Vol.2, No.3, 357-363 (2011)
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
Agricultural Scienc es
Effects of level soil bunds and stone bunds on soil
properties and its implications for crop production: the
case of Bokole watershed, Dawuro zone, Southern
Kebede Wolka1, A wdenegest Moges2, Fantaw Yimer1
1Wondo Genet College of Forestry and Natural Resources, Hawassa University, Shashemene, Ethiopia; Corresponding Author:
kebedewolka@gmail.com; fantawyimer2003@yahoo.com
2Biosystems and Environmental Engineering Department, Hawassa University, Shashemene, Ethiopia; Corresponding Author:
Received 23 March 2011; revised 21 May 2011; accepted 31 July 2011.
Level soil bunds (LSB) and stone bunds (SB)
have been widely implemented in the Bokole
watershed since 2000 through support of the
World Food Program (WFP). However, the per-
formance of them against the target of the
structure has not been studied. This study ana-
lyzed the effects of LSB and SB on selected soil
properties, when compared with nonterraced
cropland. The Bokole watershed was divided
into two units. From upper watershed, three
croplands with LSB (aged 4, 6, and 9 years) and
three nonterraced croplands each adjacent to
one of the LSB were selected. Similarly, in lower
watershed, SB aged 4, 6, and 8 years and three
nonterraced croplands each adjacent to one of
the SB were selected. From each cropland with
LSB and SB, three composite soil samples (rep-
licates) were collected systematically in X de-
signed rectangular plot. From each nonterraced
cropland, three composite soil samples (repli-
cates) were collected in X designed square plot.
A total of 36 soil samples were analyzed for Soil
Organic Carbon (SOC), Total Nitrogen (TN),
Available Phosphorus (AP), Available Potas-
sium (AK), pH, and Cation Exchange Capacity
(CEC) following standard laboratory procedures.
Most soil parameters were not significantly dif-
ferent in cropland with LSB and SB comp ared to
nonterraced. However, in LSB aged 4 years and
SB aged 6 years AP and pH were significantly
less than their adjacent-nonterraced cropland.
In SB aged 8 years, SOC, AP, AK, and pH were
also significantly less than adjacent-nonter-
raced cropland. Past erosion, and past land
uses are likely factors contributed to the ob-
served result. It was inferred that the mean con-
tribution of LSB and SB alone for crop produc-
tion with regard to analy zed so il p a rameters was
not significant in the considered sites. Addi-
tional soil fertility management practices should
be incorporated for bett er effect.
Keywords: Crop Yield; Level Soil Bund;
Nonterraced; Soil Fertility; Stone Bund; Water
Erosion; Watershed
Human activity, such as conversion of forests to agri-
cultural land, increased cultivation of marginal land,
overgrazing, and low-input or fertility-mining methods
of subsistence agriculture practiced on marginal lands
with steep gradients; accelerate soil erosion [1-3]. The
sorting action of erosion removes large proportions of
the clay and humus from soil, leaving behind the less
productive coarse sand, gravel, and in some case even
stones, impairing the quality of the remaining topsoil [4-
8]. The removal of this organic matter affects soil prop-
erties including texture, structure, nutrient availability
and biological activity [5,6] and makes soil more sus-
ceptible to further erosion as its aggregates becomes less
stable [9] thus, negatively affecting crop production [1,
8-11]. In Ethiopia, measurements from experimental
plots and micro-watersheds showed the annual soil loss
from croplands is about 42 t·ha–1·year–1 [12]. As a con-
sequence, the productive capacity of Ethiopia’s highland
soils is being reduced at an annual rate of 2% - 3%,
which certainly contributes to a higher vulnerability to
K. Wolka et al. / Agricultural Science 2 (2011) 357-363
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
famine [13].
In the agricultural production system of the Ethiopian
highlands, it is not possible to maintain year-round
vegetation cover under given ecological, economic, and
social circumstances [8,14]. According to these re- sear-
chers, structures such as the stone bunds are an indis-
pensable component of soil and water conservation
(SWC) measures for the control of erosion. It was also
reported that plots with stone bunds are more productive
than those without such technologies in semi-arid areas.
This is apparently due to the moisture conserving bene-
fits of this technology being critical in drier areas [15].
Climate change, which alters precipitation patterns and
intensities, is believed to substantially increase the risk
of runoff, soil erosion, drought and other environmental
problems. SWC measures such as soil bunds and stone
bunds are adaptation options to mitigate the problems
caused by climate change [16].
Since 2000 [17], government and nongovernment or-
ganizations such as World Food Programme (WFP) have
been promoting agricultural production through envi-
ronmental rehabilitation in the degraded Bokole water-
shed. Construction of level soil bunds and stone bunds
have been the major program activities on the watershed
croplands [17]. But the long-term effects of those inter-
ventions on production have not been investigated. This
Figure 1. Location of the study site.
K. Wolka et al. / Agricultural Science 2 (2011) 357-363
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
study assessed the effects of Level Soil Bund (LSB) and
Stone Bund (SB) on selected physical and chemical
properties of soil.
2.1. Description of the Study Area
The study area is situated in Southern Nations, Na-
tionalities and Peoples Regional State (SNNPRS) of
Ethiopia at Dawuro zone, Loma woreda. Geographically,
it lies between 6˚55N and 7˚0130N latitude and 37˚15
E and 37˚19E longitude. It is at about 470 km in south
west of Addis Ababa, the capital of Ethiopia. The study
area topography is undulating and rugged (Figure 2).
The watershed drains to the Omo River.
The study area lies between 1160 and 2300 m above
sea level and receives 1400 mm - 1600 mm rainfall an-
nually. The mean temperature ranges from 15.1˚C to
27.5˚C [18]. The soil is grouped as Orthic Acrisols [18].
Mixed agriculture is the major economic activity in this
watershed. The population of Bokole watershed is
11,798 (of which 3832 reside in the upper watershed and
7936 in the lower watershed) [19].
2.2. Methodology
Before soil sampling, two group discussions were
conducted (one in upper watershed and the other in
lower watershed, each comprises 10 farmers) with pur-
posively selected farmers from different part of the wa-
tershed on effect of LSB and SB on soil properties. Indi-
vidual farmers from whose land soil samples collected
were thoroughly interviewed on observed changes as
result of LSB and SB. Soil samples were collected from
purposively selected croplands/plot with LSBs (aged 4, 6
and 9 years), SBs (aged 4, 6, and 8 years) and nonter-
raced (adjacent to each LSB and SB). The specific sam-
pling sites were selected based on criteria: closeness of
treated and nonterraced croplands (not too far from each
other) [11]; age of the structure (4 - 9 years); number of
inter-structure plots per treated cropland (more than or
equal to 5); similarity of treated and adjacent-nonter-
Figure 2. Partial view of the topography of the study site; Up-
per watershed (a) and lower watershed (b).
raced croplands in certain management and natural set
up. Croplands with LSBs were selected from upper wa-
tershed whereas croplands with SBs were selected from
lower watershed because of the structures dominance.
All the selected croplands have been under farmer man-
The sampling plots in LSB and SB were replicated
three times systematically: the first, third and fifth plots
(inter-structure area) in between two successive LSB and
SB were selected in each treated cropland. From each
sampling plot, a composite sample from the four corners
and one at the center of an X designed rectangular plot
were taken. The X designed rectangular plot has two
sides along the contour with length of 15m each and
adjusted at 1.5 m away from LSBs and SBs [20]. By
repeating those procedures on all the selected croplands
with LSB and SB, a total of 18 composite samples (2
types of structures (LSB and SB) × 3 croplands treated
with each type of structures × 3 inter-structure area or
plot from each LSB and SB) were collected using auger
from depth of 0 - 20 cm.
From nonterraced croplands, three composite sam-
ples—replicates (from upper, middle and lower slope
position within the field) were collected from 15 m × 15
m X designed square plot. By repeating this procedures
18 (2 part of watershed that is upper and lower × 3 crop-
lands in each part of the watershed × 3 sample per crop-
land) were taken using auger at 0 - 20 cm depth.
Each time after sampling (from treated and non-ter-
raced), soil clods in samples was thoroughly broken to
make a uniform mix in clean plastic bucket. The sample
was divided in to four equal parts from which two di-
agonal parts were retained and other two removed. This
was continued until sufficient sample was retained in the
field. Samples were air dried at room temperature, ho-
mogenized and passed through a 2 mm sieve. Soil tex-
ture, Soil Organic Carbon (SOC), Total Nitrogen (TN),
Available Phosphorus (AP), Available Potassium (AK),
Soil pH (pH), and Cation Exchange Capacity (CEC) of
the prepared samples were analyzed following standard
laboratory procedure at City Government of Addis
Ababa Environmental Protection Authority. T-tests were
used to compare soil properties variation [21].
3.1. Soil Physical and Chemical Properties
The silt and clay fractions showed significant differ-
ence (P < 0.05) in croplands under LSB aged 6 year
when compared with adjacent-nonterraced croplands
while the LSBs aged 4 and 9 year was showed no sig-
nificant difference in any fractions compared to adja-
cent-nonterraced cropland (Table 1). In the SB aged 4
K. Wolka et al. / Agricultural Science 2 (2011) 357-363
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
Table 1. Mean values (± SEM) of sand, silt and clay fractions of topsoil (0 - 20 cm) from croplands with LSB aged 4, 6, and 9 years
and the respective adjacent-nonterraced (NTU) at the upper watershed (n = 3).
Soil texture LSB-4 year NTU-1 P-value LSB-6 yearNTU-2 P-valueLSB-9 year NTU-3 P-value
Sand (%) 47.17 ± 0.75 43.83 ± 1.89 0.132 47.17 ± 1.7647.83 ± 1.6 0.785 46.00 ± 2.7 47.8 ± 3.000.659
Silt (%) 17.17 ± 0.60 18.67 ± 0.80 0.166 25.67 ± 1.8019.33 + 0.95 0.011* 18.00 ± 1.00 18.17 ± 0.980.908
Clay (%) 35.67 ± 0.56 37.50 ± 1.31 0.227 27.17 ± 1.4532.83 ± 1.72 0.030* 36.00 ± 2.58 34.00 ± 2.130.563
Textural Classes Sandy clay Clay loam Sandy clay
loam Sandy clay loam Sandy clay Sandy
clay loam
*denotes significantly different values from each other at P < 0.05 by 2-tailed t-test
Table 2. Mean values (±SEM) of sand, silt and clay fractions of topsoil (0 - 20 cm) croplands with SB aged 4, 6, and 8 years and the
respective adjacent-nonterraced (NTL) at the lower watershed (n = 3).
Soil texture SB-4 year NTL-1 P-valueSB-6 year NTL- 2 P-valueSB- 8 year NTL- 3 P-value
Sand (%) 55.67 ± 1.31 59.67 ± 1.43 0.066 49.17 ± 1.4053.50 ± 1.630.071 48.67 ± 2.12 47.83 ± 1.64 0.763
Silt (%) 14.00 ± 1.39 16.83 ± 0.60 0.091 20.33 ± 0.6717.33 ± 0.950.028*23.67 ± 1.61 23.33 ± 1.20 0.871
Clay (%) 30.33 ± 1.10 23.50 ± 1.34 0.003*30.5 ± 1.1829.17 ± 1.510.503 27.67 ± 0.95 28.83 ± 1.05 0.429
Textural Classes Sandy clay loam Sandy clay loam Sandy clay
Sandy clay
loam Sandy clay
loam Sandy clay loam
*denotes significantly different values from each other at P < 0.05 by 2-tailed t-test
Table 3. Mean values (± SEM) of SOC, TN, AP, AK, pH, and CEC of topsoil (0 - 20 cm) croplands with LSB aged 4, 6, and 9 years
and the respective adjacent-nonterraced (NTU) at the upper watershed (n = 3).
Soil parameters LSB-4 yearNTU-1 P-valueLSB-6 yearNTU-2 P-valueLSB-9 year NTU-3 P-value
SOC (%) 1.23 ± 0.151.32 ± 0.23 0.736 1.41 ± 0.281.18 ± 0.110.4631.57 ± 0.27 1.68 ± 0.15 0.715
TN (%) 0.11 ± 0.020.07 ± 0.02 0.275 0.21 ± 0.130.12 ± 0.040.5150.08 ± 0.02 0.17 ± 0.06 0.138
AP (ppm) 12.04 ± 0.5616.87 ± 1.94 0.037*5.86 ± 0.953.94 ± 1.660.13110.5 ± 2.70 5.68 ± 0.39 0.105
AK cmol (+)/kg soil) 0.15 ± 0.0030.21 ± 0.04 0.138 0.23 ± 0.060.31 ± 0.130.6000.20 ± 0.06 0.14 ± 0.004 0.326
pH 5.26 ± 0.155.64 ± 0.04 0.034*5.87 ± 0.105.34 ± 0.230.0685.83 ± 0.07 5.93 ± 0.08 0.383
CEC cmol (+)/kg soil) 20.57 ± 2.6329.75 ± 3.48 0.062 17.16 ± 2.1021.27 ± 4.030.38016.75 ± 1.57 18.33 ± 1.53 0.487
*denotes significantly different values from each other at P < 0.05 by 2-tailed t-test
Table 4. Mean values (± SEM) of SOC, TN, AP, AK, pH, and CEC of topsoil (0 - 20 cm) croplands with SB aged 4, 6, and 8 years
and the respective adjacent-nonterraced (NTL) at the lower watershed (n = 3).
Soil parameters SB-4 year NTL- 1 P-valueSB-6 year NTL-2 P-valueSB-8 year NTL-3 P-value
SOC (%) 1.57 ± 0.16 1.22 ± 0 .12 0.101 1.35 ± 0.141.10 ± 0.120.206 0.69 ± 0.11 1.01 ± 0.090.048*
TN (%) 0.28 ± 0.08 0.13 ± 0. 03 0.098 0.09 ± 0.060.06 ± 0.020.619 0.41 ± 0.13 0.26 ± 0.120.409
AP (ppm) 2.92 ± 0.65 4.41 ± 0.46 0.089 1.82 ± 0.137.33 ± 1.740.010*10.62 ± 1.71 27.48 ± 6.200.026*
AK cmol (+)/kg soil) 0.45 ± 0.08 0.44 ± 0.02 0.906 1.39 ± 0.300.83 ± 0.150.123 0.59 ± 0.29 1.61 ± 0.320.039*
pH 7.06 ± 0.0347.13 ± 0.02 0.090 6.34 ± 0.056.63 ± 0.0870.014*6.41 ± 0.08 6.64 ± 0.040.03*
CEC cmol (+)/kg soil) 25.70 ± 5.8521.80 ± 5.19 0.629 30.43 ± 4.4631.43 ± 3.520.864 31.57 ± 2.96 25.93 ± 6.850.468
*denotes significantly different values from each other at P < 0.05 by 2-tailed t-test
year, significantly greater clay content was observed as
compared to its adjacent-nonterraced cropland. Ta bles 3
and 4 shows result for soil chemical properties analysis.
4.1. Soil Properties in Croplands with SWC
Structures and Nonterraced
In the study site, SOC was generally less in soils of
the study area which might be due to the practices such
as intensive tillage, continuous cropping, removal of
crop residues, and low organic carbon input in croplands.
[20] mentioned that SOC values are typically low in the
Ethiopian highlands as a consequence of stubble grazing
and the absence of fallowing.
The soil and water conservation system of LSB and
SB reduce surface runoff and soil loss, retain water that
enhances crop growth and contributes to SOC input.
Despite these all benefits, in most comparison no sig-
nificant difference in SOC observed. Even it was sig-
nificantly low (P < 0.05) in SB aged 8 year compared to
adjacent-nonterraced. This result showed that type and
intensity of other land management practices that indi-
vidual farmers adapted in the past has also role in current
level of SOC. The report by [22] around the Mediterra-
K. Wolka et al. / Agricultural Science 2 (2011) 357-363
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
nean region indicated SOC significantly differ was not
agree with result of present study in that 50 years old
stone-walled terrace was compared to nonterraced.
AP was significantly high (P < 0.05) in nonterraced
croplands adjacent to LSB aged 4 year, SB aged 6 year
and SB aged 8 year. These were perhaps due to: the dif-
ference in the past land degradation resulting from con-
tinuous cultivation, extractive plant harvest and soil ero-
sion. Similar study by [23] in Anjeni watershed (Ethio-
pia) also showed that AP on nonterraced land was higher
than the terraced.
The relatively higher AK on nonterraced cropland ad-
jacent to SB aged 8 year was most likely because of the
difference in weathering process and past erosion. The
significantly low (P < 0.05) soil pH in LSB aged 4 year,
in SB aged 6 year and SB aged 8 year compared to the
respective adjacent-nonterraced cropland were probably
due to loss of relatively more basic cation resulted from
erosion before the structures built and did not restore yet
after the structures. Under a continuous cropping system
soil acidity increases due to the gradual replacement of
basic cations by aluminum [24]. Even though soil acidi-
fication is natural process involved in soil formation [7],
it is influenced by historic land use practice and subse-
quent soil erosion.
4.2. Relating Soil Analysis and Farmers’
The LSB and SB have been accepted and introduced
to reduce soil loss by creating barrier against surface
runoff and reducing slope length and gradient in the
long-term. Farmers in thorough group discussion indi-
cated that structures improved crop yield. Those farmers
whose land the soil sample were taken also perceived
that the structure has improved crop yield when com-
pared to previous situation. However, most of the se-
lected chemical properties in cropland with structures
were not significantly higher than adjacent nonterraced.
Even for AP, pH, SOC, and AK in some sites, they have
been significantly less than nonterraced cropland. This
can be explained by the fact that, on one hand, natural
resource experts recommend the structures when the
croplands become degraded. Farmers also initially ac-
cept the structure when the land gets relatively denuded
and thus it takes time for soil to restore in the pace of
less or no additional soil fertility management. Refer-
ence [25] stated adoption of the SWC technologies is
likely to increase, among other things, with recognition
of the erosion problem and slope gradient. The tradi-
tional diversion ditches that have commonly been con-
structed on nonterraced cropland to expel surface runoff
and to reduce erosion might also have contributed for
reduction of erosion and subsequent effect on nonter-
raced croplands. Past land use and management and past
erosion and deposition also determine the current prop-
erty of soil.
SWC structures are practically used as support for
agronomic and soil management [26] and considered as
the first defense line. Thus, they alone are less likely to
improve soil properties significantly under similar man-
agement to nonterraced. Reference [27] has reported that
combining stone rows barriers to run-off with the appli-
cation of compost was significantly controlled erosion
and reduced organic C and nutrient losses than compost
or stone row alone. Related experimental study in Burk-
ina Faso [24] showed that stone lines, five years after
laying, have a limited effect on soil fertility and a drop in
soil pH, organic C, N, and P concentrations were ob-
served. Similarly, experiment in Maybar research site of
Ethiopia [14] on level soil bund without any agronomic
or biological techniques showed decrease in production
during the first 3 - 5 years, which showed probably no
improvement in soil fertility.
SWC structures such as stone bund traps finer soil
particles that were eroded by rain water and tillage from
inter-structure area. Thus fertile soil remains on the
structure and nearby at upslope side. On hand it might be
partly due to this reason that eight years after construc-
tion of LSB showed significantly less in most analyzed
nutrient concentration for sampled plot (1.5 m away
from structure) when compared with nonterraced.
The in-depth interview and discussion in the present
study watershed revealed that the respondents have posi-
tive attitudes towards introduced SWC structures by ob-
serving mainly crop performance [28]. This could proba-
bly be due to the fact that crop performance is not only
function of soil fertility but also due to water availability,
which most likely improved by water retention ability of
structures as observed by farmers. The explanation by
[29] confirms that evaluating soil fertility by crop yield
alone is not fair because crop performance is a function
of many factors including soil nutrient (fertility) itself,
soil water availability, and weed competition
Even though farmers perceived some improvements
on cropland after construction of SWC structures by
using their own criteria, the standard soil laboratory
analysis from croplands with LSB and SB and nonter-
raced did not show remarkable difference for some pa-
rameters and even less for some sites. Thus, without
withstanding the contribution of structures in reducing
surface runoff and erosion which is partially the cones-
quences of climate change, it can be concluded that the
contribution of LSB and SB alone with regard to im-
K. Wolka et al. / Agricultural Science 2 (2011) 357-363
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
proving soil properties for crop production are not sig-
nificant compared to nonterraced cropland in the con-
sidered site. The perceived improvement in crop produc-
tion was most likely due to water retention ability of the
structures which contributes for adaptation of climate
It can be inferred that soil nutrient restoration for de-
graded land takes long time in the pace of continuous
cultivation and poor soil fertility management. It was
also suspected that most of soil along with nutrient
trapped by the structures deposited on the structure and
adjacent to it at distance range of 1.5 m in upslope area.
To make watershed management particularly LSB and
SB effective for attaining and sustaining food security in
smallholder farming, soil fertility management practices
such as use of crop residue and manuring are recom-
mended beside the structures in the study area. The role
and effectiveness of traditional diversion ditch, which
has commonly been practiced on nonterraced cropland,
in alleviating soil erosion should be studied.
The Center for Environment and Society project (at Hawassa Uni-
versity), Food for Work project (in SNNPRS, Agriculture and Rural
Development Bureau), and Wondo Genet College of Forestry and
Natural Resources, Hawassa University, are gratefully acknowledged
for the financial support.
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