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Trees, Forests and People 15 (2024) 100471
Available online 29 November 2023
2666-7193/© 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-
nc-nd/4.0/).
The impact of native trees, Cordia africana and Ficus sur, and the
economically valuable Manihot esculenta on soil chemical properties in an
agroforestry system
Hizkel Gotoro Gota
a
, Aklilu Bajigo Madalcho
a
,
b
,
*
, Belete Limani Kerse
a
, Jerzy Szwagrzyk
b
,
Tamirat Solomon
a
a
Department of Natural Resource Management, Wolaita Sodo University, Ethiopia
b
Department of Forest Biodiversity, University of Agriculture in Krakow, Poland
ARTICLE INFO
Keywords:
Agroforestry practices
Cassava crop
Elevation ranges
Native tree species
Soil properties
ABSTRACT
Native trees in agroforestry systems sustain soil properties by building up and recycling nutrients in a sustainable
manner. This manuscript aimed to assess the impact of different agroforestry species on soil chemical properties.
Soil samples were collected from within and outside the canopy zones of native tree species (Cordia africana,
Ficus sur) and a perennial tuber crop (Manihot esculenta) in agroforestry systems at three different elevations. The
results showed that, the soil chemical properties were signicantly better within the canopy zones of all agro-
forestry species compared to outside. However, there was insignicant difference in pH between the soil inside
and outside the canopy of Manihot esculenta. With a few exceptions, the evaluated soil chemical parameters
exhibited minimal variations between Cordia africana and Ficus sur. Interestingly, Manihot esculenta had the least
positive impact on soil chemical properties in the agroforestry system, indicating that native tree species enhance
soil chemical properties more effectively than the tuber crop. The inuence of agroforestry species on soil
chemical properties remained consistent across all elevation ranges, suggesting that elevation does not alter the
effects of agroforestry species on soil properties. In general, native trees, Cordia africana, and Ficus sur, positively
contribute to soil chemical properties, while Manihot esculenta has a negative impact, particularly on cation
exchange capacity, soil pH, and available potassium in comparison to the native tree species. These ndings
highlight the importance of using native tree species in agroforestry systems to promote healthy soil chemical
properties and enhance the resilience of forest ecosystems.
1. Background of the study
Agroforestry is an environmentally conscious approach to resource
and land management that involves the deliberate combination of trees
or shrubs with crops and/or pastures within a single area unit (Alao and
Shuaibu, 2013; Nair, 2013). The latest denition emphasizes that the
integration of these components can take place through a geographic
mixture or a temporal arrangement, leading to ecological and economic
interactions between the woody and non-woody elements (Leakey,
2017).
Agroforestry, a land-use approach gaining global popularity, offers
economic viability for environmental restoration and sustainable agri-
cultural development (Djalilov et al., 2016; Marques et al., 2022; Tomar
et al., 2021). Furthermore, it delivers a wide array of economic,
sociocultural, and environmental benets (Kumar, 2016; Kuyah et al.,
2017). From an environmental standpoint, agroforestry practices play a
signicant role in enhancing soil chemical by effectively managing soil
erosion, bolstering soil fertility, and improving moisture retention (El
Tahir and Vishwanath, 2015; Kuyah et al., 2016; Young, 2002). These
practices lead to enhanced physicochemical properties of the soil,
resulting in improved soil productivity (Kang and Akinnifesib, 2000;
Rachel et al., 2012). Additionally, agroforestry-based land management
contributes to soil pH improvement (Pinho et al., 2012) and increases
the availability of soil nutrients (Isaac and Borden, 2019; Manjur et al.,
2014; Sileshi et al., 2020; Wang et al., 2022) by enriching soil organic
carbon and total nitrogen content (Lian et al., 2019; Lu et al., 2015).
Agroforestry is a globally recognized approach implemented in
various regions, including Africa, to enhance resilience, promote
* Corresponding author.
E-mail address: aklilu.bajigo.madalcho@student.urk.edu.pl (A.B. Madalcho).
Contents lists available at ScienceDirect
Trees, Forests and People
journal homepage: www.sciencedirect.com/journal/trees-forests-and-people
https://doi.org/10.1016/j.tfp.2023.100471
Trees, Forests and People 15 (2024) 100471
2
diversication, address nutritional and food security gaps, and mitigate
the impacts of climate change (Aklilu and Tigist, 2017; Brown et al.,
2018; Kuyah et al., 2020; Sheppard et al., 2020; Sisay and Mekonnen,
2013; Yirga 2019;). In the southern region of Ethiopia, indigenous
agroforestry techniques that have developed over time are prevalent
(Alemu, 2016), with parkland agroforestry being a commonly adopted
practice.
Parkland agroforestry practices in Ethiopia have demonstrated a
benecial impact on soil properties, encompassing enhanced soil
fertility (Madalcho and Tefera, 2015; Wolle et al., 2021), improved
nutrient cycling, effective soil erosion control, efcient water manage-
ment, and heightened biodiversity conservation. These practices have
long been employed by local communities and farmers in Ethiopia,
playing a crucial role in fostering sustainable agriculture and land
management in the region. However, it is important to acknowledge that
the effectiveness of parkland agroforestry practices in shaping soil
properties can vary depending on specic local conditions, management
approaches, and the combinations of trees and crops utilized.
The primary goal of the land use system in the parkland is to enhance
agricultural production, and thus, it is crucial for the interacting species
within this ecosystem to contribute to the long-term sustainability of soil
chemical property. Perennial crops are commonly be considered as vital
component in the parkland agroforestry, and Cassava (Manihot escu-
lenta) is the one.
Manihot esculenta is a tropical tuber crop that plays a vital role in
ensuring food and nutritional security for smallholder farmers in Africa
(Burns et al., 2010; Mupakati et al., 2017; Tabaglio et al., 2023). Manihot
esculenta is considered as resilient to water stress and high temperatures,
demonstrating its resilience to the changing climate (Pushpalatha and
Gangadharan, 2020). The crop is potentially highly resilient to future
climatic changes and could provide Africa with adaption alternatives
when other crops may fail (Jarvis et al., 2012). However, the ecological
impacts related to the cultivation in the agroforestry system is yet less
investigated.
Previous studies (Wolle et al., 2021; Tsedeke et al., 2021; Bussa and
Feleke, 2020; Asfaw, 2016, among others) have examined the impact of
parkland agroforestry practices on soil, but the inuence of specic
agroforestry species on soil chemical quality remains poorly understood.
Moreover, there is a lack of detailed understanding regarding the po-
tential effects of changing agroforestry species preferences on soil
chemical properties in the study area and whether these effects vary
across different elevations. Addressing these questions is crucial due to
the current expansion of Manihot esculenta cultivation, which is dis-
placing other vital woody species within the Agroforestry system and
posing a signicant challenge to the sustainability of agricultural soil
chemical properties.
Consequently, we formulated the following hypotheses for our study:
1) The effects of agroforestry species on soil chemical properties are
species-specic. 2) The effects of agroforestry species on soil chemical
properties are dependent on elevation. 3) The effects of agroforestry
species on soil chemical properties signicantly differ within and
outside the canopy of agroforestry species.
2. Methodology
2.1. The study area description
This study was conducted in Sime Dolaye watershed, which lies in
Kindo Didaye woreda, Wolaita Zone, Southern Ethiopia, between 6◦42
′
30" and 6◦45
′
0" North latitudes and 37◦19
′
10" and 37◦21
′
40" East
longitudes. The geography of the watershed is undulating, with heights
varying from 856 to 2285 m above sea level. Approximately 6 % of the
terrain is level, 28 % is gentle elevation zone, 30 % is undulating, and 35
% is steep elevation zone. The elevation zones face south, and all
drainage drains into the Deme River. There have been no signicant soil
surveys in the examined region. The predominant soil types, according
to the local community, are dark-brown to black clay soils. According to
the current data, the soil texture are sandy loam at upper, and middle
elevations while loamy sand at lower elevation.
Over 65.4 % of households in the study area have less than 0.19
hectares of land. As a consequence to the land shortage and productivity
challenges in the area, the most widely employed land management
strategy is agroforestry-based land use systems. Due to its undulating
topography, the study area is prone to soil erosion. In spite, bench
terrace, an indigenous land management technique, is one of the most
widely implemented strategies for conserving soil and water, besides the
agroforestry practices. The commonly adapted agroforestry practices
are home gardens, parklands, coffee-shade trees, woodlots, boundary
plantations, alley cropping, and windbreaks. Cordia africana and Ficus
sur are highly preferred tree species in the area for timber, animal fod-
der, and soil fertility maintenance in the parkland settings. Manihot
esculenta, inset (Ensete ventricosum), banana (Musa paradisiacal), Taro
(Solanum tuberosum), Coffee arabica, Pea, and Zea mays are among the
key crops commonly incorporated in agroforestry systems in the study
area.
2.2. Sampling methods and sample size determination
2.2.1. Sampling methods and sample size determination for household
survey
A two-stage sampling procedure was used to choose sample re-
spondents for the households survey. The Sime watershed was chosen
for this study rst and foremost because it possesses the most robust
agroforestry-based soil management methods in the Kindo Didaye. By
engaging 698 households, the elevation cluster-based, stratied random
sampling approach was then utilized to choose the most prevalent,
economically and environmentally suitable agroforestry species in the
watershed. The proportional samples were drawn from the population
based on the number of household heads in each cluster. According to
Kothari (2004), the overall sample size for a household survey in the
region was 101 people. The samples were then allocated proportionally
using the formula ni = (Ni ∗n)/N, and the sample size at the cluster level
was obtained. Where ni is the projected sample size percentage, Ni is the
stratum population proportion, n is the sample size, and N is the total
population. A structured questionnaire was lled out in person by
trained data collectors from each household head in each elevation
range (Table 1). Focus group discussions (FGD) were also undertaken to
assist triangulate the survey data.
Consequently, we selected three agroforestry species that exhibit
dominance in terms of ecological attributes or economic value, specif-
ically two indigenous tree species (Cordia africana (96 %) and Ficus sur
(88.1 %)) and one economically valuable crop (Manihot esculenta (88.1
%)). These species were chosen to investigate their inuence on soil
chemical properties across various elevation ranges (Appendix 1).
2.2.2. Soil sampling procedure and sample size determination
In this descriptive study, we selected mature Manihot esculenta,
Cordia africana, and Ficus sur as the focal species from each cluster, based
on data from a household survey (Appendix 1) and a focus group dis-
cussion (FGD). The aim was to investigate their impact on soil chemical
properties in an agroforestry system. Specically, for the parkland
agroforestry system, we chose Cordia africana and Ficus sur trees that
Table 1
Distribution of household survey sample size along clusters.
S/
N
Cluster Elevation ranges (m.
a.s.l.)
Household
number
Proportional sample
size
1 Upper 2121–2285 211 31
2 Middle 1351–2120 304 44
3 Lower 856–1350 183 26
Total 698 101
H.G. Gota et al.
Trees, Forests and People 15 (2024) 100471
3
were at least 30 years old, with a diameter at breast height of 35–40 cm,
a crown width of 15–20 m, and a minimum height of 15 m. A stand
density of Cordia africana, Ficus sur and Manihot esculenta was 8.9 %, 7.6
% and 20 % respectively. To minimize the inuence of other species, we
carefully collected soil samples from various target tree individuals.
Additionally, for the 2-year-old Manihot esculenta in the parkland agro-
forestry setup, we marked the ground area covered by its canopy to
ensure it was not affected by other species. The land used for cultivating
Manihot esculenta had undergone at least 15 crop rotations, approxi-
mately equivalent to the age of the selected tree species. Throughout the
past ten years, all agroforestry species followed a similar crop rotation
pattern, and no manure or household waste was applied to the research
plots. Apart from the inuence of the study species’ canopy, the control
samples collected outside the canopy had identical conditions to those
inside in all other aspects.
Then, we collected soil samples from agroforestry species at different
elevations and distances from the canopy. Three pseudo-replications
were performed for each species within each elevation range. The
samples were taken from the top 30 cm of soil beneath the canopy and
10 m away from the canopy edge. To create representative samples, the
collected soil samples were mixed, resulting in a pair of 1 kg samples
from inside and outside the canopy at each point. In total, 54 composite
samples were obtained (3 trees/Manihot esculenta * 3 replications * 3
elevation ranges * 2 sampling distances). The soil samples were then air
dried and sent to Wolaita Sodo soil testing laboratory for analysis of
various parameters including soil pH, percent organic carbon (%OC),
total nitrogen (TN), available phosphorus (Av.P), available potassium
(Av.K), and Cation-exchange capacity (CEC).
In the soil pH measurement, a soil water suspension was created by
mixing soil and water in a 1:2.5 ratio. After allowing the contents to
settle for 30 min, the pH was determined using a pH meter and a com-
bination glass electrode. To evaluate the percentage of organic carbon
(%OC), the Walkley and Black method was employed, wherein the
organic matter was oxidized by potassium dichromate (K2Cr2O7) in the
presence of concentrated H2SO4. The excess potassium dichromate was
back titrated with ferrous ammonium sulphate using a diphenylamine
indicator (Walkley and Black, 1934). The TN (total nitrogen) available
in the soil was determined by using the Kjeldahl Method (Bremner and
Mulvaney, 1982). To assess the available phosphorus (Av.P), the Olsen
extraction (0.5 M NaHCO
3
) method was utilized (Olsen and Sommers,
1982). The amount of available potassium was determined using the
Neutral Ammonium Acetate Extraction Method, and the extracted
sample was estimated using a ame photometer (Merwin and Peech,
1951). The soil’s cation exchange capacity (CEC) was measured with 1
M ammonium acetate (pH 7) (Van Reeuwijk, 2002).
2.2.3. Statistical analysis
We employed log transformation on the data to ensure its adherence
to a normal distribution. Subsequently, a paired t-test was conducted to
investigate the variations in soil properties within and outside the effect
zone of the agroforestry species. To examine differences in soil proper-
ties among agroforestry species beneath the canopy zone, and the in-
uence of elevation range on modifying soil properties under these
species, a one-way ANOVA was employed. Treatment means were
compared using the Tukey test with a signicance level set at p =0.05.
Additionally, a correlation analysis was performed to assess the extent to
which one variable affected the other. Data analysis was conducted
using Statistica 14.0.0.15 (1984–2020) software, and bar graphs were
generated using Microsoft Excel.
3. Results
3.1. Soil chemical properties inside and outside the agroforestry species’
canopy zone
The chemical properties of the soil within the canopy zone of
agroforestry species exhibited higher values for Av.K, %OC, TN, Av.P,
and CEC compared to the soil outside the canopy zone (Figs. 1 and 2).
This disparity was found to be statistically signicant based on paired t-
test t(14) and p values, which varied depending on the species. This
nding aligns with our hypothesis that the soil chemical properties are
superior within the agroforestry species in comparison to areas lacking
canopy cover. Similarly, the soil pH beneath the canopy of Cordia afri-
cana and Ficus sur was signicantly greater than outside the canopy,
whereas no signicant difference was observed in the pH between under
and outside the canopy of Manihot esculenta (Appendix 2). Furthermore,
there was no signicant variation on soil organic carbon/nitrogen ratio
between inside and outside the canopy of agroforestry species (Fig. 2).
3.2. The agroforestry species-specic impact on soil chemical properties
The mean measurements of soil chemical properties in this study
revealed that Cordia africana and Ficus sur had similar inuences, except
for TN. On the other hand, Manihot esculenta demonstrated the lowest
values overall (Fig. 3 and 4). Specically, when compared to Cordia
africana and Ficus sur, Manihot esculenta exhibited signicantly lower Av.
K, CEC, and soil pH. Moreover, Manihot esculenta had much lower %OC
and Av.P compared to the soil beneath the Ficus sur canopy zone. In
contrast to Cordia africana and Manihot esculenta, Ficus sur displayed
notably higher soil TN. However, no noticeable difference in these soil
properties was observed between Manihot esculenta and Cordia africana.
On the other hand, the impact of agroforestry species on the soil C:N
ratio was not signicantly different among species (Figs. 3 and 4).
3.3. The impact of elevation gradient on soil chemical properties under the
agroforestry species
In the upper, middle, and lower elevations, it was found that the soil
beneath Manihot esculenta exhibited noticeably lower levels of Av.K and
soil pH compared to Cordia africana and Ficus sur. However, no signi-
cant difference in these parameters was observed between Cordia afri-
cana and Ficus sur. Across all elevation ranges, the percentages of %OC
and TN under the agroforestry species followed a consistent trend. Ficus
sur consistently displayed signicantly higher values for these parame-
ters compared to Cordia africana and Manihot esculenta at all elevations.
On the other hand, there was no signicant variation in Av.P across
elevation ranges for the soil under the agroforestry species. The same
was observed for CEC in the upper and lower elevations, while signi-
cant variation among agroforestry species was noted at the middle
elevation range. At this particular elevation, Ficus sur exhibited signi-
cantly higher soil CEC, followed by Cordia africana, whereas the lowest
value was observed under Manihot esculenta. The agroforestry species
had little effect on soil C:N in the middle and lower elevations. Despite
the fact that variation in soil C:N was not signicant among woody
plants at higher elevations, Manihot esculenta had a signicantly lower
value (Table 2).
3.4. Correlation of some important dependent variables
In the upper elevation range, there were signicant correlations
observed between AV.K and certain factors, namely pH (72 %),%OC (81
%), and CEC (92 %). Similarly, CEC showed signicant correlations with
soil pH (76 %) and %OC (81 %). Moreover, %OC exhibited a high cor-
relation with TN (91 %) within this elevation range. Moving to the
middle elevation range, CEC displayed signicant correlations with Av.
K (70 %), pH (85 %),%OC (82), TN (83 %), and Av.P (83 %). Addi-
tionally, soil pH showed signicant correlations with Av.K (73 %),%OC
(74 %), TN (73 %), and Av.P (81 %) at this elevation. TN also exhibited a
strong correlation with %OC (97 %) within this range. However, in the
lower elevation range, the signicant correlations were observed only
between pH and Av.K. (Appendix 3).
H.G. Gota et al.
Trees, Forests and People 15 (2024) 100471
4
4. Discussion
4.1. Soil chemical properties inside and outside the agroforestry species
canopy zone
Woody species play an important role in managing soil chemical
properties in agricultural land, through improved nutrient availability,
organic matter buildup, and soil fertility. In agroforestry systems, the
presence of woody roots enhances water inltration, leading to a
decrease in soil erosion and an improvement in soil moisture levels.
Additionally, this promotes the enhancement of soil structure, water
retention capacity, and availability of nutrients. The inclusion of woody
species in agroforestry systems contributes substantially to the soil’s
nutrient content, including TN, OC, Av.P, Av.K, and CEC. Consequently,
Fig. 1. Comparison of the chemical properties of the soil between under the canopy zone and outside it for different agroforestry species by using paired t-test.
Different letters represent the Tukey post-hock signicant differences of the mean values of the soil parameters for the agroforestry species at p =0.05, and the error
bars display the standard error. Av.K stands for available potassium, OC (%) for percent organic carbon, and TN for total nitrogen in the soil.
Fig. 2. Comparison of the chemical properties of the soil under the canopy zone and outside it for different agroforestry species by using paired t-test. Different letters
represent the Tukey post-hock signicant differences in the mean values of the soil parameters for the agroforestry species at p =0.05, and the error bars display the
standard error. Av.P stands for available phosphorus, CEC for cation exchange capacity, and C:N for carbon/nitrogen ratio in the soil.
H.G. Gota et al.
Trees, Forests and People 15 (2024) 100471
5
these benets support the recycling and retention of nutrients in the soil,
potentially reducing reliance on synthetic fertilizers (Mason et al., 2014;
Gebirehiwot et al., 2021). Furthering, the agroforestry species’ canopies
likely offer shade, which encourages the development of understory
plants and increases litterfall and organic matter inputs into the soil, and
promote the overall soil health. The ndings emphasize the potential
advantages of using trees in agricultural systems by indicating that the
agroforestry system has a favorable inuence on various soil qualities.
The ndings also support our hypothesis that, the agroforestry species
inuence soil chemical properties positively under the canopy. Due to
the high rate of organic matter synthesis and effective nutrient cycling
mechanism, including mineralization of leaf litter and ne roots, the soil
beneath the canopy has better soil qualities than that outside the canopy
(Alemayehu et al., 2016). Asfaw (2003) also noted that the soil chemical
properties in cases of Cordia africana was greater inside the canopy zone
than outside.
Similarly, the soil pH is signicantly higher under the native tree
species compared to outside the tree canopy while the difference is not
signicant in terms Manihot esculenta. According to the correlation
analysis of dependent variables (Appendix 3), the Av.K, %OC, TN, Av.P,
Fig. 3. Comparison of agroforestry species’ impact on soil chemical properties within the canopy zone. Different letters represent the signicant differences in mean
soil property values among agroforestry species at p =0.05, the error bars display the standard error. Av.K stands for available potassium, OC (%) for percent organic
carbon, and TN for total nitrogen in the soil.
Fig. 4. Comparison of agroforestry species’ impact on soil chemical properties within the canopy zone. Different letters represent the signicant differences in mean
soil property values among agroforestry species at p =0.05, the error bars display the standard error. Av.P stands for available phosphorus, CEC for cation exchange
capacity, and C:N for carbon/nitrogen ratio in the soil.
H.G. Gota et al.
Trees, Forests and People 15 (2024) 100471
6
and CEC are all positively associated with the soil pH at middle eleva-
tion. The impact of native tree species on the soil pH might be a basic
reason for the soil property improvements under canopy than outside.
Some reports supporting our arguments, that the scattered trees in the
parkland agroforestry set up improved the soil pH, Av.K, and Av.P
(Yadessa et al., 2009, 2001). In an alley cropping system, the levels of
soil organic carbon, available nitrogen, phosphorus, and potassium were
the highest at close proximity to the canopy (Sirohi et al., 2022). Besides,
this demonstrates how the soil patches created by the tree canopy can
restore some soil qualities and improve the sustainability of nutrient
availability for crop production in small-scale farming systems.
4.2. The agroforestry species-specic impact on soil chemical properties
Manihot esculenta has been overwhelmingly expanding on farmlands
in Southern Ethiopia at the expense of other woody perennials and
agricultural crops due to the economic attractiveness. However, this
condition showed discouraging results on the soil properties (Mulualem
and Dagne, 2015). For instance, the soil under Cordia africana and Ficus
sur had much higher levels of Av.K, CEC, and pH, than Manihot esculenta;
while the woody species were more or less statistically similar. This may
be connected to a plant’s ability to extract the Av.K and other basic
cations from the soil in the root zone. In the agroforestry system, Manihot
esculenta uses the surface nutrients with its supercial rooting system,
while, the deep rooted Cordia africana and Ficus sur can draw nutrients
from deep soil layers and pumping them out to the surface soil.
For long-term agricultural productivity, soil fertility must be pre-
served and improved in the framework of sustainable land management.
Agroforestry systems can support the sustainability and health of the soil
by using plants that have a good impact on soil pH, such as Cordia
africana and Ficus sur. The long-term productivity and resilience of the
land can be increased by improved soil pH, which can enhance nutrient
cycling, encourage benecial soil microbes, and lessen the need for
external inputs like synthetic fertilizers. This can have a positive impact
on the environment and reduce negative effects on the land’s long-term
productivity (Neina, 2019).
Different agroforestry species have different amounts and types of
litter, which affects soil characteristics and microbial biomass differ-
ently depending on the species (Getaneh et al., 2022; Liu et al., 2022;
Szott et al., 1991; Yohannes et al., 2020). Ficus sur had a bigger effect on
the TN in the soil in the current study than Cordia africana and Manihot
esculenta. The Ficus sur tree’s contribution to maintaining a higher
amount of litter production and a quick decomposition rate may be
connected to the increased soil total nitrogen derived from the canopy of
the tree. It can also be realized from the very strong correlation of TN,
and %OC at upper and middle elevations, which shows 81 % and 97 %
respectively (Appendix 3). The native g Ficus species had the
second-fastest rate of litter decomposition in the trial when compared to
other woody species (Mutshekwa et al., 2020). Ficus species have a
benecial effect on the soil in the agroforestry system (Dhanya et al.,
2013). On the other hand, the soil TN,%OC and Av.P contents is not
signicantly different under Manihot esculenta and Cordia Africana. Since
the control of ecosystem carbon storage and nutrient cycling is greatly
inuenced by the pace of litter decomposition, soil fertility is governed
by this rate of decomposition (Bossa et al., 2005; Santiago, 2007; War-
dle, 2002). The current study’s observation of different soil property
variations under various species in an agroforestry system is therefore
linked to potential differences in litter quality and decomposition rates.
This justication leads us to the conclusion that the Ficus sur generally
plays a superior function in enhancing agricultural land soil chemical
quality.
However, the numerical results of the current study show that Cordia
africana also has better soil chemical properties compared to Manihot
esculenta. Several studies back up this justication (Abdella et al., 2020;
Abraham, 2014; Yadessa et al., 2009, 2001; Asfaw, 2003). For the better
soil chemical properties, native plants like Cordia africana and Ficus sur
are preferentially preserved on smallholder agricultural land (Lemage
and Legesse, 2018), albeit their contributions vary according to the
particular goal. Manihot esculenta signicantly extracts nutrients,
particularly potassium, as highlighted by Howeler (1991) and Byju and
Suja (2019), which supports the idea that this crop’s nutrient re-
quirements and root characteristics contribute to the observed variances
in soil properties. The tuber, which is the harvested part of Manihot
esculenta, contains a substantial portion of the potassium exported from
the eld at harvest. Howeler (1985) noted that Manihot esculenta accu-
mulates potassium and calcium, which emphasizes the plant’s capacity
to store these elements inside its tissues. The variations in these soil
properties between agroforestry species might also be caused by other
factors, such as the root structure, nutrient requirements, litter compo-
sition, or microbial interactions specic to each agroforestry species.
The choice of role player species in agroforestry systems is therefore,
crucial since different species might have varied impacts on soil prop-
erties. In the meantime, these ndings also underscore the importance of
considering nutrient dynamics and management strategies when culti-
vating Manihot esculenta in agroforestry systems. Efcient nutrient
cycling and replenishment practices, such as incorporating organic
matter or implementing appropriate fertilization strategies, can help
maintain soil fertility and address the potential nutrient depletion.
Similarly, the current soil condition in our study shows that, the soil
CEC is signicantly lower in line with the Av.K, and the soil pH because
of the higher rate of basic cation depletion by Manihot esculenta
compared to the native tree species. In a similar manner, Manihot escu-
lenta increases the mining of soil nutrients during crop harvest by storing
a signicant amount of Av. P and nitrogen in the tuber (Howeler, 1985).
4.3. The effect of elevation on soil chemical properties under the
agroforestry species
The study found that agroforestry species across all elevation ranges
differ signicantly in terms of pH and soil Av.K. However, the variation
in these soil properties among the agroforestry species was consistent
regardless of elevation, which is signicant. Accordingly the
Table 2
Soil chemical property differences between agroforestry species grouped along the elevation gradient. Descriptive statistics, N =18 (Mean ±Std. Dev.).
Agroforestry Species Elevation Av. K (g Kg
−1
) pH %OC TN (g/ml) Av. P (mg Kg
−1
) CEC (Cmole Kg
−1
) C:N
Cordia africana Upper 0.32 ±0.20a 6.53 ±0.20a 1.49 ±0.08b 0.13 ±0.01b 4.65 ±1.15a 20.6 ±2.01a 11.51 ±0.58a
Ficus sur Upper 0.35 ±0.12a 6.26 ±0.12a 2.09 ±0.05a 0.19 ±0.02a 5.24 ±2.04a 28.8 ±1.74a 11.06 ±0.82a
Manihot esculenta Upper 0.25 ±0.14b 5.46 ±0.14b 1.29 ±0.02b 0.14 ±0.01b 1.82 ±0.41a 18.3 ±4.06a 9.49 ±0.13b
Cordia africana Middle 0.44 ±0.21a 6.26 ±0.21a 1.78 ±0.08b 0.17 ±0.02b 5.05 ±1.26a 27.46 ±4.13b 10.30 ±0.50a
Ficus sur Middle 0.40 ±0.06a 6.26 ±0.06a 2.51 ±0.11a 0.23 ±0.03a 5.39 ±0.79a 32.46 ±2.02a 11.12 ±0.50a
Manihot esculenta Middle 0.27 ±0.11b 5.40 ±0.11b 1.41 ±0.04c 0.14 ±0.01b 2.67 ±0.58a 17.20 ±0.64c 10.15 ±1.23a
Cordia africana Lower 0.39 ±0.12a 6.86 ±0.12a 2.39 ±0.28b 0.21 ±0.04b 4.14 ±1.80a 24.00 ±4.82ab 11.55 ±0.12a
Ficus sur Lower 0.38 ±0.35a 6.26 ±0.35a 3.44 ±1.06a 0.24 ±0.02a 5.10 ±0.64a 32.40 ±2.11a 14.67 ±9.25a
Manihot esculenta Lower 0.26 ±0.12b 5.63 ±0.12b 1.85 ±0.04b 0.17 ±0.02b 3.82 ±0.29a 18.93 ±2.03ab 10.97 ±1.24a
Note: The soil properties comparison were made between the agroforestry species at each elevation separately. Note: Av. K for available potassium, pH for soil pH, %
OC for percent organic carbon, TN for total nitrogen, and Av. P for available phosphorus, CEC for Cation exchange capacity, and C:N for carbon nitrogen ratio.
H.G. Gota et al.
Trees, Forests and People 15 (2024) 100471
7
agroforestry species’ root structure, nutrient requirements, or particular
interactions with the soil, may have a greater inuence on the chemical
properties of the soil than elevation. This result implies that soil Av.K
and pH are more inuenced by the species of agroforestry that are used
than by elevational variation (Shimbahri and Hailay, 2022). The nd-
ings of the study are consistent with other studies that have shown that
agroforestry systems can improve soil chemical properties and health
based on their role in improving soil physico-chemical properties and
soil fauna (Dollinger and Jose, 2018; Dori et al., 2022; Sharma, 2011; Li
et al., 2022; Shimbahri and Hailay, 2022).
According to this result, Manihot esculenta differs from the other two
native tree species in its inuence on soil characteristics. Manihot escu-
lenta, which stores a signicant quantity of potassium in the biomass of
its tubers, is most likely to blame for the lower concentration in the soil.
As it is a tuber crop that harvested in shorter term compared to the
native tee species, it mines potassium from the soil in a high rate (Byju
and Suja, 2019). Contrarily, no signicant changes in Av.K and pH were
found between Cordia africana and Ficus sur, indicating that these two
native tree species had comparable impacts on these soil parameters
across elevation. It might imply that the soil chemistry is similarly
inuenced by their root systems, nutrient cycling, or other aspects of
these species.
The variation of %OC, and TN in the soil under the agroforestry
species were maintained similar trend across the elevation ranges except
in the middle elevation where the trend was changed for %OC. The
change of trend of variation among the agroforestry species in this
elevation for %OC supported our hypothesis that the elevation in-
uences the soil chemical property differences among the agroforestry
species. Whereas, the difference was not inuenced by the elevation in
case of TN. This fact is supported by the nding of Madalcho and Tefera
(2015), where there was no signicant difference in the soil properties
under homegarden, and ally cropping agroforestry system along the
elevation gradients. The effect of agroforestry practices, and species on
some soil properties is not altered by the elevation ranges. In addition,
the difference of %OC and TN in the soil under the agroforestry species
was species specic, and was signicantly higher under Ficus sur
compared to Cordia africana and Manihot esculenta all elevations.
Whereas, the least value o %OC was observed under the economically
attracting tuber crop, Manihot esculenta at middle elevation. The native
tree species, specially Ficus sur built up a higher value of %OC compared
to the other agroforestry species in the study, and the pattern of TN was
also aligned to it. This might be due to a high amount of annual shading
of leaf, seed and oral material during winter. The soil organic carbon
determines the sustainable functions of the soil by balancing nutrients
cycling processes (FAO and ITPS, 2015). On the other hand, it is a sign
that soil organic matter has undergone a process of decomposition, with
the potential for nutrient cycling and physical and chemical processes
that regulate the sorption, availability, and displacement of nutrients
(Clara et al., 2017). With this regard, the least %OC under Manihot
esculenta might be related to the low capacity of organic matter pro-
duction by the crop.
With the exception of CEC in the middle elevation range, the varia-
tion in elevation had little to no impact on the pattern of soil Av.P and
CEC under the agroforestry species. This nding contradicts our hy-
pothesis that the elevation range inuences the variation of soil chem-
ical properties among agroforestry species. At the middle elevation
range, there was a signicant difference in soil CEC among the agro-
forestry species. Ficus sur exhibited the highest soil CEC, followed by
Cordia africana, while Manihot esculenta had the lowest CEC value.
Cation exchange capacity refers to the soil’s ability to hold and exchange
cations, such as calcium and magnesium, among others. Soils with high
CEC can retain more cations, resulting in higher levels of calcium,
magnesium, and other cations. Ficus sur and Cordia africana, with their
higher CEC values, may have a greater capacity to retain essential nu-
trients, such as calcium and magnesium, in the soil compared to Manihot
esculenta. On the other hand, soils with low CEC are less able to hold
water and are more likely to develop cation deciencies (Saidi, 2012;
Uttam, 2022). If the crop is not managed effectively, the production of
Manihot esculenta can lead to a signicant soil erosion (Howeler, 1991),
which increases the loss of basic cations by run-off and weakens the
soil’s cation exchange capacity.
Soil chemical property deterioration in the agroforestry system can
affect the resilience capacity of the tropics by triggering an overall
deterioration of soil properties affecting its physical and chemical pa-
rameters (Bhattacharyya et al., 2016). Soil degradation can result in soil
fertility decline, nutrient imbalance, erosion, acidication, and salini-
zation (de Andrade Bonetti et al., 2017). These changes can reduce the
productivity of the land and make agriculture-based livelihoods more
vulnerable to climate change impacts. However, agroforestry can pro-
vide many ecosystem services, including enhancing physical, chemical,
and biological soil characteristics, thereby increasing soil fertility, con-
trolling erosion, and improving water availability (Masebo et al., 2016;
Muchane et al., 2020; Udawatta et al., 2017; van Noordwijk, 2021).
Therefore, it is important to carefully select plant species for agrofor-
estry systems to avoid soil degradation and maintain soil health. By
doing so, agroforestry can contribute to building the resilience of the
tropics against climate change impacts, and some native tree species can
play a model role in this regard.
5. Conclusions
The inuence of agroforestry species on soil chemical properties can
vary depending on the specic species maintained in the agroforestry
system. Cordia africana and Ficus sur are the most effective species in
improving most soil chemical properties, while Manihot esculenta has the
least favorable impact on several soil chemical properties. The effects of
agroforestry species on soil chemical properties are not inuenced by
elevation gradient in most cases. However, harvesting Manihot esculenta
in middle elevations can lead to long-term soil degradation, as it resulted
in the lowest soil cation exchange capacity and associated properties.
The growing expansion of Manihot esculenta cultivation, at the expense
of other essential woody species within the Agroforestry system, will
lead to unsustainable agricultural soil chemical properties. To ensure
sustainable soil productivity in agroforestry systems, it is recommended
to prioritize Ficus sur and Cordia africana over Manihot esculenta due to
their superior ability to improve soil chemical properties. However,
lling the limitations of information in the current research nding,
further investigation is needed to determine the rate of litter decom-
position of agroforestry species and conrm their impact on the soil’s
chemical composition. It is also important to assess the trade-offs be-
tween economic valuation and ecological function of different agrofor-
estry species to assist land users in making informed choices.
Declarations
Funding statement
This research work was nancially supported by the Polish National
Science Foundation (NCN) grant No. 2018/31/B/NZ8/02786 (project
title: “How do large-scale disturbances inuence the relationship be-
tween ungulate herbivory and natural regeneration in temperate for-
ests?”), Ministry of Science and Higher Education of the Republic of
Poland in frame of statutory activities SUB/040011-D019/2020 of
Department of Forest Biodiversity, University of Agriculture in Krakow.
The authors declare no relevant nancial or non-nancial interests.
Author contributions
All authors contributed to the study conceptualization and design.
Data curation and project admnistration (Hizkel Gotoro Gota and Aklilu
Bajigo Madalcho), fundung acquisitioninvestigation and methodology
(all authors), formal analysis, visualization and writing original draft
H.G. Gota et al.
Trees, Forests and People 15 (2024) 100471
8
(Aklilu Bajigo Madalcho), Writing - review and editing (all authors), and
All authors read and approved the nal draft.
Declaration of Competing Interest
The authors declare the following nancial interests/personal re-
lationships which may be considered as potential competing interests:
Jerzy Szwagrzyk reports nancial support was provided by Univer-
sity of Agriculture in Krakow.
Data availability
Supplementary content related to this article is available in the
Mendeley Data (data.mendeley.com) repository now, and permanently:
https://data.mendeley.com/datasets/3ytht93wcs/1
Acknowledgement
The farmers of the Sime watershed in Kindo Didaye, Ethiopia,
deserve thanks from the authors for granting permission to collect soil
samples and for participating in the survey. We would like to express our
appreciation to the Wolaita Sodo University and the Agricultural Uni-
versity in Krakow for helping us to prepare this article.
Supplementary materials
Supplementary material associated with this article can be found, in
the online version, at doi:10.1016/j.tfp.2023.100471.
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