Importance and uses of Biochar
Biochar is a carbon rich product that is produced by pyrolysis (heating in incomplete or partial absence of oxygen) of biomass at relatively low temperature (<700°C). Normally, a forest fire exceeds 800°C and a simple visible fire is already nearly 600°C. Biochar is very light carbon product. Biochar has been called Bio-Char, Charcoal (अंगार) or biomass derived black carbon, Agri-Char etc according to purpose of use. However, biochar is different from other because of the intention to incorporate in soil for agricultural and environmental benefits. Thus during the production of biochar special care are taken to optimize plant beneficial properties. It is also important to use the word ‘biochar’ in the scientific world to have consistency in research work and standardize the product.
Biochar is recently a huge interest for everyone mostly because of its two attributes. Firstly, most of the carbon in biochar is relatively stable in the soil. For example, the annual average turn over rate of the fine root system is 50% for different ecosystems i.e 50% of carbon stored in such roots will go to the atmosphere again within a year making decomposition a serious drawback for efficient carbon sequestration with biomass. But, biomass, during thermal decomposition (actually the degradation during heating is also decomposition) under absence of oxygen, attain a chemical structure making most part of biochar more resilient (>100 years) to decomposition in soil. This property makes biochar one of the potential tools to mitigate climate change through carbon sequestration in agriculture soil. Secondly, biochar has shown dramatic effects on plant production. The effects have been explained as a result of increased micronutrient and nutrient availability, increased microbial activity, increased water holding capacity, reduced soil toxicity etc. However, there are also results with no significant effects on plant production or reduced performance while biochar was applied. Until 2011, 50% of researches were positive, 30% were negative, and 20% were indifferent regarding growth and yield (Spokas, 2011).
Some reports have suggested water holding capacity as the major feature of biochar to improve crop performance. Biochar is under investigation as an approach to carbon sequestration to produce negative carbon dioxide emissions. Biochar thus has the potential to help mitigate climate change, via carbon sequestration. Independently, biochar can increase soil fertility of acidic soils (low pH soils), increase agricultural productivity, and provide protection against some foliar and soil-borne diseases. Furthermore, biochar reduces pressure on forests. Biochar is a stable solid, rich in carbon, and can endure in soil for thousands of years.
1. Carbon sink
The burning and natural decomposition of biomass and in particular agricultural waste adds large amounts of CO2 to the atmosphere. Biochar that is stable, fixed, and ‘recalcitrant’ carbon can store large amounts of greenhouse gases in the ground for centuries, potentially reducing or stalling the growth in atmospheric greenhouse gas levels; at the same time its presence in the earth can improve water quality, increase soil fertility, raise agricultural productivity, and reduce pressure on old-growth forests. Biochar can sequester carbon in the soil for hundreds to thousands of years, like coal.Such a carbon-negative technology would lead to a net withdrawal of CO2 from the atmosphere, while producing and consuming energy.
2. Soil amendment
Biochar is recognised as offering a number of benefits for soil health. Many benefits are related to the extremely porous nature of biochar. This structure is found to be very effective at retaining both water and water-soluble nutrients. The extreme suitability of biochar as a habitat for many beneficial soil micro organisms. Biochar can improve water quality, reduce soil emissions of greenhouse gases, reduce nutrient leaching, reduce soil acidity, and reduce irrigation and fertilizer requirements. Modest additions of biochar to soil reduce nitrous oxide N2O emissions by up to 80% and eliminate methane emissions, which are both more potent greenhouse gases than CO2.
3.Slash and char
Slash and char can keep up to 50% of the carbon in a highly stable form. Returning the biochar into the soil rather than removing it all for energy production reduces the need for nitrogen fertilizers, thereby reducing cost and emissions from fertilizer production and transport. Additionally, by improving the soil’s ability to be tilled, fertility, and productivity, biochar–enhanced soils can indefinitely sustain agricultural production, whereas non-enriched soils quickly become depleted of nutrients, forcing farmers to abandon the fields, producing a continuous slash and burn cycle and the continued loss of tropical rainforest.
Biochar is a desirable soil material in many locations due to its ability to attract and retain water. This is possible because of its porous structure and high surface area. As a result, nutrients, phosphorus, and agrochemicals are retained for the plants benefit. Plants therefore, are healthier and fertilizers leach less into surface or groundwater.
5. Energy production: bio-oil and syngas
Bio-oil can be used as a replacement for numerous applications where fuel oil is used, including fueling space heaters, furnaces, and boilers. If bio-oil is used without modification, care must be taken to prevent emissions of black carbon and other particulates. Syngas and bio-oil can also be “upgraded” to transportation fuels such as biodiesel and gasoline substitutes.
6. Relationship to climate change and soil carbon sequestration
As noted above, one of the most promising aspects of biochar with bioenergy production is that it could be an important renewable energy source with the potential to significantly mitigate greenhouse gas emissions and slow climate change. Figure below provides an illustration of this capacity of biochar. The percentages are estimates of potential atmospheric carbon off sets but are not yet fully documented and are used here as an illustration of the process only. The first illustration shows the carbon sequestration process. This represents the natural carbon cycle. As plants pull carbon dioxide (CO2) from the atmosphere, part of that carbon is built into the plants’ structures through the process of photosynthesis. When plants die, they sequester that embodied carbon into the soil, but most of the carbon is rather quickly released back into the atmosphere as CO2 through plant respiration and soil microbiological activity. The relative amounts of CO2 are more or less balanced and hence the process is said to be carbon neutral. Carbon neutral means that there is no net carbon added to the atmosphere other than what naturally occurs. Climate change is caused by net additions of carbon (carbon positive) to the atmosphere. These additions are primarily due to humans burning carbon-based fossil fuel stocks at an increasing rate over the past 500 years. Carbon negative refers to the actual net reduction of carbon in the atmosphere. In the case of biochar as in figure below, the natural process is interrupted by capturing part of the biomass before it reaches the soil directly and using part (25 percent in the example above) for the production of bioenergy and part for the production of biochar. The illustration shows that the biomass that is converted to energy (potentially in the forms of heat, gas or liquid fuels) releases part of the carbon in the form of CO2 back into the atmosphere in an assumed carbon-neutral process. The other part of the biomass is converted into biochar and because of its stability sequesters all but 5 percent of the carbon (in this illustration) in the soil and hence has the ability to provide a carbon negative source of energy.