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International Journal of AgriScience Vol. 2(7): 642-650, July 2012
ISSN: 2228-6322© International Academic Journals
www.inacj.com
Characterization and classification of soils on two toposequence at Ile-Oluji,
Ondo State, Nigeria
Atofarati S.O.¹, Ewulo B.S.²*, Ojeniyi S. O.²
1 Ekiti State Local Government Service Comission, Ido/Osi Local Government, Ido Ekiti
2 Crop, Soil and Pest Management Department, Federal University of Technology, P.M.B 704, Akure, Ondo State.
*Author for correspondence (email: bsewulo@yahoo.co.uk)
Received May 2012; accepted in revised form June 2012
ABSTRACT
Inadequate information on soil and the influence of landscape on soil properties is a major factor
limiting agricultural production in Nigeria. In order to characterize and classify soils on two
toposequennce at Ile Oluji, Ondo State, in southwest Nigeria, three pedons were dug respectively
on two typical hillslope and studied with regards to their morphological, physical and chemical
properties. They represented soils on the summit to shoulder (Pedon 1 and 4), backslope to
footslope (Pedon 2 and 5) and toeslope (Pedon 3 and 6) along the hillslope. Distributions of clay
increased with depth for all pedon. The soils were moderately to strongly acidic, the highest
concentration of O.C and O.M occurred at the down slope and decreased with depth for all
pedon. Exchangeable acidity (EA) were higher in the pedons of the middle slope. Pedon 1, and 2,
on the first toposequence and pedon 4, 5, and 6 on the second toposequence classify into the
order Alfisol, suborder Udalf and great group Kandiudalfs in USDA system of soil classification
and Albeluvisols in FAO system. Pedon 3 classifies in the soil order Entisol, suborder Arents and
great group Udarent in USDA system of soil classification and Eutric fluvisol in FAO system.
Keywords: clay, classification, hillslope, pedon, soil, toposequence
INTRODUCTION
A major factor limiting agricultural
development in Nigeria is the lack of
information on soil and land characteristics.
Soil topography plays a major role as one of
the factors that influence pedogenesis and in
the process that dictates the distribution and
use of soils on the landscape (Hoosebeek et
al. 2000, Esu et al. 2008). Toposequence and
catena concepts have emanated as slope-soil
evolutionary processes.
Landscape position influences rainfall,
drainage and erosion. Water velocity on a
slope affect deposition of materials in
suspension, the largest size particles, like
sand, are the first to drop out of suspension,
fine clay size particles can be carried further
away from the base of the slope before they
are deposited (Glassman et al. 1980). Hill
slope orientation also affects the
microclimate of a place, inclined surface
facing into the sun tend to be warmer and
drier than flatter surface facing away from
the sun.
Soils are classified as natural bodies, on the
basis of their profile characteristics (Brady
and Weil 1999). The need to provide this
information is more demanding than before
because of the problem arising from misuse
of land resulting in land degradation.
Increase in Nigeria population places
increasing demand on land resources,
International Journal of AgriScience Vol. 2(7): 642-650, July 2012 642

leading to the clearing of soils on slopes and
tilling soil without proper soil management
practices being put in place. This has serious
management implications, because the more
intensively cultivated upland soil
deteriorates rapidly due to erosion and
fertility depletion. There is therefore need to
identify soil and classify them for proper
management, also the relationship between
landscape and soil properties needs further
investigation.
Studies on classification of soil and soillandscape
relationships in the extensive
mountainous terrain underlain by basement
complex materials within the Ile-Oluji area
of Ondo-State are rare. The objectives of
this study is therefore; To study the
morphological, physical and chemical
properties of the soil along two
toposequences at Ile-Oluji, classify the soil
studied according to USDA (Soil
taxonomy) and FAO system of classification
and relate their properties to their positions
on toposequence.
MATERIAL AND METHODS
Site location
Ile Oluji in Ile Oluji/Oke Igbo Local
Government area of Ondo State is part of
tropical rainforest ecosystem in south-west
Nigeria. The soils of the area were formed
predominantly from Precambrian Basement
Complex which form parts of the African
crystalline shield (Alabo 1985) and have
variety of landforms that are classified into
three broad physical units: The plains, the
undulating highlands and the river valleys,
the highland however dominate the
landscape. Mean monthly temperature is
27 0 C with a monthly range of 2 0 C while
mean relative humidity is over 75%. Mean
annual total rainfall exceeds 2000mm
(Ministry of Agriculture 2010).
Field Study
Two toposequences (1 and 2) respectively
were identified, and three pedons (1.5m
wide X 1.5m long X 1.8m deep) were dug
along each of the toposequence at the upper,
middle and lower slope respectively.
Genetic horizons were designated and soil
Morphology described in the field using
Munsell soil colour charts. Soil samples
were collected from each of the horizons,
packed into polythene bags, neatly labeled
and taken to the laboratory for physical and
chemical analysis.
Laboratory Studies
The Soil samples were air-dried, gently
ground in a mortal and sieved with a 2mm
sieve. Particle size distribution was
determined by hydrometer method (Gee and
Or 2002). Soil pH was determined using a
glass electrode in 1:2 soil:water ratio
(Southern Cooperative Series Bulletin
1983). Soil organic carbon (O.C) was
determined using Walkley and Black
method (Nelson and Sommers 1996) and
Organic matter estimated by multiplying
with a factor of 1.724. Total Nitrogen was
determined by Kjeldahl digestion procedure
(Bremmer 1996). Available phosphorus was
determined using the Bray 1 Method and
exchangeable acidity by KCl extraction
method (Mclean 1965). Exchangeable Bases
(Ca, Mg, Na and K) were extracted by
leaching with 1N NH40AC (pH 7.0). Ca and
Mg were determined by atomic absorption
spectrophotometer and Na and K by flame
emission spectrophotometer. Cation
exchange capacity (CEC) was determined
by ammonium saturation method (Jackson
1968). Percent base saturation, effective
cation exchange capacity (ECEC) and
CEC/Unit clay were calculated.
RESULTS AND DISCUSSION
RESULTS:
Morphological Properties
Table 1 and 2 showed morphological
properties of soil formed along toposequenc
1 and 2 respectively. Pedons on the two
toposequence were generally deep, with
643 International Journal of AgriScience Vol. 2(7): 642-650, July 2012

Table 1: Morphological Properties of Soils formed along Toposequence 1
Pedon Soil Depth Horizon Colour Mottles Structure Consistency Root Boundary
(cm)
(moist)
1 0-10 A 7.5YR 4/4 - 1mcr fr.sst.np m.fb cs
10-44 Bt1 5YR 3/2 - 3mcr fr.sst c.fb cs
44-100 Bt2 2.5YR 4/8 - 3abk fi.np f.fb cs
100-150 Bt3 2.4YR 4/8 10YR 6/8 3abk fi.mst vf.fb cs
2 0-10 A 7.5YR 3/4 - 2mcr fr.sst m.fb gs
10-25 Bt1 7.5YR 4/4 - 2mcr fr.sst f.fb cw
25-60 Bt2 2.5YR 4/8 5YR 8/2 3abk fi.mst f.fb cw
60-150 Bt3 2.4YR 4/8 5YR 8/2 3abk
fi.mst f.fb cs
5YR 7/8 3abk
3 0-20 A 7.5YR 4/4 - 1mcrb fr m.fb cs
20-80 B 7.5YR 4/6 - 2mcrb fr c.fb cs
Keys: m – moist; f – few; c – common; m – many; ft – faint; d-distinct; pr – prominent; i – weak; 2 – moderate; 3 – strong; f – fine; m – medium; c – coarse; cr –
crumbs, abk – angular blocky; l – loose; fr – friable; fi – firm; nst – nonsticky; sst – slightly sticky; np – moderately plastic; mst – moderately sticky; f – few; m –
many; fb – fibrous; woody; cw – clear wavy; gir – gradual irregular; dh – diffuse broken1
Table 2: Morphological Properties of Soils formed along Toposequence 2
Pedon Soil Depth Horizon Colour Mottles Structure Consistency Root Boundary
(cm)
(moist)
4 0-20 A 7.5YR 3/4 - 1mcrb fr.sst m.fb as
20-90 Bt1 5YR 5/8 - 2cabk fi.mst f.fb cs
90-150 Bt2 5YR 5/8
7.5YR 5/8
- 3mabk fi.mst f.fb dh
5 0-35 A 7.5YR 3/4 - 2mabk fr.sst m.fb cs
35-9 Bt1 2.5YR 4/6 - 3mabk fi.mst f.fb cs
90-130 Bt2 2.5YR 4/6 2.5YR 2/5 3mabk fi.mst f.fb gs
6 0-40 A 5YR 4/4 - 2mcr fr.mst m.fb gs
40-85 Bt1 7.5YR 6/8
10YR 5/6
2.5YR 4/6 2msbk fi.mst f.fb dh
85-170 Bt2 7.5YR 6/8 2.5YR 4/6 3abk fi.mst f.fb dh
Keys : m – moist; d – dry; f – Few; c – common; m – many; ft – faint; d-distinct; pr – prominent; i – weak; 2 – moderate; 3 – strong; f – fine; m – medium; c –
coarse; cr – crumbs, abk – angular blocky; l – loose; fr – friable; fi – firm; nst – nonsticky; sst – slightly; sticky; np – moderately plastic; mst – moderately sticky;
f – few; m – many; fb – fibrous; woody; cw – clear wavy; gir – gradual irregular; dh – diffuse broken1
International Journal of AgriScience Vol. 2(7): 642-650, July 2012 644

depth ranging between 130 and 150cm.
Pedon 3 on the lower slope of toposequence
1 was underlain by bedrock at a depth of
80cm making it moderately deep. Pedon 6
on the lower slope of toposequence 2 was
very deep. Drainage on soils of the upper
slope of the two toposequence varied
between moderately well drained to well
drained. Pedon 2 on the midslope of
toposequence 1 was imperfectly drained as
evidenced by colour mottling starting from
25 - 150cm depth and hardpan at 135cm
depth.
Soil in the ‘A’ horizons of all pedons in both
toposequences varies; dark reddish brown
(5YR 3/2) for ‘A’ horizon of Pedon 1, dark
brown colour (7.5YR 3/4) for ‘A’ horizon of
pedon 2, light brown colour (7.5YR 4/4) for
‘A’ horizon of Pedon 3, light brown colour
(7.5YR 3/4) for ‘A’ horizon of Pedon 5,
reddish brown colour (5YR 4/4) for ‘A’
horizon of Pedon 6. 2.5YR was not
identified as the main colour of the
downslope soil (pedon 3 and 6), though it
was observed as part of colour mottling in
the subsurface horizon. Soils in all the
horizons of the six pedons have
predominantly crumb structure in topsoil to
angular blocky structure in subsoil.
Soil Physical Properties
Table 3 and 4 shows the physical properties
of soil formed along toposequence 1 and 2.
All soils of the study area were gravel free
in their ‘A’ horizons, but have some amount
of gravels in their sub-soils. Silt content was
generally low in all pedons. Topsoil was
sandy clay loam in texture. The profile
distribution of clay increases with depth for
all pedons and total sand fraction highest in
topsoil. This may be as a result of clay
eluviation – illuvation in the soil
Soil Chemical Properties
Table 5 and 6 shows the physical properties
of soils formed on toposequence 1 and 2.
The soils were moderately to strongly
acidic. pH in water ranged from 5.80- 4.31
while. O.C and O.M for the ‘A’ horizon of
all pedons examined ranges from low to
high and decreased along pedon. The lowest
concentration of O.C and O.M occurred at
the topsoil of upper slope. O.M decreased
with depth in all pedons. The level of N in
the A horizon of the upper slope is low, it
ranges between 0.06 – 0.1%. Nitrogen and
available phosphorus in all pedon correlate
positively with organic carbon, indicating
that organic carbon exist in fixed ratio with
nitrogen and phosphorus. Soil nitrogen and
phosphorus are generally low corresponding
to low organic carbon content.
All pedons are fairly well supplied with
exchangeable cations especially calcium and
magnesium. However, the high to very high
percentage base saturation of the soils of all
pedons (61.38 to 81.67%) reflects the
dominance of basic cations in the exchange
complex.
Higher level of O.C, N, P, K, Na, Ca, Mg
and CEC occured at the ‘A’ horizon of all
pedons established. Nutrients generally
decreased with depth in all pedons. The
Exchangeable acidity (EA) was generally
low but relatively higher in the middle slope
pedons (2 and 5) of both toposequence.
Exchangeable acidity decreases with depth
in all pedons considered.
DSICUSSION:
Morphological Properties
The brownish tinge in the ‘A’ horizon of all
the pedon were due to the presence of
organic matter which is the main colouring
agent in top-soil (Nuhu 1983). The influence
of physiographic position on colour has been
reported (Gerrard 1981 and Esu et al. 2008).
The variation in colour observed on the
toposequence of soils is usually attributed to
the sequence of drainage. Soil landscape
relationship has been used to study soil
variability in large geomorphic region
(Olatunji et al. 2007, Khormali and
Nabiollaby 2007).
International Journal of AgriScience Vol. 2(7): 642-650, July 2012 645

Table 3. Physical Properties of Soils Formed on Toposequence 1
Horizon Depth
Sand
Clay
Silt
Textural Class
Pedon 1
(cm)
%
%
%
A 0-10 64.80 22.20 13.00 Sandy clay loam
Bt1 10-44 58.00 36.00 6.00 Sandy clay
Bt2 44-100 47.00 48.00 5.00 Sandy clay
Bt3
Pedon 2
100-150 44.10 50.00 5.90 clay
A 0-10 50.80 29.20 20.00 Sandy clay loam
Bt1 0-25 42.00 44.20 13.80 Sandy clay
Bt2 25-60 40.00 54.20 5.80 clay
Bt3
Pedon 3
60-150 50.00 46.20 3.80 Sandy clay
A 0-20 60.80 31.20 8.00 Sandy clay loam
B 2-80 50.80 39.20 10.00 Sandy clay loam
Table 4: Physical Properties of Soils Formed on Toposequence 2
Horizon Depth
Sand
Clay
Silt
Textural Class
Pedon 4
(cm)
%
%
%
A 0-20 61.80 27.2 11.00 Sandy clay loam
Bt1 20-90 49.80 42.2 8.00 Sandy clay
Bt2
Pedon 5
90-150 50.80 38.00 11.20 Sandy clay
A 0-35 64.80 22.20 13.00 Sandy clay loam
Bt1 35-90 52.80 31.20 16.00 Sandy clay loam
Bt2
Pedon 6
90-130 43.80 48.20 8.00 loam
A 0-40 52.80 27.20 20.00 Sandy clay loam
Bt1 40-85 37.20 54.80 8.00 clay
Bt2 85-170 36.00 52.00 12.00 clay
The several colours (mottling or
redoximorphic features) recorded in the
subsoil of the soils of the middle slopes may
be due to loss (depletion) or gain
(concentration) of pigment compared to the
matrix colour which is formed by oxidation /
reduction of iron and/or manganese coupled
with their removal and translocation
(Fanning and Fanning 1989). Mottling of the
subsoil is an evidence of seasonal rise in
water table or waterlogging and hence
drainage problem (Fanning and Fanning
1989, Akamigbo et al. 2002).
Clay found in all the pedons have large
surface area by virtue of its small size. It is
the most active minerals that aids
aggregation of primary soil particles and
ensure the stability of such aggregate (Idoga
1985). The soil clay content is therefore the
primary reason why the pedons subsoil was
structurally developed. The desirable effects
of organic matter in the formation of soil
granules and in stabilizing soil aggregates
have been reported (Daniel et al. 2000).
Plant roots and roots exudates help to bind
soil particles together. The high amount of
organic matter in the ‘A’ horizons of all
pedons in both toposequence must have
contributed to structural development in the
horizon
Soil Physical Properties
International Journal of AgriScience Vol. 2(7): 642-650, July 2012 646

Table5: Physical Properties of Soils formed on Toposequence 1
HORIZON DEPTH pH O.C O.M N P K
Na Ca Mg EA CEC ECEC ECEC/% % B/S
Pedon 1
(cm)
% % % g/kg cmol/kg cmol/kg cmol/kg cmol/kg cmol/kg cmol/kg cmol/kg clay cmol/kg
A1 0-10 5.28 1.19 2.05 0.10 2.12 0.42 0.48 2.00 1.00 1.86 5.67 5.39 0.24 68.78
Bt1 10-44 5.80 0.57 0.99 0.05 1.84 0.39 0.39 2.00 0.70 1.64 4.79 4.71 0.13 72.65
Bt2 44-100 5.13 0.57 0.99 0.05 1.47 0.30 0.34 1.69 0.60 1.35 4.69 3.94 0.08 62.47
Bt3
Pedon 2
100-150 4.82 0.54 0.92 0.05 0.63 0.18 0.27 1.40 0.60 1.35 4.14 3.46 0.07 59.18
A1 0-10 5.54 2.00 3.92 0.23 5.71 0.42 0.39 3.20 1.40 2.86 8.27 6.47 0.22 65.42
Bt1 10-25 5.72 0.79 1.35 0.06 3.04 0.17 0.26 1.90 1.00 1.96 5.11 4.60 0.10 65.17
Bt2 25-60 4.41 0.29 0.50 0.03 1.57 0.15 0.25 1.90 0.90 1.65 4.90 4.44 0.08 65.31
Bt3
Pedon 3
60-150 4.62 0.25 0.43 0.002 0.55 0.13 0.22 1.00 0.60 1.26 3.46 2.65 0.06 56.36
A 0-20 5.20 1.40 2.40 0.12 2.30 0.43 0.54 2.00 1.00 1.95 5.92 3.99 0.13 67.06
B 20-80 5.20 0.52 0.89 0.04 2.21 0.21 0.28 1.40 0.70 1.16 3.75 2.89 0.07 69.07
Table 6. Physical Properties of Soils formed on Toposequence 2
HORIZON DEPTH pH O.C O.M N P K
Na Ca Mg EA CEC ECEC ECEC/% % B/S
Pedon 4
(cm)
% % % g/kg cmol/kg cmol/kg cmol/kg cmol/kg cmol/kg cmol/kg cmol/kg clay cmol/kg
A 0-20 5.26 0.73 1.25 0.06 1.52 0.24 0.31 1.80 0.90 1.78 4.53 4.67 0.17 71.74
Bt1 20-90 4.86 0.57 0.99 0.05 1.01 0.27 0.30 1.60 0.90 1.38 4.32 4.24 0.10 71.06
Bt2
Pedon 5
90-150 4.39 0.23 0.44 0.02 1.01 0.15 0.30 1.30 0.70 1.32 3.00 3.53 0.09 81.67
A 0-35 5.47 1.76 3.04 0.15 2.39 0.50 0.58 2.70 1.20 2.65 7.63 6.04 0.27 65.27
Bt1 39-90 5.04 0.59 1.02 0.05 2.30 0.46 0.40 2.30 0.90 1.75 5.81 4.80 0.15 69.89
Bt2
Pedon 6
90-130 5.82 0.36 0.63 0.03 0.92 0.33 0.35 1.20 0.50 1.46 3.84 3.40 0.07 61.98
A 0-40 5.13 1.30 2.25 0.11 3.04 0.28 0.33 1.70 0.90 2.10 5.23 3.42 0.13 61.38
Bt1 40-85 4.45 0.67 1.16 0.06 2.30 0.23 0.30 1.40 0.70 1.46 3.97 3.07 0.06 66.25
Bt2 85-170 4.31 0.19 0.33 0.02 1.66 0.21 0.28 1.30 0.60 1.16 3.75 2.37 0.06 63.73
International Journal of AgriScience Vol. 2(7): 642-650, July 2012 647

Low silt content in pedon of soil has been
reported (Esu et al. 2008) likewise increase
in clay with depth, as a result of clay
eluviation – illuvation in soil. (Ewulo et al.
2002). Water is important in clay dispersion,
the amount of dispersible clay at any given
time increases with increasing water (Perfect
et al. 1990, Kay and Dexter 1990). The
humid climate prevalent in the study site
must have predisposed the soil to dispersing
its clay content within profile making the B
horizon argillic. Clay dispersion in soil has
an effect on the extent of redistribution of
clay in pedon (Ugoleni et al. 1979, Malgwi
et al. 2000)
Soil Chemical Properties
The occurrence of higher concentration of
organic matter at topsoil of upper slope is
due to the redistributive effect of slope ((Esu
et al. 2008). Organic matter is also known to
decrease with depth in pedon (Idoga and
Azagaku 2005). Organic matter is known to
accounts for 90 to 98% and 60 to 75% soil
nitrogen and phosphorus respectively
(Konnovora 1966). It has been reported that
calcium and magnesium dominate over
potassium and sodium in exchangeable
complex of basement complex soils
(Konnovora 1966). The higher base
saturation of sub-surface horizons is due to
the contribution of clay colloids which
increases with depth (Idoga and Azagaku
2005). Higher soil mineral nutrient at ‘A’
horizon is due to nutrient biocycling
(Ogunwale et al. 2002). The influence soil
parent materials and slope position on pH
and exchangeable acidity has been reported
(Kang and Juo 1983).
Classification According to USDA
Taxonomy
Pedon 1, and 2 on the first toposequence and
pedon 4, 5 and 6 on the second
toposequence have translocated clay in B
horizon (Bt), this signified the presence of
argillic or kandic horizon. They have
medium to high supply cation, and more
than 35% base saturation by the sum of
cations. They therefore classify as Alfisol
(Soil Survey Staff 2010).
Kandic horizon were established in pedon 1,
and 2 on the first toposequence and pedon
4, 5 and 6 on the second toposequence
because they meet the requirement; coarsertextured
surface horizons over vertically
(morphologically) continuous subsurface
horizons; ECEC within subsurface B
horizons that are less than 12 cmol(+) kg –1
clay; a regular decrease in organic carbon
content with increasing depth; and all these
in addition to the requirement of clay
content increase-with-depth (Soil Survey
Staff 2010). Similar observation in soils of
southwest Nigeria has been reported (Ewulo
et al. 2002).
An udic moisture regime was inferred for all
pedon observed based on rainfall data which
suggest a soil moisture regime in which the
soil moisture control section is not dry in
any part for as long as 90 cumulative days in
normal years, the soil therefore classify into
suborder udalf (Soil Survey Staff 2010).
This soil moisture regime is common to the
soils of humid climates that have a well
distributed rainfall. Pedon 1, and 2, on the
first toposequence and pedon 4, 5, and 6 on
the second toposequence were therefore
classified into the great group Kandiudalfs.
They classify as Albeluvisols in FAO
system of classification (FAO of UN 2006).
Pedon three did not show enough horizon
differentiation and is therefore young. It
classifies in the soil order Entisol (Soil
Survey Staff 2010). The pedon did not
show any redoximorphic feature and are
better drained, and hence in the sub order
arents. The udic moisture regime (table 7)
was used to place it in the great group
Udarent (Soil Survey Staff 2010). Pedon
three classify as Eutric fluvisol in FAO
system of classification (FAO of UN 2006).
International Journal of AgriScience Vol. 2(7): 642-650, July 2012 648

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