Open Journal of Soil Science, 2012, 2, 223-233
http://dx.doi.org/10.4236/ojss.2012.23027 Published Online September 2012 (http://www.SciRP.org/journal/ojss)
223
Impact of Altitude and Land Use Type on Some Physical
and Chemical Properties of Acidic Soils in Tsegede
Highlands, Northern Ethiopia
Abreha Kidanemariam1, Heluf Gebrekidan1, Tekalign Mamo2, Kibebew Kibret1
1School of Natural Resource Management and Environmental Science, Haramaya University, Haramaya, Ethiopia; 2Ministry of
Agriculture and Rural Development, Addis Ababa, Ethiopia.
Email: abrehakidanemariam@gmail.com
Received June 5th, 2012; revised July 8th, 2012; accepted July 21st, 2012
ABSTRACT
A study was conducted in the Tsegede highlands of Tigray Region, northern Ethiopia to determine the changes in some
physical and chemical attributes across three adjacent acidic soil sites with different elevation and three land use types.
Analytical results of the collected surface layer soil samples showed significant (P 0.05) correlation of soil bulk den-
sity, OM and total N with elevation. In the lower elevation site (Indaslasie), soil OM content declined by about 43 and
52% compared with that of the two higher elevation sites (Cheguarcudo and Indamariam), respectively. Soil pH, ex-
changeable acidity, exchangeable Al, OM, total N and available phosphorus also exhibited significant (P 0.05) dispar-
ity across the three land use types of the area. Soils of the forest land were less acidic by 0.43 and 0.68 pH units than the
cultivated and grazing lands, respectively. The soil OM content of the cultivated land was significantly lower by about
25 and 35% than the grazing and forest land soils, respectively. Available soil P status was low and showed significant
correlations with pH (r = 0.65**), exchangeable acidity (r = 0.58*) and Al (r = 0.53*). In general, the study results
revealed altitude did not impose any significant effect in aggravating soil acidity whereas land use type affected signifi-
cantly not only soil acidity but also the important soil fertility related parameters such as OM, total N and available P
contents. Therefore, it can be suggested that besides to the usual acid soil management and/or reclamation practices,
introducing proper land use management systems are of paramount importance.
Keywords: Acidic Soil; Altitude Variability; Highland; Land Use Type
1. Introduction
Soil acidity is one of the most important soil factors
which influence plant growth and ultimately limit crop
production and profitability. More than 30% of the total
cultivated land area of Ethiopia is believed to be affected
by soil acidity of differing magnitude [1,2]. Accord-
ingly, together with declining levels of soil fertility under
no or only limited use of external nutrient inputs, soil
acidity is becoming one of the serious soil degradation
problems that hamper sustainable agricultural develop-
ment mainly in the highlands of Ethiopia [3,4].
Soil acidification is a natural process mainly condi-
tioned by naturally acid parent rocks and leaching of base
forming ions attributed to high precipitation [5]. Al-
though soil acidity is naturally occurring in some areas,
in many others cases, agricultural practices have acceler-
ated the process of soil acidification [6,7]. Normally, the
indication for high soil acidification in soil solution is
associated with the presence of pH levels lower than 5.5
and high exchangeable acidity [8]. The existence of high
exchangeable acidity in a soil usually indicates the occu-
rrence of exchangeable hydrogen (H), exchangeable
aluminum (Al) as either free Al3+ ion or partially neu-
tralized Al-hydroxy compounds such as Al(OH)2+ or
2

Al OH
, and weak organic acid ions held at the col-
loidal surfaces of the soil [9,10]. Although the availabil-
ity of plant nutrients such as phosphorus (P) and calcium
(Ca) can be limiting at low soil pH [11], Al toxicity is
probably the foremost plant growth and productivity lim-
iting factor in acid soils [12-14].
Soil pH may also control biotic factors such as the ac-
tivity and biomass composition of fungi, bacteria and
other micro-flora and fauna in the soils of both natural
(forests and grasslands) and agricultural lands [15,16].
This in turn affects the rates of microbial mediated bio-
chemical reactions including oxidation of organic resi-
dues, mineralization of organic nutrients and symbiotic
molecular nitrogen (N2) fixation in legume plant root
nodules.
Copyright © 2012 SciRes. OJSS
Impact of Altitude and Land Use Type on Some Physical and Chemical Properties of Acidic Soils in
Tsegede Highlands, Northern Ethiopia
224
Altitude is often employed to study the effects of cli-
matic variables on soil organic matter dynamics and the
ratio of organic carbon to nitrogen (N) which determines
the level of decomposition of the organic matter and
mineralization of organic N [17-20]. The change in alti-
tudinal gradients influences soil organic matter by con-
trolling soil water balance, soil erosion, geologic deposi-
tion processes, species and biomass production of the
native vegetation and cultivated plants [21]. Moreover,
there are reports that indicate the change in land use par-
ticularly from forest land to agriculturally managed
(grazing and cultivated) lands in the different highland
zones of the country are among the major causes of the
removal of fertile surface soils and deterioration of the
physical, chemical and biological fertility and producti-
vity levels of the soils [22-25]. Thus, assessing the influ-
ences of altitude variability and land use dynamics in-
duced changes in soil physical and chemical characteris-
tics is essential for addressing the issue of agroecosystem
transformation and the low fertility and productivity le-
vels of the acidic soils in the country at large and at the
study areas in particular.
In line with remaining high rainfall received highlands
of the country, severe soil acidity problem has also been
re- ported recently in the highland areas of the Tsegede
Dis- trict of Tigray Region located in the northern high-
lands of Ethiopia [26]. The limitation of knowledge and
detail information on the characteristic features, areal
extent and magnitude of the acidic and potentially acidic
soils of the Tsegede highlands which lead to their proper
delineation and mapping prompted this study so as to de-
velop sustainable acid soil management strategy. Fur-
thermore, studies with regard to the effects of elevation
and land use changes on the physicochemical properties
of such acidic soils are scanty. Hence, the objective of
this study was to determine the spatial variability of some
soil physical and chemical properties over elevation and
land use types in the Tsegede highlands of highlands,
Western Zone of Tigray Region in northern Ethiopia.
2. Materials and Methods
2.1. Site Characteristics
Tsegede District is located in the Western Zone of Tigray
Region between 13˚1421 and 13˚4446 north latitude
and 36˚2744 and 37˚455 east longitude within the
tropics (Figure 1). It is characterized by diverse physio-
geographic features with high and rugged mountains, flat
topped plateaux, deep gorges, incised river valleys and
rolling plains. The altitudinal variation ranges from 500
meters around Dansha to 3000 meters above sea level
(masl) at Cheguarcudo. Tsegede District has two major
agro-ecological zones; hot to warm moist lowlands (M1)
and tepid to cool moist mid-highlands (M2) [27]. As per
the Tsegede Water Resource Development Office [28],
the Tsegede highlands, where this study was carried out,
receive a mean annual rainfall of about 2224 mm and
usually rainfall starts around the end of March and ends
at early November with the highest amount of rainfall
falling in August. The mean annual temperature of the
area is 13.2˚C and ranged from 7.8˚C to 18.6˚C. The
dominant soil type in the Tsegede highlands is mainly
Humic Cambisols [29]. The major geologic parent mate-
rials of the area are principally basic volcanic rocks (py-
roxene—olivine basalt) [30]. Mixed crop-livestock pro-
duction is the dominant farming system of the area. Out
of the total area of the District, 71.45% is covered by
crop land, 19.81% is grazing land, 6.54% is under forest
vegetation and about 2.2% is estimated to be area co-
vered by rock outcrops and settlement.
2.2. Sampling Protocol
Three adjacent acidic soil sites of Tsegede highlands
namely; Cheguarcudo, Indamariam and Indaslasie, found
at the same agroecology (tepid to cool moist mid-high-
lands) with different elevation were selected. Thirty six
composite soil samples were collected from the surface
layer (0 - 30 cm depth) soils of each site. Elevation of the
sampling points from the Cheguarcudo, Indamariam and
Indaslasie sites varied from 2854 to 2965, 2845 to 2902
and 2332 to 2778 meters above sea level, respectively.
The 36 composite surface soil samples were yet again
composed of, on an average, 22, 8 and 6 samples from
three land use types (cultivated, grazing and forest) of
each site, respectively, which is proportional to their area
coverage. Each composite soil sample was prepared from
20 subsamples taken by scraping away the surface litter
of each randomly marked sampling point and inserting
the auger up to a depth of 30 cm. All the subsamples
were collected in a bucket and were thoroughly mixed.
Finally, about 1 kg of soil sample was taken using quar-
tering method from the composite bulk soil in the bucket
to a polyethylene bag and labeled with the necessary in-
formation.
A total of twenty seven undisturbed soil samples were
also collected by taking three samples from each land use
type of each site using the core method. Weight and vo-
lume of the tin bottom and top of the cylindrical core
sampler were first recorded and labeled. A smooth un-
disturbed vertical surface at each sampling point was
prepared by scraping away the surface litter and the core
sampler was pressed into the soil sufficiently to fill the
inner core without inducing compression. After careful
removal of the undisturbed soil cores with trim ends of
acceptable soil cores flush with the end of the cylinder
were collected. The GPS readings for the coordinates and
Copyright © 2012 SciRes. OJSS
Impact of Altitude and Land Use Type on Some Physical and Chemical Properties of Acidic Soils in
Tsegede Highlands, Northern Ethiopia
Copyright © 2012 SciRes. OJSS
225
Figure 1. Map of the Tsegede district and location of the study areas.
Impact of Altitude and Land Use Type on Some Physical and Chemical Properties of Acidic Soils in
Tsegede Highlands, Northern Ethiopia
226
altitude as well as the land use types were also recorded
simultaneously for each sampling points.
2.3. Laboratory Analysis
The composite surface (0 - 30 cm depth) soil samples
collected were air-dried and ground to pass through a 2
mm sieve. One hundred eight composite soil samples
were analyzed for pH and exchangeable acidity; 31 sam-
ples (from selected land uses) for soil texture, organic
matter, total nitrogen, available P and exchangeable Al.
Twenty seven undisturbed soil samples were analyzed
for bulk density. Determination of moisture correction
factor (MCF) was done on the bases of Hesse [31]. Parti-
cle size distribution (soil texture) was determined by the
Bouyoucos hydrometer method [32] and bulk density
was estimated using the core sampling method [33]. Soil
pH (1:2.5) soil to water ratio was measured using glass
electrode pH meter as described by Peech [34]. Ex-
changeable acidity and exchangeable Al were analyzed
following the procedures outlined by Sumner [35] and
Pansu et al. [36], respectively. Organic carbon (OC) was
determined by the wet acid dichromate digestion method
and soil organic matter (OM) was calculated by multi-
plying percent OC by a factor of 1.724 [37] whereas total
nitrogen was analyzed by the semi-micro Kjeldahl diges-
tion followed by ammonium distillation and titrimetric
determinations [38]. Analysis of available phosphorus
was conducted following the procedure of the Bray I
method of extraction [39] using ascorbic acid as a reduc-
tant in the presence of antimony and determined spec-
trophotometrically.
2.4. Statistical Analyses
An analysis of variance was used to test differences in
soil physical and chemical properties across the different
elevation sites and land use types. For statistically dif-
ferent parameters (P 0.05), means were separated using
the Least Significant Difference (LSD) comparison test.
Correlation analyses were also carried out to detect func-
tional relationships among key soil variables. Data analy-
ses were done using a statistical software package [40].
Soil acidity map was developed by subjecting the GPS
readings and pH data to the Arc View GIS 10 and the
degree of acidity which is expressed as a pH value was
categorized on the bases of the rating suggested by Dek-
ker [41].
3. Results and Discussion
3.1. Elevation and Its Relationship with Some
Physical and Chemical Properties of Acidic
Soils
Elevation showed statistically significant correlation with
soil bulk density, OM and total N whereas soil pH, ex-
changeable acidity, exchangeable acidity Al, texture and
available P did not (Table 1).
3.1.1. Soil Bulk Density
The overall mean value of surface soil bulk density of the
area was low (Table 2) as compared to the usual bulk
density of mineral soils suggested by Brady and Weil
[42]. It had significant correlation and variation with
elevation (Tables 1 and 3). Relatively higher average soil
bulk density was observed in the soils of lower elevation
site (Indaslasie) as compared to those of higher elevation
sites (Indamariam and cheguarcudo) (Table 3).
The low overall soil bulk density of the area and the
relatively higher bulk density soils of the lower elevation
site (Indaslasie) might be attributed to the existence of
high OM accumulation in the whole area in general and
the relatively lower OM accumulation in the lower eleva-
tion site. In connection with this, the overall bulk density
showed significant negative correlation with soil OM
Table 1. Correlation coefficient and probability values of surface layer (0 - 30 cm) soil pH, exchangeable acidity, exchange-
able Al, sand, silt and clay frac tions, OM, total N and available P with elevation.
Soil property Correlation coefficient (r) P-values
pH 0.07 0.7262
Exchangeable acidity 0.06 0.7531
Exchangeable Al 0.15 0.4075
Bulk density 0.42 0.0353
Sand 0.37 0. 0578
Silt 0.28 0.1338
Clay 0.12 0.5352
OM 0.52 0.0028
Total N 0.36 0.0441
Available P 0.23 0.1969
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Impact of Altitude and Land Use Type on Some Physical and Chemical Properties of Acidic Soils in
Tsegede Highlands, Northern Ethiopia 227
Table 2. Statistics of the overall surface layer (0 - 30 cm) soil pH, exchangeable acidity, exchangeable Al, sand, silt and clay
fractions, OM, total N and available P.
Soil property* No. samples Mean Std Dev Minimum Maximum
Elevation (masl) 108 2813 145.0 2329 2965
pH 108 5.08 0.470 4.140 6.330
Exch. acidity (cmolC·kg1) 108 1.95 1.824 0.000 6.560
Exch. Al (cmolC·kg1) 31 3.50 1.378 0.560 5.520
Bulk density (g·cm1) 27 1.00 0.170 0.741 1.305
Sand (%) 31 47.22 8.679 31.280 65.280
Silt (%) 31 39.75 7.153 24.720 52.720
Clay (%) 31 13.03 5.535 4.000 24.000
Organic matter (%) 31 8.63 4.209 1.009 21.684
Total N (%) 31 0.38 0.178 0.078 0.946
Available P (mg·kg1) 31 9.58 17.067 1.020 75.170
*masl = Meters above sea level; Exch. = Exchangeable; Std Dev = Standard deviation.
Table 3. Soil pH, bulk density, OM and total N (Means ± SE) status across three different elevation sites.
Site name Altitude (m) Bulk density (g·cm -3) Organic matter (%) Total N (%)
Cheguarcudo 2910 ± 28.27b 0.93b ± 0.05ab 11.95 ± 0.92a 0.45 ± 0.04a
Indamariam 2877 ± 27.2b 0.88b ± 0.07b 9.92 ± 0.92a 0.46 ± 0.04a
Indaslasie 2606 ± 27.49a 1.14 ± 0.05a 5.11 ± 0.92b 0.26 ± 0.04b
Mean values within columns followed by the same letter(s) are not significantly different at P 0.05.
(Figure 2). Thus, the soils with high OM accumulation
are higher in percent pore space regardless of the amount
of soil particles in the soil and results in lower bulk den-
sity whereas the soils with lower OM are lower in per-
cent pore space and results in higher bulk density. Simi-
lar report by Sanjay et al., [43] also pointed out that the
lower bulk density at top altitudes are good indication of
soils that has occupied coarser structure of organic matter
and enriches the spaces by soil organic carbon.
3.1.2. Soil Organic Matter and Total N
As per the soil OM classification suggested by Benton
Jones [44], the average value of surface soil organic
matter content (Table 2) was very high. It was also ob-
served to be affected significantly by elevation (Tabl es 1
and 3). Soil OM content of the lower elevation site (In-
daslasie) was found to be reduced by about 43% and
52% than the two high elevation (Cheguracudo and In-
damariam) sites, respectively (Table 3). Likewise, mean
value of total N was high (Table 2) as per the classifcation
rate suggested by Landon [45] and showed significant
disparity with elevation gradient (Tables 1 and 3).
The accumulation of relatively high soil OM in all the
sites in general could be ascribed to the presence of high
precipitation which promotes plant growth, cooler tem-
perature and high soil acidity of the area which could
decrease the rate of decomposition and mineralization of
soil OM. Reports have also revealed that soil OM accu-
mulation increases with increasing precipitation and de-
creases with increasing temperature [46]. Likewise, soil
pH may control biotic factors, such as the biomass com-
position of fungi and bacteria in both forests [16,47,48]
and agricultural [15,49] soils. However, the relatively
lower accumulation of soil OM in Indaslasie site might
be attributed to its significant positive correlation with
altitude difference (Figure 3). Although the information
with regard to the annul temperature of each experimen-
tal sites is not available, usually lower altitudes areas are
having higher temperature than the areas with high alti-
tude. Thus, this relatively high temperature in the In-
daslasie site might enhance the soil OM decomposition
and mineralization thereby decreases its accumulation in
the area. The change in altitudinal gradients can also in-
fluences SOM by controlling soil water balance, soil ero-
sion and geologic deposition processes [21]. In line with
this a positive correlation between SOM and altitude has
been reported by Sims and Nielsen [50], and Tate [51].
The overall high total N status of soils of the area in
general and the variation within sites in particular might
be associated to the variablity of soil OM with elevation
gradient. However, although top soils may contain seve-
ral thousand kilograms of nitrogen per hectare, most of
which might be locked up in soil organic matter and not
directly available to plants [52].
Copyright © 2012 SciRes. OJSS
Impact of Altitude and Land Use Type on Some Physical and Chemical Properties of Acidic Soils in
Tsegede Highlands, Northern Ethiopia
228
Figure 2. Relationship betw ee n soil bulk de nsity and OM .
Figure 3. Correlation between soil OM and altitude.
3.2. Land Use Type Impact on Some Physical
and Chemical Properties of Acidic Soils
3.2.1. Soil pH
The average surface soil pH value of the area was low
(Table 2) and ranged from very strongly acidic to
slightly acidic as per the pH rating category suggested by
Dekker [39]. It was observed that soil pH was signifi-
cantly affected by land use type difference (Table 4).
Soils of the forest land were less acidic by 1.16 and 1.12
units than the cultivated and grazing lands, respectively
(Table 5).
The lower pH in soils of the cultivated and grazing
lands could be attributed to the removal of basic cations
by crop produce and over grazing, respectively. Likewise,
it is reported that although acidity is naturally occurring,
agricultural practices such as the removal of plant resi-
dues carrying organic anions and excess cations from the
farm or paddock is likely to accelerate soil acidification
[6,7].
The significantly high pH of soils from the forest land
of the area might be attributed to the ameliorating effect
of the high accumulation of organic matter at surface.
This ameliorating effect of soil OM could be due to the
combined effect of the continuous releasing of basic
Table 4. F statistics and probabilities of surface layer (0 - 30 cm depth) soil properties under three different land use types of
the Tsegede highlands.
Soil property F-value P-value
Sand 1.26 0.2863
Silt 3.14 0.0631
Clay 1.25 0.3073
Bulk density 0.92 0.4176
pH 10.82 0.0001
Exchangeable acidity 7.17 0.0012
Exchangeable Al 91.35 0.0001
OM 4.02 0.0331
Total N 5.58 0.0110
Available P 9.79 0.0009
Table 5. Soil pH, exchangeable acidity (EA), exchangeable Al (Ex. Al), OM, total N and available P (Means ± SE) contents
across three land use types.
Soil property Cultivated land Grazing land Forest land
pH 4.56 ± 0.05b 4.60 ± 0.07b 5.72 ± 0.07a
Exchangeable acidity (cmolC·kg1) 4.64 ± 0.21a 3.93 ± 0.25a 0.28 ± 0.21b
Exchangeable Al (cmolC·kg1) 3.81 ± 0.21a 3.15 ± 0.26a 0
.00 ± 0.26b
Bulk density (g·cm1) 1.03 ± 0.05a 0.93 ± 0.05a 1.00 ± 0.05a
Organic matter (%) 7.07 ± 0.80b 9.51 ± 0.9da 10.42 ± 0.96a
Total N (%) 0.30 ± 0.04b 0.38 ± 0.04ab 0.49 ± 0.04a
Available P (mg·kg1) 3.04 ± 3.692b 2.93 ± 4.40b 26.17 ± 4.40a
Mean values within rows of each soil property followed by the same letter(s) are not significantly different at P 0.05.
Copyright © 2012 SciRes. OJSS
Impact of Altitude and Land Use Type on Some Physical and Chemical Properties of Acidic Soils in
Tsegede Highlands, Northern Ethiopia 229
cations from the slow decomposition rate of the accumu-
lated organic matter in that cool humid area, deposition
of basic cations at the surface by the relatively deep root
forest trees from the subsoil and the specific adsorption
of organic anions on hydrous Fe and Al surfaces and the
corresponding release of hydroxyl ions. In connection
with this, Caixan and Rengel [53] reported that trees and
shrubs may play a role in minimizing soil acidification
through the development of deep root systems capable of
taking up bases such as Ca and Mg from deep layers of
the soil profile and returning them to the topsoil as leaf
litter containing excess basic or alkaline cations.
3.2.2. Soil Exchangeable Acidity and Exchangeable Al
Mean value of surface soil exchangeable acidity of the
area was found to be High (Table 2). Highly significant
variation of exchangeable acidity within the land use
types was observed (Table 4). It showed significant in-
crement in the grazing and cultivated lands as compared
to that of the forest land soils (Table 5). Similarly, ex-
changeable Al was showed a highly significant variation
within land use types (Table 4). It was significantly
lower by 3.81 and 3.15 units in the forest land soils than
the cultivated and grazing lands, respectively (Table 5).
The high soil exchangeable acidity in the cultivated
and grazing lands might be associated to the occurrence
of lower soil pH in both the land use types. It was also
showed strong negative correlation (r = 0.77) with pH
and was much higher in the soils with a pH less than 5.5.
Reports also pointed out that exchangeable acidity is a
function of soil pH composed of compounds such as
Al(OH)2+ or 2, and weak organic acid ions held
at the colloidal surfaces of the soil [9,10,54].

AlOH
The significant variation of soil exchangeable Al
within the land use types might be closely related to their
soil pH and exchangeble acidity status differnce. A strong
negative relationship was also observed between the
overall exchangeable Al and pH (Figure 4(a)) and it was
mainly observed in soils where there was a pH of more
or less below 5. Likewise, it had also a close correlation
with exchangeable acidity (Figure 4(b)). It is generally
considered that Al increases in concentration in soil solu-
tion below pH 5.5 [12-14].
3.2.3. Soil Organic Matter and Total Nitrogen
It was observed that soil OM was significantly influ-
enced by land use type (Table 4). Although OM contents
of the soils in all the land use types were rated as high,
soils of the cultivated land was having significantly
lower by about 25 and 35 percent than the grazing and
forest land soils, respectively (Table 5). Similarly, total
N was also showed significant variation within the the
different land use types (Table 4).
Exchangeable acidity (cmolC·kg1)
(b)
Figure 4. Correlations of exchangeable Al with pH (a) and
exchangeable acidity (b).
The relatively lower accumulation of soil OM in the
cultivated land might be attributed to the process of cul-
tivation which is nearly always associated with a loss of
organic carbon. In line with our report, it is suggested
that the low accumulation of OM in cultivated land sols
could be due to 1) the reduction in total organic inputs
(litter, crop residues, manure); 2) increased mineralize-
tion rates of organic matter caused by tillage; 3) in-
creased soil temperatures due to exposure of the soil sur-
face and 4) increased wetting-and-drying cycles and the
los by soil erosion [55-57].
3.2.4. Availabl e Phosphorus
Average available surface soil P status (Bray method) of
the area was low (Table 2) as per the classification rate
suggested by Beegle and Oravec [58]. It was signifi-
cantly affected by the land use types (Table 4). In soils
of the forst land available soil P was significantly higher
by about 88% compared to that of cultivated and grazing
land soils (Table 5).
The low available P status in the cultivated and graz-
ing land soils seems to be related mainly to the presence
of low pH and high exchangeable acidity. It showed a
highly significant posetive correlation (r = 0. 65) with pH
and negative correlation (r = 0. 58*) with exchangeable
acidity. Hence, this soil with high exchangeable acidity
can have the acidic cations such as exchangeable Al, H,
Copyright © 2012 SciRes. OJSS
Impact of Altitude and Land Use Type on Some Physical and Chemical Properties of Acidic Soils in
Tsegede Highlands, Northern Ethiopia
230
and oxides of Al and Fe that could fix the soluble P in the
soil solution. A negative correlation (r = 0.53*) was
also obserbed between available P and exchangeable Al.
A significant positive relationship (r = 0.78) between pH
and P fixation as a result of these soluble acidic metal
ions was also reported from the study done to determined
the phosphorus fixing capacity of some soils of Mauritius
[59]. In the other hand, the presence of relatively higher
available P in the forest soil could be attributed to the
presence of high pH and OM which was having a posi-
tive relationship (r = 0.47*). The specific adsorption of
organic anions on hydrous Fe and Al surfaces and the
corresponding release of hydroxyl ions [60] could in-
crease the pH and available P in the soil solution.
3.3. Soil Acidity Map of Tsegede Highlands
From the analytical results and GPS readings of the total
108 surface layer (0 - 30 cm depth) composite soil sam-
ples of the three sites and land use types of Tsegede
highlands, acidity map was developed on the scale of
1:60,000. The map was made to display the different soil
acidity categories of the area. Soil acidity or basicity of
an area is normally measured by soil pH, concentration
of hydronium ion (H3O+ or, more commonly, the H+) in
soil solution. Based on this, acidity categories of Tsegede
highlands was found to have 50%, 31%, 15%, and 4% of
very strong acidic, strongly acidic, moderately acidic and
slightly acidic coverage, respectively (Figure 5).
From the map, it can be exhibited that 46%, 24% and
19% of very strong acidic coverage was in Indamriam,
Cheguarudo and Indaslasie sites, respectively. Indamariam
had very strong acidity coverage as compared to the
other two sites. This shows that elevation in the study
area doesn’t affect soil pH. This very strong acidic cover-
age might be developed due to the intensively cultivated
and over grazed lands occurred in Indamariam. The pre-
sence of relatively intensive cultivation and over grazing
lands in the area is due to the presence of large rock out-
crop coverage which leads to area limitation. Thus, this
intensive cultivation and over grazing activities could
most probably aggravate the acidification process of this
specific area.
Figure 5. Soil acidity map of Cheguarcudo, Indamariam, Indaslasie and adjacent site s of Tsegede highland.
Copyright © 2012 SciRes. OJSS
Impact of Altitude and Land Use Type on Some Physical and Chemical Properties of Acidic Soils in
Tsegede Highlands, Northern Ethiopia 231
The cultivated and grazing land use types were domi-
nated by very strong acidic and strongly acidic soils
whereas soils of the forest land were more of strongly
acidic and moderately acidic (Figure 6). Soil acidity of
the grazing lands was mainly ranged within the very
strongly acidic and strongly acidic soils only. The high
coverage of strongly acidic soils in these grazing lands
most likely indicates the strong impact of intensive over-
grazing that might aggravate acidification. In general, it
was observed that most of the soils of the cultivated and
grazing lands were fall in the very strongly acidic while
forest land were dominated by strongly and moderately
acidic because of the relatively higher pH it had.
Such strong and very strong acidity category could in-
dicate the presence of more Al ion concentration in the
soil solution of these cultivated and grazing lands. The
release of Al into the soil solution as a result of proton
buffering is suggested to have effects on root growth and
nutrient uptake [61,62]. Hence, this considerable extent
of acidity coverage could affect crop as well as forage
growth of the area. Thus, acid soil management strategy
options should be developed.
4. Conclusions
The study showed that the changes in altitude and land
use types had significant impact on the spatial distribu-
tion of some physical and chemical properties of acidic
soils in the Tsegede highlands of Tigray. Surface layer (0
- 30 cm) soil of the area showed variability in soil attri-
butes such as bulk density, OM and total N as a result of
differences in elevation whereas soil pH did not. The
variability in soil OM content among the lower and
higher elevation sites was due to the difference in tem-
perature which affects the soil OM decomposition and
mineralization which increases with increasing tempera-
ture. Thus, the surface soil OM concentration in the area
was positively correlated with altitude as temperature and
so oxidation loss of OM decrease with increasing alti-
tude.
Soil pH, exchangeable acidity, exchangeable Al, OM,
total N and available phosphorus also exhibited signifi-
cant variability across the different land use types. The
low pH and high exchangeable acidity and Al contents in
the soils of the area seems mainly associated to leaching
of basic cations by the excessive rainfall prevalent in the
area and is aggravated by their removal through crop and
forage produce.
Generally, it seems that altitude does not have any part
in aggravating soil acidity whereas the conversion of
forest land in to grazing and cultivated land aggravates
soil acidity of the area. Therefore, it is suggested that
besides to the usual acid soil management and/or recla-
Figure 6. Soil acidity category and its coverage across three
land use types of Tsegede highlands. VSA = Very strong
acidic; SA = Strongly acidic; MA = Moderately acidic; SLA
= Slightly acidic.
mation practices, introducing appropriate land use and
management practices are of paramount importance in
order to prevent the development and reduce the impact
of soil acidity.
5. Acknowledgements
This work was supported by grants of the Rural Capacity
Building Project of Ethiopia for which it is acknow-
ledged. We also would like to thank the Tigray Agricul-
tural Research Institute for providing us the necessary
resource, particularly laboratory facilities and services,
required to conduct the study.
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