IJERD – International Journal of Environmental and Rural Development (2021) 12-2

Research article
erdSoil Organic Carbon Stabilization on Forested andDeforested Red-yellow Soil under Different Temperature
Conditions
KEIJI AROSTEGUIGraduate School of Agriculture, Tokyo University of Agriculture, Tokyo, Japan
Email: karostegui@cientifica.edu.pe

MACHITO MIHARA*
Faculty of Regional Environment Science, Tokyo University of Agriculture, Tokyo, Japan
Email: m-mihara@nodai.ac.jp
Received 5 January 2021

Accepted 16 July 2021(*Corresponding Author)

Abstract Soil organic carbon (SOC) has an important role as a key indicator for soil healthdue to its contributions on mitigation and adaptation to climate change. Tropical areas coverwith Red-yellow soil (Udults) such as Amazon represents the highest amount of soil carbon
sources in the earth. Although it is affected by human impacts due to deforestation, it isimportant to maintain and increase SOC of tropical Red-yellow soil toward an optimal level
for meeting challenges such as mitigating climate change effects. The aim of this study is toanalyze the stabilization of soil organic carbon from Red-yellow soil under different
temperatures conditions. A detailed comparison was made between forested and deforested
conditions of Red-yellow soil. In order to analyze the temperature sensitivity, each treatment
was kept under 25ºC and 35ºC, and the soil respiration ratio (SRR) was measured as well as
SOC content by spectrophotometry method. Lastly, a treatment of biochar at 5% was added
as part of stabilization mechanisms of carbon. The experimental results showed that there
were significant differences in SOC content between forested conditions in contrast todeforested conditions, where 7.25 mg C/g was found in forest conditions while deforested
conditions was 5.68 mg C/g. Although it was not found significant change in SOC under
different temperature, SRR increased at 39% from 8.87 μL CO2/h/g to 11.90 μL CO2/h/g withtemperature changes from 25ºC to 35ºC. Additionally, biochar application contributes toincrease the value of SOC at more than 2.66 mg C/g in all treatments, however, it did not
make a significant difference in SRR by temperature changes. Thus, biochar works as carbon
sources to maintain and increase SOC content, but stabilization effects on Soil Respiration
Ratio (SRR) should be observed in long term.
Keywords soil organic carbon, soil respiration rate, temperature sensitive, biochar

INTRODUCTION
The SOC represents between 50% to 58% of the soil organic matter content, which has an importantfunction of storing nutrients for plants, improving soil structural stability to enhance soil fertility andproviding mechanism to mitigate climate change effects. Turnover of SOC in terrestrial ecosystems
is dynamic and human impacts can turn SOC into either a net sink or a net source of greenhousegases (GHG) to the atmosphere (Trivedi et al., 2018).
The impact of climate change on SOC stocks is variable according to the soil type and location,
however temperature changes and increasing frequency of extreme drought events are probably
leading to increased loss of SOC. Although significant scientific progress has been achieved related
to understanding of SOC dynamic, mechanism of protection and stabilization of SOC stocks in shortterm and at different conditions still face complicated challenges impeding effectives conservation
strategies (Pribyl, 2010).
The Red-yellow soil (Udults), mainly located in Amazon area, has an important role in global
carbon changes, making this area as a considerable interest to quantify emissions when deforestationⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2021) 12-2

converts these forests into pasture or other land uses (de Oliveira Marques et al., 2017). Maintaining
carbon stocks in Red-yellow soils of tropical forests such as Amazon area has increasingly becomea justification for governments to take measures of reforesting rather than allowing them to be
deforested. Nevertheless, deforestation has accelerated the process of forest fragmentation in
Amazon area, resulting in changes in carbon stocks in biomass and soil (Barros and Fearnside, 2016).
The enhance of soil microbe’s activity is stimulated by increasing of environment temperature,causing a higher release of microbial CO2 (Lloyd and Taylor, 1994), leading to soil C losses, higher
soil respiration rate and a positive contribution to global warming. In the short-term, increasing oftemperature results in a significant increase of microbial activity and decomposition rates. It has beenshown that decomposition of SOC increases with temperature, with the greatest proportional
increases being observed at low temperatures. It is a fundamental issue to estimate the extent to whichrising temperatures could destabilize SOC and make it available to decomposing microorganisms.
The proportion of SOC stored in the world’s soils is still argued and how it is vulnerable to theimpacts of warming of this century (Crowther et al., 2016).
Therefore, modeling approaches that consider changes in carbon availability and microbialactivity may be needed to improve understanding under different conditions on Red-yellow soil.
Forested and deforested conditions of soils have a significant effect on SOC that must be connectedwith respiration rate, decomposition and possible conservation strategies on Amazon area.
OBJETIVE
The present study aimed to analyze the quantity and stabilization of soil organic carbon from Redyellow soil, under different temperatures (25ºC and 35ºC) and conditions (forested and deforested).
Such study is important to provide information about potential carbon emissions and climate change
effects.
METHODOLOGYSoil Sample Source and Preparation
The current investigation involved sampling and analyzing two sites of Red-yellow soil to measure
SOC and SRR. The sites were selected from Miyako Island, which is located in Okinawa Prefecture,south of Japan. The soil sample was collected from a deforested and forested area with four samples
each site as repetitions (Carter and Gregorich, 2008). Air-dried soil at 1,000 g were sieve and weighed
into a labeled tray followed by adding 5% (w/w) of biochar as a biochar treatment. Samples werekept at approximate a field capacity moisture condition. Each treatment was divided into soil atambient conditions (25ºC) and warm conditions (35ºC), and by conditions (Forested and Deforested)
and biochar rate (0% and 5%).
Soil Organic Carbon Determination
Each one of the treatments and repetitions were analyzed by Spectrophotometric Procedure ofOrganic Carbon Contents of Soil (Wallinga et al., 1992). The soil at 50 mg were weight precisely,
and it was transferred carefully to a dry 100 mL volumetric flask. 10.0 mL of 0.333 M potassium
dichromate solution (K2Cr2O7) was added to each flask. 16.0 mL of concentrated sulphuric acid wereadded following by putting the flasks in a boiling water bath for 45 min. The samples were cooled in
the sink made up to the volume with distilled water. The samples were centrifuged for 10 min at
3,000 rpm.
For the preparation of standard series, 100 mL flasks containing sodium oxalate (Na2C2O4) withvolumes of 0, 25.0, 50.0, 75.0 and 100.0 mL were used as standard into the volumetric flask. Thesestandard series worked as 0, 5, 10, 15 and 20 mmol Cr+3 per litter of solution of standard series. Theabsorbance was measured in a 1 cm cuvette at a wavelength of 590 nm within 2 hours after oxidation.
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IJERD – International Journal of Environmental and Rural Development (2021) 12-2

SOC percentage were calculated by multiplying the Cr+3 concentrations found by 0.2250/w, where“w” is the weight of the air-dry soil sampled.
Soil Respiration Rate Determination
Air-dried soil at 10 g were weighted from each treatment into a 450 mL glass bottle followed byadding 3 mL of distilled water. The soil and water were mixed in the bottles then covered withperforated films to reduced evaporation. The SRR was determined by using the infrared gas analyzer
at time zero and measure again at the end of 1 h incubation (Sparda et al. 2016). The soil respiration
rate (SRR, μL CO2/h/g air-dried soil) was calculated as:
𝑆𝑅𝑅 = (𝐶𝑂2𝑓 − 𝐶𝑂2𝑖 ) ∗ 𝑉 ∗1000
𝑆(1)Where CO2i and CO2f are the initial and final CO2 concentrations (ppm) of the 1 h incubation,
respectively, and V is the space volume of the bottle with the soil sample (450 mL). The amount ofsoil (S) was 10.0 g. Four repetition were measured for each one of the treatments.
Statistical Analysis
The comparison of the average of each one of the treatments were analyzed through Shapiro-Wilk
Normality and Levene Homogeneity test. The one-way ANOVA test were performed to determine
if there are differences through variance analysis. Then, Tukey test was applied to determine thedifferences between treatments. In addition, a Box-Cox transformation was performed to fit theANOVA test. All the tests were performed using RStudio (version 1.2.5042) for statistical analysesof the data. Analyses were performed at the significant level of P≤0.05.
RESULTS AND DISCUSSION
Mean values and standard deviation of Soil Organic Carbon (mg/g) and Soil Respiration Rate(μLCO2/h/g) of treatments at Forested and Deforested condition, biochar rates and temperature, areshown in Table 1. The amount of organic carbon obtained in this study indicated significantdifferences (P<0.05) between treatments (Forested vs Deforested). In previous studies, the amountof Soil Organic Carbon has been analyzed at Forested and Deforested conditions (Fujisaki et al.,2017), where the values on Forested condition were found higher that Deforested condition. The
theoretical basis for this is as follows. The forest keeps equilibrium between incomes and outcomesof carbon while deforestation cuts incomes and increase outcomes in the short term.
Table 1 Soil Organic Carbon (SOC) content and Soil Respiration Rate (SRR) ofdifferent conditions, biochar rate and temperatureCondition

Biochar0%

Forested
5%0%
Deforested
5%

Tº
25º
35º
25º
35º
25º
35º
25º
35º

SOC (mg/g)
7.24 ± 0.04 a
7.61 ± 0.43 a
10.27 ± 0.39 b
10.97 ± 0.37 b
5.68 ± 0.46 c
6.6 ± 0.44 cd
4.99 ± 0.09 c
5.52 ± 0.53 c

SRR (μL CO2/h/g)
8.87 ± 0.20 a
12.14 ± 0.20 b
8.53 ± 0.04 a
11.9 ± 0.13 b
6.57 ± 0.02 c
4.93 ± 0.13 d5.51 ± 0.09 d
4.88 ± 0.24 d

The letters indicate the significant different of result among the treatments at 95% of confidence level.

On the other hand, the addition of biochar at 5% rate on soil showed a considerable different on
SOC rather than 0% treatment. Biochar is composed by high values of organic matter which includes
organic carbon (Oladele and Adetunji, 2020). The biochar increased values of SOC in ForestedⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2021) 12-2conditions at 5% rate in contrast of 0%, however, there were not differences found on Deforested at
5% in contrast of 0%. Temperature changes did not show significant difference between treatments
in short term. Liu et al. (2021) described the degradation of organic carbon in long-term by microbes
at warm conditions as a reduction in the amount of SOC, this explain the non-significant change inthe values of SOC by temperature in short-term.

Fig. 1 Soil Organic Carbon content and Soil Respiration Rate of each treatment
It can be seen in Fig. 1 that the Soil Respiration Rate was altered by temperature in the shortterm. In Forested conditions, values of SRR reached 12 μL CO2/h/g in contrast to values lower than
9 μL CO2/h/g (39% higher in warm conditions). The increased of temperature in soil reflects a
considerable change in microbial activity in the short-term, which means an increase of CO2 released.
Although biochar addition shows a considerable increase of SOC, there is not stabilization of SRR
under warm conditions. Xu et al. (2019) describe the activation and stabilization of carbon by biocharin the middle-term, which not only increase carbon but also reduce the release of it.
Deforested conditions showed values of SRR lower in comparison with Forested. It is clear due
to the low amount of carbon in the Red-yellow soil and the relation with microbial activity. The SRR
reached values of 6.57 μL CO2/h/g and the lowest 4.93 μL CO2/h/g with significant differences (25%lower than Forested conditions). Effect of temperature on Deforested conditions showed an increasedin SRR values, but in the same way, biochar did not have a significant effect. Biochar application
has affected the SOC but the effects on SRR stabilization in the short-term is depending bytemperature and the microbial activity (Xu et al., 2019).
CONCLUSIONS
It is demonstrated that Deforested condition reduces significantly the amount of organic carbon inthe soil. Although Red-yellow soil has a low organic carbon content, this reduction can be recoveredby biochar addition. The loss of carbon by microbial activity increases by the effect of temperature
which has an important role through Soil Respiration Rate. The Forested conditions of Red-yellow
soil showed an increase of microbial activity due to the high carbon content, thus, the changes on
respiration are easily affected by weather such as temperature conditions. This process of organiccarbon degradation is not stabilized by biochar addition in the short-term. Finally, biochar works as
carbon sources to maintain and increase SOC content, but stabilization effect on Soil Respiration
Ratio (SRR) should be observed in long term under warm and ambient conditions as part of thestabilization process.
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