AMERICAN JOURNAL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
© 2015,Science Huβ, http://www.scihub.org/AJSIR
ISSN: 2153-649X, doi:10.5251/ajsir.2015.6.4.74.81
Effect of Slope Gradient on Selected Soil Physicochemical Properties of
Dawja Watershed in Enebse Sar Midir District, Amhara National Regional
State
Mulugeta Aytenew
Department of Plant Science, MadaWalabu University, Bale Robe, Ethiopia
[email protected]
ABSTRACT
The present study was conducted at Dawja Watershed in Enebse Sar Midir District to investigate
the effect of slope gradient on selected soil physicochemical properties and to provide the basic
information about the fertility status of the Watershed soils. Soil samples were collected from the
0-20 cm soil depth of four slope gradient categories in three replications. Except available
phosphorus and exchangeable sodium, all the soil parameters were significantly (P < 0.05)
affected by slope gradient. The textural class of the soils varied between sandy clay loam and
-3
sandy clay. The bulk density of the soils in moderately steep slope (1.42 g cm ) was the highest
-3
-3
-3
followed by strongly sloping (1.41 g cm ), sloping (1.36 g cm ) and gently sloping (1.32 g cm ).
The total porosity varied from 46.42 to 50.10%. The pH of the soils ranged from 5.7 in moderately
steep area to 6.8 in gently sloping area. The organic matter content of the soils was generally low
and ranged between 1.25% in strongly sloping to 1.67% in gently sloping areas. Total nitrogen
content of the soils was between 0.14% and 0.18%. Available phosphorus was generally high in
-1
soils of all slope gradients and ranged between 20.47to 22.50 mg kg . Calcium (32.91 cmol(+)
-1
-1
-1
kg ), Magnesium (4.19 cmol(+) kg ), Potassium (0.78 cmol(+) kg ) and Percent Base Saturation
(92.20%) were the highest at gently sloping area followed by sloping, strongly sloping and
moderately steep areas, respectively. The results further showed that the soils were generally
-1
rich in exchangeable basic cations with CEC ranged between 28.20 cmol(+) kg in soils of
-1
strongly sloping to 41.87 cmol(+) kg in gently sloping areas. In general, soils of the study area
are good in their selected physicochemical properties for plant growth except organic matter and
total nitrogen. However, the detrimental effects of slope gradient are higher at moderately steep
and strongly sloping areas as compared to sloping and gently sloping areas. Therefore, the soil
fertility management in the study area should focus on scenarios that could improve the soil
organic matter and nitrogen levels and special management practices such as terracing and
proper land leveling are required to improve the effects of high slope gradient on soil
physicochemical properties.
Keywords: Dawja Watershed, Effect, Rating, Slope gradient
gradient is one of the important topographic factors
INTRODUCTION
that influence the process of drainage, runoff and soil
erosion thereby affects physicochemical properties
Soil is an important natural resource for agriculture
(Farmanullah, 2013). Soil loss would normally be
that is the basic economic source of Ethiopia. The
expected to increase with increase in slope gradient,
suitability of soil for crop production depends on its
because of respective increase in velocity of surface
runoff and decrease in infiltration rate (Luk et al.,
fertility level, which is evaluated based on the quality
of the soil’s physical, chemical and biological
1993; Zhang and Hosoyamada, 1996).
properties. One of the naturally occurring soils
forming factor that affecting soil properties and
Amuyou and Kotingo (2015) reported that slope
controlling soil erosion processes through the
gradients have marked influence in soil properties as
redistribution of soil particles and soil OM is
expressed in the distribution in soils along slope
topography (Ziadat and Taimeh, 2013). Slope
positions. Changere and Lal (1997) and Nejad and
Am. J. Sci. Ind. Res., 2015, 6(4): 74-81
Nejad (1997) reported the effect of topography on soil
genesis and development of soils and observed that
slope gradient had direct and indirect effect on soil
physicochemical properties. Gessler et al. (2000)
also found that variations of some soil properties
could be related to the slope gradient. The review of
Bezuayehu et al. (2002) on nature and causes of
land degradation in the Oromiya Region, Ethiopia
revealed that soils on steep slopes are generally
shallower and their nutrient and water storage
capacities are limited. They suggested that when
soils in areas having steep slopes are exposed to soil
eroding agents, they face greater degradation
consequences compared to soils in flat areas.
In the area under study, soil fertility problems relate
with poor crop cultivation practices including
cultivation on steep slopes, removal of crop residues
and overgrazing. Runoff and erosion takes place in
the study area in which slope steepness is the
dominant factor where the water removes the finer
soil particles including soil organic matter and plant
nutrients thus adversely affecting the soil
physicochemical properties and crop productivity.
Investigating the effect of slope gradient on selected
soil physicochemical properties is valuable to provide
information on nutrient status of the soil, and to
design
appropriate
management
strategies.
However, data for assessment of the effect of slope
gradient on soil physicochemical properties is limited
in the study area. This study aimed to investigate the
effect of slope gradient on selected soil
physicochemical properties and to provide the basic
information about the fertility status of Dawja
Watershed soils.
In 2015, the slope gradient of Dawja Watershed was
measured by using clinometers, and four slope
gradient categories (gently sloping, sloping, strongly
sloping and moderately steep having a slope gradient
of 2-5, 5-10, 10-15 and 15-30%, respectively) were
identified based on FAO (2006a) slope gradient
classification system. Disturbed soil samples were
collected by using auger at 20 cm soil depth of each
slope category in three replications, following the
standard procedures. A total of 12 (4 ×3) composite
samples were collected from the study area. The
samples were air-dried, crushed, and passed through
2 mm sieve for all soil parameters except for organic
carbon and total nitrogen, which passed through 0.5
mm sieve. Similarly, 12 undisturbed samples were
collected by using core samplers that were 5 cm
diameter × 5 cm length, for the analysis of soil bulk
density.
Soil texture was analyzed by determining the
percentage of sand, silt and clay in each soil sample
by following Bouyoucos hydrometer method
(Bouyoucos, 1962). Once the particle size distribution
was determined in percent, the textural class of the
soil was assigned using USDA textural triangle
classification system (USDA, 1987). Bulk density of
the samples was estimated from undisturbed soil
samples using the core method. Total porosity of the
soil was derived from the bulk and the particle
densities as:
f %  1  pb pd 100
where f = total porosity,
pb = soil bulk density and
pd = soil particle density which was assumed to
-
MATERIALS AND METHODS
have the generally used average value of 2.65 g cm
1
.
The study was conducted in Dawja Watershed, which
is found in Enebse Sar Midir District, Amhara
National Regional State, Ethiopia. In the area, the
elevation ranges from 2629 to 2965 masl and
dominated by 0-30% slope. The study area receives
average annual rainfall of 1053 mm and means
minimum and maximum temperature of 10 and
23.4°C, respectively. Vertisols are the dominant soil
types in Dawja Watershed. Crop cultivation and
animal husbandry are the main agricultural practices
in the area. Wheat (Triticum spp), teff (Eragrostis tef),
barley (Hordeum spp), faba bean (Vicia faba),
chickpea (Cicer arietinum) and grass pea (Lathyrus
sativus) are the principal crops grown in Dawja
Watershed. Cattle, sheep, goat and equine constitute
major livestock in the area.
The pH (H2O) of the soil was measured
potentiometrically in the supernatant suspension of
1:2.5 in soil: water ratio using digital pH meter
following the procedure outlined by Sahlemedhin and
Taye (2000). The soil organic carbon was determined
by the wet oxidation method (Walkley and Black,
1934) in which the sample was first digested with
potassium dichromate in sulfuric acid solution and
titrated with 0.5 N ferrous sulfate solution, and
percent organic matter was computed by multiplying
the percent soil organic carbon by a conversion factor
of 1.724. Total N content of the soil was determined
by wet-digestion, distillation and titration procedures
of the Kjeldahl method as described by Black (1965).
The available phosphorus content of the soil was
75
Am. J. Sci. Ind. Res., 2015, 6(4): 74-81
determined using Olsen extraction method (Olsen et
al., 1954).
Soil Texture, Bulk Density and Total Porosity:
The ANOVA revealed that effect of slope gradient on
particle size distribution, bulk density and total
porosity was significant (P < 0.01) (Table 1).
Accordingly, the lowest sand content (46%) was
recorded on the gently sloping area, while the highest
sand content (55%) was observed on the moderately
steep area. Similarly, the lowest silt fraction (14%)
was recorded in soils of gently sloping area, while the
highest silt content (22.67%) was in strongly sloping
area. On the other hand, the lowest clay content
(22.67%) was recorded in soils of moderately steep
area, whereas the highest clay content (40%) was
recorded in gently sloping area.
The exchangeable bases were determined through
extraction method with 1M ammonium acetate at pH
7. Amounts of Ca and Mg ions in the leachate were
analyzed by atomic absorption spectrophotometer,
while K and Na ions were analyzed by flame
photometer. Cation exchange capacity was
determined by leaching the soil sample with 1N
ammonium acetate solution followed by leaching with
neutral salt to displace the adsorbed ammonium
+
(NH4 ). Thereafter, estimated titrimetrically by
distillation of ammonium that was displaced by
sodium. The percent base saturation of the soil was
calculated as the percentage of the sum of the basic
exchangeable cations (Ca, Mg, K and Na) to the CEC
of the soil (Bohn et al., 2001).
Looking the data regarding particle size distribution, it
was observed that the clay content showed an
increasing trend as slope gradient lowers while sand
content showed a decreasing trend down the slope
gradient. This is most probably due to removal of the
clay particles by erosion is enhanced on the upper
slope gradient while deposition of these particles
occurs on the lower slope gradient. Similarly,
Mohammed et al. (2005) reported that finer soil
materials are deposit at the lower slope position,
where they are coming from the upper position.
The analysis of variance (ANOVA) was performed to
assess the significant level of difference in soil
parameters among slope gradients using the general
linear model (GLM) procedure of the statistical
analysis system (SAS) software version 9.00.
Significantly different means (P < 0.05) were
separated by using the Duncan`s multiple range test
(DMRT). Moreover, simple correlation analyses were
carried out to determine the magnitude and direction
of relationships between the selected soil
physicochemical properties using SAS statistical
software version 9.00.
According to USDA system of soil texture
classification (USDA, 1987), soils under gently
sloping area had sandy clay while other soils of the
study area are categorized under sandy clay loam
textural class (Table 1). Most field crops could grow
well in such soils having sandy clay and sandy clay
loam textural class as these soils have a potentially
well-balanced capacity to retain water, form a stable
structure and provide adequate aeration.
RESULTS AND DISCUSSIONS
Table 1. Effects of slope gradient on the selected physical properties of Dawja Watershed soils
Slope gradient
GS
S
SS
MS
LSD (0.05)
SE(±)
CV (%)
P-value
Sand
c
46.00
b
50.33
a
54.67
a
55.00
1.49
0.43
1.45
**
Particle size (%)
Clay
a
40.00
b
31.33
c
23.00
c
22.67
2.56
0.74
4.38
**
Textural class
sandy clay
sandy clay loam
sandy clay loam
sandy clay loam
Silt
c
14.00
b
18.00
a
22.67
a
22.33
1.61
0.46
4.15
**
pb
-3
(g cm )
c
1.32
b
1.36
a
1.41
a
1.42
0.02
0.01
0.85
**
f (%)
a
50.10
b
48.62
c
46.74
c
46.42
0.90
0.26
0.94
**
GS= gently sloping; S= sloping; SS= strongly sloping; MS= moderately steep
Note: - Values in the same column followed by the same letters are not significantly different at 0.05 level of significance;
pb = Bulk Density; f = Total
Porosity; LSD = Least Significant Difference, SE = Standard Error, CV = Coefficient of Variation; ** = Significant at P < 0.01; P = probability level
-3
The minimum and maximum bulk density values
were recorded for soils from gently sloping (1.32 g
-3
cm ) and moderately steep (1.42 g cm ) areas of the
Watershed, respectively. The variation of soil bulk
76
Am. J. Sci. Ind. Res., 2015, 6(4): 74-81
density among the slope gradients might be
attributed to the variation of soil particle size
distribution and disturbance of soil particles with
erosion. For instance, the relatively lowest value of
-3
bulk density in gently sloping area (1.32 g cm ) could
be due to the high clay fraction, total porosity and
less disturbance of the soil by erosion process, as
this area has relatively level land position. However,
the reverse is true for moderately steep and strongly
sloping areas (Table 1). The bulk density of the
-3
studied soils was found to be less than 1.61 g cm ,
which is common and acceptable for sandy clay and
sandy clay loam soils (Amusan et al., 2001). This
indicates that the soils of the study area are not
compacted.
(Table 2). The lowest pH in soils of moderately steep
slope gradient could be attributed to the loss of basic
cations through runoff and erosion. This in turn
+
increases the activity of H ion in the soil solution and
reduces soil pH. In line with this finding, Nega and
Heluf (2013) reported that loss of base forming
cations through leaching and runoff generated from
accelerated erosion reduces soil pH and thereby
increases soil acidity. However, the increase in soil
pH at the gently sloping gradient could be attributed
to the accumulation of bases that were presumed to
have been eroded from the moderately steep and
strongly sloping gradients. Similarly, Garcia et al.
(1990) and Hendershot et al. (1992) reported highest
basic cation concentration and pH at bottom slope
position.
Significant and negative relation of bulk density with
clay (r = -0.97**) fraction and significant and positive
relation of bulk density with sand (r = 0.96**) fraction
were observed in the correlation analysis output.
Besides, bulk density had significant and negative
relationship with OM (r = -83**) (Table 3). The
correlation indicates that the presence of relatively
higher clay fraction and OM content lowers soil bulk
density. In line with this, Achalu et al. (2012) revealed
that organic matter decreases bulk density through its
positive effect on soil aggregation.
According to Tekalign (1991) rating of soil pH, soils
with pH (H2O) > 8.0 are characterized as strongly
alkaline; 7.4-8.0 as moderately alkaline; 6.7-7.3 as
neutral, while soils with pH of 6.0-6.6, 5.3-5.9, 4.5-5.2
and < 4.5 are rated as slightly acid, moderately acid,
strongly acid and very strongly acid, respectively, in
reaction. Accordingly, the soils in the strongly sloping
and moderately steep slope gradient were
moderately acidic, while soils in the sloping and
gently sloping gradient were slightly acidic and
neutral in reaction, respectively. Soil pH was
significantly and positively correlated with CEC, OM,
clay fraction and PBS at r = 0.81**, r = 0.90**, r =
0.92** and r = 0.96**, respectively. However, it
correlated negatively with sand fraction r = -0.92**
(Table 3).
The lowest total porosity (46.42%) was recorded on
moderately steep area, while the highest total
porosity (50.10%) was on gently sloping area. The
lowest total porosity recorded in moderately steep
slope gradient could be attributed to the high bulk
density, low clay content and low organic matter
content (Table 2). This is supported by the significant
and positive correlation with OM (r = 0.83**) and
negative and highly significant correlation with bulk
density. On the other hand, the highest total porosity
was recorded in the gently sloping area with the
highest clay content, implying the positive effect of
clay content on total porosity. This was also in
consent with the positive and significant correlation
between clay content and total porosity (Table 3).
According to FAO (2006b) rating of total porosity, the
percent total porosity values in all slope gradients
were very high (greater than 40%). This indicates that
the study area soils are physically fertile.
Organic Matter, Total Nitrogen and Available
Phosphorus: There was statistically significant effect
(P < 0.01) of slope gradient on organic matter. The
minimum OM was recorded in soils of the strongly
sloping and moderately steep areas, whereas the
maximum OM was recorded in soils of the gently
sloping area (Table 2). The variation could be
contributed by the effect of slope gradient on the soil
moisture storage capacity and biomass production. In
the gently sloping area, the soil moisture storage is
better and resulting in better biomass production.
Furthermore, the expected impeded drainage could
also slow down the OM decomposition process.
However, in the strongly sloping and moderately
steep areas, there could be high drainage, low
moisture storage and less biomass production
thereby decreases soil OM content. This result is in
agreement with the work of Abebe and Endalkachew
(2012) in Nitisol of Southwestern Ethiopia. Similarly,
Soil Reaction: Soil pH (H2O) data showed significant
(P < 0.01) effect of slope gradient on soil reaction.
The lowest pH value (5.7) was recorded on soils of
moderately steep slope gradient, whereas the highest
pH (6.8) was obtained on gently sloping gradient soils
77
Am. J. Sci. Ind. Res., 2015, 6(4): 74-81
Nizeyimana and Bicki (1992) and Amuyou and
Kotingo (2015) disclosed that organic matter has
been negatively correlated with the slope gradients.
Whereas OM correlated negatively with sand (r = 0.88**) since sand particle allows further
decomposition of organic matter (Table 3). The result
is in agreement with the investigation of Teshome et
al. (2013). In contrary, Tilahun and Asefa (2009)
found that organic carbon was negatively correlated
with clay content (r = -0.49**). As most of the soil
nitrogen is found in organic form, OM and total
nitrogen had positive relationship (r = 0.80**).
According to the rating system established by
Tekalign (1991) (Table 4), organic matter content of
all the slope gradients were categorized under low
and below the critical level (3.4%). The significant low
level of soil OM in the study area could be due to
limited use of organic amendments for the
maintenance and/or improvement of soil organic
matter.
Differences of slope gradient among the areas did
not significantly (P > 0.05) affect Olson available P
(Table 2). However, numerical variations were
observed among the slope gradients. The relatively
-1
-1
lowest (20.47 mg kg ) and highest (22.50 mg kg )
contents of available P were recorded in soils of
strongly sloping and gently sloping areas,
respectively. Although it is not statistically significant,
the variation is highly associated with the variation of
organic matter content in each slope gradient. As
seen from Table 2, the variation of available P
content among the slope gradients is paralleled with
that of OM content. This shows that soil organic
matter could contribute for the presence of more
available P in the soil system. In consent with this,
Fisseha et al. (2014) found low available P with in
soils having low content of OM. However, Nega and
Heluf (2013) concluded that available P content of
tropical soils did not necessarily decrease with
decrease of organic matter.
Similar with OM, total N was significantly affected (P
< 0.01) by slope gradient. The minimum and
maximum values of total nitrogen were recorded for
moderately steep (0.14%) and gently sloping (0.18%)
areas, respectively. Results regarding total N
revealed an increasing trend from moderately steep
to gently sloping gradient, which might be due to their
downward movement with runoff water from higher
slope gradient and accumulation there at the lower
slope gradient. The result also indicates the
contribution of OM to the high total N. Total nitrogen
of all the slope gradients in the present study area
was in the range of medium based on the rating
suggested by Tekalign (1991) (Table 4). This reveals
that nitrogen is found the limiting plant nutrients in the
study area due to low level of soil organic matter
content and the limited use of nitrogen containing
inputs like commercial fertilizer, plant residues and
animal manure.
According to the soil available P rating suggested by
Cottenie (1980) (Table 4), all the slope gradients
under the study area were high in their content of
Olsen available phosphorus. The preferred ranges of
soil pH (5.7-6.8) and mineral weathering could have
considerable importance for the high content of
available P in the studied soils.
The Pearson correlation coefficient revealed that soil
OM was positively correlated with clay content (r =
0.86**). This is because of the reason that clay is
poor in aeration and slow in drainage properties
resulting in slow oxidation process in the soil system.
Table 2. Effects of slope gradient on the selected chemical properties of Dawja Watershed soils
Slope gradient
GS
SL
SS
MS
LSD (0.05)
SE (±)
CV (%)
P- value
pH
(H2O)
6.8a
6.4b
5.8c
5.7c
0.41
0.12
3.30
**
OM
(%)
1.67a
1.51a
1.25b
1.28b
0.19
0.05
6.65
**
TN (%)
0.18a
0.15b
0.15b
0.14b
0.01
0.01
4.95
**
Av.P (mg
kg-1)
22.50
21.92
20.47
20.60
4.84
1.40
11.33
NS
Soil parameters
K
Na
Mg
Ca
CEC
…………………....cmol(+) kg-1………………….
0.78a
0.73a
4.19a
32.91a
41.87a
b
b
b
b
0.64
0.44
2.81
23.87
34.00b
0.55b
0.40b
2.63bc
16.73c
28.20c
0.54b
0.39b
2.47c
16.10c
29.60c
0.13
0.27
0.18
2.23
4.29
0.04
0.08
0.05
0.64
1.24
10.57
28.10
3.06
4.98
6.43
**
NS
**
**
**
PBS (%)
92.20a
81.65b
69.82c
68.27c
5.23
1.51
3.35
**
OM = Organic Matter; TN = Total Nitrogen; Av.P = Available Phosphorus; NS = Not Significant at P < 0.05
Exchangeable Basic Cations, Cation Exchange
Capacity and Percent Base Saturation: All the
studied exchangeable basic cations except Na were
significantly (P < 0.01) affected by slope gradient.
78
Am. J. Sci. Ind. Res., 2015, 6(4): 74-81
Accordingly, the lowest and highest values of
exchangeable bases were recorded for moderately
steep and gently sloping areas, respectively (Table
2). This showed an increasing trend of exchangeable
basic cations concentration from moderately steep to
gently sloping gradient, which might be due to their
loss through run off and erosion in the high sloping
areas and accumulation in areas having lower slope
gradient.
The lowest and highest CEC values were recorded
-1
for strongly sloping (28.20 cmol(+) kg ) and gently
-1
sloping (41.87 cmol(+) kg ) areas, respectively. The
lowest CEC in the strongly sloping area was in line
with the relatively low organic matter and clay content
(Table 1 and 2). This is in agreement with the finding
of Teshome et al. (2013) in soils of Abobo area,
Western Ethiopia. Based on the rating established by
FAO (2006b) (Table 4), the gently sloping area had
very high CEC, while all the other areas had high
CEC values, which might be attributed to the high
specific surface area of the clay particles. The CEC
was positively correlated with OM (r = 0.83**) and
clay content (r = 0.95**). This indicates that the
contributions of soil OM and clay content for the high
CEC is significant. In consent with this, Fassil and
Charles (2009) disclosed that the amount of clay and
type of clay mineral present in the soils are important
controlling factors for CEC.
The presence of significant differences in clay and
organic matter content of the soil among the slope
gradients might be an important reason for the
variations of exchangeable basic cations. The special
variation of exchangeable bases depends on
particles size distribution and soil management
practices (Heluf and Wakene, 2006). According to the
rating of FAO (2006b) (Table 4), soils under the
gently sloping and sloping areas had very high Ca
and high K contents. Similarly, both Mg and Na
contents of the gently sloping and sloping area soils
were rated as high and medium, respectively.
Whereas, strongly sloping and moderately steep
slope areas had high Ca, medium Mg, K and Na
contents.
Similar with the exchangeable basic cations, percent
base saturation (PBS) was significantly (P < 0.01)
affected by slope gradient differences. Accordingly,
the PBS of the study area ranged from 68.27 to
92.20% (Table 2). The variation of PBS could
probably be associated with the variation of basic
cations and cation exchange capacity of the soils.
The PBS of the soils in all slope gradients was rated
as high according to the rating recommended by
Landon (1991) (Table 4). This indicates the generally
base-rich nature of the soils of the study area. The
high level of PBS in this study was related with the
preferable soil pH range and clay content of the study
area. The PBS of the studied soils increased with
increase in clay content (r = 0.97**), CEC (r = 0.86**)
and basic cations mainly Ca (r = 0.95**) and Mg (r =
0.87**). This reveals any factor that could affect Ca,
Mg and CEC of the soil could also affect PBS in the
same manner.
Output of the correlation matrix revealed that
exchangeable basic cations have significant and
positive correlation with clay content and soil organic
matter. This is to be expected since clay particles and
organic matter are capable of absorbing soil cations
on sites on their surfaces that carry unsatisfied
negative charges. However, all basic cations were
negatively correlated with sand content (Table 3).
This is obviously, because sand particle fractions are
chemically inert and are incapable of absorbing
cations.
Table 3. Pearson`s correlation matrix for selected soil physicochemical parameters
*
OM
TN
K
Na
Ca
Mg
CEC
PBS
sand
clay
pb
F
pH
0.90**
0.74*
0.70*
0.62*
0.90**
0.81**
0.81**
0.96**
-0.92**
0.92**
-0.89**
0.89**
OM
TN
K
Na
Ca
Mg
CEC
PBS
Sand
clay
pb
0.80**
0.66*
0.72*
0.88**
0.75**
0.83**
0.87**
-0.88**
0.86**
-0.83**
0.83**
0.63*
0.70*
0.82**
0.88**
0.82**
0.76**
-0.79**
0.80**
-0.72*
0.73*
0.83**
0.88**
0.85**
0.87**
0.83**
-0.86**
0.87**
-0.92**
0.91**
0.81**
0.80**
0.82**
0.71*
-0.74*
0.75**
-0.76**
0.74*
0.91**
0.97**
0.95**
-0.98**
0.99**
-0.95**
0.95**
0.89**
0.87**
-0.87**
0.90**
-0.86**
0.85**
0.86**
-0.94**
0.95**
-0.88**
0.88**
-0.96**
0.97**
-0.98**
0.98**
-0.99**
0.96**
-0.96**
-0.97**
0.97**
-1
79
Am. J. Sci. Ind. Res., 2015, 6(4): 74-81
Table 4. Classes or ratings considered for some soil parameters
Categories or Ratings
Sources
Medium
High
V.high
Soil OM (%)
2.59-5.17
> 5.17
Tekalign, 1991
Total N (%)
0.12-0.25
> 0.25
-1
Av. P (mg kg )
10-17
18-25
> 25
Cottenie, 1980
-1
K (cmol(+) kg
0.3-0.6
0.6-1.2
> 1.2
-1
Na (cmol(+) kg
0.3-0.7
0.7-2.0
> 2.0
FAO, 2006b
-1
Ca (cmol(+) kg
5-10
10-20
> 20
-1
Mg (cmol(+) kg
1.0-3.0
3.0-8.0
> 8.0
CEC (cmol(+) kg
12-25
25-40
> 40
PBS (%)
20-60
> 60
Landon, 1991
Amuyou, U. A. and Kotingo, K. E. 2015. Toposequence
analysis of soil properties of an agricultural field in the
CONCLUSION
Obudu Mountain slopes, cross river state-Nigeria.
European journal of physical and agricultural sciences,
This work confirmed that soils of the study area are
3(1).
Parameters
V. low
< 0.86
< 0.05
<5
< 0.2
< 0.10
< 2.0
< 0.3
<6
-
Low
0.86-2.59
0.05-0.12
5-9
0.2-0.3
0.1-0.3
2-5
0.3-1.0
6-12
< 20
good in their selected physical and chemical
properties for plant growth except organic matter and
total nitrogen. However, the detrimental effects of
slope gradient are higher at moderately steep and
strongly sloping areas as compared to sloping and
gently sloping areas. The decline in quality of soil
physical and chemical properties of moderately steep
and strongly sloping areas as compared to sloping
and gently sloping areas were presumed to be due to
past soil erosion and runoff effect that removed the
clay particles, soil organic matter and other plant
nutrients. Therefore, the soil fertility management in
the study area should focus on scenarios that could
improve the organic matter and nitrogen levels of the
soils and special management practices such as
terracing and proper land leveling are required to
improve the effects of high slope gradient on soil
physicochemical properties for improving crop
production on a sustainable basis.
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Jabbar, M.A. and Paulos Dubale. 2002. Nature and
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