Open Journal of Soil Science, 2012, 2, 33-43
http://dx.doi.org/10.4236/ojss.2012.21006 Published Online March 2012 (http://www.SciRP.org/journal/ojss)
33
Assessment of Variability in the Quality of an Acrisol
under Different Land Use Systems in Ghana
Emmanuel Osadu Ghartey, Gabriel N. N. Dowuona*, Eric K. Nartey, Thomas A. Adjadeh,
Innocent Y. D. Lawson
Department of Soil Science, School of Agriculture, University of Ghana, Legon, Ghana.
Received November 10th, 2011; revised December 20th, 2011; accepted December 30th, 2011
ABSTRACT
Three land use types (natural fallow, Leucaena leucocephala woodlot and cultivated plots) on a Ferric Acrisol in a
semi-arid tropical zone of Ghana were compared to assess their effects on variability in selected soil properties and
plant biomass accumulation. Organic carbon accumulation in the representative natural fallow profile was 22.7 g/kg,
followed by 16.5 g/kg for the Leucaena woodlot and lastly 11.8 g/kg for the cultivated site. The mean bulk density of
the natural fallow, Leucaena woodlot and cultivated sites were from 1.36 Mg/m3, 0.92 Mg/m3 and 1.33 Mg/m3 with
corresponding range in mean weight diameter of 0.5 mm - 1.2 mm, 0.6 mm - 1.2 mm and 1.0 mm - 1.2 mm, respec-
tively. The lower bulk density observed for the woodlot corresponds to increased total porosity, aeration, and root pro-
liferation due to the stronger and extensive rooting system. Significant differences (P < 0.05) in bulk density, mean
weight diameter (MWD), clay content, organic carbon and total nitrogen existed among the land use types. Variability
in pH and bulk density of the surface soils was less than 15%, in the three land use types. Generally, clay content and
exchangeable Na recorded the highest variability (≥36%). For the surface soils, exchangeable Na was very variable in
the natural fallow. Exchangeable Na, Ca and K and total nitrogen were very variable in the Leucaena woodlot and the
cultivated sites. Variability in clay content was very high in the cultivated soils only. The order cultivated land > Leu-
caena woodlot > natural fallow was noted for properties with high variability (CV ≥ 36%). Plant biomass accumulation
was 1834 kg/ha (natural fallow) and 830 kg/ha (Leucaena woodlot) indicating that natural fallows do not only maintain
soil quality but they also decrease variability in soil properties which is desirable for soil productivity and quality.
Keywords: Aggregate Stability; Bulk Density; Land Use; Mean Weight Diameter; Soil; Organic Carbon;
Soil Variability; Woodlot
1. Introduction
Soils are characterized by a high degree of variability due
to the interplay of physical, chemical, biological and an-
thropogenic processes that operate with different intensi-
ties and at different scales [1]. These processes in turn in-
fluence the nature and properties of soils. Therefore, know-
ledge of soil properties is important in determining the
best use to which a soil may be put [2]. Conversion of a
native land use system to an agricultural system may cause
drastic changes in the soil properties. These changes,
either upgrading, sustaining, or degrading are dependent
on land use as well as management practices. Also, some
soil physical and chemical properties are adversely af-
fected by the conversion of a particular land use system
to another. For example, bulk density tends to increase
significantly while plant available water capacity de-
creases in cultivated soils due to limited rooting system
and increased biological activities [3].
Acrisols, which are low activity clay soils, are the most
cultivated and dominant soils in the coastal savanna zone
of Ghana [4]. The organic matter content of some of these
soils tends to decline rapidly under continuous cultiva-
tion [5]. Linked with the loss of soil organic matter, is the
decrease in some soil nutrients such as nitrogen and phos-
phorus. In this respect, most land use systems in Sub-Sa-
haran Africa can be described as unsustainable, owing to
low nutrient resources and negative nutrient budgets [6].
Various land management systems have been proposed
to address the low nutrient levels in tropical soils. Agro-
forestry, a land use system which utilizes perennial woody
leguminous tree species to produce biomass and recycle
nutrients, is among the methods proposed for the impro-
vement and maintenance of soil quality [7-9] apart from
other traditional practices such as manuring, cover crop-
ping, mulching and shifting cultivation [10]. Evidences
*Corresponding author.

Assessment of Variability in the Quality of an Acrisol under Different Land Use Systems in Ghana
34
from research indicate that agroforestry has beneficial
effects on the physico-chemical properties of soils [11,12].
For example, soil organic carbon content of 25.6 g/kg
was reported for a Ferric Acrisol under an 8-year-old
Leucaena leucocephala woodlot compared to 15.6 g/kg
for similar adjacent soil under a Chromolaena odorata
fallow [7].
For most natural environments such as soils, it is known
that quantitatively soil properties within a site on the land-
scape are relatively similar. It is noted that spatial char-
acterization of soil properties is necessary in order to lo-
cate homogenous areas to be carefully managed for agri-
cultural sustainable development [13-15]. In this regard,
the major problems are how to identify some of the fac-
tors which influence variations in soil properties and use
this knowledge to design agricultural management prac-
tices that would be both environment friendly and highly
productive. Thus, full characterization of soils requires
the exploration of soil properties at different depths for
proper management of water and nutrient in the root zone
and in a broader perspective, for modelling of environ-
mental processes. This could provide relevant informa-
tion on patterns of nutrient accumulation and redistribu-
tion at both surface and deeper layers of the soil, as well
as the rate of net losses.
In some studies conducted on soil characterization, spa-
tial variations in soil properties were not addressed [7]. It
is worthy of note that information on variability in phys-
ico-chemical properties of soils under different land use
systems in Ghana is limited [16]. It is therefore impera-
tive that the gaps and inconsistencies in knowledge are
bridged if the productive capacities of soils are to be im-
proved. Towards this end, the objectives of this research
were to examine the extent to which different land use
systems influence some selected soil properties and their
variability in an Acrisol in the coastal savanna zone of
Ghana, and determine whether the rate of biomass turn-
over in the soils varies significantly under a natural fal-
low system and a Leucaena leucocephala woodlot.
2. Materials and Methods
2.1. Site Characteristics, Soils and Sampling
The study was conducted at a site located within the coas-
tal savanna zone of Ghana (Figure 1). Mean total annual
rainfall is about 800 mm and is bi-modally distributed.
The mean annual temperature is about 27˚C with vegeta-
tion consisting of scattered trees and grasses. The soil
(Ferric Acrisol) is a sandy loam derived from weathered
tertiary sands [17] and is among the dominantly culti-
vated soils in this part of the semi-arid tropics. Morpho-
logically, the soil is well drained and its colour varies
from red to brown.
Figure 1. Map of Ghana showing the location of the study site.

Assessment of Variability in the Quality of an Acrisol under Different Land Use Systems in Ghana 35
Three land use systems all situated on the same soil
were selected. These were 1) an over 60-year-old natural
fallow site with indigenous plant species and a soil sur-
face covered by a fairly thick layer of residue of leaves
and twigs; 2) an adjacent plot with a history of continu-
ous cultivation using conventional methods of farming
for more than five decades; and 3) a 20-year-old Leu-
caena leucocephala woodlot adjacent to the cultivated
field but originally cultivated before its conversion to a
woodlot for the collection of fuel wood (firewood); the
surface was covered with a thin layer of leaf litter. One
representative profile was dug on each land use system
and characterized. A grid plot (10 m by 10 m) was de-
marcated on each land use system and samples from the
0 - 20 cm depth were collected at 2 m along the vertical
and horizontal axes.
2.2. Laboratory and Field Investigations
Selected soil properties analyzed included particle size
distribution, bulk density, aggregate stability, pH, orga-
nic carbon, exchangeable bases and acidity, total nitrogen,
and available phosphorus. Data on plant biomass were
also collected in the field while mineralogical composi-
tion of clay fraction of the soil profile was determined.
The modified hydrometer method [18] was used to
measure particle size distribution; while the clod method
[19] was employed in the determination of bulk density.
Aggregate stability was estimated by the dry sieving me-
thod of Kemper and Rosenau [20] followed by calcula-
tion of the mean weight diameter (MWD) of each aggre-
gate [21]. Soil pH (1:1, soil:water and soil:0.01 M CaCl2)
was measured using a Pancitronic MV 88 pH glass elec-
trometer. The dry combustion method involving the use
of the Carbon Analyzer (Eltra CS 500 Carbonator) was
employed in the determination of organic carbon. Ex-
changeable bases were determined by extraction with 1
M ammonium acetate (NH4OAc, pH 7) followed by ana-
lyses for Ca and Mg by atomic absorption spectrometry
and Na and K by flame photometry. Exchange acidity
was determined using the KCl extraction method [22].
Total nitrogen was determined by the acid digestion Kjel-
dahl method [23] whereas available phosphorus was de-
termined by the method of Bray and Kurtz [24]. Minera-
logical composition of the clay fraction of selected pro-
file samples was determined by x-ray diffraction (CuKα)
at the Laboratory of Department of Mineralogy, Natural
History Museum, London, U.K.
Total biomass accumulation for each treatment was
determined to ascertain the contribution of plant litter to
organic carbon accumulation and distribution. Litter fall
from the native forest and woodlot plots was collected
periodically for a two-month interval on three different
occasions using 5 randomly placed 1 m × 1 m quadrants
at each site. The amount of plant material including leaves
and twigs collected at each respective site was weighed
and biomass accumulation on a hectare basis was calcu-
lated as:


 
Biomassweight of litter
100 m100 marea of litter box

 (1)
Data were not collected for the cultivated site because
of the regular removal of vegetation during tillage in the
cropping season and bush burning in the dry season.
2.3. Variability in Soil Properties
Coefficient of variation (CV) was used to estimate the
extent of variability in soil properties within each land
use system. This was calculated as:


CV%sz100 (2)
where s is the standard deviation and z is the mean of
population sample (36 samples for each study site). Ana-
lysis of variance using the GenStat software package (ver-
sion 9.0) was employed to assess significance of variabi-
lity among the land use systems. The LSD procedure was
conducted to compare the means of the soil properties at
a probability level of 0.05.
3. Results and Discussion
3.1. Morphological Characteristics
All the three pedons under the natural fallow (NF), wood-
lot (WL) and cultivated land (CL) showed similar char-
acteristics. They are well drained with surface granular
structure, which changes to columnar below the surface
and then breaks into strong angular blocky in the rest of
the subsoil and subangular blocky in the C horizons. The
granular structures were moderately finer in the surface
horizons of the cultivated site than in the forest and wood-
lot soils. The horizon boundary of the NF was clear and
smooth, abrupt and smooth for WL and wavy for the CL.
The wavy boundary of the surface horizons in the CL
pedon could be due to the influence of tillage; ploughing
could result in mixing and redistribution of soil particles
whereas the clear smooth boundary of the horizons of the
forest and woodlot pedons indicated less intense distur-
bance. Distinct horizons coupled with the morphological
features reflect advanced degree of profile development.
The NF pedon generally had slightly hard and friable con-
sistence, which became sticky, firm to very hard with
depth. For the WL pedon, the consistency was slightly
hard and friable becoming sticky and moderately hard with
depth. In the CL pedon, consistency was very firm at the
surface changing to sticky and hard and firm with depth.
The colour of the soil was generally dominated by red-
dish brown to bright reddish hues in all profiles. Soil co-
lour in the profiles at the natural fallow, woodlot and the
cultivated sites was generally dominated by reddish brown

Assessment of Variability in the Quality of an Acrisol under Different Land Use Systems in Ghana
36
to bright reddish hues except for the A1 horizon (forest
fallow) and A horizons (woodlot soil), which were sli-
ghtly darker, apparently due to the greater amounts of
organic matter in the horizons. Mineralogical analysis
showed that kaolinite is the dominant clay mineral with
traces of goethite and haematite. It is therefore apparent
that the reddish colours of the soils are from these two
Fe-bearing minerals, which also suggest oxidizing condi-
tions and good drainage due to the upland site of this soil.
Furthermore, the presence of the iron oxide concretions
in the subsoil (C horizon) of the profiles might have im-
parted the reddish colour to the soil during profile forma-
tion and development. The most important influence of
Fe and Al oxides in soils is increased P and micronutrient
adsorption capacity, resulting in decreased nutrient avai-
lability to plants [25]. These oxides also influence soil phy-
sical properties by stabilizing soil aggregates, in which
the stable aggregates are heavily coated with them [26].
3.2. Physical Properties
Analytical data on selected soil physical properties in the
three respective land use systems are provided in Table 1.
The texture of the soils was generally sandy clay in the
surface horizon and clayey in the B and C horizons. In
pedon NF, the clay content increased from 37.5% in the
A1 horizon to 55% in the C2 horizon. Conversely, sand
content decreased from 54.8% in the A2 horizon to
36.5% in the C2 horizon. In pedon WL, clay content in-
creased from 35% in the A1 horizon to 50% in the Bt
horizon and then increased to 55% in the C2 horizon
while the sand content decreased from 55.9% in the A1
horizon to 42.9% in the Btn horizon and then dropped to
35.8% in the C2 horizon. In pedon CL, the clay content
increased from 33.0% in the Ap1 horizon to 58% in the
Btn and C2 horizons whereas the sand content decreased
from 57.8% in the Ap1 horizon to 35.5% in the C2 hori-
zon. The mean clay content for the grid samples were
29.7%, 32.3% and 39.5% for the NF, WL and the CL
sites, respectively (Table 2).
For the profile samples, it is apparent that an inverse
relationship exists between the amounts of sand and clay
in the soils. Marked increases in the amounts of clay oc-
curred with depth in the B horizon whiles the amount of
sand decreased with depth down (Figure 2) indicating
Table 1. Selected physical properties of the pedon under natural fallow.
Horizon Depth BD† MWD‡ Particle size distribution Texture
(cm) (Mg/m3) (mm) sand silt clay
Natural fallow site
A1 0 - 7 1.13 1.1 43.8 18.7 37.5 sandy clay
A2 7 - 24 1.27 0.9 54.8 11.5 37.5 sandy clay
Btn1 24 - 51 1.41 1.2 51.0 5.2 40.0 sandy clay
Btn2 51 - 96 1.45 1.1 38.5 6.5 55.0 clay
C1 96 - 150 1.54 0.5 39.0 8.0 53.0 clay
C2 150 - 200 1.54 1.3 36.3 8.7 55.0 clay
Woodlot site
A1 0 - 7 1.04 0.8 55.9 9.1 35.0 sandy clay
A2 7 - 27 1.30 1.2 54.3 5.7 40.0 sandy clay
Btn1 27 - 60 1.37 0.9 43.1 6.9 50.0 sandy clay
Btn2 60 - 120 1.50 0.6 42.9 7.1 50.0 clay
C1 120 - 150 1.30 1.0 39.1 5.9 55.0 clay
C2 150 - 200 1.18 1.2 35.8 9.2 55.0 clay
Cultivated site
Ap1 0 - 6 1.22 1.2 57.8 9.2 33.0 sandy clay
Ap2 6 - 21 1.50 1.0 59.8 7.2 33.0 sandy clay
Btn1 21 - 5 1.57 1.0 34.6 7.4 58.0 sandy clay
Btn2 56 - 101 1.70 1.1 34.5 7.5 58.0 clay
C1 101 - 139 1.73 1.1 36.8 8.2 55.0 clay
C2 139 - 200 1.74 1.1 35.5 6.5 58.0 clay
†BD = bulk density; ‡MWD = mean weight diameter.

Assessment of Variability in the Quality of an Acrisol under Different Land Use Systems in Ghana 37
Table 2. Mean values of soil properties (n = 36; at 0 - 20 cm
depth) under different land use systems.
Land use systems†
Soil property Natural fallow Woodlot Cultivated
Bulk density (Mg/m3) 1.36 ± 0.04 0.92 ± 0.05 1.33 ± 0.04
MWD (mm) 1.00 ± 0.02 0.88 ± 0.03 1.11 ± 0.03
% Clay 29.7 ± 0.4 32.3 ± 0.8 39.5 ± 0.8
pH (H2O) 5.81 ± 0.03 5.67 ± 0.04 5.59 ± 0.05
pH (CaCl2) 5.25 ± 0.03 5.11 ± 0.04 5.15 ± 0.03
Organic carbon (g/kg) 16.2 ± 0.4 11.4 ± 0.3 8.6 ± 0.2
Total nitrogen (g/kg) 1.13 ± 0.04 0.50 ± 0.04 0.65 ± 0.05
Available P (mg/kg) 7.46 ± 0.26 6.62 ± 0.28 8.17 ± 0.41
Exch. Ca (cmol/kg) 1.33 ± 0.07 0.70 ± 0.06 1.88 ± 0.14
Exch. Mg (cmol/kg) 1.33 ± 0.05 0.63 ± 0.03 1.03 ± 0.05
Exch. Na (cmol/kg) 0.29 ± 0.02 0.12 ± 0.01 0.16 ± 0.01
Exch. K (cmol/kg) 0.50 ± 0.03 0.50 ± 0.04 0.43 ± 0.03
† = data are mean values ± standard error.
Figure 2. Distribution of clay and sand as a function of dep-
th in the profiles under the natural fallow, woodlot and cul-
tivated soil.
clay enrichment and sand depletion in all three pedons.
Furthermore, this trend indicated gradual breakdown of
sand size materials to finer sizes. The high clay accumu-
lation in the B horizon of all the three pedons might be
indicative of clay movement from the horizon above it.
The clay enrichment in the B horizon resulted in the for-
mation of an argillic horizon in all the pedons. Similar
results were reported by Dowuona [27] and Eze [28] for
similar soils in the study area. Occurrence of illuviated
clays might relate to presence of plant roots in the soils.
Plant roots were found mainly in the surface layer from
(0 - 40 cm) with fewer roots below the 40 cm depth. As
noted by some authors elsewhere [29], this is an indica-
tion of the presence of illuviated clays in the Bt horizon.
The fairly similar texture of the soils at the three sites
indicates uniformity with regard to soil development.
Generally, the A horizons of all the soils showed a
lower bulk density than the B horizons. The bulk density
of the natural fallow (NF) ranged from 1.13 Mg/m3 in the
A1 horizon to 1.54 Mg/m3 in the C2 horizon (Table 1).
In the woodlot pedon, bulk density varied from 1.04
Mg/m3 in the A1 horizon to 1.50 Mg/m3 in the B2
whereas the values ranged from 1.22 Mg/m3 in the Ap1
horizon to 1.74 Mg/m3 in C2 horizon of CL pedon. Bulk
density values were 1.33 ± 0.04 Mg/m3, 0.92 0.05 Mg/m3
and 1.36 ± 0.04 Mg/m3 for the surface (0 - 20 cm) soils at
the cultivated, woodlot and natural fallow sites, respec-
tively (Table 3). Statistical analyses indicated significant
differences (0.05 level of probability) for bulk density
values of the grid (surface) samples of the different land
use systems.
Table 3. Analysis of variance of the soil properties.
Land use systems
Soil property (5%) Natural Fallow† Woodlot† Cultivate†LSD
Bulk density (Mg/m3) 1.36a 0.92b 1.33a 0.12
MWD (mm) 1.00b 0.88c 1.11a 0.06
Clay (%) 29.65c 32.29b 39.51a 1.50
pH (H2O) 5.81a 5.67b 5.59b 0.12
pH (CaCl2) 5.25a 5.11b 5.15b 0.10
Organic carbon (g/kg) 16.15a 11.36b 8.63c 0.84
Total nitrogen (g/kg) 1.13a 0.50c 0.65b 0.12
Available P (mg/kg) 7.46ab 6.62b 8.17a 0.91
Exch. Ca (cmol/kg) 1.33b 0.70c 1.88a 0.27
Exch. Mg (cmol/kg) 1.33a 0.63c 1.03b 0.13
Exch. Na (cmol/kg) 0.29a 0.12c 0.16b 0.04
Exch. K (cmol/kg) 0.50a 0.50a 0.43a 0.09
†Means followed by the same letters are not significantly different (signifi-
cant differences at P < 0.05 in soil properties between land use types); num-
ber of samples = 36; at 0 - 20 cm depth.

Assessment of Variability in the Quality of an Acrisol under Different Land Use Systems in Ghana
38
The lower bulk density in the surface horizons could
be attributed to the relatively higher organic matter they
contained. Conversely, the higher bulk density observed
in the B horizons might be due to compaction and higher
clay content. Bulk densities are generally higher in dee-
per soil profiles probably as a result of compaction caused
by overlying layers, lower organic matter contents, less
aggregation and fewer roots as a result of root impedance
[30]. Generally, the relatively lower bulk density levels
in the NF and WL pedons were probably influenced by
the extensive rooting system of the native trees and Leu-
caena trees which also penetrated the subsoil. Presence
of many medium biopores is an indication of increased
biological activity which was common in the surface
layer of the natural fallow soils; the pores were dominant
in the woodlot but less prominent in the cropped soils.
The pores might have influenced the differences in the
bulk density and possibly total porosity of the soils under
the native, woodlot and the cropped soils.
The mean weight diameter (MWD) of aggregates ran-
ged from 0.5 mm to 1.3 mm for the NF pedon, 0.8 mm to
1.2 mm for the WL pedon and 1.0 mm to 1.2 mm for the
cultivated sites (Table 1). For the surface soils, the MWD
values values were of 1.0 ± 0.02 mm, 0.88 ± 0.03 mm
and 1.11 ± 0.03 mm, respectively, for the natural fallow,
woodlot and cultivated sites (Table 3). Significant dif-
ferences existed among the three land use systems. The
greater MWD value in the natural fallow relative to the
woodlot could be attributed to the cover provided by tree
canopy and binding action of plant roots. The relatively
larger soil aggregates at the cultivated site may be due to
campaction caused by continuous tillage. Chaudhary and
Sandhu [31] reported that variation in aggregate size
could be due to differences in texture and structure
brought about by tillage, compaction, cropping, and other
management events.
3.3. Chemical Properties
The pH (water) ranged from 5.3 to 6.5, indicative of sli-
ghtly acidic conditions (Table 4). The A horizons of the
Table 4. Selected chemical properties of the pedon under natural fallow.
Exchangeable bases
Horizon Depth pH† pH ΔpH OC† TN†Avail P†.Ca Mg K Na TEB† Al H ECEC†B.S†
(cm) (H2O) (CaCl2) --- g/kg --- (mg/kg)------------------------cmol/kg ---------------------------- (%)
Natural fallow site
A1 0 - 7 5.7 4.6 1.1 22.7 1.4 9.5 1.8 0.9 0.8 0.3 3.8 0.04 0.01 3.9 98.7
A2 7 - 24 5.6 4.8 0.7 12.4 1.2 5.1 0.6 0.8 0.3 0.4 2.1 0.09 0.03 2.2 94.6
Btn1 24 - 51 5.3 4.7 0.7 9.3 1.1 2.8 0.5 0.4 0.1 0.4 1.5 0.22 0.08 1.7 88.2
Btn2 51 - 96 5.6 4.5 1.1 8.3 0.9 2.7 0.5 0.4 0.1 0.5 1.5 0.50 0.04 2.0 73.5
C1 96 - 150 5.6 4.6 1.0 7.3 0.7 2.3 0.4 0.6 0.1 0.4 1.5 0.36 0.07 1.9 77.7
C2 150 - 200 5.8 4.4 1.4 6.6 0.8 1.7 0.4 0.2 0.1 0.3 1.0 0.54 0.08 1.6 61.7
Woodlot site
A1 0 - 7 5.6 5.0 0.6 16.5 1.3 8.8 0.6 1.1 0.9 0.3 3.0 0.04 0.02 3.0 97.9
A2 7 - 27 5.8 4.8 1.0 9.5 1.1 3.8 0.6 0.6 0.3 0.3 1.8 0.11 0.03 1.9 92.8
Btn1 27 - 60 5.9 4.8 1.1 6.0 0.7 2.7 0.8 0.5 0.3 0.5 1.9 0.24 0.05 2.2 86.8
Btn2 60 - 120 6.0 4.8 1.2 5.3 0.5 2.5 0.6 0.9 0.1 0.6 2.2 0.17 0.03 2.4 91.7
C1 120 - 150 6.0 4.5 1.5 4.0 0.4 1.4 0.5 0.6 0.1 0.3 1.5 0.43 0.04 2.0 76.1
C2 150 - 200 6.0 4.5 1.5 3.4 0.3 1.0 0.4 0.5 0.1 0.3 1.3 0.53 0.04 1.9 69.5
Cultivated site
Ap1 0 - 6 5.7 5.4 0.3 11.8 0.6 11.20.5 0.4 0.6 0.2 1.7 0.03 0.03 1.8 96.6
Ap2 6 - 21 6.0 4.9 1.0 8.5 0.8 4.1 0.8 0.7 0.2 0.2 1.9 0.05 0.02 2.0 96.4
Btn1 21 - 56 6.1 5.0 1.1 5.9 0.8 2.9 1.4 1.8 0.1 0.4 3.7 0.08 0.06 3.8 96.3
Btn2 56 - 101 6.4 5.3 1.1 4.7 0.7 2.0 1.3 1.7 0.1 0.6 3.7 0.10 0.02 3.8 96.8
C1 101 - 139 6.3 5.3 1.0 3.9 0.9 1.7 1.3 1.6 0.1 0.3 3.3 0.04 0.02 3.4 98.2
C2 139 - 200 6.5 4.9 1.6 3.8 0.8 0.7 1.1 1.6 0.1 0.3 3.1 0.19 0.04 3.3 93.1
†ΔpH = pH (H2O) − pH (CaCl2) [1:1]; Avail P. = available phosphorus; ECEC = effective cation exchange capacity; OC = Organic carbon; TN = total nitrogen;
TEB = total exchangeable bases; B.S = base saturation.

Assessment of Variability in the Quality of an Acrisol under Different Land Use Systems in Ghana 39
three pedons gave pH values that were nearly uniform. In
each profile, pH varied minimally. The change in pH va-
lues (ΔpH = pH water – pH CaCl2) was positive for all
three land use types, indicating a net negative charge on
the colloidal surfaces of the soil [32]. These pH levels
were similar to those reported in previous studies [27,28]
for similar soils elsewhere. Exchangeable bases in all the
pedons were very low (below 4 cmol/kg) with Ca and Mg
accounting for greater portion of exchange sites which
reflected the high base saturation. Effective cation ex-
change capacity is very low due the dominance of low
activity clays.
Organic carbon, total nitrogen and available phosphor-
rus contents were highest in the A horizon and then de-
creased with depth in all the three pedons except nitrogen
content in the cultivated soils (Figure 3). The NF profile
recorded the highest organic carbon content, which re-
duced from 22.7 g/kg in the A1 horizon to 6.6 g/kg in the
C2 horizon. In pedon WL, organic carbon varied from
16.5 g/kg in the A1 horizon to 3.4 g/kg in the C2 horizon.
Similarly, in pedon CL, organic carbon content reduced
from 11.8 g/kg in the Ap1 horizon to 3.8 g/kg in the C2.
The mean respective OC content for the surface samples
at the NF, WL and CL sites were 16.2 ± 0.4 g/kg, 11.4 ±
0.3 g/kg and 8.6 ± 0.2 g/kg (Table 2). The NF, WL and
CL sites had mean nitrogen contents of 1.13 ± 0.04 g/kg,
0.50 ± 0.04 g/kg and 0.65 ± 0.05 g/kg, respectively. It is
apparent that total nitrogen content of the natural fallow
soil was significantly higher than those of the woodlot
and cultivated sites. Changes in organic carbon and nitro-
gen contents among the different land use systems were
minimal in the subsoil of the pedons compared to the sur-
face soils, indicating that the surface soil layers was most
affected by different land use systems. Yifru and Taye
[33] noted higher nitrogen content in natural forest soils
than in cultivated soils in southeastern Ethiopia.
The differences may be attributed to losses from plant
uptake at the cultivated site and low build up under the
woodlot. Differences in OC content among the sites were
significant (Table 3). Available P content of the surface
soils (0 - 20 cm) varied from a mean value of 7.46 ± 0.26
mg/kg (NF), 6.62 ± 0.28 mg/kg (WL) and 8.17 ± 0.41
mg/kg (CL). The low levels of available P confirm the
inherent low P fertility status of the soil as noted in other
studies elsewhere [28].
3.4. Management-Induced Changes in
Soil Properties
As noted in the Sections 3.1 to 3.3, organic carbon, ag-
gregate stability and bulk density were the soil properties
which were responsive to land use change, especially in
the surface soils. Soil organic carbon (SOC) in the natu-
ral fallow soil was the highest followed by the woodlot
and the cultivated land. Generally, the trend in organic
carbon content was in the order NF > WL > CL (Figure
4). The highest SOC in the natural forest fallow might be
due to greater addition of organic materials to this soil.
Lower rate of accumulation due to continuous tillage
operation accounts for the relatively lower SOC at the
cultivated site. These observations are consistent with find-
ings of other studies elsewhere where greater SOC con-
tents were recorded in virgin or forest lands compared to
cultivated lands [33-36] possibly due to increased de-
composition and mineralization of organic materials [37].
Riezebos and Loerts [38] observed that clearing of fo-
rests for crop production invariably resulted in a loss of
soil organic matter because of the removal of large quan-
tities of biomass during land clearing, a reduction in the
quantity and quality of organic inputs added to the soil
and increased soil organic matter decomposition rates.
Figure 3. Changes in organic carbon, total nitrogen and
available phosphorus as a function of depth in the profiles
the under natural fallow, woodlot and cultivated soil.

Assessment of Variability in the Quality of an Acrisol under Different Land Use Systems in Ghana
40
Figure 4. Organic carbon distribution with depth in the pro-
files under the natural fallow, woodlot and cultivated soil.
Higher decomposition rates associated with these condi-
tions are due to enhanced biological activity caused by
soil mixing from tillage and higher temperatures from in-
creased soil exposure [39]. The reduction in organic car-
bon content was gradual in the cultivated and woodlot
soils as compared to that of the natural forest land. This
may be due to mixing up of soil in the surface by tillage
or the burrowing actions of soil fauna in the cultivated
and woodlot pedons.
The significantly high amount of total nitrogen (TN)
contents recorded for the NF pedon as opposed to the
WL pedon might be due to the higher biomass accumula-
tion in the surface horizons of the NF pedon. It is noted
elsewhere that total tree harvesting caused three-fold re-
moval of soil nutrients, including nitrogen, under con-
ventional tillage practices [40]. In addition to losses from
biomass removal, soil nutrients can also be lost from the
cultivated sites by increased soil nutrient immobilization
and leaching when little vegetation is present for nutrient
uptake [41].
The MWD interrelated well with organic carbon in all
the land use types (Table 3). The higher organic carbon
content of the natural fallow was associated with higher
aggregate stability. It therefore appears that the NF site
would be the most resistant to degradation and erosion.
Improvement in soil structure due to high organic carbon
content under L. leucocephala provided a favourable mi-
croclimate, which might enhance micro fauna activities,
thereby leading to soil water holding capacity enhance-
ment and nutrient recycling by beneficial biological or-
ganism. Also, the microclimate provided by the L. leu-
cocephala trees might have allowed other fauna to bur-
row into the soil and promoted good soil structures lead-
ing to better aeration and root development. The obser-
vations in this study are in conformity with the findings
of similar studies elsewhere [42-43].
The significant differences in organic matter among the
land use types could be due to the different levels of bio-
mass accretion. The relationship between organic matter,
bulk density level and soil structure could be moderated
by cultivation [44]. According to Seubert et al. [45] and
Allen [46] soil compaction from tillage practices often
results in a decline in macro-porosity, higher susceptibil-
ity to erosion, and decreased hydraulic conductivity [47].
It is therefore likely that the cultivated soils could be sub-
ject to these hazards in the long term leading to perma-
nent land degradation.
3.5. Plant Biomass Accumulation
Data on plant litter accumulation indicated that the natu-
ral fallow accumulated greater amount of plant litter (Ta-
ble 5). Biomass accumulation per hectare during the stu-
dy period on the natural fallow (5610 kg/ha) was more
than twice that of the woodlot (2560 kg/ha). On an an-
nual and area basis, the 1830 kg/ha biomass translates
into 11.22 tons of litter/ha/yr while the annual rate of
accumulation in the woodlot was 5.12 tons of litter/ha/yr.
These levels of litter accretion were comparable to those
recorded by Dowuona et al. [7] in some Acrisols else-
where in the coastal savanna zone of Ghana. Although
the quality of litter was not determined in this study,
Dowuona et al. [7] noted that C/N ratios of 5.1 to 6.6 for
Leucaena litter suggested a favourable decomposition of
organic material to increase soil organic matter content.
As noted by Lal [11], soil organic matter rejuvenates de-
graded soils, increases biomass production and reduces
the rate of enrichment of atmospheric CO2. It is, there-
fore likely that the natural fallow and woodlot land use
systems present sustainable options for maintaining soil
productivity.
3.6. Variability in Soil Properties
Data on calculated coefficient of variation are presented
in Table 6. The classification system of Wilding and
Drees [48] based on the relative values of the percent
coefficient of variability (% CV) was adopted to deter-
mine the extent of variability in selected soil properties
under the different land use types. The coefficient of va-
riation is dimensionless hence values from one parameter
to the others can be compared. A coefficient of variation
value of 0 - 15, 16 - 35, and ≥36 represents little (group
I), moderate (group II) and high variability (group III),
respectively.
Coefficient of variation, which is an approximation of
heterogeneity of the sampling site, was compared among
the three land use types. Majority of soil properties in the
natural fallow classified as groups I and II. For the wood-
lot, groups I, II and III were noticeable. In the cultivated

Assessment of Variability in the Quality of an Acrisol under Different Land Use Systems in Ghana 41
Table 5. Biomass accretion under the natural fallow and
woodlot land sites.
Land use Weight of plant litter collected† Biomass
P1 P2 P3
----------------(kg)----------------- (kg/ha)
Natural fallow (NF) 0.192 0.183 0.186 5610
Woodlot (WL) 0.089 0.082 0.085 2560
† = mean of 5 samples.
Table 6. Variation in soil properties (n = 36; at 0 - 20 cm
depth) within land use sy ste m s.
CV† group in land use systems
Soil property Natural Fallow Woodlot Cultivated
pH (H2O) I I I
pH (CaCl2) I I I
Organic carbon (g/kg) I II I
Total Nitrogen (g/kg) II III III
Available P (mg/kg) II II II
Exchangeable Ca (cmol/kg) II III III
Exchangeable Mg (cmol/kg) II II II
Exchangeable Na (cmol/kg) III III III
Exchangeable K (cmol/kg) II III III
Bulk density (Mg/m3) I I I
MWD (mm) I II II
% Clay II I III
†I = CV < 15%; II = CV 15% - 35%; III = CV ≥ 36%.
soils, however, groups II and III were more prominent. The
woodlot had four soil properties (total nitrogen, ex-
changeable Ca, exchangeable Na and exchangeable K)
that were very variable (group III). Lastly, five soil prop-
erties namely, total nitrogen, exchangeable Ca, ex-
changeable Na, exchangeable K, and clay content were
very variable (group III) at the cultivated site. It is ap-
parent that the natural fallow plot was more homogenous
than the other land use systems. Only exchangeable Na
was very vari- able (group III) in the natural fallow soil.
These results suggest that soils under the natural fal-
low showed improvements (or better fertility build-up)
and decrease in variability in soil properties. The large
variability in soil properties under the cultivated soil is
the result of disturbance from tillage and uptake by
plants.
4. Conclusion
Changes in land use type had significant effect on char-
acteristics of the soil studied. Variations in organic car-
bon, nitrogen, bulk density and aggregate stability among
different land use systems were minimal in the subsoil as
compared to the surface soil layer of all the pedons, in-
dicating the impact that the different land use practices
had on these properties. Cultivation caused decreases in
soil organic matter and aggregate stability and increase in
bulk density. Conversion of native lands to agricultural
systems may cause drastic changes in soil properties,
thereby inducing variability. This suggests the need for
sustainable cropping systems such as addition of organic
matter and crop residues and crop rotation to mitigate the
negative impact of cultivation. Agroforestry using fast
growing leguminous trees improves build of organic
matter and development of good soil structure. Natural
fallows do not only improve soil fertility but also de-
creases soil variability which is desirable for both practi-
cal and experimental agriculture. Cropping in between
forest trees may be a feasible and sustainable method of
improving crop production while conserving soil produc-
tivity.
5. Acknowledgements
The authors wish to thank the Technical staff at the De-
partment of Soil Science and the Ecological Laboratory,
University of Ghana for the assistance during the labora-
tory investigations. We are grateful to Dr. Bill Dubbin,
Department of Mineralogy, Natural History Museum,
London, U.K., for the support in mineralogical analyses
of selected soil samples in their Laboratory.
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