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.
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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
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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.
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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
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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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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.
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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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