Analysis of the Mineral Content of Wood Ashes of Selected Plants Used for Soil Amendments in Eritrea

Abstract

Wood ash contains all the components of wood in a concentrated form, except for carbon, hydrogen and nitrogen which evaporate during the burning of wood. The mineral concentration of the ashes from seven selected trees namely Acacia seyal, Acacia etbaica, Acacia albida, Acacia
tortilis, Leucaena leucocephala, Olea europea, Musa sapientum found in Eritrea was studied. Most of the trees are commonly used for household fire in the rural and urban communities of Eritrea. The purpose of this study was to assess the levels of minerals and thus determine the application
of the ashes of the selected trees for soil amendment. Moderately sized tree branches were ashed in a furnace at 600ºC for 6 hours and the resulting ash was homogenized, filtered and digested. Aqua-regia was used to digest the ash samples and ICP-OES was employed to analyse the levels of the elements. Based on the analysis, the digestion method was found to be effective in recovery of minerals from the wood ashes. The percentage of ashes produced from the trees, except Musa sapientum, ranged from 0.88 up to 4.66. The results of the study revealed that the ashes of the selected plants contained various concentrations of the minerals vital for soil enrichments. The major elements found in the wood ashes include Ca, K, Mg, P, S, Fe and Na. The level of the major elements in this report was consistent with previously published reports. Moreover, the
concentration of heavy metals in the studied plant ashes was below the permissible limits and therefore the ashes can be employed as liming agents and sources of important nutrients in soil enrichment. This is a very first report related to the levels of minerals in wood ashes in the country
and thus can be used as reference for further detailed studies.

Full text

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*Corresponding author: E-mail: nebyat1997@gmail.com;
International Journal of Plant & Soil Science
25(6): 1-12, 2018; Article no.IJPSS.45727
ISSN: 2320-7035
Analysis of the Mineral Content of Wood Ashes of
Selected Plants Used for Soil Amendments in Eritrea
Goitom Kfle
1*
, Tesfamichael Haile
1
, Mussie Sium
1
, Semere Debretsion
2
,
Henok Abrham
1
, Martha Ghirmay
1
, Helen Tsegay
1
and Filimon Nega
1
1
Department of Chemistry, College of Science, Eritrea Institute of Technology, Asmara, Eritrea.
2
SGS, Mineral Assay Laboratory, Bisha Mining Share Company, Asmara, Eritrea.
Authors’ contributions
This study was carried out in collaboration among all authors. Authors GK, TH, MS and SD designed
the experiment, supervised the study and wrote the manuscript, and authors HA, MG, HT and FN
carried out the sample collection, lab works, and literature review of study. All authors read and
approved the final manuscript.
Article Information
DOI: 10.9734/IJPSS/2018/45727
Editor(s):
(1)
Dr. Alejandro Hurtado Salazar, Professor, Departamento de Produccion Agropecuaria, Universidad de Caldas, Colombia.
(2)
Dr. Omer Kilic, Bingol University, Turkey.
(3)
Dr. Radim Vacha, Associate Professor, Deputy Director of Research and Development, Research Institute for Soil and
Water Conservation, Prague, Czech Republic.
Reviewers:
(1)
Phyu Phyu Myint, University of Yangon, Myanmar.
(2)
Miguel Aguilar Cortes, Universidad Autonoma Del Estado De Morelos, Mexico.
(3)
Nkwoada, Amarachi Udoka, Federal University of Technology Owerri, Nigeria.
Complete Peer review History:
http://www.sciencedomain.org/review-history/27961
Received 06 October 2018
Accepted 10 December 2018
Published 24 December 2018
ABSTRACT
Wood ash contains all the components of wood in a concentrated form, except for carbon,
hydrogen and nitrogen which evaporate during the burning of wood. The mineral concentration of
the ashes from seven selected trees namely Acacia seyal, Acacia etbaica, Acacia albida, Acacia
tortilis, Leucaena leucocephala, Olea europea, Musa sapientum found in Eritrea was studied. Most
of the trees are commonly used for household fire in the rural and urban communities of Eritrea.
The purpose of this study was to assess the levels of minerals and thus determine the application
of the ashes of the selected trees for soil amendment. Moderately sized tree branches were ashed
in a furnace at 600ºC for 6 hours and the resulting ash was homogenized, filtered and digested.
Aqua-regia was used to digest the ash samples and ICP-OES was employed to analyse the levels
of the elements. Based on the analysis, the digestion method was found to be effective in recovery
of minerals from the wood ashes. The percentage of ashes produced from the trees, except Musa
sapientum, ranged from 0.88 up to 4.66. The results of the study revealed that the ashes of the
Original Research Article

Kfle et al.; IJPSS, 25(6): 1-12, 2018; Article no.IJPSS.45727
2
selected plants contained various concentrations of the minerals vital for soil enrichments. The
major elements found in the wood ashes include Ca, K, Mg, P, S, Fe and Na. The level of the major
elements in this report was consistent with previously published reports. Moreover, the
concentration of heavy metals in the studied plant ashes was below the permissible limits and
therefore the ashes can be employed as liming agents and sources of important nutrients in soil
enrichment. This is a very first report related to the levels of minerals in wood ashes in the country
and thus can be used as reference for further detailed studies.
Keywords: Wood ash; digestion; mineral concentration; soil amendment.
1. INTRODUCTION
In the past, ash from the combustion of wood
was sent to landfills. The growing expenses
associated with landfilling and the reluctance to
open new waste landfill sites have brought about
the increasing interest in alternative methods of
disposal. Among these is the use of wood ash
for the purposes of soil amelioration and soil refill
in agriculture, horticulture and forestry [1,2]. The
application of biomass ash to soil offers an
alternative for its disposal and for nutrient
recycling. Wood ash contains most of the
minerals that a tree will take up during its lifetime.
These comprise the three main categories
including macronutrients, micronutrients and
heavy metals [3,4]. Wood ash was confirmed to
be a good source of K, P, Mg, Ca and other
micronutrients [5]. The application of wood ash to
soil had a relatively long-term increasing effect
on the pH, the concentrations of exchangeable
base cations (Ca
2+
, K
+
, Mg
2+
, Na
+
), effective
cation exchange capacity and base saturation in
the humus layer of soil [6,7]. The issues
concerning wood ashes are still valid, because
rural inhabitants continue to use firewood to a
large extent [8]. Wood ash contains all the
nutrients that were taken up by trees from soil,
except nitrogen and sulfur that volatilize during
the combustion process and the fertilizer
components contained in them are easily
absorbed by plants [8,9].
When loose wood ash is dissolved in water, a
highly alkaline solution (pH 11-13) is produced.
Oxides, hydroxides, hydrogen carbonates and
carbonates are responsible for the rapid
change in the pH level [10,11]. Neutralization
as well as fertilization effects of wood ash
especially on forest soil can be significant and of
long duration. When applied according to
limestone needs, wood ash would be considered
a valuable soil amendment, for the reason that it
will not cause additional soil pollution. In addition
to base cations, wood ash contains harmful
heavy metals such as Cd, Hg and Pb, of which
Cd is probably of most concern because it is
considered to be one of the most toxic heavy
metals present in wood ash [10,12].
The use of ashes from the combustion of
biomass in agriculture is found to have a positive
effect on the decrease in the amount of toxic
exchangeable aluminum [9]. Similarly, in the
investigation of the effects of wood ash
fertilization on soil chemical properties, it was
observed that wood ash significantly increased
the effective cation exchange capacity and base
saturation [5]. Returning biomass ash to
agricultural land is beneficial to the fertilizing
potential which is determined by the levels of
major- and micronutrients, and the highly alkaline
pH [9]. Accordingly, it is crucial to assess the
levels of the main elements present in the ashes
of the selected plant species contributing to the
soil fertility and thus play a good role of fertilizers.
The aim of the present study was to assess the
levels of the minerals found and thus determine
the agricultural usefulness of the wood ashes
obtained following the combustion of the woods
of the seven trees namely Acacia seyal, Acacia
etbaica, Acacia albida, Acacia tortilis, Leucaena
leucocephala, Olea europea, and Musa
sapientum. Most of the woods of those plants
have been extensively used in household fires in
rural and urban communities of Eritrea.
2. MATERIALS AND METHODS
2.1 Sample Collection and Preparation
Moderately sized tree branches of the plants
were collected for the purpose of this study. Four
of the seven trees are highly distributed in the
lowlands and highlands of Eritrea but Olea
europea is highly dispersed in the Eastern
escarpments. Except Leucaena leucocephala
and Musa sapientum, each plant species is
common to specific region of the country (Table
1) and intensively used for household fires and
other purposes. The plant species were collected
from diverse sites of the country and all were

Kfle et al.; IJPSS, 25(6): 1-12, 2018; Article no.IJPSS.45727
3
authenticated by a taxonomist in Eritrea Institute
of Technology, EIT (Voucher specimen of the
plants has already been deposited in the
Herbarium of EIT). The wet woods of all the
selected plants were chopped and shade dried
for several days. Each dry wood was weighed to
obtain dry weight and then inserted into a muffle
furnace (Carbolite, Shfld.) set at 600ºC for 6 hrs.
The ash residues were collected and allowed to
pass through a sieve having mesh size of 0.1
mm and thus were kept in appropriate labeled
vials until further use.
2.2 Chemicals and Reagents
Analytical grade chemicals and reagents were
purchased from Sigma-Aldrich Company. 65%
nitric acid (HNO
3
) and 32% Hydro chloric acid
(HCl) were used for digestion purposes.
Ultrapure-deionized water (18Ω) was used
throughout the study. The glassware was soaked
in 3 M HNO
3
for the whole night and washed and
rinsed with deionized water to minimize the
chances of interferences. All the chemical
analyses were conducted under extractor hood
and a digital IR Vortex Mixer (S/N296058 made
in Italy) was used for mixing of the solutions.
2.3 Instrumental Analysis
A dual viewing ICP-OES (Perkin Elmer Optima
8300, made in Singapore) coupled to an
ultrasonic nebulizer CETAC 6000AT + (CETAC,
Omaha, NE, USA) was employed for the
analysis of the trace and other elements. The
Windows 7 compatible S/W provided by Perkin
Elmer was used to process the spectral data for
calculating sample concentrations by comparing
light intensities measured at various wavelengths
for standard solutions with intensities from the
sample solutions. The operating conditions set
for the ICP-OES are shown in Table 2.
2.4 Sample Digestion
The powdered ash samples prepared were
digested as follows: Each ash sample (2 g) and
certified reference materials were weighed and
transferred into a beaker containing about 60 ml
of aqua-regia. The mixture was placed in a hot
plate at 100ºC until the volume was reduced to
40 ml. Each solution was then transferred to
conical flask and diluted to 100 ml using
Ultrapure-deionized water. At last, approximately
20 ml of the diluted solution was transferred into
glass test tubes for analysis using ICP-OES. The
analysis was conducted with special emphasis to
the levels of K, P, Ca, Mg, S, Mn, Ag, As, Cd,
Co, Cr, Cu, Fe, Hg, Ni, Pb and Zn.
Before the analysis of the elements, the
accuracy of the methods was verified using in-
house certified reference materials (CRMs)
digested using dry ashing; the method was
adopted from Sium et al. [13]. Fig. 1 displays the
calculated relative errors of some of the
elements. Except for Al, all the elements
demonstrated negligible relative errors and the
deviations from the mean values were very
small. There was no significant difference in the
measured and certified values. Therefore, the
calculated relative errors revealed high accuracy
of the method, suggesting that this method can
be used for routine analysis of trace and heavy
metals in wood ash samples. The concentrations
of the elements analysed using the ICP-OES are
displayed in Table 4, Fig. 2, Fig. 3, Fig. 4 and
Fig. 5.
Table 1. List and details of the plants selected for this study
Scientific
name
Local
name
English
name
Commonly locations
In Eritrea
Place
collected
Acacia seyal Chea White Whistling thorn Highlands and lowlands Hazemo
Acacia etbaica Seraw *** Highlands and lowlands Segeneiti
Acacia tortilis Ala *** Highlands and lowlands Barentu
Acacia albida Momona Apple ring acacia Highlands and lowlands Shiketi
Olea europea
Awlee
African wild olive
Eastern escarpments
Filfil
Leucaena
leucocephala
Luciana Lucinia Halhale Research Institute Halhale
Musa sapientum Banana Banana Lowlands Teseney
NB: ‘***’ - English name not found

Kfle et al.; IJPSS, 25(6): 1-12, 2018; Article no.IJPSS.45727
4
Table 2. The operating conditions of the ICP-OES used for the analysis
Condition Setting
Power 1.3 kW
Plasma gas flow 15 L/min
Auxiliary gas flow 1.5 L/min
Spray chamber type Glass cyclonic (single-pass)
Torch Standard one-piece quartz axial
Nebulizer type Sea spray
Nebulizer flow 0.7 L/min
Pump speed 2-4 rpm
Total sample usage 2 mL
Replicate read time 5 s
Number of replicates 3
Sample undertake delay time 15 s
Stabilization time 40 s
Rinse time 20 s
Fast pump Off
Background correction Fitted
Fig. 1. The relative errors calculated based on comparison of the certified and measured
values of some elements
3. RESULTS AND DISCUSSION
3.1 The Ash Content
The ash content of the plants, furnished in Table
3, was calculated and Musa sapientum gave the
highest ash content (7.44 %) among the others.
This could be due to nature of the plant species
and soil composition. The ash content of the
other six plants falls in the range of 0.88 (for Olea
europea) up to 4.66% (for Leucaena
leucocephala). The results of the ash content of
the plants in this study are higher than those
reported by Wang and Dibdiakova [14] and
Dibdiakova et al. [15]. The increase in the mass
of the ash was relatively higher due to the effect
of temperature employed for the ashing process.
Usually if the furnace is set over 600ºC, there is
further decomposition of carbonates of both
calcium and potassium and thus the ash content
decreases [16]. However, the overall percentage
of the ashes seems to fit the values for the ash
content (3–5% ash) of dominant types wood
present available for use [17].
Ag Al Co Cr Cu Ni Pb Zn
Relative Error -0.03 7.8 -0.02 -0.02 0 0.02 -0.01 -0.02
-1
0
1
2
3
4
5
6
7
8
9
relative error
Comparison of certified and measured values

Kfle et al.; IJPSS, 25(6): 1-12, 2018; Article no.IJPSS.45727
5
Table 3. The ash content of the seven plants (in % of the dry mass)
Scientific name Ash content (%)
Acacia seyal 2.01
Acacia etbaica 3.27
Acacia tortilis 4.21
Acacia albida 3.34
Olea europea 0.88
Leucaena leucocephala 4.66
Musa sapientum 7.34
3.2 Elemental Composition of the Ashes
of the Selected Trees
The concentration of the elements present in the
wood ashes, determined by ICP-OES, is
represented in Table 4. The results of the
recovery of the elements from the ash samples
shows that the digestion method employed was
found to be effective in recovering most of the
elements. In this report, the main essential
minerals found in the wood ash samples were
Ca, K, Mg, P, and S. The levels of the major
elements in ascending order were S< P < Mg <
K< Ca, and this was consistent with previously
reported results from Czech Republic [9]. The
other major elements identified were Na, Fe, Sr,
Mn, Ti, Cu, Ba, Zn, V, and Ni. In general, the
mineral concentrations including Ca, Cr, Cu, Fe
and Ni of the ashes in this study were higher
than those reported by Huang et al. [18] and
lower than those reported by Etiegni et al. [19]
and G´orecka et al. [1]. Moreover, the levels of
metals including Al, Cd, Mn, Pb, Sb, Sn and Zn
were much lower and the levels of the metals like
K, Mg, Na, and Zr were higher than those
reported by Huang et al. [18], Etiegni et al. [19]
and G´orecka et al. [1] (Table 4 and Table 5).
According to Demirbas [20], the composition of
ash is dependent on the plant species, growth
conditions and ash fraction.
The reasons for the difference in concentration of
the metals could be attributed to the difference in
the type of plant species, soil composition and
degree of environmental pollution in which the
plants grew up. Many authors reported that the
levels of minerals in the wood ashes is variable
and depends on the type of the tree species, the
segments of the tree used, soil properties and
the climate on which the tree grows. The nutrient
content of roots and branches is usually much
higher than the nutrient content of logs [2,14].
Ashes formed from the top branches contain
substantially high levels of K and P. These two
typical mobile elements in plants are often found
in twigs containing a large amount of young and
biologically active tissues [15]. Likewise, in the
present study, the tree branches were analysed
for their mineral content because these tree parts
are used frequently for fire in rural and urban
Eritrea.
3.2.1 Nitrogen and sulphur content
The nitrogen content in wood ash is normally
insignificant due to the conversion of most of the
wood nitrogen to NH
3
, NO
X
and N
2
during the
combustion of wood [7,9] and sulphur is usually
lost during combustion process similar to
nitrogen. Furthermore, depending on the
amounts of wood ash applied and the
consequent rise in the soil pH, the concentration
of nitrogen decreases in the upper soil layers
[11]. Consequently, if wood ash is to be used as
a fertilizer, nitrogen and sulphur would need to
be supplied from other sources. However, wood
ash should not be added along with nitrogen
fertilizers such as ammonium sulfate, urea or
ammonium nitrate as these fertilizers lose their
nitrogen in the form of ammonia gas when mixed
with high pH material [21]. Here, the highest level
of S was found in Acacia albida (3.50 %) and
lowest in Acacia tortilis (0.38 %) collected from
Shiketi and Barentu, respectively. The levels of S
were significantly different ( < 0.01) among the
plants.
3.2.2 Phosphorus content
The ash sample of Acacia albida was found to
contain the highest concentration (4.26 %) of
phosphorus followed by Acacia etbaica (2.38 %)
and Acacia seyal (1.98 %) and the lowest
concentration (0.14 %) was found in Olea
europea. The levels of P were significantly
different ( < 0.01) among the various plants
studied. Even though the phosphorus absorption
and bioavailability depends up on the pH

Kfle et al.; IJPSS, 25(6): 1-12, 2018; Article no.IJPSS.45727
6
buffering capacity of the soils [19], the ashes of
the tree species including Acacia albida, Acacia
etbaica, and Acacia seyal can be used as
important sources of phosphorus in P-deficient
soils. Phosphorus is the second most limiting
nutrient in crop production, playing its most
critical role in plants in energy transfer and
storage. It is a structural component of nucleic
acids, nucleotides, and coenzymes. Low
availability of phosphorus is a limiting factor to
plant growth [22]. Reutilizing biomass ashes in
agriculture can substitute inputs of P from finite
primary sources [23]. Studies have also reported
that better levels of phosphorus supply had a
beneficial influence on potassium uptake and
potassium concentrations in plants [9]. The
processes of anabolism and catabolism of the
carbohydrate metabolism in plants would only
proceed normally when the organic compounds
had been esterified with phosphoric acid [5].
Okmanis et al. 2016 [24] reported that
fertilization with wood ash shows the best results
in stands with visual symptoms of phosphorus
deficiency on nitrogen rich drained peat soils.
Moreover, these plants being the most important
sources of fuel in household fires and other
applications, massive amount of ash is produced
from them in rural as well urban areas of Eritrea,
making them ideal phosphorus suppliers.
3.2.3 Potassium content
The ash of Musa sapientum was found to contain
the highest concentration of K (31.74 %) followed
by Acacia albida (25.05 %) and the lowest
concentration of K was observed in Olea
europea (0.86 %). The levels of P varied
significantly ( < 0.01) among the different
plants. Since the potassium fertilizers are usually
expensive, the ashes from Musa sapientum,
Acacia albida, Acacia etbaica, Acacia seyal and
Acacia tortilis could be good alternatives of
potassium for potassium deficient soils.
Considering that the content of phosphorus in
wood ash is low, potassium content is
predominantly responsible for a positive impact
of the wood ash applied as a fertilizer [24]. The
solubility and the potential availability of the
macronutrients to plants in wood ash are high,
and K has highest bioaccumulation relative to
Mg, Ca and P [11]. Musa sapientum bears
hanging clusters of elongated fruits which are
consumed in huge amount per day everywhere
in the world and the skins of the fruit are
disposed giving little attention to them. Thus,
based on the results of this study, collecting the
Musa sapientum skins and converting them in to
ash makes them ideal candidates for potassium
deficient soils.
Potassium was found to accumulate in the parts
of the plant in which cell division and growth
processes were actively proceeding [5]. K
balances the charge of organic acids and is
known to participate as a cofactor at least in 50
different enzymatic reactions in plants [11].
G´orecka et al. [1] reported that plant availability
of wood ash potassium is the same as in
potassium fertilizers, but phosphorus was lower
when compared with phosphorus fertilizers. A
study on Norway spruce, standing on drained
organic and drained mineral soils have shown a
correlation between the tree foliage damages
and the potassium content in soil [24]. Studies
also revealed that soil available potassium levels
increased with the application of wood ash and
the resulted increase in soil available potassium
is attributed to release of potassium by wood ash
as well as to the replacement of potassium on
soil exchange sites by Ca and other
exchangeable cations released directly from
wood ash into the soil suspension [1]. Wood ash
treatment experiments showed an increase of K,
B, Mg, Fe, and Zn in tissues of Scots pine
needles [11].
3.2.4 Calcium content
Based on the results of this study the ash sample
of Acacia tortilis is found to contain the highest
concentration (22.93 %) of Ca followed by Acacia
etbaica (21.78 %) and Olea europea (21.53 %)
and lowest concentration of Ca was observed in
Musa sapientum (1.44 %). The levels of Ca were
not significantly different among the plants. Thus,
the ash sample from Acacia tortilis, which is the
dominant plant species in the lowlands of Eritrea,
can be applied to Ca demanding soils. Calcium is
an important macronutrient which influences the
water economy of the plant and the protein
carbohydrates in many physiological processes
[5]. The high content of Ca and Mg in ash
accounts for high pH of the ash. It is reported
that wood ashes contain significant amounts of
basic oxides which can be used to deacidify
acidic soils. When deciding on the use of these
ashes for soil deacidification, it should be borne
in mind that Ca and Mg are present in the oxide
(fast-acting) form [8,25]. As previously reported,
wood ashes have the same liming effects as
commercial lime and was comparatively found
to give better plant growth responses than
limestone because of the additional nutrients
that the ash contained [5].

Kfle et al.; IJPSS, 25(6): 1-12, 2018; Article no.IJPSS.45727
7
Table 4. The concentrations of elements found in the ashes of the trees studied
Element
Acacia
seyal
Acacia etbaica
Leucaena
leucocephala
Olea
europea
Acacia
albida
Musa sapientum
Acacia tortilis
Ca (%) 18.66 ±
0.22 21.78 ±
0.31 11.77 ±
0.24 21.53 ±
0.18 8.96 ±
0.10 1.44 ±
0.00 22.93 ±
0.00
K (%) 11.07 ±
0.51 11.54 ±
0.38 3.22 ±
0.02 0.86 ±
0.01 25.05 ±
0.24 31.74 ±
0.12 5.83 ±
0.00
Mg (%) 5.37 ±
0.13 4.07 ±
0.01 1.91 ±
0.00 1.03 ±
0.00 4.21 ±
0.02 0.76 ±
0.01 3.52 ±
0.01
P (%) 1.98 ±
0.04 2.30 ±
0.04 0.37 ±
0.00 0.14 ±
0.06 4.26 ±
0.01 1.04 ±
0.01 1.45 ±
0.04
Na (%) 0.40 ±
0.00 0.39 ±
0.00 1.20 ±
0.00 0.50 ±
0.01 0.19 ±
0.01 0.23 ±
0.00 0.86 ±
0.00
Al (%) 0.62 ±
0.00 0.21 ±
0.00 0.25 ±
0.00 1.91 ±
0.01 0.41 ±
0.00 0.31 ±
0.00 0.68 ±
0.01
Mn (mg/Kg) 224.33 ± 5.06 129.94 ± 2.22 144.81 ± 4.20 329.20 ±2.70 198.34 ±1.36 171.92 ±1.16 783.14 ±5.69
Ni (mg/Kg) 13.21 ±
0.76 16.25 ±
0.15 4.54 ±
0.15 13.83 ±
0.10 25.19 ±
0.20 3.53 ±
0.03 6.39 ±
0.05
Fe (%) 0.62 ±
0.00 0.23 ±
0.00 0.22 ±
0.00 1.65 ±
0.01 0.50 ±
0.00 0.38 ±
0.00 0.84 ±
0.00
S (%) 1.10 ±
0.02 0.71 ±
0.00 0.39 ±
0.00 0.45 ±
0.00 3.50 ±
0.00 0.67 ±
0.01 0.38 ±
0.01
Sb (mg/Kg) 0.52 ±
0.04 1.18 ±
0.06 0.04 ±
0.01 1.23 ±
0.07 0.23 ±
0.04 0.82 ±
0.06 1.24 ±
0.08
V (mg/Kg) 13.23 ±
0.33 4.88 ±
0.21 5.28 ±
0.09 39.73 ±
0.38 10.72 ±
0.23 10.71 ±
0.22 28.91 ±
0.13
Zn (mg/Kg) 277.69 ± 2.26 205.09 ± 3.20 56.09 ±
0.38 88.95 ±
0.12 331.44 ±1.12 101.56 ±0.33 484.19 ±7.57
Table 5. The levels of elements of the ashes of various trees previously reported
Published papers
Elements analysed in the wood ashes
Al (%)
Ca (%)
Fe (%)
K (%)
Mg
(%)
Na
(%)
P
(%)
Mn
(mg/Kg)
Ni
(mg/Kg)
Zn
(mg/Kg)
Bi
(mg/Kg)
Sb
(mg/Kg)
(Etiegni et al. 1991) [15] 2.36 31.74 1.95 4.13 2.25 0.34 1.40 6700 47.00 700.00 - -
(Huang et al. 1992) [14] 1.30 10.94 0.33 2.86 1.62 0.16 0.69 3470 12.00 794.00 - -
(G´orecka et al. 2006) [1] 0.65 29.30 0.85 6.70 2.68 0.30 1.63 8,535 65.17 1,172 39.79 3.31
NB: ‘-’ not reported

Kfle et al.; IJPSS, 25(6): 1-12, 2018; Article no.IJPSS.45727
8
3.2.5 Magnesium content
The ash sample from Acacia seyal was found to
contain the highest concentration (5.37 %) of Mg
followed by Acacia albida (4.21 %), Acacia
etbaica (4.07 %) and Acacia tortilis (3.52 %) and
the lowest concentration (0.76 mg/Kg) of Mg was
observed in Musa sapientum. There was
significant difference ( < 0.01) in the levels of
Mg among the plants. Thus, the ash samples
from these plants can be good sources of Mg. It
was confirmed that Mg is a constituent of the
chlorophyll, protochlorophyll, pectin and phytin.
Micronutrients such as Mg though required in
very small quantities, are also involved in the
plant metabolic processes [5]. As shown in Fig.
2, Ca was the dominant element in most of the
plants including Acacia seyal, Acacia etbaica,
Leucaena leucocephala, Olea europea and
Acacia tortilis. However, K was the most
dominant element in Acacia albida and Musa
sapientum. For most of the plants, the level of
Mg was relatively lower as compared to Ca and
K.
3.2.6 Heavy metal concentrations
As presented in Fig. 3, Fig. 4 and Fig. 5, the
highest levels of Pb was observed in Olea
europea (9.78 mg/Kg) followed by Acacia albida
(3.47 mg/Kg) and Acacia tortilis (3.13 mg/Kg).
Among the trees, the highest levels of Hg and Co
were found in Acacia seyal (3.92 and 5.37 mg/Kg
respectively) and the lowest non-detectable
levels of Hg were observed in Musa sapientum
and Acacia tortilis. Though the concentrations
were small, relatively the highest level (0.13
mg/Kg) of Cd was found both in Musa sapientum
and Olea europea. Similarly, the highest levels of
Zn and Mn were found in Acacia tortilis (484 and
783 mg/Kg respectively). The lowest
concentrations of Zn (56.09 mg/Kg) and Mn
(129.9 mg/Kg) were found in Luciana and
Acacia etbaica respectively. Acacia seyal
displayed the highest levels of Cr (11.57 ppm)
and Co (5.37 mg/Kg) compared to the other
trees. The highest (25.19 mg/Kg) and lowest
(3.53 mg/Kg) levels of Ni were found in Acacia
albida and Musa sapientum respectively. The
levels of Mn, Zn, Cr, Ni, Pb, Fe and Hg ( <
0.001), Cu and As ( < 0.01) were statistically
different among the plants. However, the levels
of Co and Cd were not statistically different
among the studied plants. Moreover, the
concentrations of heavy metals, including the
toxic metals (Pb, Cd and Hg), in the
studied ashes were below the permissible limits
and thus the ashes can be used for soil
improvements.
The low concentration of heavy metals in the ash
of the studied plants was consistent with some
similar studies previously reported [8,26]. The
ashes obtained following the combustion of wood
of fourteen tree species from Poland reported by
G´orecka et al. [1] were characterized with higher
levels of Cd, Pb, Zn, Cu, Mn, Ni and Cr as
compared to the results of the present study.
Fig. 2. Some of the major and essential elements found in the selected plants
NB: Concentration expressed as mean ± SD (

=3);
∗∗∗

< 0.001, NS - not significant (relative to the other plants)
0
5
10
15
20
25
30
35
Chea Seraw Lucinia Awlee Momona Banana Ala
Levels of elements (mg/Kg)
The plants studied
Comparison of the Levels of the Major Elements
Ca K Mg P S
***
***
NS
***
***

Fig. 3.
Concentration of Cu, Zn and Mn in the selected plants
NB: Concentration expressed as mean ± SD (
∗∗∗

< 0.001,
Fig. 4.
Concentration of Cr, Ni and Co and As in the selected plants
NB: Concentration expressed as mean ± SD (
∗∗

< 0.01, NS
This could be attributed to the diversity of the
plants and their geographical location; previous
study also describes the relationship between the
levels of heavy metals in wood ashes relative to
their geographic origins [27]
. Olanders and
0
100
200
300
400
500
600
700
800
900
Chea Seraw
Concentration (mg/kg)
Levels of Heavy Metals Present
Cu (mg/Kg)
0
5
10
15
20
25
30
Chea Seraw
Concentration (mg/kg)
Levels of Heavy Metals Present
NS
Kfle et al.; IJPSS, 25(6): 1-12, 2018
; Article no.
9
Concentration of Cu, Zn and Mn in the selected plants
NB: Concentration expressed as mean ± SD (

=3);
< 0.001,
∗∗

< 0.01 (relative to the other plants)
Concentration of Cr, Ni and Co and As in the selected plants
NB: Concentration expressed as mean ± SD (

=3);
∗∗∗

< 0.001,
< 0.01, NS
- not significant (relative to the other plants)
This could be attributed to the diversity of the
plants and their geographical location; previous
study also describes the relationship between the
levels of heavy metals in wood ashes relative to
. Olanders and
Steenari
[28] reported that the ash from biomass
fuel contains only trace amounts of heavy
metals, which makes them fairly easy to dispose
of and they can be good fertilizers.
incineration has been used increasingly for the
Lucinia Awlee Momona Banana
The Studied Plants
Levels of Heavy Metals Present
Zn (mg/Kg) Mn (mg/Kg)
**
Lucinia Awlee Momona Banana
The Studied Plants
Levels of Heavy Metals Present
***
***
**
; Article no.
IJPSS.45727
[28] reported that the ash from biomass
fuel contains only trace amounts of heavy
metals, which makes them fairly easy to dispose
of and they can be good fertilizers.
Biomass
incineration has been used increasingly for the
Ala
***
***
Ala
Cr (mg/Kg)
Ni (mg/Kg)
Co (mg/Kg)
As (mg/Kg)

Fig. 5.
Concentration of Cd,
NB: Concentration expressed as mean ± SD (
∗∗∗

< 0.001, NS
generation
of heat and/or electricity. The
utilization of bottom ash has the advantage
of lower heavy metal concentrations but
the disadvantage of higher nutrient losses.
Mixtures of fly ash and bottom ash may be
useful to achi
eve optimum nutrient delivery
within limits for heavy metal concentrations
[26,29].
4. CONCLUSION
On the basis of the results observed, the
concentration of minerals in the studied wood
ashes including Musa sapientum,
Acacia albida
Acacia seyal and Acacia tortilis
were found to be
good sources of K, P, Mg and Ca. Moreover, the
levels of toxic elements in the wood ashes were
in full compliance with the regulatory
requirements and therefore the wood ashes
investigated in this report can be employed in
amendments according to the mineral needs of
the soil. Although wood ashes could be good
sources of various elements, however they are
not readily available to plants and environment
and therefore their bio-
availability to specific
plant requires furt
her investigation. This is a
very first kind of report related to the levels of
minerals in wood ashes in the country and
thus be used as reference for further detailed
studies.
0
2
4
6
8
10
12
Chea Seraw
Concentration (mg/kg/ %)
Levels of Heavy Metals Present
Kfle et al.; IJPSS, 25(6): 1-12, 2018
; Article no.
10
Concentration of Cd,
Pb, Fe and Hg in the selected plants
NB: Concentration expressed as mean ± SD (

=3);
< 0.001, NS
- not significant (relative to the other plants)
of heat and/or electricity. The
utilization of bottom ash has the advantage
of lower heavy metal concentrations but
the disadvantage of higher nutrient losses.
Mixtures of fly ash and bottom ash may be
eve optimum nutrient delivery
within limits for heavy metal concentrations
On the basis of the results observed, the
concentration of minerals in the studied wood
Acacia albida
,
were found to be
good sources of K, P, Mg and Ca. Moreover, the
levels of toxic elements in the wood ashes were
in full compliance with the regulatory
requirements and therefore the wood ashes
investigated in this report can be employed in
soil
amendments according to the mineral needs of
the soil. Although wood ashes could be good
sources of various elements, however they are
not readily available to plants and environment
availability to specific
her investigation. This is a
very first kind of report related to the levels of
minerals in wood ashes in the country and
thus be used as reference for further detailed
ACKNOWLEDGEMENTS
The authors would like to acknowledge the
Department of Chemistry of EIT for their support
in sample preparation and facilitation of the
overall project. Moreover, we thank Bisha
Mining Share Company for their support in the
analysis of the wood a
shes of the different plant
samples.
COMPETING INTERESTS
Authors have declared that no competing
interests exist.
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