Corn-cob Biochar Characterization and Application Effects
10
1337 *Corresponding Author: [email protected]Corn-cob Biochar Characterization and Application Effects to Carbon Dioxide (CO 2 ) Evolution in Acid Soil Added with Different Types of Fertilizers Arsenio D. Bulfa Jr. 1,2 *, Gina Villegas-Pangga 3 , and Jose Edwin C. Cubelo 1 1 College of Agriculture, Silliman University, Dumaguete City, Negros Oriental 6200 Philippines 2 Graduate School, University of the Philippines Los Baños, College, Laguna 4031 Philippines 3 Agricultural Systems Institute, College of Agriculture and Food Sciences University of the Philippines Los Baños, College, Laguna 4031 Philippines Biochar, a carbon (C) rich material produced from biomass, is an inexpensive means of removing C from the atmosphere by incorporating it into the soil, where C sinks are formed for sequestration. The slow release of carbon dioxide (CO 2 ) from the soil is related to C sequestration, long-term storage of CO 2 , or other forms of C that help lessen CO 2 concentration. An incubation study was conducted in a laboratory to determine the effect of corn-cob biochar (CCB) application on Luisiana clay (Orthoxic Palehumults) acidic soil. The CO 2 evolution from the incubation of various mixtures of organic materials, inorganic fertilizers added with CCB was measured using a titration of hydrochloric acid (HCl). The biochar application rate was 10 t/ha, and the organic fertilizers at 5 t/ha. Results show that CCB contained essential plant elements like C, K (potassium), Si (silicon), Cu (copper), Na (sodium), and Cl (chlorine). It also possesses a large surface area and high average pore size. The CO 2 evolution increased in the first two weeks with a peak at Day 2, and the amount of cumulative CO 2 decreased after that in all treatments during the incubation period. Treatments with CCB showed a constant reduction in the amount of CO 2 . Keywords: biochar, biomass, CO 2 evolution, corn-cob, fertilizers, organic carbon INTRODUCTION Biochars are new, C-rich materials that could sequester C in soils and improve soil properties and agronomic performance (Glaser et al. 2015). Biochar has drawn interest among researchers because of its inherent benefits in the soil when applied. Biochar produced by the heat treatment of biomass under limited oxygen is highly stable and resistant to microbial decay (Prayogo et al. 2014). It is composed of recalcitrant C structures, and these properties prevent biochar from decomposition, which leads to long- time C storage (Surampalli et al. 2015). The pyrolysis conversion of waste biomass into biochar has attracted attention for two reasons. First, it can be used as a soil amendment for improving soil quality; second, storing biochar in soils is regarded as a means for permanently sequestering C (Lehmann et al. 2011). C sequestration, rehabilitation of degraded lands, reduced greenhouse gas (GHG) emissions, adsorption of contaminants to offset streams, and groundwater pollution are among the environment-related benefits linked with biochar. Studies have shown that biochar application into the soil can reduce CO 2 , CH 4 , and N 2 O (Hussain et al. 2016). Moreover, it is also known to improve the physical, chemical, and biological properties of soil. Philippine Journal of Science 150 (5): 1337-1346, October 2021 ISSN 0031 - 7683 Date Received: 19 May 2021
Corn-cob Biochar Characterization and Application Effects
Added with Different Types of Fertilizers
Arsenio D. Bulfa Jr.1,2*, Gina Villegas-Pangga3, and Jose Edwin C.
Cubelo1
1College of Agriculture, Silliman University, Dumaguete City,
Negros Oriental 6200 Philippines 2Graduate School, University of
the Philippines Los Baños, College, Laguna 4031 Philippines
3Agricultural Systems Institute, College of Agriculture and Food
Sciences University of the Philippines Los Baños, College, Laguna
4031 Philippines
Biochar, a carbon (C) rich material produced from biomass, is an
inexpensive means of removing C from the atmosphere by
incorporating it into the soil, where C sinks are formed for
sequestration. The slow release of carbon dioxide (CO2) from the
soil is related to C sequestration, long-term storage of CO2, or
other forms of C that help lessen CO2 concentration. An incubation
study was conducted in a laboratory to determine the effect of
corn-cob biochar (CCB) application on Luisiana clay (Orthoxic
Palehumults) acidic soil. The CO2 evolution from the incubation of
various mixtures of organic materials, inorganic fertilizers added
with CCB was measured using a titration of hydrochloric acid (HCl).
The biochar application rate was 10 t/ha, and the organic
fertilizers at 5 t/ha. Results show that CCB contained essential
plant elements like C, K (potassium), Si (silicon), Cu (copper), Na
(sodium), and Cl (chlorine). It also possesses a large surface area
and high average pore size. The CO2 evolution increased in the
first two weeks with a peak at Day 2, and the amount of cumulative
CO2 decreased after that in all treatments during the incubation
period. Treatments with CCB showed a constant reduction in the
amount of CO2.
Keywords: biochar, biomass, CO2 evolution, corn-cob, fertilizers,
organic carbon
INTRODUCTION Biochars are new, C-rich materials that could
sequester C in soils and improve soil properties and agronomic
performance (Glaser et al. 2015). Biochar has drawn interest among
researchers because of its inherent benefits in the soil when
applied. Biochar produced by the heat treatment of biomass under
limited oxygen is highly stable and resistant to microbial decay
(Prayogo et al. 2014). It is composed of recalcitrant C structures,
and these properties prevent biochar from decomposition, which
leads to long- time C storage (Surampalli et al. 2015).
The pyrolysis conversion of waste biomass into biochar has
attracted attention for two reasons. First, it can be used as a
soil amendment for improving soil quality; second, storing biochar
in soils is regarded as a means for permanently sequestering C
(Lehmann et al. 2011). C sequestration, rehabilitation of degraded
lands, reduced greenhouse gas (GHG) emissions, adsorption of
contaminants to offset streams, and groundwater pollution are among
the environment-related benefits linked with biochar. Studies have
shown that biochar application into the soil can reduce CO2, CH4,
and N2O (Hussain et al. 2016). Moreover, it is also known to
improve the physical, chemical, and biological properties of
soil.
Philippine Journal of Science 150 (5): 1337-1346, October 2021 ISSN
0031 - 7683 Date Received: 19 May 2021
1338
Soil physical properties such as bulk density (BD), particle
density (PD), soil porosity (SP), soil water infiltration, and
water holding capacity can be improved by biochar (Blanco-Canqui
2017). BD gradually decreases with increases in biochar
applications because it has a natural low BD that can also reduce
soil BD by interacting with soil particles and improving
aggregation and porosity, which improves water holding capacity as
a result. The large decreases in BD and PD resulting from biochar
application can influence SP. Changes in SP are attributed to the
low PD of biochar like its effect on the soil BD, and PD decreases.
However, biochar has a varying effect on water infiltration by
reducing the water movement along with the soil profile of sandy
loams while increasing it in the clay loam soil that improves water
(Blanco-Canqui 2017; Hussain et al. 2016; Surampalli et al. 2015).
Wilson (2013) states that adding biochar into unfertile and sandy
glacial soil would convert the gritty and granular sand into sponge
cake (thick, light, fluffy large chunks soft lump) with the ideal
image of a perfect “crumb” structure. This is evident in the
nutrient retention of biochar in the soil by stimulating plant
growth and increasing fertilizer efficiency, especially when added
to organic fertilizers such as compost (Schulz et al. 2013).
The soil chemical properties such as pH, organic matter (OM),
cation exchange capacity (CEC), electrical conductivity (EC), and
essential elements were improved by biochar in research findings.
Adekiya et al. (2020) mentioned that biochar application in most
degraded monoculture sites increased the pH and enhanced OM. This
is supported by also Hailegnaw et al. (2019), stating that biochar
addition increased pH significantly in incubated soils. Improvement
in EC, CEC, organic carbon (OC), and some essential plant nutrients
such as total nitrogen (N), exchangeable cations, and available
phosphorous of the soil was also observed. Similarly, Surampalli et
al. (2015) also state that biochar in the soil improves soil
nutrient retention capacity (e.g. increased NH4
+ and P concentrations and decreased NO3 – in
soil, reduced leaching of nutrients from the soil).
Biological properties soil properties are influenced by biochar
application. In particular, microbial populations that stimulate
the microbial activity of the soil were observed after biochar
applications (Surampalli et al. 2015). Recent studies have shown
that biochar stimulates plant growth and increases fertilizer
efficiency, especially when biochar is mixed with organic
fertilizers such as compost (Schulz et al. 2013). This is due to
the fungal- grown biomass in the soil. Interactions between the
biochar and the microbes are that biochar can act as a microbial
shelter with its pore structure and maintain nutrients for
microbial growth (Zhu et al. 2017).
Apart from these advantages of biochar applications, there is a
piece of evidence suggesting that a co-benefit of biochar amendment
is a reduction in soil CO2 emissions
(Lehmann et al. 2011). Since the 2000s, studies have been
accelerated on developing biochar-related technologies for
restoring C to depleted soils and sequestering significant amounts
of CO2. It appears that adding biochar would be a much more
efficient strategy for C sequestration. Further understanding of
the mechanisms of biochar amendment on soil organic C retention and
CO2 emission reduction in acid soil still needs to be established.
This experiment examined 1) the physical and chemical
characteristics of CCB and its 2) effect on the rate of CO2
evolution from the decomposing organic materials and inorganic
fertilizers mixed with biochar using CO2 as an index. Specifically,
this study hypothesizes that the addition of CCB will result in the
reduction of CO2 evolution in acid soil.
MATERIALS AND METHODS
Soil Collection The Luisiana clay loam soil (Orthoxic Palehumults)
was used in the experiment. The topsoil (up to 30 cm depth) was
collected and air-dried. After it was air-dried, it was cleaned
where all organic material debris and stones were removed and
sieved (2 mm).
Collection and Preparation of Corn-cob Feedstock The corn-cob was
collected from the newly harvested corn from the Agricultural
Science Institute (ASI) Composting and Demonstration Area, Pili
Drive, University of the Philippines Los Baños (UPLB). The corn-cob
was air-dried for a week to remove excess moisture. After drying,
the corn-cob was chopped into small pieces (3–5 cm) before placing
it inside the pyrolytic cookstove, where it was slowly
pyrolyzed.
CCB Production and Yield Through Slow Pyrolysis Biochar Cookstove
Production of CCB through slow pyrolysis at 300–650 °C was
conducted at ASI Composting and Demonstration Area using the
biochar-producing stove. Four (4) kg of dried corn-cob with 11.90%
moisture content was placed inside the feedstock vessel of the
stove. The cookstove was lighted through the adjustable inlet at
the bottom of the cookstove. The inlet controls the temperature and
air entry inside the feedstock vessel. The heating temperature was
measured at different time intervals using the K-type thermocouple
within 1 h heat treatment. After heating, the biochar was
transferred to an air-drying galvanized metal sheet.
CCB, Luisiana Clay Loam Soil, Organic Fertilizer, and Plant Tissue
Samples (Rice Straw and Gliricicidia sepium Leaves) Analyses CCB
was analyzed for total N by the Kjeldahl method
Philippine Journal of Science Vol. 150 No. 5, October 2021
Bulfa et al.: Corn-cob Biochar Effect on CO2 Evolution
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(Grewling and Peech 1960), total phosphorus (P) by the
Vanadomolydate method (Kitson and Mellon 1944), total K by flame
photometer (Grewling and Peech 1960), total calcium (Ca) by the
ethylenediaminetetraacetic acid (EDTA) method (Cheng and Bray
1951), total magnesium (Mg) by titration of Ca plus Mg with EDTA
(Cheng and Bray 1951), OC by the Walkley and Black method (Jackson
1958; Walkley 1947), and others (Fe, Zn, Cu, and Mn) using an
atomic absorption spectrophotometer (Russell et al. 1957) to assess
the magnitude of elements present in the CCB after slow
pyrolysis.
The clay loam soil was analyzed for pH at a soil-water mixture
ratio of 1:1 (w/v), biochar at biochar-water ratio 1:10 (w/v) using
a glass electrode pH meter, EC at soil-water ratio 1:1 (w/v) (Piper
1942), OM by the Walkley and Black method (Jackson 1958; Walkley
1947), available P using the Olsen method (Jackson 1958; Bray and
Kurtz 1945), and exchangeable K using a flame photometer (Black
1965; Peech 1945). The organic fertilizer produced from ASI
Composting and Demonstration Area was used in the experiment.
Organic fertilizer sample was also analyzed for chemical analysis
for total N by the Kjeldahl method (Grewling and Peech 1960), P by
the Vanadomolydate method (Kitson and Mellon 1944), K by flame
photometer (Grewling and Peech 1960), total Ca by the EDTA method
(Cheng and Bray 1951), total Mg by titration of Ca plus Mgwith EDTA
(Cheng and Bray 1951), and OC by the Walkley and Black method
(Jackson 1958; Walkley 1947), respectively. The plant tissue
samples of rice straw and Gliricidia sepium leaves were analyzed
for total N by the Kjeldahl method (Grewling and Peech 1960), total
P by the Vanadomolydate method (Kitson and Mellon 1944), and total
K by flame photometer (Grewling and Peech 1960). The analyses of
all samples were conducted at the ASI, Analytical Service
Laboratory, UPLB, Laguna, Philippines.
CCB Brunauer-Emmett-Teller (BET) Analysis and Transmission Electron
Microscope (TEM) Imaging and Energy Dispersive X-ray Spectroscopy
(EDS) The BET analysis was performed to determine the physical
adsorption of gas molecules on the solid surface and serves as the
basis for a critical analysis technique for measuring the average
surface area, pore size, and pore volume of CCB. The physical
properties were analyzed using the Quanta Chrome Nova 22200BET
automated N multilayer physisorption system at the Nanotechnology
Laboratory, UPLB. The sample was thoroughly mixed and oven-dried
for 24 h at 105 °C. The 100 mg dried sample was transferred to a
round bottom powder cell sample holder then subjected to an
automated degassing system at 300 °C at varying times. After the
degassing, the sample was subjected to a multipoint BET to
determine the average surface area, average pore radius, and
average pore volume.
TEM imaging was performed to reveal the accumulation of C and other
abundant essential elements located in discrete spots of the CCB
surfaces by obtaining the HAABF images. The surface morphological
of biochar samples was viewed at different magnifications from
1,000–40,000x using the JEOL JEM-2100F FE-TEM at the Materials
Science Division, Industrial Technology Development Institute,
Department of Science and Technology, General Santos Avenue,
Bicutan, Taguig City, Philippines.
CO2 Measurement Setup The mason jar (500 mL) with a dimension of
7.8 cm width x 13.7 cm height was used in the incubation of samples
(Figure 1). Fifty (50) g of soil was placed in the jar, and soil
moisture was maintained at a field capacity of 45% water-soil (w/w)
during the incubation period. The opening of each jar was wrapped
with plastic and tightened with a rubber band before the glass jar
cap was closed tightly. This glass jar was sealed to avoid leaking
gasses from the decomposing organic materials.
Figure 1. Incubation setup.
Philippine Journal of Science Vol. 150 No. 5, October 2021
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The CO2 that evolved from the soil added with different organic
materials and inorganic fertilizers was trapped by the sodium
hydroxide (NaOH) contained in a beaker inside the incubation jar.
CO2 concentration trapped in NaOH was determined by titration of
HCl.
The 10 treatments with three replicates and the amounts of added
materials used in this study are shown in Table 1. Fresh Gliricidia
sepium leaves were collected from the ASI Composting and
Demonstration Area. The leaves were air- dried, pulverized, and
sieved using a 2-mm sifter. Moreover, the rice straws were gathered
from the Philippine Rice Research Institute, Los Banos, Laguna,
Philippines. The treatments with mixed inorganic fertilizers were
composed of the following fertilizers and fertilizer grades:
complete fertilizer (14-14-14), ammonium phosphate (16-20-0), and
muriate of potash (0-0-60).
Organic sources of fertilizers that were added into the soil such
as rice straw and G. sepium were also weighed (0.5 for each sample
and 0.25 g for biochar); based on the fertilizer recommendation of
90 N, 60 P2O5, and30 K2O kg/ha, the total weights of inorganic
fertilizer sources added were 2.25 g N, 1.5 g P2O5 , and 0.75 g K2O
per 50g of soil per mason jar.
CO2 Evolution Determination by Titration In the data collection
during the incubation period, the NaOH contents from incubation jar
samples were transferred from the 50 mL beaker to a 125 mL
Erlenmeyer flask. Two to three drops of phenolphthalein and 1.0 mL
of 50% BaCl2 were added before titration using an acid burette. The
data collected from titration at Days 2, 5, 7, 14, 21, and 28 were
used to calculate the CO2 that evolved, and the results were
expressed as mg CO2 produced per 100 g soil. The formula used in
calculating the CO2 evolved was:
(1)
where mg of CO2 is the mg CO2 produced per 100 grams soil, B/V is
the volume of HCl (mL), N is the concentration of HCl (mol mL–1), M
is the molecular mass of CO2 (44 g mol–1), T is time in days, and 2
is the coefficient. Fifty (50) g of soil was used in this
incubation study, but the results were expressed as mg CO2 produced
per 100 g soil.
Statistical Analysis The data gathered in this study that was laid
out in a completely randomized design were analyzed using one- way
analysis of variance and least significant difference (LSD) through
the Statistical Tool for Agricultural Research (STAR) 2.0 software
developed by the International Rice Research Institute to determine
the
differences between treatment means at a 5% level of significance
by LSD.
RESULTS
CCB Production The quality and recovery of biochar after slow
pyrolysis may vary due to the feedstock’s different types and
moisture content, cooking temperature, and residence time, even
with the same feedstock used. In this study, a recovery of 1.75 kg
(43.75%) CCB from 4 kg biomass was recorded.
CCB Chemical Properties Table 2 shows the chemical properties of
CCB. The pH is very high (10.1), which is expected since biochar
generally has a very high pH and contains nutrient elements
(Villegas-Pangga 2021). Total N is low in the resultant biochar,
which may be attributable to the heating process. The total P is
low, while total K is high due to ash components of the biochar. Ca
concentration is low, while Fe is high at 1024 ppm. Mg is low, Zn
is very high at 220 ppm, Cu concentration is high at 14 ppm, and Mn
is observed to be high at 85 ppm. The yielding capacity of biochar
dramatically varies depending on the feedstock type because a
material typically comprises labile and recalcitrant oxygen and
hydrogen-containing fractions (Piash et al. 2017). Low temperature
and long residence time promote the production of biochar (Miranda
et al. 2012). The resultant CCB had higher pH and nutrient status
compared to its original feedstock. Since biochar is derived from
plant biomass, it has a high concentration of C and contains a
range of plant macronutrients like N, P, K Ca, Mg, and
micronutrients such as Fe, Zn, Cu, and Mn (Naeem et al.
2017).
Soil Chemical Properties The Luisiana clay loam is characterized as
a strongly acidic soil with pH 4.68 and has very low EC with 0.049
mS/cm. Soil EC is a crucial soil health indicator. It affects
plants’ performance, including soil microorganisms that have
critical roles in soil processes, including GHG emissions like CO2.
Although soil EC is not always directly correlated with specific
ions or salt concentrations in soil, it has been associated with
concentrations of essential plant nutrients like nitrates, K, and
Na. It is assumed that a strongly acidic lowers available P (6.24
ppm) and makes the soil deficient in K [0.08 cmol (+)/ kg soil]
(Table 3).
The rating of OM in the soil is moderate at 2.75%. The OM can be
derived from the decomposition of organic materials and is critical
in the soil’s physical, chemical,
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Table 1. Treatments of the incubation study on CO2 evolution.
Treatment Added organic materials (g)
Added inorganic nutrients (mg)
T3: soil + fresh Gliricidia sepium leaves 0.5 g G. sepium – –
–
T4: soil + biochar (10t/ha) + fresh Gliricidia sepium leaves
0.25 g biochar 0.5 g G. sepium
– – –
T6: soil + biochar (10t/ha) + dried rice straw
0.25 g biochar 0.5 g rice straw
– – –
0.25 g biochar 2.25 1.5 0.75
T9: soil + organic fertilizer (5t/ha) 0.125 g organic fertilizer –
– –
T10: soil + biochar (10t/ha) + organic fertilizer (5t/ha)
0.25 g biochar 0.125 g organic fertilizer
– – –
Table 2. Chemical properties of CCB.
Parameter pH OC N P K Ca Mg Fe Zn Cu Mn
(%) (ppm)
Corn-cob 10.1 8.76 1.37 0.67 2.70 0.22 0.51 1024 220 14 85
Table 3. Chemical properties of Luisiana clay loam soil used in
incubation.
Parameters Concentrations
Exchangeable K (cmol (+)/kg soil) 0.08
Table 4. Chemical properties of organic fertilizer, rice straw, and
Gliricidia sepium leaves.
Chemical properties
Organic materials
Organic fertilizer
OC 4.97 – –
Total N (%) 1.23 1.11 3.92
Total P (%) 4.43 0.15 0.23
Total K (%) 2.94 2.34 2.14
Total Ca (%) 5.40 0.19 1.14
Total Mg (%) 0.26 0.03 0.07
and biological health. The presence of OM as cementing agent is
essential in helping clods and aggregates resist abrasion. Even at
high OM, fertilizer application is suggested as a “starter” since
the N release is very low or unknown depending on soil conditions
that affect the mineralization rate. The available P concentration
is medium, while the exchangeable K is deficient.
Organic Fertilizer, Rice Straw, and Gliricidia sepium leaves
Chemical Properties Organic fertilizer. The OC, total N, total K,
and total Ca are very high at 4.97, 1.23, 2.94, and 5.40%,
respectively (Table 4). However, total P and total Mg are low at
4.43 and 0.26%, respectively. The OC content of organic fertilizer
can be of equal or greater importance than its N and P contents.
The application of organic fertilizer stimulates heterotrophic
bacterial biomass, which helps in the mineralization of nutrients
to facilitate primary productivity (Green 2015).
Rice straw. The total N and K are very high in rice straw at 1.11
and 2.34%, respectively. In contrast, total P, Ca, and Mg are very
low at 0.15, 0.19, and 0.03%, respectively.
Gliricidia sepium leaves. As expected, it was analyzed to have
higher concentrations of N (3.92%), followed by K (2.145) and Ca
(1.14%). However, it has a low total
Philippine Journal of Science Vol. 150 No. 5, October 2021
Bulfa et al.: Corn-cob Biochar Effect on CO2 Evolution
1342
P (0.23%). The high N-content of G. sepium is a critical feature to
be used as a raw material for composting.
CCB TEM Imaging and EDS The biochar particle analysis using TEM
shows heterogeneity at both presences of dominant elements and
percent by weight of each component (Figure 2). The CCB is highly
heterogeneous, and different particles have a unique and complex
composition (Joseph et al. 2010). It
increases with heat treatment by creating pores and cracks in the
biochar’s basal-structural sheet (Novak et al. 2009). The high
surface area and porosity relate to its high adsorption and
retention ability. These physical properties of CCB influence its
essential function in the soil and other related environmental
management strategies (Villegas-Pangga 2021). This is confirmed by
Hussain et al. (2016), noting that biochar application increases
soil pH, porosity, and water holding capacity plus stabilizes soil
OM through increased soil aggregation and reduced soil bulk density
(SBD) and tensile strength.
Figure 2. TEM image at 10,000x magnification (a). Bright field TEM
image of CCB particle at 30,000x magnification (b). HAABF image and
spectrum and elemental map (c). HAABF elemental map from (d) from
area of interest (A).
is influenced by the initial feedstock, heating duration and heat
treatment temperature, and the environment within the
biochar-producing cookstove. The high angle annular bright-field
(HAABF) spectrum on the areas of interest of the biochar sample is
shown in Figures 2a and b. C is the most abundant element of CCB
analyzed with EDS in weight percent (wt%) of the area analyzed. EDS
also indicates the presence of other elements such as Si, Cu, and
K. The elemental mapping shown in the figure by transmission
electron microscopy can mean many things. Still, looking at it from
the soil and soil microorganisms’ perspective, the presence of C is
engaging. Biochar rich in C can affect the diversity of
microorganisms and their metabolic activity, and the essential
elements it contains can be a good source for plant
nutrition.
BET Analysis CCB has a higher surface of 10.416 m2 g–. It also has
a larger average pore size of 21.496 and a higher average pore
volume of 0.002 cm3 g–. The surface area
Figure 3. BET surface area and pore size analysis (a). Multi-point
BET plot of CCB surface area at 10.416 m2 g–. (b) BJH method
desorption dV(log r) of CCB pore size at 21.495 and pore average
pore volume at 0.002 cm3g–.
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CO2 Evolution Figure 4 shows the cumulative CO2 evolution from
different treatments. Results show that a faster rate of CO2
release was observed in the first 14 d with a peak at Day two and
reduced after that in all treatments during the 4-wk incubation
period. These observations were similar to the incubation study of
Shen et al. (2017), stating that the highest CO2 efflux was
observed on the second day after the incubation started in the
soil, and amendment with biochar alone significantly decreased the
soil CO2 efflux on the first day of incubation.
DISCUSSION
Biochar Production through Slow Pyrolysis by Biochar-producing
Cookstove Several factors influence biochar yield. The type of
organic material and the conditions under which biochar is produced
dramatically affect its quality (Villegas-Pangga 2021). Novak et
al. (2009) showed that more biochar is recovered at the lower
pyrolysis temperatures due to minimal condensation of aliphatic
compounds and lower CH4, H2, and CO2 losses. Herbaceous feedstock
has a shorter duration of charring unlike woody feedstocks, which
usually take a more extended period in the slow pyrolysis process.
The yield of biochar is highly dependent on the pyrolysis
conditions (e.g. temperature, heating rate
Figure 4. Cumulative CO2 evolution during the incubation period of
biochar added with organic materials and inorganic fertilizers for
28 d.
T3 had the highest amount of CO2 evolved, followed by T4 and T5.
The CCB with inorganic and organic mixtures show a constant
decrease in the CO2 evolution compared to treatments without CCB
added. There was low CO2 evolution observed in both T9 and T10,
which had organic fertilizer addition because the organic
fertilizer had undergone substantial decomposition.
Total CO2 Evolution The total CO2 evolution of the treatments
ordered from highest to lowest were T3 (65.39 mg), T4 (63.81 mg),
T5 (25.99 mg), T6 (24.09 mg), T7 (13.18 mg), T8 (11.95 mg), T9
(10.48 mg), T10 (9.20 mg), T1 (9.74 mg), and T2 (9.52 mg), which
are highly significantly different (p < 0.01). It was observed
that treatments with biochar added reduced the CO2 evolution during
the decomposition of the materials inside the incubation jars. The
treatment
Figure 5. Total CO2 evolved after the incubation period.
with the highest CO2 evolution is T3 composed of soil and
Gliricidia sepium leaves, followed by T4 composed of soil,
Gliricidia sepium leaves, and biochar with a 1.58 mg CO2
difference. In contrast, T1 (soil alone) and T2 composed of soil
and biochar have the lowest evolutions with 9.74 mg and 9.52 mg,
respectively, with the lowest difference of 0.22 mg CO2. This
observation suggests that the application of CCB at 10 t/ha (0.25g)
to decomposing Gliricidia sepium leaves in 50 g soil hold as much
as 1.58 mg CO2. T5 composed of soil and rice straw compared to T6
composed of soil, rice straw, and biochar (which had 1.90 mg CO2)
had the highest evolution difference observed. The average CO2
evolution from all the treatments is 1.42 mg, estimated to be 56.81
kg CO2/ha (2,000,000 kg soil).
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Bulfa et al.: Corn-cob Biochar Effect on CO2 Evolution
1344
and time) and the physical and chemical properties of the raw
feedstock material. In this study, the heating time of 4-kg raw
corn-cob is 1 h to produce a 1.75 kg (43.75% recovery) CCB at
300–650 °C heating temperature.
Biochar Properties Chemical properties. The varying properties of
biochar can be due to the wide range of biomass materials and
production conditions (Villegas-Pangga 2021). The results of
chemical analysis and HAABF images of CCB are consistent with
Wijitkosum and Jiwnok (2019) study, which indicated that CCB
yielded the highest amount of C (81.35%). However, CCB in this
study has 88.4% analyzed with EDS in weight percent (wt%) on area
analyzed. The EDS also indicates the presence of other elements
such as Si, Cu, and K. The pH of CCB is also related to the
findings of Villegas-Pangga (2021), noting a mean pH value of 10.1
indicated high alkalinity. The alkalinity generally results from
the salts present in the ash. The high pH value of biochar might
result from the high K content, which coincides with the results of
this study. However, biochar products made from different
feedstocks could vary in chemical properties, even if the same
process was used to manufacture them (Villegas-Pangga 2021).
BET physisorption analysis. The CCB has a high surface area, high
average pore size, and high pore volume. Villegas-Pangga (2021)
stated that light biomass materials can have increased surface
areas and average pore size plus pore volume compared to woody
materials. The high surface area, high average pore size, and high
total pore volume make biochar appropriate for soil amendment in
capturing CO2 and other GHGs, decreasing SBD, increasing soil
moisture retention and aeration, and reducing leaching of plant
nutrients from the rhizosphere (Wijitkosum and Jiwnok 2019; Batista
et al. 2018). The increased surface area, pore size, and pore
volume of biochar is a crucial physical attribute of biochar
(Villegas- Pangga 2021). This structure can protect beneficial soil
microorganisms that help decompose organic materials providing OM
for the soil, which binds together soil particles and holds soil
nutrients for plant growth (Atkinson et al. 2010). Also, the
binding effect of biochar increases soil aggregation, which is the
reason to reduce soil losses in agriculture (Jien et al.
2015).
HAABF images and EDS analysis. The TEM images of CCB at different
magnifications in Figure 2 shows that it is mainly composed of C
and other essential plant elements such as Cu, O, Na, K, and Cl.
There are also traces of S, Si, Ca, Al (aluminum), and Fe (iron).
The HAABF images and elemental X-ray mapping of CCB show the
precise combination of fine and coarse cellulosic features related
to its raw material (Villegas-Pangga 2021). The EDS of CCB showing
mostly C can likely influence its
performance as a C sink in the soil and essential elements such as
soil amendment (Villegas-Pangga 2021).
CO2 Evolution Even in a short period, biochar addition decreases
CO2 evolution, which can be related to long-term storage of
atmospheric CO2 that may mitigate or defer global warming. Vasu
(2015) revealed that the addition of biochar reduces C loss and
increases soil C storage. The addition of biochar with organic and
inorganic fertilizers in acidic soil decreased CO2 evolution. This
is confirmed by Batista et al. (2018), noting that CO2 was
successfully captured by biochar related to both the surface
adsorption and chemical reaction. Findings such as these can be
assumed that incorporated biochar helps capture CO2 when added into
the soil.
The low CO2 evolution in biochar treated soil can be assumed that C
was retained in the soil medium. Thammasom et al. (2016) observed a
significant decrease in the intensity of GHGs from rice production
when applied with biochar. This observation was related to the
findings of Jien et al. (2015), stating that the CO2 evolution rate
was slightly lower with biochar addition within 70 days of
incubation.
CONCLUSION This study examined the characteristics of CCB and its
effect on the CO2 evolution from soil added with different
fertilizers. Findings show the CCB has a higher average surface
area, average pore size, and average pore volume. The CCB retained
most of the C and some essential plant elements from the original
organic raw material. It was also found out that its application in
acid soil with organic materials and inorganic fertilizers
decreased the CO2 evolution. Findings such as these can be assumed
that incorporated biochar helps capture CO2 when added into the
soil.
RECOMMENDATION The incubation study showed that the addition of CCB
into the soil reduces the CO2 evolution; hence, C is stored in the
soil, causing OC to increase in the ground that favors crop
productivity. Other research findings emphasize moisture’s
importance as an essential parameter to consider when measuring the
CO2 evolution rates. It is recommended that another study will be
done to identify the consistency of the CO2 evolution of different
organic materials mixed with biochar under other moisture
conditions.
Philippine Journal of Science Vol. 150 No. 5, October 2021
Bulfa et al.: Corn-cob Biochar Effect on CO2 Evolution
1345
ACKNOWLEDGEMENTS The authors would like to thank the German
Academic Exchange Service and the Southeast Asian Regional Center
for Graduate Study and Research in Agriculture for the research
funds.
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