Characterization, genesis, and classification of rice soils of Eastern Region of Varanasi, Uttar Pradesh

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Agropedology 2005, 15 (I) 29- 38
Characterization, genesis and classification of rice
soils of Eastern Region ofVaranasi, Uttar Pradesh
I.S. SINGHl AND H.P. AGRAWAL
Department of Soil Science and Agricultural Chemistry, Institute of Agricultural
Sciences, Banaras Hindu University, varanasi
221 005,
India
Abstract: Rice growing soils of eastern
Ll.P
have developed from the Quaternary Gangetic
alluvium of the Holocene period into very deep, well to imperfectly drained soils with strong
horizon differentiation. These soils showed clay illuviation. Micromorphological study of
thin sections of Bt horizons of pedons
I
and 3 showed that there was a moderate plasma
separation along voids and grains. The CEC values were low to medium and consistent with
clay fractions dominated by the illite and kaolinite minerals. The dominant basic cation was
Ca which influenced the development of the soil. The pedons I and 3 were classified as
Typic Hapludalfs whereas
pedon
2 as Dystric Eutrudepts and
pedon 4
as Typic Ustifluvents.
Additional key words:
Alluvial parent material, mineralogy. alkalization.
micromorphology
Introduction
Rice is an important staple food crop of tropical
andsubtropical climatic regions. In eastern India. rice is
dominantly grown as rainfed
kharif
crop with the onset of
south-west monsoon. Due to variation in physiography, the
studyarea has all three types of rice cultivation,
i.e.
upland
rice,mid-upland rice and lowland rice. Rice has got a potential
togrow in various types of soils and under a wide range of
climatic conditions. The wide variety of ecological
conditions under which rice is growing is matched by the
diversity of soils which support this crop, so that in reality
there is probably no such thing as a 'rice soil'. The natural
drainagevaries from good to poor. The parent materials range
fromrecent alluvium to well weathered residual materials in
upland sites. Soil texture varies from heavy clay to sand;
organic matter from less than I % to more than 50%; salt
content from near 0 to I%; and pH from less than 3 to more
than 10 (De Datta 1981). Thus it is likely that the crop can
alsobe grown under various soil water regimes. which vary
from near saturation to about 10-50 ern of standing water
(Mandai 1984). The continuous submergence of soil causes
changes in physical and chemical characteristics of the soi Is
and these changes are distinctly different from those of
mid-upland and upland rice growing soils (Mandai 1984)_
Puddling in rice growing soils affects physical properties of
soil. This results in breaking the natural larger aggregates
into finer ones, with considerable expenditure of energy
(Ghildyal 1978). The bulk density is decreased. the capillary
pore space is destroyed and hydraulic conductivity is
reduced, as is the free percolation of water. Soil aeration is
minimised in the major upper tilled layers of the soil. Sharma
and De Datta (1985, 1986) also reported the drastic changes
in pore- size distribution of the soil as a result of pudclling.
Information on characterization of rice growing soils of U.P.
is available in literature but only sporadic attempts (Agarwal
and Mehrotra 1952-; Agarwal 1961; Shankarnarayana and
Hirekerur 1972 and Singh
et al,
1989) have been made to
classify such soils using Soil Taxonomy. In view of the above
facts, the present investigation was undertaken in part of
eastern
Uttar Pradesh India to unclerstandthe characteristics
and genesis of the soil in relation to physiography and
distance from the river flowing in the region.
'Scientist
(Soil Physics and SWC). CIAH Beechwal, Bikaner 334 006, India.

30
Materials and Methods
The study area lies between 25° 10' and 25° 30'
North latitudes and between 83° 0' and 83° 30' East
longitudes covering part of Chandauli (erstwhile Varanasi)
district of eastern Uttar pradesh. The area has a semi-arid
and subtropical monsoonic type climate with a mean annual
rainfall of 1060 rnrn. The mean annual summer and winter
temperatures are 32° and 19.3°C respectively. The temperature
regime of the area is
hyperthermic
whereas the moisture
regime is
udic.
Four observations were made which are
representative of the selected landforms in village; Dhanapur
(PI), Shahjaur (P,), Sakaldiha (P3), and Hardhanjura (P4).
Morphometric observations were made as per Soil Survey
Division staff 1995; I.A.R.I. Manual 1970). The soils were
analysed for their physical and chemical properties following
methods described by (Black 1965; Jackson 1950). Separation
of clay and chemical composition of soils (MgO, CaO, SiO"
Rpv Fep) was determined according to Jackson (1950,
56). Elemental analysis of the soil was done by fusing the
soils with anhydrous sodium carbonate (Jackson 1967). XRD
study of whole clay of the PI and P
3
pedons for the identification
of layer silicates was done according to the procedures
outlined by Jackson (1979). Micromorphological investigations
were carried out at National Bureau of Soil Survey and Land
Use Planning, Nagpur for the selected B horizons of PI and
Po pedons. The thin sections were prepared following
methods described by Jongerius and Heintzberger (1963).
Description of the plasmic fabrics was done as per the
terminology of Brewer (1964) and Bullock
et al.
(1985). These
soils were classified according to Keys to Soil Taxonomy
(Soil Survey Staff 1998).
Table 1. Site characteristics of rice growing soils
I.S. Singh and H.P. Agrawal
(
Results and Discussion
The soils of P: were relatively yellower (5Y 6/2)
than those of pedons PI, p, and P4. The slightly redder hue
(1OYR 5/2) was dominant in PI.The exclusively rice growing
soils (PI, P2 and PJ), in general, had chroma of 2 in their
surface horizons, which were indicative of localized anaerobic
(anthraquic) conditions (Sawhney and Sehgal 1989). The
upland rice soils (P.) had chrornas up to 4 suggesting
non-aquic conditions in the surface horizons. The redder
hue in case of PI, P2 and PJ soils might be attributed to the
ferruginous nature of alluminiurn / prolong redoxirnorphic
conditions. Intense mottlings were observed in all the
profiles except P4 because of water logging owing to their
lower physiographical positions in comparison to P4(Table I).
Soil structures were dominantly moderately developed,
medium to coarse subangular blocky types, most likely as a
result of the lower clay contents and the dominance of the
bivalent Ca
2
+
and Mg
2
+
cations over the monovalent ions on
the exchange complex, which had resulted in the soils being
well flocculated. The soils were friable (moist) due to low to
medium clay contents and this was attributed to good
aggregation of the soil particles. Fe and Mn concretions
were present in PI, P2and P
J
soils whereas calcretes were
present in significant amount in PI and p, (Table 2).
The physical properties of these soi Is showed
an uneven distribution of mechanical separates which
may be clue to different depositional environment of the
sediments. Bulk density increased with depth for all the
soils (Table 3). The lowest density was observed in Ap
horizons which may be due to the effect of organic matter.

(11
..-
;:r- ;:r-
:r
Po
(1i
in
0. V
\J-
-
,.
:; '0
(1) (1)
ye
.",-.~~--,
'lable 2_ Morphological characteristics of the soils
Veplh (m) Horizon Boundary Colour Moltle Texture Structure Fe-Mn Calcretes
Roots
Etfcrvcsccuce
matrix colour Co nc r e t
i
o n s
(Moist)
Pedon I: Fine-Ioamy, mixcd, hyperthermic Typic Hapludalfs
O.O-O.IS Ap cs IOYRS/2 scl
fl
gr
III III
e
0.IS-0.40 2A2 gs IOYRS/2 el 1112
sbk
vr
fff
e
OAO-0.60
3Btl gs IOYRS/3 flf 7.SYR6/8
cl
1113 sbk f f 111f vf fcs
.60-0.8S 3Bt2 gs IOYR3/3 c2d 7.5YR6/6 el c3 sbk 111111 111f cs
.8S-I.OS 3Bt3 gs IOYR313 e2d 7.SYR6/6 cl 1112 sbk 111111 f f cs
I.OS-I.SO 4C IOYR413 Is
o
sg ff c
Pedon 2: Fine-loam)', mixed, Hyperthermic Dystr!c Eutrudepts
0.0-0.20 Ap cs SY 5/2 scl 1112shk
elll
0.20-0.65 2A2 gs 5Y 6/2 mlf2.5YR4/4 scl 1112 sbk fill fc
0.6S-0.8S
2Bwl
gs
SY
S/3
f2f 2.SYR 3/4 scl 1112 sbk ff
vf
f
0.8S-I.20 2Bw2
gs
2.SY 5/4 f1d 2.SYR 3/4 scl c2 sbk ff
1.20-I.S5 2Bw3 2.5Y 5/4 1112d 2.SYR 3/4 scl e3
sbk
vf f
Pedon
3:
Fine-loamy, mixed, Hyperthermic Typic
Hapludalfs
O.O-O.IS Ap cs 2.5Y 4/2 Ifl gr 111111
0.IS-O.4S Bt gs 2.SY 5/4 f1d 2.SYR 4/4 scl fI sbk vf f ff e
OA5-0.80
Btl gs 2.SY 5/4 f1d 2.SYR 3/4 scl 1111
sbk
ff
ff
vf f e
0.80-1.20 Bt2
gs
2.5Y 5/4 eld 2.SYR 3/4 I 1112
sbk
l11e
f f
es
1.20-1.60 2Bt3 2.5Y 5/4 e2d 2.5YR 3/4 scl 1112 sbk e c
III
f
es
Pedon 4: Course-loamy, mixed, Hyperthermic Typic Ustiftuvents
O.O-O.IS Ap cs 2.5Y 4/4 sl f
gr
111m
cs
1.15-0.-10 ACI
gs
2.5Y
4/-1
sl
r
gr
fill
e-,
lAO-O.75 AC2 ds 2.5Y 5/4
sl
fgr vf f cs
.75-1.05 AO ds 2.5Y 5/-1 sl fgr vf fcs
.05-1.35 AC4 ds 2.5Y 5/4 sl f gr
vf
r
cv
1.35-1.55 AC5 2.5Y 6/-1 S
() s~
C"
Abbreviations as per
Soil SlIn'~Y
Manual
(Soil Survey
Slaff 1951)
•...
(')
::r
5
n
~
::l.
N
§.
o
::>
o
...,.,
....•
n'
(1)
'"
o
:r.
'.-.l

32 I.S. Singh and
H.P.
Agrawal
Table
3.
Mechnical composition of soil (per cent on oven dry basis)
Depth Coarse Fine Silt Clay Texture Sandi Sandi Silt! Bulk
(01)
sand sand silt clay clay density
~
(%) -
-7
ratio ratio ratio (Mg m')
Pedon 1 : Fine-loamy, mixed, hyperthermic Typic Hapludalfs
0.0-0.15 0.3 50.5 24.2 25.0 scl 2.09 2.03 0.96
lAD
0.15-0.40 0.1 41.6 30.3 28.0
cl
1.37 1.48 1.08 1.45
0.40-0.60 44.2 23.3 32.5 cl 1.89 1.36 0.71
IA7
0.60-0.85 45.6 21.8 32.6 cl 2.09 1.39 0.66 1.53
0.85-1.05 45.5 21.3 33.2 cl 2.13 1.37 0.64 1.57
1.05-1.50 1.5 72.5 18.5 7.5
Is
4.00 9.86 2.46 1.61
Pedon 2: Fine-loamy, mixed, hyperthermic Dystric Eutrudepts
0.0-0.20 1.3 52.0 23.0 23.7 scl 2.31 2.24 0.97 1.38
r">
0.20-0.65 0.8 48.0 25.3 25.9 scl 1.92 1.88 0.97 1.42
0.65-0.85 45.4 27.3 27.3 scl 1.66 1.66 1.00 1.49
0.85-1.20 46.5 27.5 26.0 scl 1.69 1.78 1.05 1.52
1.20-1.55 47.2 27.6 25.2 scl 1.71 1.87 1.09 1.55
Pedon 3 : Fine-loamy, mixed, hyperthermic Typic Hapludalfs
0.0-0.15 0.0 49.1 30.6 20.3
1
1.60 2.41 1.50 1.35
0.15-0.45 0.0 46.0 27.4 26.6 scl 1.68 1.72 1.03 1.36
0.45-0.80 0.0 47.1 25.7 27.2 scl 1.83 1.73 0.94 1.41
0.80-1.20 0.0 44.5 30.5 25.0 1.45 1.78 1.22 1.45
1.20-1.60 0.0 47.4 25.1 27.5 scl 1.88 1.72 0.91 1.47
Pedon 4: Coarse-loamy, mixed, hyperthermic Typic Ustifluvents
0.0-0.15 3.5 54.5 30.0 12.0 sl 1.93 4.83 2.50 1.48
0.15-0.40 1.8 57.2 27.9 13.1 sl 2.11 4.50 2.12 1.55
0.40-0.75 1.6 57.3 30.0
II.!
sl 1.96 5.25 2.70 1.57
0.75-1.05 1.5 56.4 31.8 10.1 sl 1.82 5.75 3.14 1.58
"......
1.05-1.35 2.5 59.7 30.7 7.1
sl
2.02 8.76 4.32 1.63
1.35-1.55 5.0 81.1 8.9 5.0 s9.67 17.22 1.78 1.65
The increase in bulk density with depth was attributed to
lower organic matter, more compaction and less
aggregation. The silt contents
of
the soils were
relatively high, ranging from 20-34 per cent. The clay
content (5.0 to 33.2%) varied widely and in general, increased
with depth. This may be due to abrupt change in sand/silt
ratio between the horizons. Abrupt increase in clay content
in B horizon of
PI
without any sign of argillic horizon was
indicative of lessivage. Lower silt/clay ratio, especially in B
horizons of
PI
and
P
J
suggests that most of the primary
minerals had been transformed to clay-sized secondary
minerals since silt/clay ratio reflects the ratio of primary to
secondary minerals. The abrupt change in the sand/silt
and sand/clay in lower most horizons of
P.
indicated
lithologic discontinuity (Sidhu et al . 1976). These soi Is were
low in organic carbon content due to high rate of
decomposition of organic matter under the subtropical
conditions.Organic carbon content decreased down the depth
in all the pedons except P. where its distribution was irregular.
The organic carbon varied from 3.30 g kg' to 7.65 g kg' in
I
I"
I~
. I
L~
c
tl
o
n
11
(:
h
e
d
d
b
d
T

. surface layers. Generally surface soils were rich in
ic carbon (Ponnamperuma 1972). These soils were
Iralto moderately alkaline in reaction (pH 7.1 to 8.3), low
tEe
[8.2 to 20.2 cmol (p+) kg'] but high in base status
,0to99.0%). The higher pH of P, might be ascribed to the
'gh
content of free calcium carbonate (Table 4). The
trical conductivity of all soils were very low. Irregular
tribution of CaCO) with depth may be attributed to
erential dissolution by CO
2
rich water which is moderated
physiography, rising and receding water table and
inageconditions. Ca was the most dominant exchangeable
ble 4. Chemical characteristics of the soils
33
cations followed by Mg, Na and K (Table 4). Exchangeable
Ca and Mg in all the soils showed higher accumulation in
the subsurface horizons. Relatively high exchangeable Ca-'
and Mg+2 in the lower layers might be due to the deposition of
calcitic or dolomitic parent materials carried by the ri vel'
during fluvial cycle in the past (Walia and Charnuah 1994).
The morphological, physical and chemical properties
of pedons (Table I and 2) indicated marked differences in
soil genesis. However, all the pedons developed over similar
parent material and climatic condition but dissimilar
topography. Pedon P4 did not show distinct horizonation
IiI
EC OC
Exchangeable-Bases
CF.£
Base
(dSm·
l)
(g kg:')
Ca
Mg
Na
K
Saturation
(
cmol (p+) kg'!
~
(%)
Pedon
1:
Fine-loamy, mixed, hyperthermic Typic Hapludalls
.0.0-0.IS 7.4 0.09 3.85 6J 6J OJ 0.9 15.5 87.7
O.1S-O.4D 7.5 OJ6 3.00 7J 5.9 0.4 0.5 15.6
<XJ.4
I
6.4 0.5 0.5 16J 90.8
" 0.4M.60 7.4 OJ7 l.98 7.4
. 0.ffi.O.8S 7.7 0.42 l.89 8.0 5.6 0.4 0.4 15.5 93.0
0.8S-I.OS 7.6 0.45 l.80 8.1 5.6 0.6 0.6 17.0 87.6
.1.0S-I.S0 7.7 0.43 l.80 8.1 3.1 0.7 0.5 14.0 88.5
Pedon 2: Fine-loamy, mixed, hyperthermic Dystric Eutrudepts
.0.0-0.20 7.1 OJO 5.56 8.6 4.1 0.1 l.2 17.5 80.0
0.20-0.6S 7.1 0.41 5.00 9.7 6.0 0.2 0.8 19.7 84.8
0.6S-O.8S 7.2 .0.44 3.21 10.7 5.8 0.5 0.4 20.2 86.1
0.8S-1.20 7.4 OJ5 2.85 11.3 3.9 0.6 0.5 18.5 88.1
1.20-l.S5 7.5 OJ8 2.60 1l.4 4.0 0.6 0.5 18.5 89.2
Pedon 3 : Fine-loamy, mixed, hyperthermic Typic Hapludalfs
0.0-0.15 7J 0.14 7.65 9.1 5.5 0.4 OJ 16.8 91.0
0.1S-O.45 7.6 0.15 5.40 10.5 6J OJ OJ 18.6 93.5
0.4S-O.80 7.6 0.16 3.19 10.8 4.1 0.2 0.4 16.6 93.4
0.80-1.20 7.7 0.15 3.15 11.3 4.1 0.1 0.4 17.9 94.4
1.20-l.60 7.8 0.17 2.05 12.1 5.0 0.1 0.4 18.4 95.6
Pedon 4 : Coarse-loamy, mixed, hyperthermic Typic Ustitluvents
0.0-0.15 8.0 0.15 3JO 5.8 2.0 0.5 0.2 10.1 84.1
O.IS-O.4D 8.2 0.16 3.26 5.6 3.5 0.3 0.5 10.0 99.0
0.4M.75 8.2 0.15 2.42 5.7 3.6 0.7 OJ 11.3 91.1
0.7S-I.05 8.1 0.18 2.56 5.7 4.1 0.8 OJ IJ.3 %.4
"1.0S-1.35 8.1 0.20 2.00 6.2 3.6 0.8 0.3 11.2 97.3
1.3S-1.55 8J 0.22 2.25 4.1 2.1 0.7 0.2 8.2 86.5

34
due to alternate washing and deposition of newer alluvium.
On the other hand, pedons
I,
2 and 3 reflected more or less
well developed characters vit;.,
illuviation
of clay. Chemical
composition of the soils of PI, P2 and P3 (except P4) showed
fairly high Si0
2
and SiO/Alp3and SiO/RP3 molar ratios in
surface soils (Table 5). This indicates less siliceous substratum
and thereby advanced stage of pedogenic development
(Singh and Mishra 1994). Sudden change in sand/silt and
sand/clay ratios of two lower most horizons of pedon land 4
was indicative of lithological discontinuities due to stratified
nature of parent materials in the profile. The alumina content
was negatively correlated with Si0
2
and sand content
I.S. Singh and
H.P.
Agrawal
and the finding was similar to Choudhari (198i\). The depth
function of CaO and MgO were not clear. It was noticed
that in majority of the soils, their contents decreased in
horizons next to the Ap and A2 horizons but increased in
the lower most horizons. Maximum content
of
KzO was
observed in Bt horizons of PI and
P,
which may be
due
to
higher amount of
clay-sized
mica. The silica content tended
to decrease in Bw and
Bt
horizons because of illuviation
(Walia and
Rao
1996). This was also reflected in the
decrease of molar ratios of
Sial /
AIP3 and SiO) RP3
down the profile for PI, P2 and P3.
Table
S.
Chemical composition of the soils (per cent on oven dry basis)
Depth(m) Si0
2
AIZO) FeZO) R
2
O)
Cao
MgO
~O SiO/R
2
O.
l
SiO/AIPJ
Pedon
1:
Fine-loamy, mixed, hyperthermic Typic Hapludalls
0.0-0.15 78.2 5.0 2.6 7.6 1.0 0.4 0.9 19.96 26.59
0.15-0.40 7103 7.1 2.7 9.8 0.9 0.6 l.l 13.73 17.07
0.40-0.60 72.4 9.8 2.5 1203 1.3 0.5 1.6 10.80 12.56
0.60-0.85 74.5 10.1 2.8 12.9 3.4 0.6 203 10.65 12.54
0.85-1.05 74.2 10.9 3.1 14.0 4.6 0.6 2.4 9.79 11.57
1.05-1.50 80.0 4.5 1.3 5.8 6.5 0.6 0.5 25.51 30.22
Pedon 2 : Fine-loamy, mixed, hyperthermic Dystric Eutrudepts
0.0-0.20 75.0 12.5 2.6 15.1 2.1 203 0.8 9.00 10.20
0.20-0.65 73.5 12.2 3.0 15.2 2.2 2.4 1.0 8.85 10.24
0.65-0.85 7203 11.8 3.1 14.9 2.1 1.2 l.l 8.92 10.42
0.85-1.20 70.1 14.2 3.0 17.2 2.6 l.l l.l 7.39
8.3c)
1.20-1.55 54.4 19.0 3.0 22.0 2.9 1.2 l.l 4.42 4JP
Pedon 3: Fine-loamy, mixed, hyperthermic Typic Hapludalfs
0.0-0.15 84.0 9.8 4.5 1403 1.8 0.5 1.7 11.27 14.57
0.15-0.45 82.6 11.0 2.6 13.6 1.6 0.8 1.6 I
Iff)
12.77
0.45-0.80 75.6 15.4 4.6 20.0 2.6 0.7 203 7.01 8.35
0.80-1.20 73.2 16.5 4.8 2103 1.5 0.8 2.2 6036 7.54
1
1.20-1.60 66.5 16.8 5.2 22.0 2.5 0.8 203 5.62 6.73
, J
Pedon 4: Coarse-loamy, mixed, hyperthermic Typic Ustilluvents
I
i
0.0-0.15 84.2 8.8 0.6 9.4 2.4 0.2 0.5 15.59 16.27
0.15-0.40 81.5 9.8 0.7 10.5 2.4
OJ
0.5 13.54 14.16
0.40-0.75 75.0 7.5 1.2 8.7 2.5 0.6
OJ
15.42 17.00
0.75-1.05 70.2 7.4 1.2 8.6 2.6 0.1
OJ
14.62 16.13
1.05-1035 7803 5.6 103 6.9 3.9 0.4
OJ
20.71 23.78
1035-1.55 80.2 4.6 J.3 5.9 3.8 0.4
OJ
25.11 29.6:1
I
j'
.. J
,.
Ch.
ofi
I 6
cia
eas
soi
inc
of
wi
w.
M
(F
w;
di
ca
o(
sb
I •

X-ray diffraction analysis indicated the presence
ofilliteas the dominant clay mineral followed by kaolin (Fig.
1&2). Singh et al. (1991) also found illite as the dominant
clay
mineral in the alluvial soils of the Varanasi district of
easternUttar Pradesh. They also reported that some of the
soilshad small amounts of kaolin. Sand mineralogy also
indicatedthe dominance of mica and quartz. Thin sections
of P3showedmoderately developed subangular blocky structure
withchannels and vughs micro-structure. Plasma separation
wasweak to undiffemtiated (Fig. 6). 1-2% of mottles and Fe/
Mn concretions were observed under thin section of PI
(Fig.5).Moderate plasma separation along voids and grains
wasrecorded under thin section of soils of PI (Fig. 4). Their
distribution pattern was porphyric and pedogenic
carbonate(Fig.
5)
were in the range of 2-3 per cent which
occurredas discrete nodules. The clay oriented around the
skeletongrains probably created congenial conditions for the
_______________ n~ _
loll I..J5
e.,
u
"100)1
)0
28 26 24 22 20 18 16 14 12 10
2·2 8 -------------------
4
Fig. 1. Representative X-ray diffractograms of the total
clay fractions
«2 £IV
of the soils. M = Mica,
K= Kaolinite ofPedon 1.
35
retention of moisture in the pedon (Venugopal et at.
1989).
The presence of suppressed argillans (Fig. 3) in Pi was an
indication of submergence of field for longer time.
Soil genesis
The contents of AlP3' Fe.O, and K
2
0 were very
low in the recently deposited river sands of P3. Generally
soil forming processes lead to addition, losses, translocation
and transformation of various clements. Although all pedons
developed over similar parent material and under similar
climatic conditions, nevertheless their rate and state of
weathering was quite different. Total chemical analysis (Table 5)
indicated that CaO, MgO and Kp contents constituted less
than 5 per cent of the soil mass which reflected in moderate
weathering conditions (Gupta and Tripathi 1993). The Polsoils
did not show much horizonation which was due to its
youthful nature. The soils of PI, P2 and P, were more
__-- n~--- _
L~'.
I.])
&.»
e.,
KlOO)1
)0 2t 26 24 22 20 IB 16 II. 12 10
2·2 8 -------------------
Fig. 2. Representative X-ray diffractograms of the total
clay fractions
«2
n~of the soils. M = Mica,
K = Kaolinite ofPedon 3.

36
Fig: 3 Showing presence of suppressed argilans (X40)
Fig: 5 Showing presence of pedogenic CaC03in the
aggregated ferriargilans (X40)
weathered than P4 because of their location in mid-upland
and lowland topographical situation where water works
for a longer duration, accelerating the leaching of clay and
translocation of Alp) and Fe.O, . It was also observed that
stratification was maximum nearby the river but pedogenesis
was maximum away from the river. Fine sand mineralogy
showed the dominance of quartz followed by biotite,
muscovite and feldspars. Relatively high quartz content in
these soils could be due to granite gneissof the Himalayan
origin (Pettijohn 1957). Primary minerals were almost
common in these soils suggesting similarity in parent
material. As these soils were derived from alluvium of the
Indo-Gangetic plains, originating from the Himalayas,
quartzite, sandstone, slate, limestone, schists and
conglomerate were the chief rock types observed (Bhargava
and Sharma 1982). Some of the transparent heavy minerals
identified were anatase, zircon and tourmaline. These soils
I.S. Singh and
H.P.
Agrawal
Fig: 6 Showing presence of pedogenic CaCO) (X40)
appeared to have developed from pre-existing sediments
(Pettijohn 1969). Majority of these quartz grains appeared as
rounded one indicating that these have formed on
transported materials. Direct conversion of mica (Oekimpe
and Tardy 1969) to kaolinite may be one of the causes of
substantial quantity of kaolinite in these soils, although
condition did not support kaolinite genesis.
P
3
soils
exhibited lithologic discontinuity between Bt2 and Bt3 horizons
because of the abrupt change in sand/silt ratio. These soils
were mainly derived from sedimentary rocks such as shale.
This is evident from dominant proportions of mica in these
soils and neutral rock weathering and soil forming processes
may have favoured the concentration of mica in clay fraction
of these soils (Reichenback et al. 1975). Little or no pedogenic
processes were evident in the P4 soils as there was no plasma
separation or movement of clay. Sand was present in the
highest amount in this pedon. Pedogenic carbonates in the
Chura
form
grour
More
subsi
other
expe
were
Soil
and I
Staf
hype
arid
of
d
plac
a
us
org,
at
a
US!
any
sub
coa
and
hor
epi
Th(
foil
we:
mi
qu:
Eu
car
de'
M<
or
ho
C(
mi
Of!
Bt

of nodules (1%) but mainly as micrite crystals in the
undmass appeared in the thin section of PI and p) soils.
reover, the occurrence of carbonate concretion in the
bsurface of the soils was indicative of translocation. The
er observed features indicated that the soils of PI and P3
perienced lessivage, illuviation and calcification which
ere the dominant soil forming processes active in these soils.
iI
Classification
The diagnostic criteria for classification of PI, P2
dP, according to the USDA Soil Taxonomy (Soil Survey
taff 1998) include an udic soil moisture regime and an
yperthermic soil temperature regime chracteristic of semi
id to subhumid subtropical monsoonic climate. Absence
f
diagnostic sub-surface horizons in
p.,
qualified it to be
p'~'d under the order Entisols. In essence, its properties of
a ustic soil moisture regime and irregular distribution of
organic carbon, the value of which is more than 0.2 per cent
t a depth of 125cm, qualified it for the great group
Ustifluvents. Since the soils did not have chracteristic of
any
of the subgroup recognized, it keyed out to the
suborder Typic Ustifluvents and at family level as
coarse-loamy, mixed, hyperthermic. Typic Ustifluvents. PI
andP, were characterized by ochric epipedons and argillic B
horizons, whereas, P
2
had a cambic B horizon and ochric
epipedon. Base saturation was high, generally above 80%.
The clay mineralogy of the soils was dominated by illite
followed by kaolinite. Such base saturated soils of PI and P
3
weretherefore, classified at the family level of as fine-loamy,
mixed, hyperthermic Typic Hapludalfs: whereas, P
2
qualified as fine-loamy, mixed, hyperthermic, Dystric
r
idepts
as the particular pedon did not have free
carbonates throughout the horizon beginning from 85 em
depth which is within 100 ern of the mineral surface.
Moreover, P
2
soils did not have any sulfuric horizon, duripan
orfragipan but had more than 60% base saturation In all the
horizons.
Based on morphological, physical, chemical and
mineralogical data these soi Is were placed under three
orders, Alfisols, Inceptisols and Entisols. Thin sections of
Bthorizons of PI and P, showed argillans and argiferrans
37
along with irregular voids. Illuviation, lessivage and
calcification were the dominant soil forming processes in PI
and P, soils. The farmers may be advised to follow
intermittent rice cultivation practices to reduce the rising
concentration of Fe- Mn in the solum of the soils. The data
generated from this study may be helpful for the decision-
makers in framing the standard cultivation measures for
enhancing the productivity of rice soils of this region.
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Received December 2003; Accepted, February 2005