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.

mailto:[email protected]

INDIAN J. MAR. SCI., VOL. 48, NO. 11, NOVEMBER 2019

1784

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

SHARMA et al.: CLAY MINERALS IN ALLUVIAL SOILS

1785

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


1786

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.


1787

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 :


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.


1788

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 :


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.


1789

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


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


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


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


1791

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


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


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


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


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.


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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