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European Journal of Applied Sciences – Vol. 10, No. 4
Publication Date: August 25, 2022
DOI:10.14738/aivp.104.12491. Amosa, B. P., Imo, T., Latu, F., Ieremia, R., Simi, I., & Gese, G. (2022). Analysis of Chemical Properties in Soil in the Selected Sites in
Samoa. European Journal of Applied Sciences, 10(4). 170-183.
Services for Science and Education – United Kingdom
Analysis of Chemical Properties in Soil in the Selected Sites in
Samoa
Bernadette P. Amosa
Faculty of Science, National University of Samoa, Samoa
Taema Imo
Department of Science, National University of Samoa, Samoa
Faainuseiamalie Latu
Department of Science, National University of Samoa, Samoa
Roya Ieremia
Department of Science, National University of Samoa, Samoa
Ietitaia Simi
Department of Science, National University of Samoa, Samoa
Gese Gese
Department of Science, National University of Samoa, Samoa
ABSTRACT
Chemical properties of soil are of importance as they influence the fertility of soil
i.e., what types of plants can grow and determines how well they will grow; as well
as the extent to which organisms habituating will survive and withstand changes
presented by any change. Since the pool of soil health data is still in the process of
advancing, this study proceeded to build a baseline that would be useful for future
research. Thus, the main research question was diverted directly to determine the
health of Soils in Samoa through the assessment of its individual property, i.e.,
chemical properties. In addition, results were used to generate inferential analysis
to denote climatic changes to the soil tested. The following are the overall results
for the chemical properties across the four sites during the 6 months period: pH=
6.4 ± 0.16; EC= 35 mS/s ± 4.55; CEC= 21.22 meq/100g ± 4.13; SOC= 2.14% ± 0.73 and
C:N ratio= 16:1± 4.01.
Keywords: Soil health; Climate change; Human activities; Environmental issues; Chemical
properties.
INTRODUCTION
Soil is defined as a natural medium that enables the growth of plant species and is the habitat
for micro-and macro-organisms. It is an interface that links all the spheres in the ecosystem
together. Soil plays a vital role in regulating the stability of ecosystem well-being and prevents
over-bearing effects of natural disasters or human activities on the environment. For instance,
it acts as a regulatory buffer to water balance due to its capacity to store soil and acid inputs
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Amosa, B. P., Imo, T., Latu, F., Ieremia, R., Simi, I., & Gese, G. (2022). Analysis of Chemical Properties in Soil in the Selected Sites in Samoa. European
Journal of Applied Sciences, 10(4). 170-183.
URL: http://dx.doi.org/10.14738/aivp.104.12491
through a base-cation exchange process and nutrient pollutants which influence most
ecological soil functions [1]. The organic material of the soil consists of 85% of post-mortal
substance, 10% plant roots, and 4% bacteria and fungi with 1% soil fauna [2]. The various
changes in climatic conditions have the potential to threaten the productivity of soil by altering
its properties and processes [3]. The two distinct weather seasons in Samoa are wet and dry,
where 70% of rainfall is expected throughout the wet season from May to October. Recently,
floods have occurred in a very abnormal state due to extensive rainfall that is recorded
throughout both weather periods. Cyclone Evan was the strongest tropical cyclone to ever hit
Samoa in 2012, which led to intense flooding along the Vaisigano River catchment and
prompted soil erosion. Samoa also recorded the highest rainfall levels and subsequently the
greatest flooding events in December 2020 and January 2021.
Waste is another area of concern in the environment of Samoa due to poor disposal methods at
the household level and on the national level despite expensive collection and disposal methods
established. The accumulation of man-made chemical substances from hazardous and solid
waste gives potential pathways for leachates to enter the soil and thus gives rise to the
degradation of soil health. Soil is addressed as a sub-topic under other environmental issues
such as climate change and deforestation yet, on its own, masking threats can influence vital
soil characteristics. According to a study conducted on the capacity of soil as a sink, it stores
about 2,500 pg of carbon more than other fields of terrestrial biota sink or harbouring about
two-thirds of carbon in ecosystems [4]. Healthy soils showcase good quality for growth and are
a major factor in an ecosystem’s productivity. Soil Health is not a single measurement rather, it
encompasses all the properties; biological, chemical, and physical that function internally
together to maintain the ability of soil to function and support life. In addition, healthy soil is
always the foundation of the food production system. Soils help to produce healthy crops. In
the natural environment, soil pH has an enormous influence on soil biogeochemical processes.
Soil pH is, therefore, described as the “master soil variable” that influences myriads of soil's
biological, chemical, and physical properties and processes that affect plant growth and
biomass yield [5].
In spite of this, there is limited data available on the current situation regarding soil health and
whether its soil properties are different at this time compared to the past. Soil health is essential
because of its roles/functions to the ecosystem as a whole and there should be great interest
should be taken into account towards this component of the environment as well as the well- being of Earth in general. Therefore, this paper aims to address the well-being of soils in Samoa
in midst of climatic changes it is experiencing at the moment. It is also in hopes, that this paper
will provide more data to contribute more to Samoa’s pool of knowledge regarding soil.
Furthermore, it hopes to gather factual information that contributes to the pool of knowledge
in Samoa primarily and then worldwide comprehension. The main research question for this
study is: What is the current trend of the health status of soil in Samoa from ridge to reef (R2R)
and how does climate change a global issue influences the changes within the properties of Soil?
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METHODOLOGY
Sample sites
Figure 1: Selected sites along the Vaisigano River Catchment
Sample preparation
A composite sampling was used to collect each soil sample from the four selected soil sites. A
random area was chosen based on whether it was both safe and easy to access, then a 15m
measuring tape was laid in a zig-zag position to have different margins of the chosen area
instead of a straight-line extraction which would have not been represented. An auger was used
to drill each point marked, 15 cm deep into the soil. There were about 15 sub-samples from
each of the four selected sites of two samples, transferred into a plastic bag and tied tightly to
prevent any excess moisture or air from entering the samples as they were transported to the
laboratory straight after a day later the most. The samples were then air-dried in an open,
screen-wired room for a week. The GPS readings were done on all the days the collection was
conducted this was to, later on, provide an average location across the spell of the research to
assist in the development of a sample site map.
Sieving samples
When the soil samples have been fully dehydrated and deprived of moisture, they underwent
sieving where the samples were passed through a 2mm filter plate for most of the physical and
chemical analyses. Total nitrogen and organic carbon were however sieved under 0.25mm as
the particles required for the two analyses must be very finely ground. Sieving was especially
important to assure that the mixture was consistently homogeneous [6] throughout the six
months of sampling.
Analytical analysis of samples
The pH and temperature were measured using a digital pH and temperature meter. The
procedure of soil microbial biomass carbon (SMBC) was an amalgamation of two methods: (1)
fumigation- extraction [7] and (2) dichromate digestion and spectrophotometric measurement
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Amosa, B. P., Imo, T., Latu, F., Ieremia, R., Simi, I., & Gese, G. (2022). Analysis of Chemical Properties in Soil in the Selected Sites in Samoa. European
Journal of Applied Sciences, 10(4). 170-183.
URL: http://dx.doi.org/10.14738/aivp.104.12491
of light absorbance [8]. The Cation Exchange Capacity (CEC), Organic carbon (OC), and Nitrogen
were also measured.
Statistical analysis
When data is obtained from the laboratory tests, the statistical software Minitab will be used to
generate these numbers. This is to attain descriptive analysis of this study’s central tendencies;
mean, standard deviation, minimum and maximum for comparison purposes and to see the
trend amongst the samples. Furthermore, inferential analysis was also taken into account, to
seek the differences in means across each variable across the period of the study and the
selected sites, using the regression analysis. To find the correlation the relationship between
variables, this study made use of the One-Way Analysis of Variance (ANOVA).
RESULTS
Analysis of Soil Health Indicators by Site
A total of 12 samples were collected for each of the four sites across the time frame in which
the study was conducted, stretching from March and April (wet season) through May-August
(dry) all within the year 2021.
Table 1: Mean distribution of pH, EC, CEC, SOC, Total N, and C: N of all sites (mean ± SE)
Site pH EC mS/m CEC meq/100g SOC % C: N Ratio
Ala_a 6.48 ± 0.11 30.47 ± 3.48 15.89 ± 4.11 2.69 ± 1.47 10.5:1 ± 2.62
Ala_b 6.38 ± 0.12 42.33 ± 4.82 25.07 ± 4.92 1.73 ± 0.16 11.7:1± 2.27
Vail_a 6.17 ± 0.11 40.78 ± 3.64 22.43 ± 5.04 5.02 ± 3.02 13.6:1 ± 3.48
Vail_b 5.08 ± 0.49 24.15 ± 5.45 16.77 ± 2 1.31 ± 0.26 8.9:1 ± 1.36
Mag_a 6.62 ± 0.1 29.7 ± 10.4 14.77 ± 0.7 1.78 ± 0.41 23.3:1 ± 8.02
Mag_b 7 ± 0.08 28.57 ± 6.9 16.66 ± 1.43 1.14 ± 0.12 13.7:1 ± 2.09
Vais_a 6.83 ± 0.11 39.27 ± 3.05 24.3 ± 5.26 1.29 ± 0.12 16.2:1 ± 4.47
Vais_b 6.5 ± 0.14 44.8 ± 9.06 33.88 ± 9.61 2.14 ± 0.31 30.4:1 ± 7.94
Total
mean
6.4 ± 0.16 35 ± 4.55 21.2 ± 4.13 2.14 ± 0.73 16:01 ± 4.01
The mean of the site overall is 6.4 ± 0.2, with a minimum and maximum mean value ranging
from, 5.08 ± 0.49 to 7 ± 0.08 respectively. A pH of 7 is an indication of neutrality amongst all- natural entities and may be unexpected for tropical soils as they are expected to be more acidic.
Nevertheless, the pH for the four sites is within the ideal range for soil pH [9], especially in the
normal range for tropical countries. Although the range of pH of the sites is not statistically
variant, the ANOVA (Table 2) contradicts that there is a significant difference across the sites
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with a p-value of 0.00 which is below the null hypothesis of 0.05. Thus, a Tukey- post hoc, was
conducted to showcase which of the pairings from the sites influenced this p-value. By the
graph, Vailima sub-sample B (Vail_b) is the most significantly different from the other three
sites and was responsible for the dissimilarity of means overall across the sampled sites. The
Electro-conductivity overall site mean is 35.01 ± 5.85 with the minimum value found in Vailima
and the maximum value in Vaisigano. Thus, the EC of the sites does not coincide with the
optimal levels of 110 – 570 mS/m [10]. ANOVA analysis (table 3.3) for EC across the means of
the sites is at a p-value of 0.219, greater than p- 0.05 thus accepting the null hypothesis that all
means are equal. Cation exchange capacity means of the four sites combined is 21.22 ± 4.13,
with the maximum mean found in site B of Vaisigano and the lowest mean from site A of Magiagi
(Table 2). The CEC mean meets the measured CEC of the district of Afiamalu of 21.6meq/100g
but is greater than the mean CEC of the selected sites of that study by 10meq/100g. Although
the CEC among the sites (Alaoa, Vailima, Magiagi, and Vasigano) appear varied, ANOVA (Table
2) proves that the means are not significantly different but rather, comparable.
Table 1: Anova comparisons of pH, EC, CEC, SOC, Total N, and C: N between the 4 selected sites
p-value
pH 0.34
EC 0.22
CEC 0.12
SOC 0.38
C: N 0.04
Table 2 gives the soil organic carbon spatial mean is 2.14% ± .73, where the highest mean was
found in site A of Vailima and the lowest mean in site B of Magiagi respectively. The study on
Samoa’s soil sequence is within Upolu’s overall average of 2.6%, while it meets the suggested
2% for aggregation stability of SOC [11]. Despite the SOC appearing variant, the ANOVA analysis
(table 3.3) gives a p-value which also shows that there is not enough evidence to conclude that
there are differences among the means at the 0.05 level of significance. The C: N ratio in total is
16% ± 4.03, where the highest level is found in site B of Vaisigano and the lowest in site B in
Vailima. Furthermore, the ratios of carbon to nitrogen vary across the site, hence the p-value
<0.05. Figure 3.2 shows these significant differences: Vaisigano and Magiagi do not share a
significant similarity of means to Alaoa while Vailima’s mean of C: N ratio is mutually similar to
the other selected three sites.
DISCUSSION
pH
Most plants flourish in considerably acidic (4- 5) soils because pH provides them with easy
access to all nutrients, at the same time is accepted well by some micro-organisms
(earthworms) that convert nitrogen into forms that plants use. The mean range of pH across
the four sites was a minimum of 5.08 to a maximum of 7, denoting that the sampled soils were
within a scale of alkalinity to neutral. In tropical locations, this range is normal [12], [13] and
aligns with previous studies of soil in different locations of Samoa; Afiamalu with pH of 5.3;
Lalonea farm pH ranging from 4.8- 6.2 [14] and soils of selected farms exporting taros in Upolu
with an overall pH of 5.44 [15]. However, pH does not indicate soil fertility but it does interfere
with the availability of nutrients from the soil to plants. Soil pH affects the number of nutrients
and chemicals dissolved in the soil water and thus affects the number of nutrients available to
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Amosa, B. P., Imo, T., Latu, F., Ieremia, R., Simi, I., & Gese, G. (2022). Analysis of Chemical Properties in Soil in the Selected Sites in Samoa. European
Journal of Applied Sciences, 10(4). 170-183.
URL: http://dx.doi.org/10.14738/aivp.104.12491
plants [16]. Temperature and precipitation affect the rate of leaching and weathering of soil
minerals, yet for this study, the temperature was not measured as only rainfall trends were
acquired as an independent variable. Some nutrients are more readily available in acidic
conditions, while others are more readily available in alkaline conditions. In hot and humid
environments, soil pH decreases over time due to acidification from leaching from high rainfall
[17], which can account for the low pH quantified from the site Vailima. However, pH can’t
change over time due to heavy rainfall; rather, significant heavy rainfall trends over a
significantly long period. Topography is another factor that affects the pH levels of the soil in
two ways; it controls the water flow and material transport; the elevation can observably
influence the local temperature and precipitation. A study by [18] has determined that there is
a strong correlation between the chemistry of soil and topography in the O horizon (30- 60 cm
below the A and B horizon) thereby indicating that the topsoil (0- 20 cm) is strongly exposed
to topographic changes. Moreover, relatively high pH reduces the availability of nutrients to the
plants and microbes that require them in the soil [19]. Nevertheless, the pH ranges across all
sites found in this study, are within optimum levels to provide productive minerals for plant
support and the verdant physical surroundings take account of this statement.
Soil electroconductivity
Soil particles contain within them negative and positive ions that are opposingly attracted to
each other. As a result, that enticement has led to the possibility of the electrical current it
initiates to be measured, numerically. In addition, this transmission of electroconductivity is a
highway system that which the nutrients within the soil can mobilise and are readily made
available for the benefit of living things. Moreover, electrical conductivity (EC) is an index of
salt concentration and an indicator of electrolyte concentration of the solution [20]. The mean
soil EC range of this study has a minimum of 24.15 mS/m from site B of Vailima to 44.8 mS/m
of site B of Vaisigano. The overall mean for the four selected sites across the six-month-time
period of sampling and laboratory tests is 35 mS/m-1. Table 3 below shows the mean EC of
other studies conducted in New Zealand and Fiji where they share similar values and are below
40 mS/m-1, which according to [21] indicates that the soils are non-saline or contain low
amounts of excess salts. These studies were chosen for level comparisons specifically due to the
mutual depths of soil samples that were extracted and analysed. In general, a higher EC hinders
nutrient uptake by increasing the osmotic pressure of the nutrient solution, wasting nutrients,
and releasing more nutrients into the environment, leading to pollution, and congruently, lower
EC can seriously affect plant health and yield [22]. As EC increases, soil microorganism activity
decreases, impacting respiration, residue decomposition, nitrification, and denitrification.
Sodic soils have poor soil structure and poor infiltration or drainage as well as increased
toxicity. EC indirectly indicates the quantity of water and water-soluble nutrients that the
surrounding plants are accessible to.
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Table 2: Soil EC comparisons of the mean EC of this study to studies from Fiji and NZ
SITE EC REFERENCE
ALAOA, VAILIMA, MAGIAGI & VAISIGANO,
APIA, SAMOA 35 mS/m-1 This study
MASSEY UNIVERSITY, PALMERSTON NORTH,
NZ 21.9 mS/m-1 [23]
REWA DISTRICT, FIJI 31 mS/m-1 [22]
The major factor that influences soil electroconductivity is moisture, however, there are a few
factors that exist that also play a part in the electric current of soil [24]. Moisture can increase
and decrease the conductivity of moisture as it is capable of freeing ions within soil particles
into its system [25]. In agricultural fields, irrigation is the promptest way in which moisture
rapidly escalates in the soil as the large mass of agricultural growths could easily consume the
soil’s internal water storage. A physical property such as soil texture also has an impact on soil
EC through the size of particles that the aggregates are composed of. Therefore, indicates that
soils that have a greater content of smaller soil particles such as clay can conduct more electrical
current than do soils that have a higher content of larger/big soil particles such as silt and sand
particles (low levels of clay contents) [26], [27]. Furthermore, the previous factor rationales the
increase of electroconductivity as it moves into the deep depths of soil [28]. In the deeper
horizons or depths of the soil profile, it is very rich in organic matter, nutrients, and water which
can be supplied from aquifers of groundwater table, which are some of the favourable
conditions that EC voluntarily excels in and is also unideal of enzyme activities as it declines in
the deeper compartments [29]. Therefore, according to [30] from its study, soil EC was tested
on different soil samples with different depths whether it was pervaded with fertilizers or not.
The collected results concluded, that the electrical conductivity of the soil is directly
proportional to the nutrient concentration and contrariwise Ly comparative to a depth of soil.
Moreover, as stated before, the EC of soil is also an index measurement for the amount of salt
concentration in the soil. If the value of EC in the soil is recorded to be relatively high or above
the ideal range for the respective soils in any location, then in regards to fertilization, it is not
required to spray any amounts in those soils, rather flush it with water to avoid damage to plant
roots [31]. As follows, the mean range of soil EC obtained for this study (Table 3) is low by the
studies shown in Table 4 construing that the soils tested are non-saline soils.
Cation Exchange Capacity (CEC)
Although the overall soil texture for this study resulted in sandy loam where the sand particles
are dominant, this texture still contains enough clay and sediments that are competent enough
for soil fertility and structure [32], hence, the more relevant cation exchange capacity analysis.
CEC is a useful indicator of soil fertility because it shows the soil's ability to supply important
plant nutrients and soil’s ability to hold cations by electrical attraction. The mean soil CEC and
mean range soil CEC range are 21.2 meq/100 and 14.77 meq/100 to 33.88 meq/100
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Amosa, B. P., Imo, T., Latu, F., Ieremia, R., Simi, I., & Gese, G. (2022). Analysis of Chemical Properties in Soil in the Selected Sites in Samoa. European
Journal of Applied Sciences, 10(4). 170-183.
URL: http://dx.doi.org/10.14738/aivp.104.12491
respectively. The mean soil CEC of this study lies within the same range as the means recorded
for Upolu- 29.6 meq/100g, scoping down more to Afiamalu of 21.6 meq/100g. By a standard of
CEC for each soil texture by the University of Georgia (Table 4), the mean CEC for this study falls
within the range of the clay loam texture, even though the overall texture is sandy loam.
Table 3: CEC at the pH 7.0 of different soil textures and soil
Soil texture CEC (meq/100g)
Sand 1-5
Fine Sandy Loam 5-10
Loam 5-15
Clay Loam 15-30
Clay >30
Retrieved from: [33]
The CEC of soils is influenced by different factors, one of them being soil type. The texture of
the soil is classified into three main groups: sand, clay, and silt; and each texture holds different
concentrations of CEC. Clay textures consist of the highest number of cations due to the nature
of their particles and the level of organic matter in them. As for silt, the number is less than clay
but greater than sand, which has the least or to nil. Nevertheless, the overall soil texture of this
study- sandy loam still contains 10-20% of clay constituents (Evans, 2001). Organic matter is
another factor that contributes to the level of CEC in soil. In a study exploring the challenges of
soil fertility restoration, it was found that the addition of compost caused the increased levels
of CEC in soil [34]. So, the highest recorded CEC was found in the site of Vailima (24.3 and 33.88
meq/100g), which then can be assumed that from the analysed samples, it had the highest
content of clay compared to the three selected sites. Although it does directly stimulate the rate
of soil CEC, rainfall is also a conduit as it promotes rapid decomposition of dead plant materials
that later on accumulate in the soil [35]. In regards to pH and its impact on soil CEC, it has been
presumed that most soils, especially clay textures are dependent upon pH. As soil acidity
increases (pH decreases), more H+ ions are added to the colloid. They push other cations from
the colloid into the soil aqueous solution. Conversely, as the soil becomes more alkaline
(increasing pH), the number of cations available in the solution decreases and this is because
fewer H + ions push positive ions out of the colloid into the soil solution and thus increase CEC
[36]. Accordingly, low pH and CEC could be assumed that there is a nutrient deficiency and
require additions of fertilizers. When CEC and pH are too high, then the soil can facilitate
without necessitating the need for fertilizers but rather, could lead to the event of leaching that
is bound to occur. Excessive or deficient measurements of CEC are not ideal for plant growth.
However, the correlation of this study’s CEC to pH is not statistically significant according to the
p-value from the regression test of 0.616> 0.05. This could be justified as the statement
regarding pH is specifically directed to the groups of clay as the overall soil texture for this study
is sandy loam, where the major component is sand. Nevertheless, the CEC across the four sites
seems to be adequate in providing the major cation nutrients, as the physical surrounding of
these sampled sites are flourishing in regards to plant or green cover.
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Soil Organic Carbon (SOC)
The trend of organic carbon in the soil samples collected ranged from 1.3% minimum to a
maximum of 5% being found in site A of Vailima. There is room for a possibility for differences
to be seen between the opposite sides of a river; due to the reason, that there were different
activities ongoing on one side that are not seen on the other. The samples site A of Vailima is
within a patch of plantation crops and is surrounded by a large forest cover and is exactly 3m
away from a cleared dirt road, for transporting to and from an EPC station in Vailima, as it is
the only accessible way for human mobilisation. In addition, there was an ongoing digging,
removing large rocks or clearance during the time of the study. In a study that investigated the
long-term effect of soil erosion, it was concluded that accelerated soil erosion associated with
conventional agriculture could occur at rates up to 100 times greater than the rate at which
natural soil formation takes place [37].
Land-use and land management practices can also influence the amount of organic matter in
the soil. Land management affects soil carbon due to the balance of carbon inputs against
outputs (i.e., how much organic matter is produced, how much is removed from the site, and
how much remains to be added to the soil). These two human activities interrupt the systems
that generate more organic matter and retain it on-site and tend to have higher soil organic
carbon levels. Schorth’s study was carried out before the establishment of the SWA and EPC
stations in Vailima and Alaoa, the increase of households near the Vaisigano banks down at
Magiagi and Vaisigano. These changes have the potential to participate in the decrease of SOC
in soils. Land management conversion can cause disruptions leading to imbalances between
the input and output equilibrium, between soil and the atmosphere. It is widely known that soil
is the largest terrestrial carbon sequestration pool. So, when more plants are being removed
and cultivated during a period and are not replaced in the same manner, then the amount of
carbon released is most definitely to be higher than that being absorbed and stored.
Accordingly, topsoil soil organic carbon that has been under conventional farming management
for some time will either be irreversible or decline altogether [38]. Agriculture conversion is
the biggest land-use change mismanagement that pushes more SOC out of the soil and less
absorbed. In a meta-analysis study, it was indicated that the soil C stocks decline after land-use
changes; from pasture to plantation (-10%), native forest to plantation (-13%), native forest to
crop (-42%), and pasture to crop (-59%) [39]. However, several practices exist that can be
incorporated by farmers or those who are in the agriculture/environment sector to assist in
preventing more loss of organic carbon from the soil. [40] concluded in their study that,
improved grazing management, fertilization, sowing of legumes and improved grass species,
irrigation, and conversion from cultivation all tend to lead to increased soil C, at rates ranging
from 0.105 to more than 1 Mg C·ha−1·yr−1. A periodical study in the eastern regions of China
found indicated by spatial statistics, showed that land-use changes had caused 30.7 ± 13.64Tg
of surface soil organic carbon loss, which accounts for 0.33% of the total carbon storage of 9.22
pg [41].
Soil moisture is also a confirmed potential factor that is capable of affecting SOC indirectly [42],
[43], [44] however, it is determined through the increase of soil organic matter production
evidently the dynamics of soil organic carbon. An increase of soil moisture from rainfall refers
to the long periods (weeks, months, or years) as misunderstandings that events such as floods
are beneficial, but in this case, it is not. When soil becomes overly saturated due to the
prolonged period that floods occur, oxygen becomes less available and prohibits bacteria from
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organic matter with nitrogen fertilizer, e.g., urea, this will make the carbon eating bacteria
develop faster [53].
CONCLUSION
Existing previous studies in Samoa have addressed analysing the properties of soil individually
and for crop development. Yet, there appear to be no studies based on the health of Samoa’s
soil as a whole. This study, therefore, was conducted to collect soil samples along the Vaisigano
river catchment and analysed statistically to provide an answer to the main research question
as follows:
What is the current trend of the health status of soil in Samoa from ridge to reef (R2R) and how
does climate change a global issue influences the changes within the properties of Soil?
The overall pH measured was 6.4, falling within the acidic spectrum but is close to neutral.
Acidic soils are common in the tropics due to heavy rainfall that is found throughout the year.
The highest record pH was found in site B of Magiagi- pH 7/neutral, whereas the lowest was
recorded in site B of Vailima with 5.08.
Soil electroconductivity is the pathway that allows cations and anions in the soil to mobilise to
cater to plants and organisms. The overall EC was 35 mS/m and is categorised as non-saline
soils as the EC measured was <50 mS/m. Regression analysis for the relationship of moisture
factor and EC resulted in 0.007, confirming the influence of water in soil particles on the level
of EC.
The Cation exchange capacity (CEC) is a useful indicator of soil fertility because it shows the
soil's ability to supply three important plant nutrients: calcium, magnesium, and potassium.
The soil texture as mentioned previously is sandy loam, however, this texture does contain
contents of clay. So, therefore, the overall CEC quantified was 21.22 mS/m.
The overall SOC was 2.14%. Mis-management of land-use practices is acknowledged as an
anthropogenic activity with a great impact on the level of organic carbon in the soil. It refers
specifically to the act of deforestation or the removal of trees, that cater to the needs of people
due to population growth or for national economic development. The amount of water in the
soil, both indirectly and directly, affects the decomposition rate of organic matter. Thus, the
higher the rainfall the faster the decomposition rate increases as well. In combination with
changes in other properties, organic carbon will continue to rise in output rates than input and
stored.
The overall ratio was 16 C in 1 of Nitrogen ratio (16: 1). The highest recorded mean of C: N ratio
is found in the site of Vaisigano with a 30.4:1 ratio whereas site B of Vailima recorded the
minimum value of 8.9:1. C: N ratio between 20-30 leads to net nitrogen mobilization which is
Vaisigano. Above this, the mineral nitrogen is to be fixed by the microorganisms. On the other
hand, C: N ratio below 20 causes a very fast decomposition process resulting in ammonia and
soil carbon losses, which are the other studied sites.
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Amosa, B. P., Imo, T., Latu, F., Ieremia, R., Simi, I., & Gese, G. (2022). Analysis of Chemical Properties in Soil in the Selected Sites in Samoa. European
Journal of Applied Sciences, 10(4). 170-183.
URL: http://dx.doi.org/10.14738/aivp.104.12491
References
1. Carr, G., Nortcliff, S., & Potter, R. B. (2010). Water reuse for irrigated agriculture in Jordan: Challenges of soil
sustainability and the role of management strategies. Philosophical Transactions of the Royal Society A:
Mathematical, Physical and Engineering Sciences, 368(1931), 5315–5321.
https://doi.org/10.1098/rsta.2010.0181
2. Idowu, J., Es, H. Van, Schindelbeck, R., Abawi, G., Wolfe, D., Thies, J., Gugino, B., Moebius, B., & Clune, D.
(2003). Soil Health Assessment and management: The concepts. Analysis.
3. Brevick, E. C. (2013). Soils and Human Health- Overview. Soils and Human Health, 29–56.
4. Deb, S., Bhadoria, P. B. S., Mandal, B., Rakshit, A., & Singh, H. B. (2015). Soil organic carbon: Towards better
soil health, productivity and climate change mitigation. Climate Change and Environmental Sustainability,
3(1), 26. https://doi.org/10.5958/2320-642x.2015.00003.4
5. Ndema, N. E. ne, Etame, J., Taffouo, V. D. sireacute, & Bilong, P. (2010). Effects of some physical and chemical
characteristics of soil on productivity and yield of cowpea (Vigna unguiculata L. Walp.) in coastal region
(Cameroon). African Journal of Environmental Science and Technology, 4(3), 108–114.
https://doi.org/10.5897/ajest09.160
6. Motsara, M. R., & Roy, R. N. (2008). Guide to laboratory establishment for plant nutrient analysis. In Fao
Fertilizer and Plant Nutrition Bulletin 19.
7. Doyeni, M. O., Baksinskaite, A., & Suproniene, S. (2021). Effect of Animal Waste Based Digestate Fertilization
on Soil Microbial Activities , Greenhouse Gas Emissions and Spring Wheat Productivity in Loam and Sandy
Loam Soil.
8. Cai, Y., Peng, C., Qiu, S., Li, Y., & Gao, Y. (2011). Communications in Soil Science and Plant Analysis
Dichromate Digestion – Spectrophotometric Procedure for Determination of Soil Microbial Biomass Carbon
in Association with Fumigation – Extraction. April 2015, 37–41.
https://doi.org/10.1080/00103624.2011.623027
9. Schroth, C. L. (1971). Soil Sequences of Western Samoa. Pacific Science, 25(3), 291–300.
http://hdl.handle.net/10125/6055
10. Corwin, D. L., & Lesch, S. M. (2003). Application of Soil Electrical Conductivity to Precision Agriculture.
Agronomy Journal, 95(3), 455-471. https://doi.org/10.2134/agronj2003.0455
11. Post, W. ., & Mann, L. . (1990). Changes in Soil Organic Carbon and Nitrogen as a Result of Cultivation. Soils
and the Greenhouse Effect, 401–406.
12. Food Agriculture Organisation (FAO). (2006). The State of Food and Agriculture.
13. Nair, P. K. R. (2002). The Nature and Properties of Soils, 13th Edition. By N. C. Brady and R. R. Weil.
Agroforestry Systems, 54(3), 249. https://doi.org/10.1023/A:1016012810895
14. Morrison, R. ., & Ashgar, M. (1992). Soils of the Laloanea Farm, Northwestern Upolu, Western Samoa. Pacific
Science, 46(1), 35–45.
15. Guinto, D. F., Lauga, S., Dauara, L., Walasi, E., & Autufuga, D. (2015). SOIL HEALTH ASSESSMENT OF TARO (
C olocasia esculenta ) FARMS IN SAMOA. Wright 1963, 1–7.
16. Neina, D. (2019). The Role of Soil pH in Plant Nutrition and Soil Remediation. Applied and Environmental
Soil Science, 2019(3).
17. Osang, J. E., Uquetan, U. I., Oko, P. E., Egor, A. O., Ekwok, S. E., & Ekpo, C. M. (2017). Effect on pH Value of Rain
Water and Soil pH in River State Nigeria. Environ. & Forestry, 110(September 2018), 48174–48183.
18. Seibert, J., Stendahl, J., & Sørensen, R. (2007). Topographical influences on soil properties in boreal forests.
Geoderma, 141(1–2), 139–148. https://doi.org/10.1016/j.geoderma.2007.05.013
19. Costa, M. M., de Queiroz, D. M., de Assis, F., de Carvalho, P., dos Reis, E. F., & Santos, N. T. (2014). Moisture
content effect in the relationship between apparent electrical conductivity and soil attributes.Acta
Scientiarum - Agronomy, 36(4), 395–401. https://doi.org/10.4025/actasciagron.v36i4.18342
Page 13 of 14
182
European Journal of Applied Sciences (EJAS) Vol. 10, Issue 4, August-2022
Services for Science and Education – United Kingdom
20. Nemali, K. S., & Van Iersel, M. W. (2004). Light intensity and fertilizer concentration: II. Optimal fertilizer
solution concentration for species differing in light requirement and growth rate. HortScience, 39(6), 1293–
1297. https://doi.org/10.21273/hortsci.39.6.1293
21. Sachan, H. K., & Krishna, D. (2018). Nutrient status and their relationship with soil properties of dalo
(Colocasia esculenta (L.) Schott) growing areas of Rewa district in Fiji. Indian Journal of Agricultural
Research, 52(6), 696–699. https://doi.org/10.18805/IJARe.A-310
22. Samarakoon, U. C. (2006). Effect of Electrical Conductivity [EC] of the Nutrient Solution on Nutrient Uptake,
Growth and Yield of Leaf Lettuce (Lactuca sativa L.) in Stationary Culture Effect of organic matter
application on Cd accumulation of rice grains. View project Translocati. January.
https://www.researchgate.net/publication/260364158
23. El-naggar, A., Hedley, C., Horne, D., Roudier, P., Clothier, B., North, P., Zealand, N., Road, R., & Road, B. (2017).
USING ELECTRICAL CONDUCTIVITY IMAGING TO ESTIMATE. 2050(30), 1–13.
24. Doerge, T., Kitchen, N. R., & Lund., E. D. (1999). Soil Electrical Conductivity Mapping. Crop Insights, 9(19), 1–
4.
25. Hawkins, E., Fulton, J., & Port, K. (2017). Using Soil Electrical Conductivity (EC) to Delineate Field Variation.
https://ohioline.osu.edu/factsheet/fabe-565
26. USDA. (2000). Erosion and Sedimentation on Construction Sites. In Soil Quality – Urban Technical Note No.
1 (Issue 1).
27. Mojid, M. A. (2018). Agricultural of the Bangladesh Ban g ladesh Ban. February.
28. Corwin, D. L., & Lesch, S. M. (2003). Application of Soil Electrical Conductivity to Precision Agriculture.
Agronomy Journal, 95(3), 455. https://doi.org/10.2134/agronj2003.0455
29. Dick, R. ., & Kandeler, E. (2005). Enzymes in Soils. Encyclopedia of Soils in the Environment, 448–456.
https://doi.org/https://doi.org/10.1016/B0-12-348530-4/00146-6.
30. Othaman, N. N. C., Isa, M. N. M., Ismail, R. C., Ahmad, M. I., & Hui, C. K. (2020). Factors that affect soil electrical
conductivity (EC) based system for smart farming application. AIP Conference Proceedings, 2203(January).
https://doi.org/10.1063/1.5142147
31. Geren, H. (2015). Effects of different nitrogen levels on the grain yield and some yield components of quinoa
(Chenopodium quinoa willd.) under mediterranean climatic conditions. In Turkish Journal of Field Crops
(Vol. 20, Issue 1). https://doi.org/10.17557/.39586
32. Thompson, D. (2018). Characteristics of Sandy Loam Soil. Retrieved October 20, 2021, from
https://homeguides.sfgate.com/characteristics-sandy-loam-soil-50765.html
33. Sonon, L. S., Kissel, D. E., & Saha, U. (2017). Cation Exchange Capacity and Base Saturation-UGA Cooperative
Extension Circular 1040. 1–4. https://secure.caes.uga.edu/extension/publications/files/pdf/C 1040_2.PDF
34. Schlecht, E., Buerkert, A., Tielkes, E., & Bationo, A. (2006). A critical analysis of challenges and opportunities
for soil fertility restoration in Sudano-Sahelian West Africa. Nutrient Cycling in Agroecosystems, 76(2–3),
109–136. https://doi.org/10.1007/s10705-005-1670-z
35. Fatubarin, A., & Olojugba, M. . (2014). Effect of rainfall season on the chemical properties of the soil of a
Southern Guinea Savanna ecosystem in Nigeria. Journal of Ecology and The Natural Environment, 6(4), 182–
189. https://doi.org/10.5897/jene2013.0433
36. Halvin, J. ., Beaton, J. ., & Tisdale, S. . (2005). Soil Fertility and Fertilizers: An Introduction to Nutrient
Management.
37. Montgomery, D. R. (2007). Soil erosion and agricultural sustainability. 104(33), 13268–13272.
38. Liu, Z., Lozupone, C., Hamady, M., Bushman, F. D., & Knight, R. (2007). Short pyrosequencing reads suffice for
accurate microbial community analysis. Nucleic Acids Research, 35(18).
https://doi.org/10.1093/nar/gkm541
Page 14 of 14
183
Amosa, B. P., Imo, T., Latu, F., Ieremia, R., Simi, I., & Gese, G. (2022). Analysis of Chemical Properties in Soil in the Selected Sites in Samoa. European
Journal of Applied Sciences, 10(4). 170-183.
URL: http://dx.doi.org/10.14738/aivp.104.12491
39. Guo, L. ., & Gifford, R. . (2002). Soil carbon stocks and land use change: a meta analysis. Global Change
Biology, 8, 345–360.
40. Costa, M. M., de Queiroz, D. M., de Assis, F., de Carvalho, P., dos Reis, E. F., & Santos, N. T. (2014). Moisture
content effect in the relationship between apparent electrical conductivity and soil attributes.Acta
Scientiarum - Agronomy, 36(4), 395–401. https://doi.org/10.4025/actasciagron.v36i4.18342
41. Xia, X., Yang, Z., Xue, Y., Shao, X., Yu, T., & Hou, Q. (2017). Spatial analysis of land use change effect on soil
organic carbon stocks in the eastern regions of China between 1980 and 2000. Geoscience Frontiers, 8(3),
597–603. https://doi.org/10.1016/j.gsf.2016.06.003
42. Hursh, A., Ballantyne, A., Cooper, L., Maneta, M., Kimball, J., & Watts, J. (2017). The sensitivity of soil
respiration to soil temperature, moisture, and carbon supply at the global scale. Global Change Biology,
23(5), 2090–2103. https://doi.org/10.1111/gcb.13489
43. Kerr, D. D., & Ochsner, T. E. (2020). Soil organic carbon more strongly related to soil moisture than soil
temperature in temperate grasslands. Soil Science Society of America Journal, 84(2), 587–596.
https://doi.org/10.1002/saj2.20018
44. Safford, L. . (1975). Effect of manganese level in nutrient solution on growth and magnesium content of
Pinus radiata seedlings. Plant and Soil, 42, 239–295.
45. Balasubramanian, A. (2017). Soil Erosion- Causes and Effects Soil Erosion – Causes and Effects By Prof . A .
Balasubramanian Centre for Advanced Studies in Earth Science , University of Mysore , Mysore. February.
https://doi.org/10.13140/RG.2.2.26247.39841
46. Sakin, E., Deliboran, A., Sakin, E. D., & Aslan, H. (2011). Carbon and nitrogen stocks and C:N ratios of Harran
Plain soils. Romanian Agricultural Research, 2(28), 171–180. https://doi.org/10.15835/nsb245437
47. Neugebauer, M., Solowiej, P., Piechocki, J., Czekala, W & Janczak, D. (2017). The imfluence o the C: N ratio on
the compositing rate. International Journal of Smart Grid and Clean Energy. http://
doi.org./10.12720/sgce.6.1.54-60
48. Sosulski, T., Mercik, S., & Stepien, W. (2006). Content of nitrogen forms in soil and maize yeilds depending
on pH, organic carbon content and forms of nitrogen in fertilizers. 513, 447–455.
49. Nicholas, J. . (1984). Relation of organic carbon to soil properties and climate in the southern Great Plains.
Soil Science Society of America Journal, 48, 1382–1384.
50. Yuan, M., Fernández, F. G., Pittelkow, C. M., Greer, K. D., & Schaefer, D. (2020). Soil and crop response to
phosphorus and potassium management under conservation tillage. Agronomy Journal, 112:, 2302– 2316.
https://acsess.onlinelibrary.wiley.com/doi/10.1002/agj2.20114
51. Miller, A. J., Amundson, R., Burke, I. C., & Yonker, C. (2004). The effect of climate and cultivation on soil
organic C and N. Biogeochemistry, 67(1), 57–72. https://doi.org/10.1023/B:BIOG.0000015302.16640.a5
52. USDA. (2000). Erosion and Sedimentation on Construction Sites. In Soil Quality – Urban Technical Note No.
1 (Issue 1).
53. Post, W. ., & Mann, L. . (1990). Changes in Soil Organic Carbon and Nitrogen as a Result of Cultivation. Soils
and the Greenhouse Effect, 401–406.