,c m c f nil 8.06 0.57 0.43 0.15 84.5 4.8 10.7
100-140 A3 10YR3/4 ls f 1 sbk fr sopo m m c f nil 8.08 0.58 0.57 0.14 82.9 6.2 10.9
140-175 A4 10YR3/4 ls f 1 sbk fr sopo m m c, f f nil 8.12 0.53 0.66 0.09 82.2 7.4 10.5
Lower plains with a mean annual rainfall 700-800 mm
P9: Akola , 25o 21' 52" N, 74o 43' 30" E, altitude- 399 m, Classification: Coarse-loamy, mixed, hyperthermic Typic Haplustepts
0-19 Ap 10YR5/4 ls m 1 sbk l sspo m,c c,m vf,f m,c e 9.31 0.31 1.14 0.53 75.2 18.0 6.8
19-45 A1 10YR4/4 sl m 1 sbk l sspo m,c c f c,f nil 8.62 1.42 1.00 0.21 70.1 17.2 12.7
45-85 Bw1 10YR4/4 sl m 2 sbk fr spo m,c c f,c f e 8.49 1.56 1.25 0.17 69.4 21.2 9.4
85-125 Bw2 10YR4/4 sl m 2 sbk fr spo m,c c f,c f e 8.66 1.41 1.46 0.14 67.1 21.3 11.6
125-170 Bw3 10YR4/3 sl m 1 sbk fr spo m,c c f f e 8.71 1.24 1.27 0.11 69.1 21.6 9.3
aFor detail descriptions please refer table number 2, 3 and 4.
SHARMA et al.: CLAY MINERALS IN ALLUVIAL SOILS
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Table 2 — Pedomorphic features of representative pedon P1 (Baniyon Ka Kheda) in upper rolling plains
Classification: Coarse-loamy, mixed, hyperthermic Fluventic Haplustepts
Location :
Climate :
Parent material :
Slope :
Landform :
Drainage :
Erosion :
Land use :
Height from MSL :
Latitude: 25o 23’50” N, Longitude: 74o03’00” E
Semi-arid
Granitic gneiss alluvium
8-15 %
Rolling plains
Somewhat excessive
Severe
Cultivated single/double crop (wheat/barley, gram)
592 m
Depth (cm) Horizon designation Soil morphology
0-10 Ap Dark yellowish brown (10 YR 4/4 M); loamy sand; medium, weak, subangular
blocky structure; slightly sticky, non-plastic; fine to medium, common to many
pores; very fine, fine common roots; clear smooth boundary; pH 7.85.
10-26 Bw1 Dark yellowish brown (10 YR 3/4 M); loamy sand; medium, weak, subangular
blocky structure; slightly sticky, non-plastic; medium, many pores; very fine, fine
common roots; clear smooth boundary; pH 7.50.
26-46 Bw2 Dark yellowish brown (10 YR 3/4 M); loamy sand; medium, moderate, subangular
blocky structure; slightly sticky, non-plastic; fine common, medium many pores;
very fine few roots; clear smooth boundary; pH 7.08.
46-65 Bw3 Dark yellowish brown (10 YR 3/4 M); gravelly loamy sand; medium, weak,
subangular blocky structure; slightly sticky, non-plastic; fine common, medium
many pores; very fine few roots; clear smooth boundary; pH 7.12.
65-80 Bw4 Dark yellowish brown (10 YR 3/4 M); gravelly loamy sand; medium, weak,
subangular blocky structure; slightly sticky, non-plastic; fine common, medium
many pores; very fine very few roots; clear smooth boundary; pH 7.87.
80+ C Weathered material.
Table 3 — Pedomorphic features of representative pedon P6 (Sarano Ka Kheda) in middle sloping plains
Classification : Coarse-loamy, mixed, hyperthermic Typic Ustifluvents
Location :
Climate :
Parent material :
Slope :
Landform :
Drainage :
Erosion :
Land use :
Height from MSL :
Latitude: 25o 22’00” N, Longitude: 74o26’30” E
Semi-arid
Alluvium
3-8 %
Gently sloping plain
Well
Moderate
Cultivated double crop (cotton/cluster bean, barley)
455 m
Depth (cm) Horizon designation Soil morphology
0-18 Ap Dark yellowish brown (10 YR 4/4 M); loamy sand; single grain structure; loose,
non-sticky, non-plastic; medium, coarse many pores; very fine few, fine common
roots, clear, smooth boundary; pH 8.15.
18-50 A1 Dark yellowish brown (10 YR 3/4 M); sand; single grain structure; loose, non-
sticky, non-plastic; medium, many pores; coarse, common roots, abrupt, smooth
boundary; pH 8.10.
50-100 A2 Dark yellowish brown (10 YR 3/4 M); loamy sand; fine, weak, subangular blocky
structure; friable, non-sticky, non-plastic; medium, coarse many pores; coarse, few
roots; clear smooth boundary; pH 8.06.
100-140 A3 Dark yellowish brown (10 YR 3/4 M); loamy sand; medium, fine, weak, subangular
blocky structure; friable, non-sticky, non-plastic; medium, many pores; coarse few
roots; clear smooth boundary; pH 8.08.
140-175+
A4 Dark yellowish brown (10 YR 3/4 M); loamy sand; fine, weak, subangular blocky
structure; friable, non-sticky, non-plastic; medium, many pores; coarse, fine few
roots; pH 8.12.
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Dominant minerals in sand were quartz followed by
feldspars and mica. Less than 100 mesh size sand
fraction exhibited a prominent peak of quartz at 3.36
Å and it was altered to 3.30 Å in >100-mesh size
fraction due to some artifacts in analysis. XRD graph
for sand of Baniyon Ka Kheda (P1) representing the
upper plains is presented in Figure 2. Fine sand
showed a peak at 4.26 Å which was vanished in
coarse sand. Feldspar peak was appeared prominently
at 3.17 Å in coarse sand fractions and became
subdued in fine sand. Relatively higher content of
feldspars in coarse sand indicated higher resistance to
weathering in Aravalli alluvia. XRD showed a
reflection of mica at 10 Å flowed by quartz (3.3 Å) in
fine sand fractions. More or less the sand mineralogy
was showed a similar mineralogical composition all
over the soils of Kothari river plains. Quartz,
feldspars and micaceous mineralogical compositions
of sand size particles was reported in arid ecosystem1, 2
due to resistance in weathering.
Mineralogical compositions of silt fraction
Semi-quantitative analysis of silt size fraction
indicated dominance of minerals in the series of
mica>smectite>kaolinite>quartz>feldspars>chlorite and
vermiculite (Table 5). Quite similar mineralogical
composition was observed in silt and clay fractions.
Quartz and feldspars were present in higher amount in
silt whereas clay was dominated by 2:1 or 1:1 type clay
minerals. Silt was dominated by mica followed by
smectite or kaolinite. Youthful nature of soils of upper
and middle plains was indicated by XRD reflection of a
peak at 8.41 Å (Dulkhera-P4). It showed the presence of
Amphiboles in silt fraction (Fig. 3).
Illite or mica content didn’t show any significant
variation among the plains. However, amount of mica
was higher in silt of high elevation (592 m) and low in
lower elevations (399 m). Mica content decreased in
sub-surface layers progressively in majority of soils.
These were rich in micaceous minerals like biotite as
well as muscovite. It was indicated by the ratios (>1)
of first order and second order of basal reflection in
silt fraction4.
Smectite content in silt fraction was increased with
increasing depth in all three plains. It was also noted
that 2:1 type clay mineral (smectite) was higher in
soils of lower plain followed by middle and upper
plains. The alluvium suspended in Nile river were
dominated in illite and smectite clay minerals13
which
Table 4 — Pedomorphic features of representative pedon P9 (Akola) in lower plains
Classification: Coarse-loamy, mixed, hyperthermic Typic Haplustepts
Location :
Climate :
Parent material :
Slope :
Landform :
Drainage :
Erosion :
Land use :
Height from MSL :
Latitude: 25o 21’52” N, Longitude: 74o43’30” E
Semi-arid
Alluvium
1-3 %
Gently sloping plain
Well
Very slight
Cultivated double crop (cluster bean/maize/mustard, wheat/barley)
399 m
Depth (cm) Horizon designation Soil description
0-19 Ap Yellowish brown (10 YR 5/4 M); loamy sand; medium, weak, subangular blocky structure;
loose, slightly sticky, non plastic; slight effervescence; medium common, coarse many pores;
very fine many fine common roots; clear smooth boundary; pH 9.31.
19-45 A1 Dark yellowish brown (10 YR 4/4 M); sandy loam; medium, weak, subangular blocky structure;
loose, slightly sticky, non plastic; medium, coarse, common pores; fine common, few roots, clear
smooth boundary; pH 8.62.
45-85 Bw1 Dark yellowish brown (10 YR 4/4 M); sandy loam; medium, moderate, subangular blocky
structure; friable, sticky, non plastic; slight effervescence; medium, coarse common pores fine,
coarse few roots; clear smooth boundary; pH 8.49.
85-125 Bw2 Dark yellowish brown (10 YR 4/4 M); sandy loam; medium, moderate, subangular blocky
structure; friable, sticky, non plastic; slight effervescence; medium, coarse common pores; fine,
coarse few roots; clear smooth boundary; pH 8.66.
125-170
Bw3 Dark brown (10 YR 4/3 M); sandy loam; medium, weak, subangular blocky structure; friable,
sticky, non plastic; slight effervescence; medium, coarse common pores; fine, few roots; clear
smooth boundary; pH 8.71.
170+ C Coarse sandy material.
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Fig. 2 — Representative XRD patterns of 50-2000 m sand fraction of the Ap horizon of Baniyon Ka Khera, soils of upper rolling plain
Table 5 — Mineralogical composition: Semi-quantitative mineralogical estimation of silt fraction (ranking according to abundance)
Profile Smectite Mica Talc Amphiboles Kaolinite Quartz Feldspar Chlorite Vermiculite
Upper rolling plains with a mean annual rainfall <600 mm
Baniyon Ka
Khera P1/1
IV I VI VI II V III V VI
P1/3 II I VI VI II V IV VI III
Dulkhera P4/1 III I VII VII IV VI II VII V
P4/3 I II VI VI V IV II III VI
Middle sloping plains with a mean annual rainfall 600-700 mm
Sarano Ka
Kheda P6/1
III I nil
VI
II IV III V VI
P6/4 I I nil V III III II IV nil
Hamirgarh
P8/1
II I nil nil III V IV VI VI
P8/4 II I nil nil IV VII V VI III
Lower plains with a mean annual rainfall 700-800 mm
Akola P9/1 IV I nil nil V III II VI VI
P9/4 II I nil nil III III I V VI
Akola P11/1 I II nil nil III VI IV nil V
P11/3 I III nil nil II VII IV V VI
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1790
was very close to the silt mineralogy of alluvia of
Kothari river. Preferential translocation of expanding
and contracting type of clay minerals from surface to
sub-surface in coarse loamy soils under fluvial
conditions might be one of the several causes for
enrichment of smectites in lower horizons14
. The
swell-shrink type of clay minerals might be the
product of micaceous minerals through 1.0 to 1.4 nm
mixed minerals stage under prevailing semi-arid
climate15
. The third significant mineral of silt fraction
was kaolinite. No definite trend was noticed in the
lateral or vertical distribution of kaolinite. Vermiculite
and chlorite were also present in association of quartz
and feldspars. Talc, a trioctahedral unstable mineral
was noticed in silt fraction of upper plain indicated
the juvenile stage of soil development.
Mineralogical compositions of clay fraction
Estimation of clay minerals through semi-
quantification of peak area of XRD reflection gave
the approximate percentage of minerals present in
clay matrix7 are presented in Table 6 and Figure 4.
Smectites
Smectites are formed in the area where soils are
imperfectly drained, developed from basaltic parent
materials with alkaline soil reaction (pH>8.0) under
high concentrations of silica, calcium and magnesium
ions16
.
Smectite was the second most important clay
mineral after illite/mica in the studied soils and
increased from the soils of upper to lower plains. The
smectite increased with soil depth in upper rolling
plains (P1-P4) and remained almost constant in other
two plains (P5 to P12)1. Alterations and distributions
of the clay minerals in soil profile is the combined
effect of climate, topography and time on parent
material. Preferential translocation of smectites from
ploughing layer to subsurface layer, transformation of
mica to smectites, destruction or removal of smectites
Fig. 3 — Representative XRD patterns of 2-50 m silt fraction of the Ap horizon of Dulkhera, soils of upper rolling plain: Ca = Ca-
saturated, K-25/110/ 300/550 = K saturation and room temperature (250C), K-saturation and heated to 110 0C, 300 0C and 550 0C; Sm =
smectite, Ch = chlorite, V= vermiculite, M = mica, K= kaolin, Q = quartz, F = feldspar, Am = amphibole
SHARMA et al.: CLAY MINERALS IN ALLUVIAL SOILS
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Table 6 — Mineralogical composition: Semi-quantitative mineralogical estimation of total clay fraction (ranking according to
abundance)
Profile Smectite Mica Talc Kaolinite Quartz Feldspar Chlorite Vermiculite
Upper rolling plains with a mean annual rainfall <600 mm
Baniyon Ka Khera
P1/1
III I V II VII IV VI VII
P1/3 II I VI IV VII V VII III
Dulkhera P4/1 II I VII III VI V IV VII
P4/3 I II IV III V IV V VI
Middle sloping plains with a mean annual rainfall 600-700 mm
Sarano Ka Kheda
P6/1
III I VI II IV nil V VI
P6/4 II I VII III VI V IV VI
Hamirgarh P8/1 II I V III V IV V V
P8/4 II I VI IV V V VI III
Lower plain with a mean annual rainfall 700-800 mm
Akola P9/1 I II nil III V IV IV VI
P9/4 I II nil III V nil VI IV
Akola P11/1 I III nil II V V VI IV
P11/3 I II nil III V nil VI IV
Fig. 4 — Representative XRD patterns of <2m clay fraction of the Ap horizon of Akola, soils of lower plain: Ca = Ca-saturated, K-
25/110/ 300/550 = K saturation and room temperature (25 C), K-saturation and heated to 110 C, 300 0C and 550 C; Sm = smectite, Ch
= chlorite, V= vermiculite, M = mica, K= kaolin, Q = quartz, F = feldspar
INDIAN J. MAR. SCI., VOL. 48, NO. 11, NOVEMBER 2019
1792
from plough layer might be the key explanations for
mineralogical alterations14
. In the present study the
swell-shrink clays might be the product of mica
alteration under prevailing semiarid climatic
conditions15
. A base rich parent material and scanty
rainfall with ample amount of silica under higher pH
level originated the expanding and contracting type of
clay minerals in soils situated on low lying plains.
Since, these conditions were existed in all three plains
of river which were more prominent in low lying area.
The smectites in upper and middle plains were mainly
inherited from the parent material17
but there were
some evidences that the smectites were formed
through the process of neoformation following the
pathway suggested by Jackson18
in lower plains.
Illite/Mica
Illite or mica content was ranked as first mineral in
terms of its proportion in soils of upper and middle
plains whereas it was ranked second in lower plain.
The mica has been transformed/altered to smectite
due to the combined effect of factors of soil
formation19
. Semi-quantitative estimation of mineral
and interpretation of XRD differactograms showed
that mica was highest in middle plain which is a
weathering product of mica flakes in the form of
tectosilicates. Mica was present in form of muscovite
and biotite4 because the ratio of first and second order
basal reflections was >1.0. The mica present in clay
fraction was altered to pedogenic chlorite20
,
interstratified or hydroxyl-aluminum-inter-layered
clay minerals with the age of soil.
It was thought that mica might have been inherited
from the parent material because mica was also
observed with similar trend in the sub-surface soils21
.
The scope of alteration of K-saturated smectites to
mica-like products was found to be limited except
soils of lower plain, due to presence of recent alluvia
in the study area and time frame does not permit such
conditions. Illite might be a secondary product of di-
octahedral muscovite mica in soils of lower plains.
The potassium is lost due to physical weathering22
and
produced additional negative charges on illite clays.
Kaolinite
XRD analysis of clay fraction indicates the existence
of kaolinite in all three plains. Semi-quantification of
minerals showed that kaolinite was the third abundant
mineral in study area. Kaolinite content was declined
down the depth of profile in all soils excluding the
pedon-P9 where it was almost constant. Acidic soil pH,
low base status and moderate silica concentration are
the favorable soil environment for genesis of kaolinite
clay mineral23
. Such conditions operate in soil
environments for very short period in rainy season
especially in soils of upper and middle plains that
support for neosynthesis of kaolinites in study area.
There are several researchers, reported that kaolinite
may also occur through direct conversion of mica to
kaolinite3. The presence of kaolinite in this region can
either be due to inheritance directly from parent
material or synthesized in place due to depleting
conditions and good internal drainage.
Chlorite and Vermiculite
A trace amount of chlorite and partially chloritized
vermiculite found in clay fractions. It showed a
substantial variation between the soils of different
landforms. Most of the vermiculite and chlorite in
soils of this investigation were formed either by
weathering of mica25
or it might be derived from the
parent materials in the form of chlorite and changed to
interstratified chlorite-vermiculite through chemical
oxidation and selective extraction of interlayer
hydroxide sheet24,25
.
Talc
Talc is the an unstable trioctahedral mineral found
in trace amount in clay of upper and middle plains
(P4-P8) and it was not present in the soils of lower
plains (P9-P12). It indicated the juvenile stage of soil
development at higher elevation. Talc might be
derived from low grade metamorphic rocks of
ultrabasic or basic igneous provenance26
.
Quartz and Feldspars
A trace amount of quartz and feldspars were
present in clay matrix. Their distribution did not
follow any specific pattern, in some soils it was
present and in others absent.
Role of mica/feldspars in Potassium Release
Potash feldspars and mica were the major
potassium supplying clay minerals in the soils. The
primary source of potassium nutrition is micas
followed by K-feldspars to plants27
. However, size of
particle, surface area, concentration of K+
and other
cations decide the release rate of K+ ions in to soil
solution for plant uptake. It also depends on
weathering status of feldspars and micas in edaphic
environments28
. Muscovite is relatively a stable
mineral and generally may not release K in the soil
SHARMA et al.: CLAY MINERALS IN ALLUVIAL SOILS
1793
environment29
. Besides muscovite, biotites are also
significantly present in these soils which could have
contributed to the predominance of plant available
K30,31
.
Crops in micaceous alluvial soils of the sub-humid
and semi-arid climates rarely respond to K bearing
fertilizers under intensive cropping systems of Indo-
Gangetic alluvial plains over long periods of time21
where as in soils of the per-humid climate, crops do
respond33
. The amount of K taken by crop plants in
soils of Aravalli alluvium could easily be replenished
by biotitic K stock initially and muscovite later on.
Review on the role of clay minerals in potassium
nutrition in soils of India indicates that weathering of
muscovite in presence of biotite is improbable28
.
Pedogenetic studies showed that muscovite gradually
transformed to biotitic mica under natural soil
forming factors.
Genesis of clay minerals
Granite and quartzites were the common rocks in
Aravalli hills intermixed with gneissic complex and
micaceous minerals. A little variation in topographical
positions and rainfall patterns could significantly
influence pedogenic development. The soil on upper
rolling plain is younger and relatively mature on
lower plain. Mica or illite present in clay fractions
was the weathering product of parent material of
Aravalli. The mica further altered to smectites and
vermiculites20
through the physical and chemical
process of weathering.
Smectites and vermiculites were concentrated in
clay fraction of lower plains due to translocation and
deposition of finer fraction in low lying area.
Interpretation of XRD data on mineralogical
properties indicated a wide variation in clay
mineralogical make of these three landforms20
. Total
elemental composition of soils showed a high content
of silica coupled with alkaline reaction which
developed a suitable environment for formation of
smetites. Calcium saturated clay fraction showed a
basal spacing 16-17 Å on solvation with ethylene
glycol strengthen the hypothesis that smectites
originated through the process of neoformation. The
high purity of swell-shrink clays justified that part of
smectites originated by neoformation under imperfect
drainage in soils of lower plain and rest from the
alteration of mica. Mica was the major source of
smectites in upper and middle plains. Biotitic mica
was undergone to the repotassication under high
concentration of K and Mg in soil solution. Therefore,
we have inferred that contracting and expanding type
of clay minerals were formed in situ or during the
transportation of alluvia from higher elevation to low
lying area. Trapping of Mg in interlattice space of
smectites released from weathering of chlorite and
talc originated the vermiculites in the clay fraction of
middle and lower plains. There were some evidences
that kaolinite might be transformed from mica up to a
certain extent. Besides these minerals, kaolinites,
chlorites, talc, amphiboles, feldspars and quartz are
inherited directly from the parent materials. In the
broader view, the clay mineralogy of the soils would
have been all most identical, if there would be no
variation in topography and rainfall. Clay content in
the soils has increased with increasing soil
development, where as silt decreases.
Clay mineral transformations in historical perspective
The variation in mineralogical framework of
various soil size fractions and their depth distribution
had been evident in different landforms of Aravalli
system. For instance, the mica content was higher in
silt size fraction than clay fractions and a reverse
trend was observed in case of smectite distribution.
Further, the pedons of middle sloping plains shows
the dominance of trioctahedral and dioctahedral mica
in the silt fractions. The clay fractions in soils of
lower plain contain significant amount of smectites
which buffers the plant available nutrients as per
requirement. The increasing amount of smectites from
the silt to the clay fractions at the expense of mica and
vermiculite. This suggests early stages of weathering
of biotite to mixed-layered minerals containing
vermiculite layers34
. Clay illuviation is observed in
pedons of lower plain where major alteration of
biotite to smectite presumable occurred during the
post depositional period. Weathering of muscovite is
very sensitive to potassium concentration in soil
solution. Biotite releases considerable amount of K in
soil solution, and as a result, weathering of muscovite
is inhibited4. Therefore, formation of smectite is very
rare from muscovite35
. Semi-arid climatic conditions
facilitate the formation of CaCO3 from plagioclase36
,
mica may not yield so much smectite as observed in
soils of lower plains. It might be formed as an
alteration product of plagioclase37
. Mineralogical
investigations indicate that clay minerals are inherited
from the weathering of existing rock formations of
area as well as past geological cycles. Many minerals
are not formed in the present climatic environment
and appears to be sedimentary origin.
INDIAN J. MAR. SCI., VOL. 48, NO. 11, NOVEMBER 2019
1794
Conclusion
The salient findings and conclusions of the study are:
i. The soils were moderately deep to deep, coarse
loamy with juvenile stage of soil development.
ii. Increasing trend of silt and clay fractions down
the depth was noted in all three plains but it was
more prominent in the soils of lower plains due
to downward movement of clay (illuviation)
and micro-low topography that could have
favoured chemical alteration of primary
minerals in the sand fraction to secondary
oxides of silt and clay.
iii. Feldspars and quartzite were high in coarse sand
and low in fine sand.
iv. 2:1 type clay mineral smectite followed an
increasing trend from upper rolling plains to
lower plains. A supply of cations, iron,
magnesium, calcium and sodium, excess of
dissolved silica, and an alkaline environment
besides low-lying topography, poor drainage
and base rich parent material like biotites,
positively influence the smectite formation. The
smectites in upper and middle plains were
mainly inherited from the parent material but in
lower plains smectites were formed through the
process of neoformation.
v. Acid conditions with moderate silica activity and
small amounts of base cations operate in soil
environments during rainy season especially in
soils of upper and middle plains that might have
favoured the formation of kaolinites.
vi. Vermiculite and chlorite were formed by
weathering of mica or by the process of Mg
trapping in the interlattice space of smectites in
soils of middle or lower plains.
vii. Biotites present in these soils significantly
contributed to the predominance of plant
available K.
Our study concludes that the minerals from the
present study such as, kaolinites, chlorites, talc,
amphiboles, feldspars and quartz might have been
partly inherited from the parent materials and mixed
with minerals formed during past geological cycles.
Many minerals are not formed in the present climatic
environment and appears to be sedimentary origin.
Acknowledgement
The authors are grateful to Dr. M. S. Rathore and
Dr. F. M. Qureshi, Ex-professors, Department of Soil
Science and Agricultural Chemistry, Rajasthan
College of Agriculture, MPUA&T, Udaipur for their
guidance and support during the study. We are very
thankful to Dr. D. K. Pal, Ex. Principal Scientist
& Head, Division of Soil Resource Studies,
ICAR-NBSS&LUP, Nagpur for mineralogical
analysis and interpretations of data.
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