Application of coconut shell biochar and rhizobacteria consortium to increase cocoa production (Theobroma cacao L.)

This research is aimed to study and investigate how coconut shell biochar interacts with rhizobacteria in increasing cocoa plant growth and production. This research was conducted at Kodeoha, North Kolaka, Southeast Sulawesi with an alluvial soil type and average rainfall is 192.17 mm from October 2022 until January 2023. The experiment was set using a split plot design with biochar dosage as the Main Plot consisted of four levels, namely 0 ton ha−1 (control), 2.5 ton ha−1, 5 ton ha−1, and 7.5 ton ha−1 and rhizobacteria concentration as Sub Plots consisted of four levels, namely 0 mL L−1, 50 mL L−1, 100 mL L−1, and 150 mL L−1. The results of the recent research show a significant interaction between biochar 10 ton ha−1 and rhizobacteria 150 mL L−1 on the parameter of percentage of cherelle wilt (60.47 %) and percentage estimated of surviving pods (28.68%). This doses suggested to be applied to cocoa plantations in the field to maintain maximum production. In addition, there is a need for further research using spesific bacteria especially potassium solvents in order to maximize the production potential.


Introduction
Cocoa (Theobroma cacao L.) is one of the industrial commodities that mostly managed by smallholder plantations in Indonesia.This can be proven by data from [1], which shows that Indonesia has produced around 15% of cocoa globally and is the world's sixth largest producer after several countries including Ivory Coast, Ghana, Ecuador, Cameroon, and Nigeria.The condition of community cocoa development carried out in various regions of Indonesia, has been facing issues that in turn have a direct impact on the worldwide price competitiveness of Indonesian cocoa products.
One of the major challenges is the Indonesia's cocoa yields in recent years that varied and tended to decrease year after year.The same trend also occurs in North Kolaka because of the increasing area of old, damaged, unproductive, and attacked by pests and diseases with heavy attack rates.This is supported by [2], which states that productive plant have decreased from 996,761 ha to 984,610 ha, while damaged plant have increase to 252,506 ha.
The declining production of the local cocoa also can be attributable to the soil fertility deterioration in cocoa cultivation regions [3].The deterioration is caused by erosion, nutrient leaching, poor land management techniques, and post-harvest nutrient extraction.About 546 kg of N, 96 kg of P, 246 kg of 1230 (2023) 012185 IOP Publishing doi:10.1088/1755-1315/1230/1/012185 2 K, and other nutrients such as Mg, Ca, and Fe are transported in every 1000 kg of cocoa beans harvested [4].
Soil degradation can be restored to its fertility potential.Biochar is an alternative soil amendment that may be employed.Biochar is a natural substance created by burning biomass in low or no oxygen condition so that it may be used by the soil as a source of organic matter.In this case, biochar will accumulate in the soil by maintaining a balance of soil properties to minimize the risk of nutrient leaching and ultimately have an impact on improving environmental quality [5].
Coconut shell is one of the basic materials that may be used to produce biochar.The potential for coconut shells is very large because the area of coconut plantations in Indonesia reaches 3.36 million ha with a production of 2.78 million tons year -1 and also the proportion of the shell of one coconut can reach around 15-19%.Coconut shell biochar has a relatively high carbon content (80.59 %).The high proportion of carbon content can affect the availability of nutrient N (0.12 %) and P (26.48 ppm) [6].The use of coconut shell biochar has been proven to improve soil pH and CEC.Increasing soil CEC by biochar minimizes the risk of cation leaching, such as K + and NH4 + .This is supported by [7] study, which found that applying 5 t ha -1 coconut shell biochar increased maize yields in terms of dry cob weight (2.37 t ha -1 ), dry biomass weight (4.04 t ha -1 ), and dry grain weight (1.85 t ha -1 ).
The advantages obtained from the use of biochar basically cannot replace the function of fertilizer.Hence, nutrients from other fertilizers must be added to increase the effect of biochar on plants.Addition of rhizobacteria consortia to the soil together with the biochar is one method for increasing the availability of soil nutrients.Rhizobacteria are bacteria found around plant roots that able to synthesize and regulate the concentration of various growth regulators.The bacteria also can serve as nutrient providers by fixing the N2 in the air and dissolving P nutrients in the soil asymbiotically [8].
The potential of biochar to create a suitable and adequate habitat for soil microbes by enhancing the physical structure of the soil shows the correlation between biochar and rhizobacteria.It is evident that by improving soil and ambient conditions, the process of deterioration by bacteria will accelerate [9].The effectiveness of biochar with the addition of soil microbes can also be supported by [10]'s research results which show that 30 g biochar with 40 mL local microorganism had a significant effect on improvement cocoa seedling, consisting of accelerated the height of plant (69.16 %), shoot dry weight (92.22 %), and root dry weight (7.0 %).

Location and experimental design
The research was conducted in the form of an experiment at a smallholder cocoa plantation in Kodeoha, North Kolaka, Southeast Sulawesi which is located in the northern part from north to south between 3°20' South Latitude -3°30'0' South Latitude and extends from west to east between 120°55'0' East Longitude -121°10'0' East Longitude.The trial was carried out from October 2022 until January 2023.The research was carried out as an experiment using a Split Plot Design with the main plot consists of 4 levels of coconut shell biochar, 0 ton ha -1 (control), 2.5 ton ha -1 , 5 ton ha -1 , and 7.5 ton ha -1 .The subplots consisted of 4 levels concentrations of the rhizobacteria consortium, 0 mL L -1 (control), 50 mL L -1 , 100 mL L -1 , and 150 mL L -1 .Each treatment was repeated three times with two sample plants for each experimental unit so that there were 96 experimental units.

Biochar preparation
Biochar material of coconut shells wastes were collected from farmers surrounding the research site.The coconut shell biochar was prepared with the steps as follows: a. Prior to pyrolysis process, the coconut shells were dried under the sun for 7 days.When smoke starts escaping from the chimney, the combustion indicator works properly.c.After 3.5 hours of combustion, the biochar was immediately sprayed with water to keep it from turning into ashes, then dried in the sun and crushed until the diameter was less than 2 mm.

Observation parameters and data analysis
Observations were made on parameters of number of flower buds produced, percentage of detached flower buds, number of cherelle produced, percentage of cherelle wilt, and percentage of estimated surviving pods.The observation was carried out ten times every two weeks starting from 2 to 20 weeks after treatment (WAT).Data was analysed in the form of variance (ANOVA).Data that demonstrates significant or very significant will be continued with further tests using the Least Significant Difference (LSD) α0.05.

Results and discussion
3.1.Results

Effect of Coconut Shells Biochar and Rhizobacteria on the Cocoa Flower Growth and Development
Application of coconut shell biochar inoculated with rhizobacteria improved the growth and development of cocoa flowers.The effect of biochar and rhizobacteria on the number of flowers, percentage of detached flower, and number of cherelle produced of cocoa are shown in Table 1.Numbers followed by the same letters in columns (a,b,c) are not statistically different in the LSD test α0.05.

Effect of Biochar and Rhizobacteria on Cherelle and Pod Development
Based on the ANOVA, it was found that there was a significant interaction between biochar and rhizobacteria treatments on the number of coco cherelle that can survive to develop into cocoa pods.Table 2 shows the percentage of cherelle wilt, while percentage of surviving pods is shown in Table 3.

Discussion
The results showed that there was an interaction between biochar and rhizobacteria on the percentage of cherelle wilt and percentage estimated of surviving pods.The interactions that occur are due to the synergy of biochar with best doses (10 tons) in providing a suitable habitat for the development of rhizobacteria.These bacteria can carry out their metabolic activities properly due to the sufficient energy needed in the C-organic form of the biochar.This can be seen in Tables 4 that there was an increase in soil organic C as the increasing dose of biochar.High source of organic matter through rhizobacteria can increase the efficiency of soil microbes to increase soil fertility.This is in line with a similar study by [11], which explained that the number of soil microorganisms in the field is strongly influenced by the balance of organic matter and good soil fertility conditions.
Improved soil qualities by biochar are linked to greater microbial enzymatic performance, particularly during nodulation because it is at the appropriate dose of 10 tons ha -1 and concentration of 100 mL L -1 .[12] found that biochar can enhance the efficiency of rhizobacterial nodulation with plants due to increased aeration by biochar, allowing the bacteria to live longer in the charcoal pores and infect the roots.This demonstrates that the use of biochar with suitable doses can improve the microbial mutualistic connection and allowing cocoa pods to develop until they mature.
The great yield potential demonstrated is also inextricably linked to rhizobacteria's function.There is evidence supporting the biochar particle small size, which increases their potential to be degraded by bacteria.This proves that a dose of 10 tons of biochar is sufficient doses so the surface between pores is relatively narrow.The smaller surface morphological structure of the biochar, the more chances for positive or negative charges from the biochar's surface during hydrolysis in the soil.The resulting positive or negative charge can promote the exchange of cation or anion soil nutrients for utilization by plants.This is consistent with the findings of [13], who claim that the particle size of biochar has a significant impact on the distribution of soil porous structure.
The increased yield component is further supported by the plants high water absorption capacity as a result of the biochar administration, allowing the plants to efficiently transfer the photosynthate results to the harvested portion.This is consistent with [14] opinion, which states that the ability of plants to produce photosynthates (source), provide and produce clean photosynthates to storage organs (sinks), and the ability of sink users to convert photosynthates into economic results all play a significant role in a plant's production increase.
The addition of rhizobacteria to biochar not only boosted the number of pods collected, but it also suppressed the growth of cherelle wilt compared to the treatment without biochar and rhizobacteria.These conditions imply that rhizobacteria at 150 mL L -1 concentrations are successful in delivering micronutrients as a result of the dissolving process, and the balance of phytohormones such as auxins, cytokinins, and gibberellins in the pod valves becomes more satisfied.Increased phytohormone concentration in the pods helps the fruit to develop more ideally, which indirectly increases the percentage of cherelle wilt.This situation is further supported by the Hormone Directed Transport idea proposed by [15] in [16], which states that assimilates travel towards plant sections with high concentrations of growth chemicals.
The ability of rhizobacteria to enhance fruit growth also suggests a significant interaction in the rhizosphere, where when biochar comes into contact with root hairs, a potential difference between the roots and the soil is created, inducing the microbes surrounding the roots to boost their capacity to release ions, nutrients, and electrons.This is consistent with [17] claim that a change in the potential of the root membrane causes biochar to behave like a circuit board between resistors and capacitors, allowing plants to release and even store nutritional ions and electrons at any moment.
The results suggest that using the rhizobacteria consortium produced a better response than using no rhizobacteria.This is because the N-fixing and P-solvent groups are the primary components of rhizobacteria.The formation of organic acids is the method by which rhizobacteria fix and dissolve macronutrients from insoluble forms or structural forms that are not accessible.The protons (H + ) generated by the bacteria will subsequently be in charge of replenishing nutrients at the adsorption site so that they become accessible to plants.According to [18], soil microbes have the ability to secrete organic acids such as acetic acid, formic acid, lactic acid, oxalic acid, malic acid, citric acid, and amino acids, as well as regulatory substances, to play a role in decreasing soil pH and breaking bonds in several forms of macronutrient compounds to increase nutrient availability in soil solution.
Increased macronutrient levels as a result of the usage of rhizobacteria consortia at a suitable concentration on 150 mL L -1 also imply an increase in the quantity of CO2 that may be digested, which can indirectly improve photosynthetic product assimilation.According to [19], if a plant lacks one of the macronutrients, the transfer of carbohydrates from the leaves to other organs is impeded, causing photosynthetic results to accumulate in the leaves and slow the rate of photosynthesis.This assertion was also corroborated by [20], who stated that following the wilting period, there is no more conflict between the fruit and other organs for assimilates in the form of carbs, therefore fruit growth becomes more optimum.
The amount of plant response is not primarily due to the usage of biochar and rhizobacteria, but rather these components work as facilitators to efficiently absorb nutrients from NPK fertilizer.This is because, while biochar with carbon as its principal element can improve the physical and chemical qualities of the soil, it cannot operate as a true nutritional enhancer in the same way that fertilizer does.[21] agree, stating that biochar may be loaded with nutrients from fertilizers, boosting soil buffering capacity while simultaneously increasing fertilization efficiency.

Conclusion
Based on the results of the recent study, it can be concluded that there is significant effect of interaction between biochar 10 ton ha -1 and rhizobacteria 150 mL L -1 on the parameter of percentage of cherelle wilt (60.47 %) and percentage estimated of surviving pods (28.68%).Biochar 10 ton ha -1 independently showed best results for number of flowering buds (43.83 buds) and biochar 15 ton ha -1 showed best results for percentage detached flower buds (75.60 %) and cherelle produced (35.29 cherelle).In addition, rhizobacteria 150 mL L -1 showed best results for number of flowering buds (43.29 buds) and rhizobacteria 100 mL L -1 showed best result for percentage detached flower buds (75.67 %) and cherelle produced (32.13 cherelle).
b.A basic vertical pyrolysator composed of 2 drums was used, with air cavities added at the bottom, center, and top of the drum to ensure equal combustion.A bimetal thermometer was positioned in the center of the tool to help in regulating the combustion temperature ranged, between 300 o C and 1230 (2023) 012185 IOP Publishing doi:10.1088/1755-1315/1230/1/0121853 560 o C. When the temperature in the drum exceeds 200 o C, the pyrolysator is closed.

Table 1 .
Effect of Coconut Shell Biochar and Rhizobacteria on the Cocoa Flower Growth

Table 2 .
Effect of Interaction of Biochar and Rhizobacteria on the Percentage of Cherelle Wilt.
Numbers followed by the identical letters in columns (a,b,c) and rows (p,q,r) are not statistically different in the LSD test α 0.05.(CV: Comparison value)

Table 3 .
Effect of Interaction of Biochar and Rhizobacteria on the Percentage Estimated of Surviving Pods (%).
Numbers followed by the identical letters in columns (a,b,c) and rows (p,q,r) are not statistically different in the LSD test α 0.05.(CV:Comparisonvalue)3.1.3.Effect of Biochar and Rhizobacteria on Soil Chemical PropertiesApplication of coconut shell biochar inoculated with rhizobacteria improved the soil chemical properties.The effect of biochar and rhizobacteria on pH, organic matter, P2O5, and exchange cation are shown in Table4.

Table 4 .
Results of Soil Analysis Before & After Treatment.