Charcoal is simply carbon–rich product resulting from heating processes of organic materials such as wood, coconut shell, and other agricultural waste, without or with limited air. The process heating is also called as pyrolysis. Within the last decades, study on the role of charcoal agriculture or biochar has significantly increased, in line with increasing concern and tread of global warming, climate change, and environment degradation. Charcoal utilization is powerful approach to provide many problems solving such as food security, fuel scarcity, environment deterioration, and global warming in a simple and practical way. Charcoal approach is an ancient as well as the most recent technology utilized in human history. Further, due to it's important and strategies of utilizing charcoal on agriculture or biochar, it's said that the biochar approach is the single most important innovation for humanity`s environmental future .
Role of biochar on global warming mitigation
Climate change due to increasing green house gasses (GHGs) has became significant concerned in the last couple decades. It is indicated that increasing GHGs in the atmosphere will end up in catastrophic event in the near future. It provides clear and strong justification to take action on reducing GHGs emission and increasing GHGs sequestration. Three most important GHGs related to agriculture or any activities on soil are carbon dioxide (CO ), nitrous oxide (N O), and methane (CH ). Soil is both the source as well as the sink of these GHGs. Among them, CO is the most abundance in the atmosphere . Human activities contributing to N O to the atmosphere more than 3 Gt carbon dioxide equivalents (CO e) or about 8 % of global emission, in 2004, where agriculture was responsible for 42 % of the total emission .
The role of charcoal or biochar in mitigating global warming is through reducing GHGs emission or increasing GHGs sink in soil. As the global warming potential of CH is 25 times, and N O is 298 times of equivalent mass of CO , taking little action on reducing CH and N O emission or increasing their sink could be of significant benefit to the environment . Previous study by incorporating biochar or charcoal derived from agriculture waste into Typic Hapludand in laboratory experiment and reported that N O emission from charcoal treated soil was reduced up to less than 15 % compare to the N O emission of charcoal untreated soil . It was reported from their field experiment that application of charcoal capable of reducing N O emission from soil up to 15 mg N O · m in the initial year . They also noted that application of charcoal shown increasing soil pH; cations exchange capacity (CEC), potassium availability (K), as well as water retention in the soil . It is also noted that the quality of the charcoal itself has significantly affect its role in controlling N O and CH emission and sequestration. It was reported from their laboratory experiment that manure derived charcoal made in high temperature reduced N O emission to 0 %, while the manure derived charcoal made in low temperature has emitted N O gas 100 % compare to charcoal untreated soil . Besides reduction on N O emission, they also reported that application of charcoal made from caliandra, could completely suppressed the CH emission from soil .
Physically, charcoal surface is heterogeneous consisted of defect structure and complex metallic and organic compounds. The highly porous of charcoal has been shown to adsorb N O, CH4 and also CO as well as substrate for N O production including NH and NO . On the soil surface, charcoal adsorbs more sun energy than soil due to its darker color, causing higher temperature, than the surrounding micro environment, it may induce reaction rates.
Biochar stability in soil
Biochar/charcoal stability is one of many important aspects of biochar characteristics. Stability shows how long biochar is survived in soil system with minimum or without degradation. The more the biochar survive in soil system the better the biochar stability is. It means that the C applied in soil will remain in soil system for long time; means reduced C emission from soil system to the atmosphere. It is the purpose of managing GHGs to mitigate climate change. Other positive value of the biochar stability is how long the presence of biochar in soil system provides benefit to enhance soil properties and water quality. Previous studies showed that charcoal were very stable in soil environment. Charcoal has been found more than 10 000 yr as residues from forest fire [7,8]. Early research of carbon dating found that biochar in “Terra Preta” soils of Amazon range from 500 yr to 7 000 yr BP, it is more than 7 000 yr to 9 000 yr until now [9,10]. Although study of biochar has continuously in progressed, information on what is the residence time of biochar has not been widely agreed. It was suggested mean residence times of 1 300 yr to 2 600 yr under the dry land conditions of Northern Australia. The charcoal mean residence time vary with charcoal material as well as the soil environment condition where the biochar presence . Despite of its debate on the methodology to determine the biochar residence time, the great age of biochar in soil studies and many archeological finding of biochars are proof of its stability in soil system.
Role of biochar on Agriculture
Study on the effect of biochar application in soil to crop productions have been conducted in many countries with various climates during the last couple decades [12–16]. It has been reported that application of rice husk charcoal on soil developed from volcanic ash parent material in Indonesia, increased root nodule formation, plant growth and yield of soybean . Blackwell et al. also reported that the residual effect of charcoal application still detected until the tenth rotation especially for corn . Similar result also reported by other study that application of charcoal also increased nodule formation, mycorrhizal infection rates and the spore number of soybean planted in volcanic ash soil [12.]
Effect of charcoal application on maize and sorghum productions have also been reported that charcoal application increased colonization of roots by mycorrhizal fungi, reduced exchangeable Al, increased yield up to 30 %, 51 %, and 100 %, reduced soil acidity and increased K uptakes. The studies have been conducted in various country and climates such as Kenya, Australia, Colombia, and Indonesia [13,17,18].
Incorporating biochar of 0.79 t · ha into an Oxisol in Brazil capable of increasing 115 % to 320 % rice biomass. The charcoal was made from wood in local kilns, which was traditionally managed for long time . Other study conducted in Australia indicated that charcoal application of: 6 t · ha and 1.5 t · ha banded fertilizer into Haplix Xerosol increase 3 kg · ha to 400 kg · ha wheat yield.
Increasing agriculture production as effected by charcoal application in line with increasing soil nutrient transformation shown by increasing P and N uptake by plants. Despite its significant effect on nutrient transformation, the mechanism of how the stimulation of nitrification is still in the subject of on going debate. Most studies of biochar on agriculture was conducted in relatively short time period ranging from one to couple years, showing various result with general trend that biochar has positive effect on soil quality, plant growth and production. Couple studies however indicated that charcoal application need long term to effect on both soil properties as well as plant growth and production. Previous studied of Cheng  also confirm that significant microbial-induced changes take place in biochar in the long term and that the initial abiotic oxidation could facilitate further microbial oxidation.
This information that relatively different from most charcoal studied is of important information for further studied. The purpose of this study was to evaluate the effect of short-term biochar application on Ultisol properties in Bengkulu.
2. Materials and Methods
Data in this paper were apart of long-term biochar application in palm oil plantation established on Ultisol of Bengkulu starting in 2012. The same plots were used for multi year's biochar application, by applying of 12 ton · ha biochar per year or burning the biomass as well as chopping the biomass on the existing plots. In this particular paper, data has been collected from March 2013 to May 2014. Research was arranged in completely randomized block design with four treatments utilizing four difference biochars, they were: A (control without biochar); A (burned biomass presence on each plot); A (wood charcoal of 12 ton · ha ), and A (coconut cell charcoal of 12 ton · ha ). All treatments were repeated 12 times resulting in 48 experiment units.
Soil properties were recorded and used as variable in statistical analyses. The recorded soil physical properties including Bulk density (gravimetric method), Soil porosity (calculated based on BD and particle density method), soil aggregate stability (wet sieving method), water holding capacity (gravimetric method), field soil moisture (gravimetric method), and air-dried soil moisture (gravimetric method). The chemical soil properties were Soil pH (pH H O 1:2.5 measured with pH mater), Organic C (Walkey and Black method), Available N (wet destruction, Kjeldahl method), P (Bray I) and K (flame photometer), as well as cation exchange capacity.
All data were statistically analyzed using analysis of variance (ANOVA), F test with P 0.05. All significant difference variables were analyzed using Duncan Multiple Range Test (DMRT) at P 0.05.
3. Result and Discussion
Most biochar application did not significantly affect soil physical as well as chemical properties except available K. Resume of statistical analyses of all soil properties studied were presented in Table 1.
Among the 12 soil properties, only soil available K was significantly affected by application of biochar in this study. Further analysis utilizing Duncan Multiple Range Test showed that coconut cell biochar was the best charcoal in this study (0.65 me · 100 g ) compare with control (0.30 me · 100 g ), burned existing biomass (0.39 me · 100 g ), and wood biochar (0.33 me ·100 g ) (Table 2).
Application of 12 t · ha biochar did not affect most of recorded soil variables. It is probably insufficient amount to give significant effect to the recorded soil parameters. Studied conducted by Christophe reported that application of 11 t · ha charcoal in Amazonian soils did not give significant effect on CEC due to insufficient amount of added charcoal . Beside it insufficient amount, addition of fresh biochar could have contributed to its minimum effect on some soil properties. Lehmann indicated that fresh biochar has lower CEC than the aged biochar . Effect of biochar application on soil water holding capacity (WHC) has also been studied. It indicated that application of biochar did not significantly affect soil WHC, except for soil with sandy texture. Literature study of Glaser reported that application of biochar even reduces WHC on soil with clayey texture .
Application of biochar was expected to have significant effect on micro-environment through increasing solar energy adsorbed by the added biochar, which in turn capable of increasing soil temperature and microbial activities. This process was not detected in this study, most likely because the plots studied were under 3 yr old of oil palm vegetation, where their canopy overshadow most of the plots. Besides its oil palm canopy, the application of the biochar was incorporated in the top soil up to 10 cm depth, therefore most part of applicated biochar were inside the soil surface therefore the biochar has no effect on solar radiation adsorption.
Besides comparing among treatments to determine the best biochar application in this study, some data were also compared with the previous data, from previous study in the same plots. It was to evaluate if there was any change after a year of biochar application. Some selected data were presented in Table 3. Although statistical analyses were not performed on this data set, Table 3 shows that no parameter has significant change after one year of biochar application. It suggested that sufficient amount of biochar as well as sufficient time were required to enhance soil properties.
|Year I||Year II||Year I||Year II||Year I||Year II||Year I||Year II|
|Bulk Density (g · m )||1.08||1.07||1.08||1.02||1.04||1.06||1.00||1.01|
|Water Holding Capacity||0.76||0.78||0.79||0.85||0.79||0.77||0.85||0.77|
|Source: Rostalina and Prawito . A0 = Control (without biochar); A1 = Burned Existing Biomass; A2 = Wood Biochar (12 ton · ha ); A3 = Coconut Cell Biochar (12 ton · ha ).|
Short–term application of biochar in Ultisol of Bengkulu did not affect most of selected soil properties. Among those selected soil properties (bulk density, soil porosity, soil aggregate stability, water holding capacity, field soil moisture, air dried soil moisture, soil pH, organic C, available N, P and K, and cation exchange capacity) only available K was affected by biochar application. Coconut cell biochar showed best effect on available K (0.65 me 100 · g ) compare with control (0.30 me · 100 g ), burned existing biomass (0.39 me ·100 g ), and wood biochar (0.33 me · 100 g ). To use biochar as soil amendment, sufficient amount of biochar as well as time period should be considered.
Thanks and appreciation credited to Pevi, Atri, Bayu Gatra, and Renita, for their data collection in the first year of these experiments. Thanks, and appreciation also extended to Tia, Vitri, and Vera for their contribution on both field and laboratory data collection in the second year of these experiments. Special thank send to Junar for his serious and meticulous work nurturing these field experiments.