Journal of Global Resources

Volume 2

January 2016
Page 76-83
ISSN: 2395-3160 (Print), 2455-2445 (Online)

10
CLASSIFICATION OF SOILS ALONG OGOCHIE RIVER FLOODPLAIN IN NGOR-OKPALA,IMO STATE, SOUTHEASTERN NIGERIA
1

Ernest C.I. and 2Onweremadu E.U.
Department of Soil Science and Technology,
Federal University of Technology, Owerri, Nigeria.
Email: ernest.dozie@yahoo.com
Abstract: The study classified soils of three topographic units of Ogochie River floodplain in
Ngor-Okpala Local Government Area of Imo State. A transect was used to connect the topo
units, namely; summit, mid slope and foot slope. Nine (9) profile pits, 3 in each topo unit were
dug and described using FAO guidelines. These profile pits were geo-referenced using hand
held Global Positioning System (GPS) Receiver. Soil samples were collected from horizons,
air-dried and sieved for standard routine analysis.The results showed that the soils wereshallow in depth, colours ranged from hue of 7.5YR and 5YR with chroma greater than 3. The
texture ranged from sand, sandy loam and loamy sand in the surface and sandy clay loam in
the subsurface horizons. The structure ranged from weak, fine to strong massive angular
blocky as depth increases. The soil pH varied from strongly to moderately acid (4.9-5.36). The
Electrical Conductivity was low with mean values less than 1dsm-1. The contents of Organic
Matter (0.4-1.68 %), Total Nitrogen (0.02-0.08%), available Phosphorus (1-2.92 ppm) andECEC (3.97-5.25 cmol/kg). Soils were classified using Soil Taxonomy (USDA 2010) as Aeric
kandic plinthiaquults (footslope), Aeric typic hydraaquent (Midslope), and Aeric aquandic
fluvents (summit) and correlated with World Reference Base (2006) as Haplic plinthosol(footslope), Haplic fluvisol ( (Midslope) and Haplic fluvisol (footslope).
Keywords: Wetlands, Soil, Classification, Toposequence, Tropical Nigeria
Introduction
Wetlands (fadama) are permanently or seasonally flooded low lying lands occurring alongwater courses, or on valley bottoms and which usually have high water table (Adeniran et al.,2010; Tiner, 1999). A combination of hydric soil, hydrophitic vegetation and hydrology
properties define wetlands as described in the National food security act manual and corps ofengineers wetland delineation manual (Brinson, 1993). Wetlands are among the mostimportant ecosystems on Earth and are unique because of their hydrologic conditions and roleas transitional ecosystems (Mitsch and Gosselink, 2000) stated that the total wetland area in
Africa amounts to about 5.6 million Km2, which is about 16 percent of the total area of thecontinent (Ojekunle, 2011). In Nigeria, wetland comprises inland swamp, mangrove and fresh
water swamp and shallow to deep water fadama (Ayotade et al., 1980). The important
wetlands available in Nigeria are Hydejia and Kirikasama, Lake Chad, Komduge, Yobe, Kanji
Lake, Baturiya, Adiami- Nguru flood plains, Matgadru- Kabok flood plains, the Niger-Delta
flood plains and the coaster lagoons near Lagos and delta of Cross river. In many parts of theworld, wetlands have historically been reviled as disease ridden wastelands and actively
drained. Drained wetlands are among the most productive agricultural and forest soils, therelatively level topographic position of wetlands is desirable for construction practices.
Currently, wetlands cover less than seven percent of the Earth’s land area (Mitsch andGosselink, 2000). There is significant pressure to develop critical wetland ecosystems in thetropics because these areas are highly sought after for agricultural and construction practices(Stanturf et al., 2000). USDA (2002) defined wetland soils as soils that formed under76

conditions of saturation, flooding or ponding long enough during the growing season todevelop anaerobic conditions in the upper part. Under natural conditions, these soils are either
saturated or inundated long enough during the growing season to support the growth andreproduction of hydrophilic vegetation. Wetland soils also known as hydric soils have anumber of agricultural and non-agricultural applications. In order to determine whether a
specific soil is a hydric soil or non-hydric soil, more specific information about the depth andduration of water table is needed (Soil Survey Staff, 2010). Hanselman and Noll (2003)
reported that little work has been published on natural variability of wetland soils. In Nigeria,
there is scarcity of data on the properties of fadama soils and their critical moisture contents
for tillage. The major objective of this study was to classify and characterize the wetland soilsof Ogochie River in Ngor Okpala Local Government Area of Imo state.
Materials and Methods
Ogochie River is located at Ngor- Okpala Local Government Area of Imo State which lies
between latitudes 50201N and longitude 7081E with an elevation of 52m above sea level. The
hydrology of Ogochie River is governed by Imo River and affected by tides, although seasonal
influences which are related to the climatic regime are evident. The area lies within the humid
tropics with a mean temperature range of 26-290C. The climate of the area is characterized by
distinct wet and dry seasons. The wet season begins in April and lasts till November, while thedry season begins in November till March. A short period of draught is usually experienced inJuly and August, while a period of harmattan characterized by cold dry winds and lower
temperatures normally occurs between December and February (Moses, 1979; Enemugwem,
2009).
Table 1: Co-ordinates of Pedons
Pedon
NumberPedon 1
Pedon 2
Pedon 3
Pedon 4
Pedon 5
Pedon 6
Pedon 7
Pedon 8
Pedon 9Co-ordinates
0

1

11

Lat.5 20 10.7 N,
01
11
Lat.5 20 12.2 N,
01
Lat.5 20 14.911N,
01
11
Lat.5 20 16.4 N,
01
11
Lat.5 20 17.8 N,
01
Lat.5 20 19.311N,
0
1
11
Lat.5 20 21.6 N,
01
11
Lat.5 20 22.7 N,
01
Lat.5 20 24.911N,

Elevation
0 1

11

Long. 7 8 48.1 E
0 1
11Long. 7 8 48.1 E
0 1
Long. 7 8 48.111E
0 1
11Long. 7 8 48.1 E
0 1
11Long. 7 8 47.2 E
0 1
Long. 7 8 47.211E
0 1
11Long. 7 8 47.2 E
0 1
11Long. 7 8 47.2 E
0 1
Long. 7 8 47.211E

45m
43m
47m
47m
46m
46m
44m
45m
46m

Physiographic
Unit
Footslope
Footslope
FootslopeMidslope
Midslope
Midslope
SummitSummitSummit

The relative humidity is high throughout the year especially in rainy season averaging 85
percent. The mean annual rainfall ranges from 2500-3000mm (Ofomata, 1975).The major
parent material in the study area is the coastal plain sands and flood plains (Benin formation
and Deltaic deposits) and marine deposits. The area has generally a lowland geomorphology,
less than 80m above sea level. They belong to the group of soils termed the acid sands insouthern Nigeria (Obihara, 1961). The natural vegetation of the study area is tropicalrainforest. The plant species are arranged in tiers with the forest floor harbouring a great
category of sun heating species. The rain forest is highly depleted of plant species due tohuman activities. The dominant plant species is the Oil palm (Elaeis guineensis), others
include; Oil bean tree (Pentaclethra macrophyla), Gmelina (Gmelina arborea), Butterfly pea(Centrosema pubescens), Raffia palm (Raphia vinifera), Wine palm (Butia capitata), Water
fern (Histiopteris incisa), Cassava (Manihot esculenta.), WaterYam (Dioscorea alata.). Cereals
and grasses include; Elephant grass (Pennisetum purpureum,), Giant star grass (Cynodon
plectostachyus), Siam weed (Chromolaena odorata), Goat weed (Ageratum conyzoides) andclusters of bamboo and shrubs.

77

Field Studies
A reconnaissance visit was carried out with the aid of a location map of the study area to
identify the areas to be studied and the locations were georeferenced using a global
positioning system (GPS) receiver. A combination of transect and random samplingtechniques were used as a traverse was cut along the river bank in sampling. Three topounits
were identified namely footslope, midslope and summit, a total of nine (9) profile pits were dug,
three on each topounit and described using FAO (2006), USDA Soil Taxonomy (2010) andWorld reference base (2006) procedures. Core samples were collected from each horizon.
Samples were collected from the bottom to the top according to horizon differentiation in eachprofile pit and the maximum depth of soil examination differed for each pit. In total, 34 soil
samples were collected. Surface humidity was dry at the time of sample collection, which wasin the dry season between in January, 2013. Soil samples were air-dried, gently crushed,sieved using 2-mm sieve and analysed in the laboratory.
Laboratory Analysis
Particle size distribution was determined by hydrometer method according to the procedure of(Gee and Or, 2002). Bulk Density was measured using core method as Grossman and
Reinsch (2002) recommended. Soil pH was determined in 1:2.5 soil liquid ratios in water and
0.1N KCl using pH meter (Hendershot et al., 1993).Organic carbon was determined using wet
oxidation method described by (Walkley and Black, 1934; Nelson and Sommers, 1982).
Available phosphorus was determined using Bray II solution method (Olsen and Sommers,
1982). Electrical conductivity was measured in 1:2 saturation extract (Udo et al., 2009).
Exchangeable bases (magnesium, calcium, sodium and potassium). Exchangeable Na and K
were extracted using 1N NH4OAc using flame photometer (Jackson, 1964), while Ca and Mg
were determined using ethelene diamine tetracetic acid (EDTA) (Thomas, 1988). Total
nitrogen was determined by Kjehdahl digestion method (Jackson, 1964; Bremner andYeomans, 1988). Exchangeable acidity was determined titrimetrically (Mclean, 1982).
Effective cation exchange capacity (ECEC) was calculated from the summation of all
exchangeable bases and exchangeable acidity (Soil Survey Laboratory Staff,
1992).Percentage base saturation (percent BS) was determined by computation.
Soil Classification
Based on the results obtained from the laboratory analysis and field morphological properties,
the soils were classified according to soil taxonomy (Soil Survey Staff, 2010), and correlatedwith world reference base (2006). Data collected from the study site were subjected tosummary statistics such as Mean. Also, Coefficient of variation (CV) was used to estimate thedegree of variability existing among soil properties in the study site. Coefficient of variation isranked as follows; low variation ≤ 15 percent, moderate variation 15 percent≤ 35 percent andhigh variability 35 percent (Wilding et al., 1994). Pearson correlation analysis was
implemented to determine the relationship between the soil properties.
Table 2: Mean values of soil physical properties
ProfileSand
Silt
numberg/kg
Peodn 1857
7Pedon 2854
10Pedon 3813
34
Pedon 4809
40
Pedon 5784
30
Pedon 6820
36Pedon 7811
47
Pedon 8817
34
Pedon 9824
20
Texture: SL=Sandy loam, LS= Loamy Sand

Clay

Texture

136
136
153
151
186
144
142
149
156

SL
SL
SL
LS
SL
SL
LS
SL
SL

78

MC
g/kg
456
679
400
458
646
273
689
401
297

BD
3
g/cm
1.68
1.5
0.83
1.24
1.42
0.82
0.95
1.29
0.99

T.porosity
percent
36.6
43.7
68.4
53.5
46.7
69.2
64.4
51.4
62.6

Results and Discussion
Physical and Morphological Properties
The soils were characterised with strong brown, reddish brown, reddish yellow to yellowish red
colour matrix of hues of 7.5 to 5 years and chroma values of 4-8 in all horizons. These colours
indicate a relatively high amount of iron oxide, which may be due to the parent material(Nkheloane et al., 2012). The alternate wetting and drying conditions in these soils resulted in
the reduction and subsequent release of iron oxides which are accumulated in the form ofstrong brown, brown and red mottles in the subsurface of the profiles, also in very shallow
pedons, melanization may occur. The structural development of the soils in the study siteranged from fine-weak to massive-strong sub-angular blocky peds. In moist state, the soils
were friable and firm, soils were observed in dry consistence to be hard to extremely hard as
depth increases. The main factor influencing the structure of floodplain soils is thehydrology/water table. Base presence of roots decreased with depth in all pedons due to highwater table. The inadequate root room in wetland soils for the study area can be represented
by the critical limits of effective root depth caused by anaerobic condition of the soil andhardpan. The particle size distribution pattern shows that the sand contents were high in all
pedons between 784-857 g/kg. The general sandy nature of the study site could be due to theclimate and parent material of the area as well as the depositional activities of the Ogochie
River. The bulk density of the study site ranged between 0.83-1.68 g/cm3, this is due to highwater absorption capacity. The bulk density increased down the profile, increased bulk density
in the subsurface horizon is an indication of low soil porosity and soil compaction. It may cause
restrictions to root growth and poor movement of air and water through the soil. The moisture
content of the soils sampled in the study site ranged between 273-689 g/kg. The epipedon of
all profiles were partly saturated to unsaturated having lower moisture content compared withthe subsurface horizon with moisture content at field capacity. Moisture content increased as
depth increased. The study area could be said to be endosaturated due to the unsaturation to
partly saturation of the soil surface and total saturation of the subsurface horizons. Moisture
content range between 10 percent -15 percent (dry basis) is workable and trafficable forcultivation practice. Beyond the critical moisture content, cultivation becomes tedious, leading
to high slippage, sinkage of machinery and lose of trafficability (Adeniran et al., 2010).

79

Table 3: Mean Values of Soil Chemical Properties
3+

Al

+

H

TEA

Ca

++

Mg

+

K

pH

O.M

BS

Av.P

Al

EC

number

H2O

KClpercent

percent(ppm)

percent(dSm )

Pedon1

5.37

4.05

0.4

0.4

0.3

0.7

0.02

1.5

0.9

0.19

0.10

2.68

3.38

80.1

1.04

12.88

0.10

Pedon2

5.36

4.08

1.27

0.8

0.5

1.3

0.06

2.0

1.3

0.21

0.08

3.59

4.84

71.5

0.68

16.18

0.11

Pedon3

5.25

4.15

0.95

0.7

0.3

0.1

0.04

2.0

1.2

0.19

0.13

3.06

4.48

77.5

1.44

16.69

0.10

Pedon4

5.60

4.04

1.01

0.5

0.5

1.1

0.05

1.7

0.9

Pedon5

4.90

4.39

0.83

0.6

0.2

0.8

0.04

2.6

1.6

0.24

0.15

3.0

3.97

75.7

2.51

11.92

0.13

0.12

0.13

4.45

5.25

84.4

0.67

11.72

0.11

Pedon6

5.33

3.96

1.04

0.6

0.3

0.9

0.05

1.8

1.0

0.22

0.08

3.18

4.08

77.6

2.04

15.69

0.11

Pedon7

5.19

4.02

1.48

0.5

0.5

1.0

0.07

2.7

1.0

0.27

0.09

4.35

5.35

78.6

2.92

11.85

0.10

Pedon8

5.16

4.12

0.86

0.3

0.2

0.8

0.04

2.1

1.3

0.23

0.09

3.78

4.58

81.8

1.0

14.58

0.07

Pedon9

5.28

3.91

1.68

0.7

0.2

0.9

0.08

1.9

0.1

0.21

0.10

3.11

4.11

76.6

1.03

18.2

0.11

percent

Na+pH

cmol/kg

T.N++

ProfileTEB

ECEC

cmol/kg

1

OM = Organic matter, AI= Aluminum, Ca=Calcium, Mg= Magnesium, P=Phosphorus, K=Potassium, Na= Sodium,
TEA=Total exchangeable acidity,T.N=Total nitrogen, TEB= Total exchangeable bases, ECEC= Effective cation exchange capacity,
BS= Base saturation, Avail. P= Available phosphorus, EC= Electrical conductivity.

80Chemical Properties
Soil reaction of the study site were strongly to slightly acidic ranging between 4.90-5.60 and
3.91-4.39 in water suspension and 1N KCl respectively. Ideally floodplain soils experiencechanges in soil reaction due to fluctuating high water table. Low values (<5) could be due tothe dominance of Al++ and H+ ions in the soil exchange complex (Soil Survey Staff, 2003). The
soils have low amount of organic matter content which ranged between 0.4-1.68 percent, thelow availability of O2 is the most important factor limiting rates of decomposition in wetland
soils, others include temperature, nutrient availability, the molecular composition of organic
matter, and acidity. The average total nitrogen content of the study site was low, ranging from0.02 percent-0.08 percent, corresponding with organic carbon content compared with thecritical value of 0.2 percent recommended (FPDD,1989). The low N level may be associatedwith intermittent flooding and drying which is known to favour nitrogen loss throughnitrification-denitrification process (Wong et al., 1991). Also low N may be partially attributed tothe predominantly sand texture of the soils. Available P content of the soils were low ranging
from 0.67-2.92ppm, low level of available P indicates that P may be chemically bound as
phosphates of Fe and Al owing to the observed high acidity of the soil of the study area
(Effiong et al., 2006) or due to absolute low value of soil P or that P is removed by
sedimentation (Ogban, 1999; Patrick, 1990). Total exchangeable bases ranged between 2.684.45 cmol/kg and were dominated by calcium (Ca2+) and magnesium (Mg2+) ions. The lowcontents of basic cations may be due to low pH, intense leaching weathering and ferrolysis,hence low inherent fertility status with regards to the major nutrients. Exchangeable acidity
values were moderate to high with mean values of 0.1-1.3cmol/kg, slightly below the criticalvalue of 2.0cmol/kg, depicting the strongly and slightly acidic nature of the soils, although theexchangeable acidity may affect sensitive crops. The percentage aluminium saturation of thestudy area slightly high to high, with mean values ranging from 11.72 percent -18.2 percent,Soil clay minerals contain aluminium but it has no impact on plant productivity unless pHw fall
below 5.4. The mean base saturation percentage values ranged between 71.5 percent- 84.4
percent, though above 50 percent, the separating index between fertile and less fertile soil
(Landon, 1984). However, Astera (2008) noted that the strongest, healthiest and nutritious
crops are grown in soils where percentage base saturation is above 90 percent, this does not
only provide luxury levels of nutrients to crop and soil life, but are strongly affected by soil
texture and pH. Electrical conductivity of the saturation extract of the study site ranged
between 0.07-0.13 dSm-1, which is seen as low being <1 dSm-1, indicating non saline nature of
the soils and the fresh water status of the hydrology of the study site. The ECEC values in thesoils of the study site were low and ranged between 3.38-5.35 cmol/kg, High annual
precipitation, small amount of basic cations in the parent materials, the low buffering capacity
to retain them against leaching and removal by erosion probably explain the low ECEC in thefloodplain.
Soil Classification
The soils of the study area were classified according to soil taxonomy (Soil Survey Staff, 2010)
and correlated with world reference base (2006). The mean annual soil temperature of the soil
and study area was above 250 C , thereby isohyperthermic, located in an aquic moistureregime which had ochric epipedon and kandic sub surface horizon in the soil profile.

81Table 4: Taxonomic classification of the soils
Pedon
NumberPhysiographic
Unit

1
2
3
4
5
6
7
8
9

Footslope
Footslope
FootslopeMidslope
Midslope
Midslope
SummitSummitSummitClassification
Soil Taxonomy
Aeric Kandic Plinthiaquults
Aeric Kandic Plinthiaquults
Aeric Typic Hydraaquents
Aeric Typic Hydraaquents
Aeric Typic Hydraaquents
Aeric Aquandic Fluvents
Aeric Aquandic Fluvents
Aeric Aquandic Fluvents
Aeric Aquandic Fluvents

World Reference Base
Haplic Plinthosols
Haplic Plinthosols
Haplic Fluvisol
Haplic Fluvisol
Haplic Fluvisol
Haplic Fluvisol
Haplic Fluvisol
Haplic Fluvisol
Haplic Fluvisol

Temperature regime is isohyperthermic in all pedons
The footslope was characterised with high chroma of 4 or more, having an iron- rich,humus-poor mixture of clay with quartz. It soils changed irreversibly to an iron stone hard pan
on exposure to air, however it was soft in moist state. The soils had CEC less than 24cmol/kg ,thus classified as Aeric kandic plinthiaquults (Soil Taxonomy); Haplic Plinthosols, (World
Reference Base). The midslope was characterised with loamy sand and had chroma of 4 ormore. The soils more than 8 percent or more clay in the fine earth fraction and classified as
Aeric typic hydra aquent (Soil Taxonomy); Haplic Fluvisol (World Reference Base),while thesummit was characterised with chroma of 4 or more, the organic carbon content decreased
irregularly within the soil profile. The soils were sandy with a bulk density of 1.0g/cm3 or less.
They were classified as Aeric aquandic fluvents (Soil Taxonomy); Haplic Fluvisol (World
Reference Base).
Conclusion
The soils of the study area were shallow in depth with strong evidence of reduction of Fe3+ toFe2+ and development of reddish, yellowish and brown colours. The textures were sandy
loams to loamy sands at the surface horizons and sandy clay loam in the sub soil horizons.
Weak, to sub-angular blocky structures, hard consistence as depth increases, concretions ofFe and Al in the lower horizons, and the presence of gradual boundary between the horizons
were some of the physical and morphological evidences of the youthfulness and subtle
horizonations within the soils. The soils varied in chemical characteristics with strongly tomoderate acid conditions, low in organic matter, total nitrogen; available phosphorus, cationexchange capacity, sodium percentage and electrical conductivity. These were indications of
low nutrient reserves of the soils.Based on measured physical, chemical and morphologicalparameters, results showed that the soils have limited suitability for conversion to productive
uses unless amended.
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