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PAT June, 2012; 8 (1): 153 -163; ISSN: 0794-5213
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Publication of Nasarawa State University, Keffi
Soil Water Characteristics and structural stability of a Typic Paleustult Under
Different Vegetation Cover.
Enyioko, C. O 1 . Obi, M. E 2 . and Eneje, R. C 3* .
1 Department of Forestry and Land Resources, Umuahia, Abia state.
2 Department of Soil Science, Faculty of Agriculture University of Nigeria Nsukka, Enugu State.
3 Department of Soil Science And Meteorology, Michael Okpara University of Agriculture Umudike,
Nigeria.
Email: chizma2001@ yahoo.com
Abstract
The effect of different vegetation cover on soil water characteristics and aggregate stability of
a Typic Paleustult was carried out. The different cover management practices were bare
fallow, (BF), cassava cultivation (CS), groundnut cover (GN), manured groundnut cover GN+
PM) and Panicum maximum(PMC), while the soil properties studied were water drop
energy(impact), macro porosity, micro porosity, saturated hydraulic conductivity, soil
moisture content at 6kpa, soil aggregate stability, and penetration resistance. Data were
subjected to analysis of variance using RCBD, and results show that soil resistance to
penetration was highest in the bare fallow treatment (1.7kg/m 2 ) and lowest under the manured
groundnut treatment (1.0kg/m 2 ), Soil total porosity and macro porosity were highest (50.84
and 24.4% respectively) under the manured groundnut treatment and lowest (43.16 and 16%
respectively) under the cassava plot. Saturated hydraulic conductivity was lowest in the
cassava plot (23.3cm/h) but highest in the manured groundnut plot. The management practices
significantly increased the number of water drops and the energy required to breakdown soil
aggregates to pass through a 4.75mm sieve. The highest drop number and energy values were
obtained for aggregates formed under Panicum cover whereas the lowest values were
obtained for aggregates of the bare soil The percent aggregate stability > 0.5 was not
statistically significant but was highest for the Panicum maximum treatment closely followed
by the bare fallow treatment and GN+PM treatment. The overall trend in changes in soil
water properties (Ksat, PT, and macro-porosity) was BF≤ CS

PAT 2012; 8 (1): 153-163: ISSN: 0794-5213; Enyioko et al,: Soil Water Characteristics ……….154
instance found that ground cover control infiltration, while Lugo Lopez et. al, (1981)
reported that infiltration is a function of soil properties such as bulk density, pore size
distribution and aggregate stability. According to Adeoye (1982), deep tillage of Alfisol
in Northern Nigeria result in increased porosity, while Tollner et. al, (1984) reported
that beneficial effects of tillage on soil include an in increase the number of drainage
pores in the soil. According to Papendick and Campell (1981), water retention in soils is
influenced by texture, organic matter content and the physical composition of the soil.
Soil with high amount of clay content and organic matter for instance hold considerably
more gravimetric water at a given water potential than soil with a high content of sand.
Also, Mbagwu and Ekwealor (1990) reported high moisture retention for different soils
amended with brewer’s spent grain, while Mbagwu (1989) reported that addition of
organic matter at any rate significantly increased soil water retention except at
1.500kpa. However, for exposed soils especially highly degraded soils in the tropics
water retention is reduced and this is attributable to runoff and possibly a reduction in
porosity due to high bulk density.
Therefore, in this study we set out to study the water characteristics of a Typic
paleustult (Nkpologu sandy loam soil) under bare fallow, cassava cultivation,
leguminous plant (groundnut) and grass plant (Panicum maximum) management. The
main objective was to relate these characteristics of the soil as well as determine which
of these cover crop management type best influenced the soil property for crop growth.
Material and Methods
Experimental site
The experiment was carried out at the University of Nigeria Nsukka, teaching and
Research farm located on latitude 06 o 5 2’N and longitude 07 o 24’E. The area has an
annual rainfall of about 1700mm. The rainfall distribution is bimodal, a wet (April to
October) and dry (November to March) season (Obi, 1982). The soil is deep, porous
and red to brownish red derived from sandy deposits of false bedded sand stone. It is an
Ultisol belonging to Nkpologu series and is classified as Typic paleustult (Nwadialo,
1989).
Field layout
The field was laid out in Randomized complete Block Design (RCBD) with four
replications. Four treatments were applied on the plots of 4m X5m with 0.5m spacing
between plots and 1m between replications. The treatments were as follows;
( i) Bare fallow (BF)- The land was placed under fallow and was kept free of
weed and crop through out the period of research, weeding was done manually.

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(ii) Cassava cultivation (CS); Cassava (Manihot esculentus var. NR8082) was
planted on flats at a spacing of 1m X 1m giving a plant population of 10,000stands per
hectare.
(iii) Panicum maximum cultivation (PMC); Guinea grass was allowed to
dominate this plot for about three years.
(iv) Groundnuts (Arachis hypogea) cultivation (GN); Groundnuts was planted on the
flat at a spacing of 25cm X 50 cm (intra and inter row respectively) giving a total plant
population of 76,000stands per hectare which ensured proper ground cover.
Sample collection
Undisturbed soil samples were collected at the start of the experiment using core of
dimensions 7.6X 7cm (length and diameter). Auger soil samples were also collected
from0-15cm depth and both samples subjected to physical and chemical analysis.
Laboratory Analysis
Soil water content
This was determined by the gravimetric method, the soil core samples were
saturated in water and their weights at saturation were taken, then the samples are oven
dried at 105 0 c for 24hours. Dry samples were cooled in a desicator and reweighed
again.
Moisture content was computed as;
Moisture content =Ww – Dw x 100
Dw 1
Where;
Ww = Wet weight of soil
Dw = Dry weight of soil
Soil bulk density, porosity and pore-size distribution
Core samples were collected from experimental plots carefully trimmed and one
end tied with calico cloth. The weight of core samples were taken and samples were
soaked for 24hours in a pan containing about 5cm of water after 24hrs, the water level
in the pan was raised to ensure complete saturation of the soil samples. Then the
samples were weighed after 24hrs and placed on a tension table adjusted for 60cm of
tension for 24hrs, the soil core samples were removed from the tension tables and
weighed and oven-dried for 48hrs at a temperature of 105 o C and weighed again.
Calculations were made as follows:

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(i) Bulk density = Oven-dry mass(g)
Vol of soil (cm3)
(ii) Total porosity= Vol of water at saturation X 100
Vol of soil 1
(iii) Air space porosity= Vol of water drained at 60cm tension X 100
Vol. of soil 1
(iv) Capillary porosity= Vol of water retained at 60 cm tension X 100
Vol of soil 1
Saturated hydraulic conductivity
This was determined using the modified Klute (1965), method Saturated hydraulic
conductivity was calculated as follows:
Ksat = QL
∆HAT
Where:
Ksat = saturated hydraulic conductivity (cm/hr) ; Q= quantity of water (cm3)
L= length of core (cm) ; H = hydraulic gradient (cm)
A= cross-sectional area of core (cm2) ; T= Time elapsed (hr)
Aggregate stability
A modification of Yoders (1936) wet sieving technique was used to determine
aggregate stability. The set of sieves used had size openings ranging from 2mm to
0.25mm (2, 1, 0.5 and 0.25mm). A 25g soil (pre-sieved through 4.25mm) was soaked
for 5minutes on the top-most sieve. Shaking was done by vertically oscillating the set of
sieve in water for 80 times. The resistant aggregates were carefully washed out of the
sieve into evaporating dishes and oven-dried for about 24hrs. The sample weights were
recorded. To correct for sand in the sample, soils in sieves of 2mm to 0.5mm were
returned to a dish and soaked with 5ml of sodium hexametaphosphate. Enough water
was added to cover the aggregates. Thereafter, the suspension was stirred for about 30
minutes and sand particles larger than 0.5mm were removed by washing dispersed
aggregates through a 0.5mm sieve, the sand was washed into an evaporating dish and
oven dried for 24hrs at a temperature of 105 o C, the weight of sand was taken.
Aggregate stability was calculated using the formula:
Percent aggregate stability (%AS) = wt of WSA>0.5mm-wt of sand X 100
Wt of sample-wt of sand 1

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Other soil properties determined in the laboratory include, soil water retention,
which was determined by the hanging column of water method as described by Richard
(1957) using water retention at 60 cm tension. Soil particle size, was determined by the
hydrometer method Bouyoucos (1951), with sodium hexameaphosphate as the
dispersant. Total aluminum was determined by the method of Vogel (1961), and total
iron determined by colorimetric methods AOAC (1970). Soil P H was determined in
water and KCl in 1:2.5 soil water suspension using p H meter (Jackson 1958)
Statistical Analysis
Data obtained from the study were subjected to analysis of variance test in
Randomized Complete Block Design as outlined by Steel and Torrie (1980). Simple
linear correlation of selected parameters was carried out as described by Little and Hills
(1972).
Result and Discussions
The soil used for this study is a sandy loam (Table 1). The dominance of sand fraction is
attributable to the dominance of parent material, in this case, -false-bedded sandstone
(Akamigbo and Igwe, 1990).
The soil management practices increased organic matter content of the soil at the end of
the experiment except the plot planted with groundnut alone that recorded a reduction in
percent OC content in the soil at the end of the experiment (Table 3); this is expected
since groundnut a legume could mobilize OC in the soil for profuse foliage production.
Also the plant cover system resulted in reduced compaction in the soil as indicated by a
reduction in bulk density of the soils except the plot planted up with cassava, which
experienced an increase in bulk density indicating poor structural status of the soil since
increased BD is associated with high clogging of soil pores and compaction with hard
pan formation. The trend in BD explains the observation in the total porosity of where
the percent age of pore space reduced up to 22% in the cassava plot. Also this result
agree with the observation of Adekalu and Osunbitan (2001) that BD is indirectly
affected by cultivation, thus variations in BD and macro porosity are attributable to land
use. Earlier, Obi and Nnabude (1988), reported significant reduction in bulk density
under continuous Centrosema pubesscens and Panicum maximum covers and attributed
this to high root density and high organic matter accumulation under continuous covers.
However the soil moisture content at 6kpa was highest in this same plot, indicating that
compaction may have resulted in ponding of the soil. This agrees with the observation
of Obi and Nnabude (1988), since an increase in bulk density is associated with

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decreased pore volume and increased micro-porosity and pore space discontinuity, thus
affecting the consistency of the soil and its capacity to conduct and retain water
(Richards and Wadeigh, 1952).
Table 1: Physico-chemical characteristics of soil at the start of the experiment
Soil Property
Mean value
Sand (%) 61.3
Silt (%) 11.0
Clay (%) 27.7
Textural class
Sandy loam
Dry Bulk density(g/cm3) 1.48
Total porosity(%) 55.94
Macro porosity(%) 28.08
Micro porosity (%) 27.85
Saturated hydrualic conductivity 24.76
Infiltration rate (cm/h) 50.28
Soil p H (H2O) 4.8
Soil p H (KCl) 3.8
Organic carbon (%) 0.84
Total Al(Meq/100soil) 0.24
Total Fe(Meq/100soil ) 35.27
Aggregate Stability (%) 96.68
Table 2: Property of the poultry manure used in the study
Property
Poultry manure
OM (%) 33.17
Total N (%) 2.86
Total P (%) 2.00
Total K (%) 1.50
C:N Ratio 7:1
C:P ratio 10:1

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Table 3 : Soil Physicochemical properties at the end of the experiment.
Soil property
Land Management practice
Bare
Fallow
Cassava Panicum
Max.
Groundnut Groundnut+Poultry
Manure
OM (%) 1.05 0.88 1.10 0.73 1.36 Ns
pH (H2O) 4.3 4.4 4.6 4.4 5.3 Ns
pH(KCl) 3.9 4.0 4.0 3.9 4.9 Ns
Fe (meq/100gsoil) 31.90 42.01 46.14 42.75 38.15 Ns
Al (meq/100gsoil) 0.14 0.23 0.17 0.14 1.79 1.179
Fe/Al
227.86 182.65 271.41 305.36 -
(meq/100gsoil)
BD(mg/m 3 ) 1.44 1.51 1.43 1.45 1.42 Ns
Micro-
25.1 26.8 23.5 22.7 26.5 Ns
Porosity(%)
Macro-
20.4 16.4 22.5 22.4 24.4 4.83
Porosity(%)
Total porosity (%) 45.53 43.16 46.00 45.11 50.84 3.349
Ksat (cm/h) 28.6 23.3 55.6 35.2 61.6 22.63
Soil moisture 0.25 0.27 0.23 0.23 0.27 0.03
(6kpa)
Water drop* 41 48 87 41 68 28.05
Penetro-meter 1.7 1.3 1.1 1.2 1.0 0.32
resistance( kg/m 2 )
Kinetic energy 6.42 7.52 x10 -6 1.34 x10 -5 6.42 X10 6 1.03X10 5 -
x10 -6
AS >0.5 (%) 90.30 87.30 93.9 82.1 89.3 Ns
*Mean of 15 determinations
F-LSD 0.05
Soil structural stability assessed by percent aggregate stability (AS>0.5) indicated
stability was higher for all the cover crop management practice at the end of the
experiment, however the plot supporting the Panicum maximium had the highest level
of stability of micro aggregates (about 94%), this was closely followed by the bare
fallow (about 90%) with the least percent aggregate stability found in plots planted with
groundnuts. Similar trend was observed with the OC content at the end of the
experiment while Fe/Al ratio showed a reversal, with GN, which had the lowest AS%
and OC, suggesting that GN must have provide an environment that encouraged higher
concentration of Fe but lower concentration of Al. his observation agrees with the report
of Jonsson and Abubakar (1996), that fallow play important roles in soil fertility and
crop yield, also different land management type resulted in varying inputs in the total
OM content of the soil, however according to Lugo et al (1981) and Houghton et al
1991) the rate and duration of the increase will depend on the method of conversion ,
intensity of the subsequent land use as well as the climatic, physical and chemical

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property of the soil under study. Generally, in this study, higher contents of Fe/Al ratio
suggest soil acidity and this corresponds with the acidity level as indicated by the
observed pH values ranging from 3.9 to 4.4 for all the cover management practices
studied.
Penetrometer resistance is an index of soil surface structure, the penetrability of a soil to
any probing instrument is a rheological property which depends on the texture,
structure, mineralogical composition, moisture content and compactness of the soil, thus
in this study with no significant differences in BD and moisture content it is expected
that the penetration resistance, would depend more on the mineralogical compositions
of different plots which can be influenced by the management practice, thus in this
study, the soils resistance to penetration was significantly(p= 0.05) influenced by
management practice, the manure and cover management practice reduced penetration
resistance relative to the bare fallow (Table 3), this also agrees with the report of kuldip
et al., (1996).
The management practices significantly increased the number of water drops
and the energy required to breakdown soil aggregates to pass through a 4.75mm sieve.
The highest drop number and energy values were obtained for aggregates formed under
Panicum cover whereas the lowest values were obtained for aggregates of the bare soil.
This resistance to breakdown impact could be attributed directly to the effect of
Panicum maximuim on soil organic matter fraction resulting in soil aggregate formation
and stabilization or indirectly to the cementation of clay particles by iron and
aluminium oxides as indicated by a positive and significant correlation (r =0.819)
between water drop impact and iron content in this study. Earlier reports of Mbagwu
and Bazzoffi (1998) also suggest that for an aggregate to be destroyed, the detaching
force of raindrop must overcome the intrinsic resisting force of soil aggregate, which
depends on the cohesive forces holding the structural units together of which organic
matter, iron and aluminum play important role.
The management practices also influenced total porosity and macro porosity of the soil,
the manure groundnut plot had the highest values for total porosity and macro porosity
while he lowest values were obtained in the cassava plots. There were however no
significant differences in soil bulk density under the different management practices and
this could be attributed to the organic matter contents of these plots which were
generally very low, this observation agree with the findings of Thomas et. al, (1996)
that indicated that the amount of organic matter in any soil significantly affects its bulk
density. There were significant differences in saturated hydraulic conductivity (Ksat)
for the different management practices (Table3), Higher Ksat in the GN+PM, PMC and

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GN plots is an indication of the ameliorative effect of these practices on soil structure as
indicated by improvements in total porosity and Ksat in this study. This observation is
confirmed by a significant and positive correlation(r= 0.8387, P= 0.01) obtained
between total porosity and Ksat. (Table 4). This agrees with the findings of Obi and
Ofoduro (1999).
Table 4: Correlation coefficients of selected parameters
Parameter
r-value
TP vs. Ksat 0.8387*
TP vs. sand 0.8376**
Ksat vs. sand 0.9294**
BD vs. penetrometer resistance
0.1727 ns
Water drop impact vs. Total iron 0.8109**
** Significant at p= 0.01 ns =non significant
Conclusion
Conclusively, the management practices significantly influenced the water properties of
the soil under study. For instance, the highest drop number and energy values were
obtained for aggregates formed under Panicum cover whereas the lowest values were
obtained for aggregates of the bare soil, the overall trend in changes in soil water
properties (Ksat, PT, and macro-porosity) was BF≤ CS

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