“Biochar can be used to address some of the most urgent environmental problems of our time–soil degradation, food insecurity, water pollution from agrichemicals, and climate change…”
Dr. Johannes Lehmann
Professor of Soil Sciences, Cornell University
WHAT IS BIOCHAR?
In physical terms, biochar is simply the charred remains is formed when plant material is heated in an oxygen free environment–a process scientists call “pyrolysis.” Unlike charcoal which is very similar, biochar is created specifically to improve soil structure and ehnance crop productivity. “Net energy,” or the total amount of energy yielded from the process, is positive meaning it generates more energy than it consumes. Because not all of the carbon is combusted (approximately 10-50 percent of the total carbon is retained as biochar), significant carbon can be returned to the soils and therefore the process is considered to be “carbon negative.”
Unlike other biofuels and bioenergy platforms, biochar does not necessitate using valuable agricultural lands or deforesting already vulnerable ecosystems as many other bioenergy systems would required. This is due to the wide range of feedstock that can be used to produce biochar.
In short, it seems possilbe that we can produce energy, reduce waste, sequester carbon, and create a powerful soil amendment in the form of biochar all in a single process. It is for this reason that many are calling biochar a “win-win-win” strategy.
While the potential benefits are large, there is a great deal of research that needs to be conducted, technologies that need to be developed, and policies that need to implemented before a “biochar revolution” observational data and research that still needs to be assessed and conducted in order to get a full picture. Issues of contamination, nitrogen immobilization, and sustainable sourcing of feedstock all need to be addressed.
BIOCHAR: SIMPLICITY AND COMPLEXITY
On one hand biochar is fairly simple. It is a black, fine grained, extremely porous, light weight and stable form of carbon very similar to charcoal. It has certain physical and chemical properties that make it a potentially powerful soil amendment. In this respect, biochar is quite simple and really not all that unique.
On the other hand, biochar represents a dynamic strategy that could help solve many of the world’s most pressing problems. The process of creating biochar could sequester billions of tons of carbon from the atmosphere every year (somewhere on the order of 5-30% of global emissions) while simultaneously producing clean renewable energy to replace fossil fuels.
Add on top of these two incredibly important functions, the benefits of preventing groundwater pollution, enhancing fertilizer efficiency, decreasing greenhouse gas emissions from soils, increasing famer’s profitability, providing low cost water filtration for developing countries, providing an alternative to slash-and-burn agriculture, and reducing the amount of material going to the landfill by aproximately a third. And then, of course, there is the benefit that biochar which can be added to the soil to greatly enhance crop production and soil fertility, particularly in degraded soils.
Biochar can be used to stop desertification and increase carbon in dryland soils. Pyrolysis can be used in conjunction with decentralized heat and power plants. Biochar can be produced in high efficiency cookstoves. Biochar can be used in developing countries to help cope with food security and as adaptive measure in cases of drought. Thus, while biochar may be a rather simply substance, it also represents a complex and multifaceted strategy which is gaining attention of farmers, energy experts, and climate scientists around the world.
The concept of using charcoal to improve soils is not new. The concept of using biochar emerged from the study of “Terra Preta” soils in the Amazon Basin. Researchers uncovered large land areas of incredibly rich black soil on which plants grew better, nutrient retention was stronger, and overall soil quality was superior to that of neighboring soils. Researchers eventually hypothesized that it was native peoples who were adding large amounts of biochar in addition to organic wastes in order to permanetly increase soil productivity in these habitation sites. The following excerpt from “The Secret of El Dorado” provides an overview of Terra Preta and modern interest in creating a new modern day Terra Preta, or “Terra Preta Nova.”
The current knowledge about biochar is limited and there remains a lot we don’t know. A signficant amount that research must be conducted to assess the value, performance, cost-benefit analysis, life cycle analyses, scaling, and carbon sequestration potential of biochar. Nonetheless, the initial findings are extremely suggestive that biochar may offer a promising triple-benefit scenario for agriculture, climate and energy production.
WHAT IS “TERRA PRETA”?
Terra Preta (TP) is an extremely rich and dark soil layer found in around the Amazon Basin which is of anthropogenic origin containing high levels of pyrogenic material (i.e. biochar), other organic inputs, pottery shards, other human artifacts. The TP sites, presented in the map below, are typically 10-30 hectares in size, though plots of 300+ hectares have been discovered, suggesting that settlements in the area prior to Western Europe colinization were probably much higher and societies far more complex than originally assumed by early anthropologists and historians.
TP soils were likely created between 500 and 2000 years before present by pre-Colombian Ameri-Indians. Many questions about the origin and properties of TP soils remain unanswered. For instance, whether TP soils were created through deliberate soil management practices or whether they were simply the result of habitation will probably always remain unknown. While biochar is considered by many to be the main constituent of TP soils responsible for increased fertility, many questions remain regarding complementary practices that may have also led to increased soil fertility. Questions also remain about “regenerative properties” of biochar in which excavated TP sites have been puportedly observed to renew themselves over time. This has led some to speculate about the importance of biological components (e.g. microbial bacteria such as Aspirgillus niger or arbuscular mycorrhizal fungi) that may help to explain this phenomenon, but no research exists to verify these claims.
TP soils generally have much higher levels of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca); are less acidic; are less dominated by clayey soil types; have higher levels of SOM (soil organic matter) and SOC (soil organic carbon); and generally support greater plant productivity than neighboring soils–typically Ferrasols, Oxisols, or Xanthasols–charcterized by a high degree of weathering and low soil fertility (Lehmann, “Bio-Char Soil Management in Highly Weathered Soils in the Humid Tropics”.)
TP soils high carbon levels with between 3 and 6% of the soil consisting of pyrogenic charcoal corresponding to up to 150 grams carbon per kilogram soil compared to surrounding Ferrasols and Oxisols which contain practically no pyrogenic charcoal and have carbon levels of 20 to 30 grams carbon per kilogram soil. TP soils are prized by growers of papaya, mango, and other high-end crops which are reported to grow nearly three times as fast on TP soils than on neighboring soils . The high fertility of TP soils explains why locals routinely excavate and bag TP soils to be sold as a soil fertilizer and conditioner.
Biochar is the charcoal-like byproduct of a carbon-negative energy production method called “pyrolysis.” Pyrolysis is a process in which biomass is heated or partially combusted in the absence of oxygen or in an oxygen limited environment wherein volatile gases are driven off of the biomass. During this process, called “thermal decomposition,” the biomass starts to break down at a molecular level and volatile gases called “syn-gas,” or “producer gases” are released. These gases are then directly combusted or condensed in a clean and efficient process to generate various forms of energy.
Approximately half of the carbon is released as carbon dioxide during the process; the other half is trapped within the biochar co-product. Because plants actively remove carbon from the atmosphere through photosynthesis, the process would be “carbon nuetral” if all of the carbon were emitted. However, because a portion of carbon is essentially locked into a stable biochar structure the process becomes “carbon negative” thereby allowing us to trap a greater portion of carbon than is released during the full-lifecycle production of biochar provided that the biochar feedstock material is sourced or grown in a sustainable manner and that carbon emisssions from transportation of both the feedstock and the biochar are reduced to the greatest extent possible.
There are several different methods by which biochar can be made including slow pyrolysis, fast pyrolysis, gasification, and carbonization. Each of these has costs and benefits. Carbonization, the traditional method for making charcoal, for example, is technologically simple and inexpensive, but emits greenhouse gases such as methane (CH4) and sooty black particles (referred to in the scientific literature as “black carbon“) which could be detrimental to the climate system and to human health.
Slow pyrolysis is slightly more technologically advanced and can optimize for biochar production with approximately 40% of the biomass transformed into biochar. Fast pyrolysis is generally used to maximize for bio-oils but also generates a fair amount of biochar. Gasification for energy production with minimal biochar production.
Thus, the various methods for producing biochar can be optimized for different circumstances. Modern methods of producing biochar differ significantly from traditional less-efficient methods of making charcoal. In modern pyrolysis cookstoves, kilns, retorts, or in combined heat and power bioenergy powerplants dangerous greenhouse gases are re-combusted in order less hazardous emissions.
BENEFITS OF BIOCHAR TO SOILS
Biochar has a unique physiochemical structure which has lead to increased soil fertility and crop yields, particularly in degraded or highly-weathered soils. The potential improvements to soil are numerous and can work synergistically to improve soils, which also makes it difficult to ascertain which characteristics are the most beneficial. Further, biochar has a huge amount of variability depending on the type of feedstock material and pyrolysis conditions used to make it.
WHAT IS BIOCHAR MADE FROM?
One of the greatest advantages of biochar is that it can be made from a wide variety of feedstocks that does not require competition with food crops or land for growing food crops.
Many of the feedstocks can come from waste-streams such as sawmill waste debris, wood chips, pelletized sawdust, urban lawn debris (such as leaves, grass clippings, and tree branches), poultry litter, sewage sludge, hurricane debris, biomass from invasive species, and used cardboard products.
Other feedstocks can come from agricultural debris and crop residues such as wheat straw, corn stover, rice husks, sugar cane bagasse, and nut shells. However, it is vital to stress the importance of leaving crop residues on fields in order to protect from erosion and to provide important decomposable carbon sources for healthy soil functioning. Research in Ohio, for instance, has shown that removal of greater than 25% of crop residues for bioenergy production can lead to detrimental impacts on soil carbon and quality.
Lastly, under certain circumstances, it may be worthwhile to consider purpose grown bioenergy crops that can be grown on marginal lands that do not compete with food crops. These might include species such as miscanthus (Mixcanthus X giganteus), switchgrass (Panicum virgatum L.), sorghum (Sorghum bicolor), bamboo (Bambuseae) , elephant grass (Pennisetum purpureum), hybrid poplar (e.g. P. nigra × P. deltoides), fast rotation willow coppice (Salix L.), as well as various low-input, high-diversity (LIHD) “polycultures” grasses. Algae may also be an interesting option and could be fed with CO2 coming off of the flue gas stream.
It is critical that a particular feedstock be analyzed in terms of its lifecycle analysis and overall sustainability. Additionally, feedstock materials will greatly influence the ultimate characteristics of the resulting biochar, and thus it is important that this material be carefully selected to optimize for those qualities deemed most valuable for the intended application.
Serious concerns have arisen from first-generation biofuels such as corn ethanol and soy biodiesel. These include the conversion of “food-to-fuel” and the energy used and greenhouse gases emitted to grow these crops. An advantage of biochar over first-generation biofuels is that bioenergy crops need not compete with food crops and require very little inputs.
Perennial grasses and prairie land, for instance, do not need to be planted every year, do not require fertilizer or irrigation, and often can sequester carbon in their root structures after harvest. Bioenergy crops can be grown on marginal or degraded land that are currently out of production because the soil is poor, the topography is too steep, or the area is prone to flooding. The use of biochar on fields such as these could actually improve soil conditions while also producing a valuable feedstock material.
COMPARING BIOCHAR TO OTHER BIOENERGY PLATFORMS
Biochar differs from other bioenergy and biofuel systems in a number of important regards. This includes:
- Use of waste biomass instead of food crops
- A relatively high net energy production level
- Multiple benefits to soils and climate in addition to energy production
Many bioenergy production systems (e.g. corn ethanol and soy biodiesel) have come under increasing scrutiny and criticism as they compete for land and resources with food production systems thereby leading to higher food costs. Pressure for productive tillable land has also led to increasing deforestation, particularly in the tropics for palm oil production. Further, the energy gains of corn ethanol and biodiesel are relatively low in comparison to the energy investment in fertilizers, tillage, and transport.
In order to fully analyze the costs and benefits of any particular energy production system one must ask the question: “How much energy is produced from the process compared to the amount of energy needed to run process?” “Energy out” subtracted from “energy in” is what is referred to as “net energy” or EROEI (Energy Returned On Energy Invested.)
The yield of energy from corn ethanol minus the amount of energy required to put into the process is nearly a wash. In other words, there is little to no energy gained in the process and therefore the whole corn ethanol industry is a highly questionable use of resources and land. Biodiesel from soybean production suffers from similar difficulties.
What distinguishes biochar production from many of the other biofuels schemes is its ability to produce energy from biomass in an efficient manner. Gaunt and Lehmann (2008) report that for every one unit of energy put into the process, approximately 2-7 units are extracted using “slow pyrolysis” optimized for biochar production and up to 9 units when optimized for energy production.
In simple terms, this means that the amount of energy generated by slow pyrolysis is 2 to 9 times greater than the amount of energy required to grow, harvest, transport, and fire the process. Thus, pyrolysis is a “net-positive” process in terms of energy production in addition to having the benefits of capturing carbon and producing a beneficial soil amendment.
It should be noted that the net energy from the pyrolysis process could be increased even further if the biochar itself were combusted. This would, however, effectively negate the ability to sequester carbon from the atmosphere and thus would lose one of the most important features of biochar production (Gaunt and Lehmann, 2008).
BIOCHAR AND CLIMATE CHANGE
Biochar is one of the only energy production systems that can actually sequester more carbon than it produces, thereby, creating a “carbon negative.” Presently there are no other carbon negative energy productions systems in the world, to my knowledge, that are as economically feasible as pyrolysis or that can simultaneously have so many beneficial effects.
Basically, biochar production (pyrolysis) effectively locks up atmospheric carbon dioxide (CO2) by partially combusting plant material (biomass) that are continuously removing carbon dioxide from the environment as they carry out photosynthetic processes necessary for growth. The plants are harvested and turned into biochar.
Approximately 40% of the carbon content of the plant is locked up as biochar which becomes a safe, stable and beneficial form of soil carbon that can last hundreds to thousands of years. If we were to rapidly scale this technology up in order to meet our energy needs, we would effectively be able to sequester large quantities of carbon on an annual basis.
Prior to the industrial revolution there was approximately 280 parts per million (ppm) of carbon in the atmosphere—today that number is over 385 ppm. Recent research suggests that the safe upper limit of CO2 in the atmosphere is no more than 450 ppm. James Hansen, Director of NASA’s Goddard Institute of Space Studies, has suggested that the safe upper limit of CO2 in the atmosphere is likely 350 ppm or below. In either case, directly capturing CO2 from the atmosphere may be necessary to prevent dramatic changes in the climate system.
A wide range of estimates have been made that quantify the ability of biochar to sequester carbon with many of these suggesting a range between 0.5 and 3 gigatons (billion metric tons) of carbon per year. In comparison to the approximate 9.5 billion metric tons of carbon emitted every year from the burning of fossil fuels, cement production, and deforestation, this would equate to a sequestration potential of roughly 5-30% of global emissions on an annual basis.
STABILITY OF BIOCHAR IN SOILS
It is widely established that charcoal can persist in soils for thousands of years based on studies of anthropogenic biochar additions (such as was done by Amazonians to create Terra Preta) and from naturally deposited charcoal resulting from forest fires, however studies indicate that a certain amount of carbon is initially lost from raw biochar applications.
Chemically biochar is composed of highly stable poly-aromatic bonds which generally resist weathering and decomposition by microbial communities. “Aromacity” refers to a special form of chemical bonding in which a tightly joined ring of atoms form being held together in a series of single and double bonds which freely pass electrons between themselves thereby switching between the two bonding states continuously in a sort of intermediate bond. In short, the group of atoms stick together really well—much better than they would otherwise if they were in chemical chains. It is this chemical stability which gives biochar it’s highly recalcitrant nature.
While it is known that charcoal can last in the soil for decades, centuries, millennia and even tens of thousands of years, several studies suggest that there is a certain portion of freshly produced charcoal which is not so resistant to weather and that this could be readily broken down and released as carbon dioxide into the atmosphere. This is referred to as “labile” carbon, the carbon that is easily degraded, as opposed to “recalcitrant” carbon which resists degradation. Generally, the labile portion of biochar is found is approximately 2-10% of the total carbon content of the biochar.
Major et al. (2009) found that approximately 2.2% of carbon being lost from soil respiration while a much larger percentage of biochar (approximately 50% in their study) is subject to removal from the field from erosion–large-rainfall events in particular.
Research is needed to determine the proportions labile and recalcitrant carbon in fresh biochar. It is likely that this may be influenced by the pyrolysis technique (e.g. slow vs. fast pyrolysis) utilized, the feedstock material used, and the temperature and residence times which the biomass is subjected to.
Support for biochar is growing as recognition is beginning to take place among policy makers about the potentials benefits associated with biochar.
The 2007 U.S. Farm Bill(HR 2149: “The Food and Security Act of 2007”) initiated support for biochar research in section 9012. Read the 2007 section of the Farm Bill pertaining to biochar here.
The 2008 U.S. Farm Bill (HR 2149: “The Food and Security Act of 2008”) extended support to biochar as a policy mechnanism to improve farming and sequester carbon. Page 353, section 52 states that, “Grants can be made under this section for research, extension, and integrated activities relating to the study of biochar production and use, including considering action of agronomic and economic impacts, synergies of co-production with bioenergy, and the value of soil enhancements and soil carbon sequestration.” Read the 2008 Farm Bill here.
In 2008, the United Nations Convention for Combating Desertification (UNCCD) recommended that biochar be considered an important approach to mitigating climate change. The UNCCD Secretariat proposed that, “policy actions should take into account carbon contained in soils and the importance of biochar (charcoal) in replenishing soil carbon pools, restoring soil fertility and enhancing the sequesteration of CO2.” Read the UNCCD statement here.
In 2008, the United Nations Framework Convention on Climate Change (UNFCCC), The Federated States of Micronesia formally filed a submission that biochar be considered as a “fast-track” mitigation tool for combating global climate change. Read the full Micronesia proposal here.
In 2009, the Food and Agriculture Organization (FAO), recommended to the UNFCCC that soil carbon sequestration technologies be formally adapted into policy measures to mitigate climate change in a submission entitled “Enabling Agriculture to Contribute to Climate Change Mitigation.” Read the submission here.
In 2009, the United Nations Framework Convention on Climate Change (UNFCCC) included biochar in the first draft negotiation text of the post-Kyoto Copenhagen agreement. Biochar was explicity named as a potential solution pathway in the “Enhanced Action on Mitigation” section of the working draft. The proposal states that:
“Agriculture: 134. Parties shall cooperate in R&D of mitigation technologies for the agriculture sector, recognizing the necessity for international cooperative action to enhance and provide incentives for mitigation of GHG emissions from agriculture, in particular in developing countries. Consideration should be given to the role of soils in carbon sequestration, including through the use of biochar and enhancing carbon sinks in drylands.” Read the Copenhagen working draft here.
As of May 2009, 13 Countries and Parties to Kyoto have jointly endorsed biochar and petitioned for it’s inclusion in the post-Kyoto climate acccords including Micronesia, Belize, Swaziland, Gambia, Ghana, Lesotho, Mozambique, Niger, Senegal, Tanzania, Uganda, Zambia, and Zimbabwe.
“WECHAR” Bill introduced in the US Senate by Senators Harry Reid, Max Baucus, John Tester, and Tom Udall. The bill (Water Efficiency via Carbon Harvesting and Restoration of 2009) proposes to fund biochar research and development projects and provides loans for biochar projects. Read the IBI summary of the WECHAR bill here, or the full text of the WECHAR bill here.
BENEFITS FOR DEVELOPING COUNTRIES
According to the World Bank, approximately 1.2 billion people live on less than $1 per day and 2.7 billion people live on less than $2 per day. In short, we live in a world defined by vast economic inequality.
While the mechanisms of lifting people have been discussed, programs set forth, declarations made, theories debated, and monies applied in a variety of ways, the difficulty of getting half of the world out of poverty remains and will remain a significant problem for quite some time. It will also be further exacerbated by the present economic collapse, climate change, peak oil, and the attendant decline in food security.
Biochar could offer a powerful a multi-pronged tactic for fighting poverty. Biochar offers a means of boosting crop production, increasing on-farm income for subsistence farmers, providing the opportunity for community projects to access global the emerging global carbon market, promotes job creation through the use of local resources, reducing smoke-inhalation through improved biochar cookstoves, the development of decentralized heat and power facilities, reducing pressure on forest ecosystems, providing a medium for water filtration, and reducing the drugery of hauling firewood.
Thus, biochar may provide a powerful means of driving people out of poverty through sustainable regenerative systems that have self-reinforcing positive feedback cycles.
Biochar production would be even more powerful if the world community would put a price on sequestering carbon in the soil through good agricultural practices and addition of biochar to soils. This might be one of the most important steps we can take at this moment on planet Earth: Pay farmers in developing countries who desperately need the resources to do the most important tasks to ensure human survival: protect forests, reforest deforested areas, practice good farming techniques that increase soil organic carbon (SOC), reverse desertification, and apply biochar to their soils.
Poverty reduction through the use of biochar will only be had if there is a strong effort to insure that development of pyrolysis systems jointly benefits both larger scale higher technology projects in developed countries as well as sustainable, efficient, and small scale development in the least developed countries.
BIOCHAR INITIATIVES FOR DEVELOPING COUNTRIES
Though the concept of biochar is relatively new, several significant initiatives have been launched to bring the benefits of biochar to least developed countries.
WorldStove Company, Robert Flanagan and others are developing a small-scale biochar cookstoves which could replace biomass and charcoal fueled cooking methods. The potential benefits from small-scale, high-efficiency range for reduced drudgery (especially for women and children) in fuel wood collection, reduced smoke inhalation (especially for women and children), reduced pressure on forest ecosystems, increased time to engage in micro-enterprises, creation of fertilizer which could improve household self-sufficiency, and potential wealth generation from access to carbon markets.
Aqueous Solutions is developing low cost water treatment methods for resource-poor communities in the developing world using biochar as a filtration medium. Supported by researchers at North Carolina State University and the University of California-Berkley, the organizations is working on identify the best feedstock materials and pyrolysis processes to create a biochar that could filter water by removing harmful contaminants.
The Biochar Fund is working on a social profit model of reversing the downward spiral of environmental destruction and resource impoverishment by bringing the benefits of biochar to improve soil fertility, stave off hunger, create financial opportunities for the poorest people of the world access to carbon credit markets, reduce deforestation, create a distributed electrical power grid that runs on biomass, and provide perhaps one of the lowest cost means of sequestering carbon while simultaneously lifting people out of poverty.The Biochar fund has recently won a prestigious award and funding from the Congo Basin Forest Fund (CBFF.)
CONCERNS AND CRITICISM OF BIOCHAR
Arguments against the use of biochar have been made though they are relatively few in number. I tend to view criticism and critique of biochar production as a healthy and helpful dialectic process which will keep the promoters of biochar honest and keep biochar on a sustainable and socially-responsible path forward.
Like any technology, biochar has the potential for misuse, and there are several important concerns that need to be addressed, studied, and, if possible, mitigated. A list of critiques and criticism of biochar are provided on our “Research” page.
1. Biochar production could lead to competition with food crops and/or deforestation
The concern that biochar could lead to competition with basic food crops and/or promote higher levels of deforestation is both serious and extremely valid. It is raised in a critical paper on biochar entitled “Biochar for Climate Change Mitigation: Fact or Fiction” by Ernstin and Smolker (2009) suggesting that biochar is, “inherently risky and will likely encourage further land conversion and expansion of industrial monocultures.”
It is conceivable that if scaled up without any foresight, regulatory standards, or intelligent policies, biochar production could lead to increased deforestation and competition with food crops. However, biochar production need not have any of these results.
First, biochar is most easily made from waste feedstock materials and not primary or secondary growth forests.
Second, biochar does not require purpose grown feedstocks. In other words, it is not necessary to grow crops in order to be pyrolyzed, although it may be prudent to consider growing bioenergy crops if it can be accomplished in an efficient and sustainable manner such that it does not compete with agricultural land.
Third, biochar offers several pathways for actually halting and even potentially reversing deforestation by transition from slash-and-burn agriculture to slash-and-char; allowing for the rehabilitation of degraded and desertified soils back into productive soils capable of supporting plant life; increasing productivity on already farmed lands therefore offsetting need for continued encroachment on forests; and, providing an efficient and sustainable heat and power source for the developing world that will replace overharvesting of fuelwood from endagered forest lands.
2. Biochar production if scaled up to the extent necessary to sequester massive amounts of carbon dioxide from the atmosphere would lead to the establishment of vast monoculture plantations.
Forest plantations are large-scale tree farms which are often composed of a single species (i.e. monoculture) grown for timber or pulp production. Plantations have been criticized as having little resemblance to natural ecosystems therefore being capable of supporting far less biological diversity than would naturally occur.
There is concern that if biochar were scaled up to the extent necessary to play a large part in mitigating climate change, then it would require the planting of massive monoculture forest plantations in place of natural forest ecosystems to provide biomass feedstock material. Thus, biochar could have significant detrimental impacts on biodiversity of natural ecosystems as they are converted to single-species monocultures.
The International Biochar Initiative (IBI) does not factor in the use of any forest plantations when calculating potential biochar production and carbon sequestration numbers:
“The maximum amount of global NPP used in our scenarios is 3.2%. Estimates of the fraction of global NPP that can be used for sustainable bioenergy production go as high as 13% (e.g., Sims et al., 2007, using the assumptions of Amonette et al., 2008). The higher estimates in that paper assume dedicated bioenergy plantations. Because there are doubts about the sustainability of some biomass plantations, we have excluded plantations from this analysis, producing an overall conservative result.”
Thus, biochar production does not require forest plantation monocultures.
Lastly, forest biomass production need not be inherently unsustainable, monoculture, or large-scale “factory” farming. Forest biomass production could include diverse sustainable agroforestry, agroecosystem, and permaculture approaches that simultaneously produce food, fiber, construction materials and which generate wealth for local communities in addition to producing energy.
These could operate in the form of community and cooperative forestry management. In conclusion, due to high availability of other biomass materials, biochar systems need not require monoculture forest plantations, though it may be prudent to examine sustainable methods of bioenergy crop production from forested lands.
3. Biochar production could prevent agricultural wastes from being recycled back into soils.
This is yet another important and valid concern. Organic materials such as corn stalks, rice husks, and wheat straw are often tilled back into the soil or, as with is the case with conservation tillage, left on the surface layer of the soil to prevent erosion and crust formation. Alternatively, crop residues can be composted or burned instead and then subsequently added to the soil.
Returning these materials is vital to soil health as they contain high proportions of nutrients that would otherwise be mined from and never returned to the soil, thus leading to severe nutrient depletion. The concern is that “agricultural wastes” are actually extremely valuable nutrients that should be recycled back into the soil. If biochar requires constantly harvesting these crop residues it could lead to a dangerous mining of soil nutrients thereby leading to harmful soil depletion.
Fortunately, this need not be the case. First, we may choose only to make biochar from waste streams and not from agricultural residues.
Second, if agricultural residual material were used, the biochar that results from pyrolyzing the material could be used to add fertility to that field. Since biochar production retains most of the nutrients, they would effectively be recycled back into the soil.
Third, 80 to 90% carbon from crop wastes would be mineralized (decomposed and released into the atmosphere as a gas) out within 10 years, whereas biochar offers a much longer term repository for carbon. Fourth, agricultural residual material need not be harvested every year. Because biochar is recalcitrant it can be applied, say, once every 5 or 20 years, thus making biochar application a one-time input with significant long-term benefits. Crop residues from all other years could still incorporated into the soil through conservation tillage and no-tillage methods.
4. Biochar can lead to faster decomposition rates of native carbon stocks in soils.
There is concern that biochar applications could actually lead to greater carbon emissions as it would lead to higher microbial populations and faster decomposition rates. Wardle et al. (2008) published a study that indicated that biochar applications may cause a loss of humus in northern latitude boreal forests entitled “Fire-Derived Charcoal Causes Loss of Forest Humus.” (Read the response by Lehmann and Sohi here.) The study found that when bags of equal parts of humus and charcoal were placed in a field and allowed to sit for 10 years the amount of carbon loss from the bags was greater than expected.
The proposed explanation for the loss of carbon is that the charcoal leads to greater levels of microbial growth which, in turn, speeds up decomposition rates of the humus. The paper concludes, “Although several studies have recognized the potential of black C for enhancing ecosystem C sequestration, our results show that these effects can be partially offset by its capacity to stimulate loss of native soil C, at least for boreal forests.” In other words, biochar may have harmful effects on soil that partially or fully negate the potential benefits of carbon sequestration and soil improvement. The experiment was conducted in highly fertile soils with high carbon content in the boreal forests of Sweden, and thus may have a limited applicability to other environments.
A critique of this study, “Comments on ‘Fire-derived Charcoal Causes Loss of Forest Humus’” was written by Johannes Lehmann and Saran Sohi which calls into question the methodology and conclusions of Wardle’s paper. Namely, Wardle et al assume that all of the carbon loss is a result of decayed humus as opposed to a combination of loss from both the charcoal and the humus; the assumed loss does not include the possibility that carbon could have been physically transferred from the mesh bags to the exterior via dissolved carbon; and that simply placing a mesh bag method the leaf litter layer of a forest does not sufficiently resemble the incorporation of biochar into a mineral soil.
Recently Major et al. (2009) found that addition of biochar lead to increases in carbon mineralization when biochar was added to tropical soils likely resulting from greater microbial activity, however, the addition of biochar lead to net increases of soil carbon stocks due to greater biomass growth and subsequent residue buildup.
This is certainly an important topic that requires further research. More discussion can be found on the “Farm” section of the website.
5. Biochar may introduce dangerous compounds into soils
The potential for introducing or locking up harful compounds is an important concern with biochar prouction. Sohi et al. (2009) have written that, “Analysis of a limited number of biochar samples has indicated concentrations of toxic combustion products such as polycyclic aromatic hydrocarbons that are not at environmental risk level. However, a more systematic evaluation for a more complete range of other potentially harmful chemical contaminants associated with combustion, as well as toxic substances within feedstocks, has not been made.”
An important concern is whether biochar could have unintended deleterious effects on soil quality or plant productivity. Several studies have reported negative results in crop yields from biochar applications. Kishimoto and Sugiura (1985)observed a 37% and 71% decrease in soybean yield with biochar applied to soils (volcanic ash loam) at rates of 5 t ha⁻¹ and 15 t ha⁻¹, respectively. Similarly, Baronti et al (2008) reported decreased ryegrass (Lolium perenne L.) production of 8% and 30% vis-à-vis the control at application rates of 100 t ha⁻¹ and 120 t ha⁻¹, respectively; despite, observing increases of 20% and 52% at application rates of 20 t ha⁻¹ and 60 t ha⁻¹, respectively.
Negative results have been hypothesized to result from a number of factors. N immobilization due to high C:N ratios (Gaur and Adholeya, 2000; Lehmann et al, 2003b; Rondon et al, 2007), liming of alkaline-intolerant species (Mikan and Abrams, 1995), and hydrophobic properties associated with some biochars (McClellan et al, 2007) have been provided as explanation.
The formation of PAH during pyrolysis has been well documented (Painter, 2001; Ledesma et al, 2002) although the concentration and availability of PAH with respect to biochars is still uncertain. Garcia and Perez (2008) reported lower presence in bio-oils derived under fast pyrolysis conditions (<10 ppm) and higher in slow pyrolysis conditions (>100 ppm). While PAH may be harmful to most plant and microbial communities, relatively rapid decomposition of these compounds by certain microbial populations has been observed (Ogawa, 1994; Zackrisson et al, 1996) and PAH compounds may be fully consumed within one to two growing seasons under many conditions (Thies and Rillig, 2009).
Additional concerns are whether biochars could introduce toxins such as volatile organic compounds (VOC), dioxins, cresols, xylenols, formaldehyde, and acrolein (Thies and Rillig, 2009; Garcia-Perez, 2008; McClellan, et al, 2007). High concentrations and availability of heavy metals such as cadmium (Cd), copper (Cu), chromium (Cr), nickel (Ni), and zinc (Zn) have been reported from pyrolyzed biosolids and sewage sludge (Brindle and Pritchard, 2004; Hospido et al, 2005).
The above concerns highlight the need for standardized protocols for characterization, classification, and safety insurance of biochar products (Joseph et al, 2009) through the third-party providers such as the American Society for Testing Materials (ASTM) or similar organizations. In many cases, it appears that introduction of harmful compounds can be mitigated or prevented entirely through careful selection of feedstock material, well designed pyrolysis units, and post-production testing. More research into possible negative impacts is warranted.
The potential presence of PAHs and dioxins is, in my opinion, the most pernicious issue facing widespread adoption today. A careful, unbaised, and critical examination of this issue is necessary. More discussion on this can be found in the “Farm” section of the website.
Ledesma, E.B., Marsh, N.D., Sandrowitz, A.K., Wornat, M.J., (2002) “Global kinetic rate parameters for the formation of polycyclic aromatic hydrocarbons from the pyrolysis of catechol, a model compound representative of solid fuel moieties. Energy and Fuels 16, 1331-1336.
Painter, T.J. (2001) “Carbohydrate polymers in food preservation: An integrated view of the Maillard reaction with special reference to preserved foods in Spangnum-dominated peat bogs”, Carbohydrate Polymers, vol 36, pp335-347.
Thies, J.E., and Rillig, M.C. “Characteristics of Biochar: Biological Properties” in Lehmann, J.; Joseph, S. (2009) “Biochar for Environmental Management: Science and Technology” Earthscan, Sterling, Va.
6. Poor biochar production practices could actually lead to greater greenhouse gas emissions and detrimental air quality.
This is an absolutley true statement–if biochar production is not accomplished using safe, efficient, and reliable equipment, it could cause a release of extremely harmful pollutants and greenhouse gases. These include methane (CH4) and nitrous oxide (N2) both extremely potent greenhouse gases with global warming potentials 24 and310 times that of carbon dioxide (CO2), in addition to black carbon (BC) particles formed during incomplete combustion of fossil fuels or biomass which are currently thought to have a strong warming potential higher than previously expected. Thus, the ability for biochar production to sequester carbon and therefore help the climate could be completely negated if we were use inappropriate, polluting technologies for producing biochar.
A study by Pennise et al. (2001) found the following emissions products (expressed as grams per kilogram of emissions) when measuring traditional charcoal making kilns in Kenya and Brazil: carbon dioxide (CO2) at 543-3027 grams, methane (CH4) at 32-62 grams, carbon monoxide (CO) at 143-373 grams, nitrous oxide (N2O) at 0.011-0.3 grams, and “Noxes” (NOx) at 0.0054-0.13 grams, and total suspended particles (TSP) at 13-41 grams.
Albert Bates taped a traditional Mayan method for making charcoal:
In short, we must devise technologically elegant, scientifically calibrated pyrolysis units capable of combusting the flue gases in order destroy the N2O and CH4 while giving off no black carbon soot particulates. Fortunately, construction such systems can be relatively easy even by the non-expert. For instance, reused 55-gallon drums can be made to cleanly and efficiently convert biomass into biochar with only slight modifications.
7. There has been little research on biochar and we don’t fully know how it will effect soils or crops.
It is clear that research on biochar is nascent and that significantly greater experimental and observational data are required in order to characterize and quantify how biochar affects various soil quality and crop production under various agricultural and climatic conditions; whether and how biochar can mitigate climate change; and attendant benefits for developing communities. The data collected thus far, however, is fairly extensive and is strongly suggestive that biochar offers a promising means of helping to solve some of the most pressing challenges now facing humanity. To say that there is “little” or “no data” to support biochar production, is to exclude more than 20 years experimental data, and extensive observations of Terra Preta soils in the Amazon.
For a partial listing of research on Biochar production please visit the “Research” section of the website.
HOW WAS “TERRA PRETA” MADE?
Terra Preta soils are estimated to cover roughly 10% of the Amazon—some 650,000 square kilometers or nearly the size of France. The soils are clearly darker and richer than the neighboring soils, however, the methods and motivations for creation of Terra Preta soils by Ameri-Indians will probably remain an area of active research for the indefinite future.
One can picture the first gathering of native peoples on a piece of land that would eventually become a Terra Preta site. They could have been practicing “slash-and-burn” agriculture, though some have suggested it was more likely “girdle-and-burn” that wouldn’t require the energetic costs of felling of large trees with stone axes.
Instead of reducing the biomass to ash as is done when simply combusting it during slash-and-burn, the biomass was somehow pyrolyzed to produce charcoal. The techniques by which were used to accomplish this are not known. Perhaps the charcoal was just the discarded stuff from their daily cooking routine. Perhaps they had integrated an intricate ritual practice that included the purposeful charring of biomass. Maybe it was the byproduct of profligate pottery making which had some sort of trading value—there certainly is enough potsherds to suggest this might be the case. They may have simply recognized the benefits of adding charcoal and started the practice of gathering large quantities of biomass from the neighboring sites charring it in huge earthen kilns as is done today to produce charcoal for cookstoves.
In any case, they must have quickly realized that adding this black charcoal to the soil where they grow their crops resulted in larger yields. Unlike fields where slash-and-burn or girdle-and-burn which is performed (which yields only 1-5% charcoal), the addition of large quantities of charcoal eventually allowed for the creation of permanent agriculture sites with high productivity.
The Terra Pretaians did well on their new fertile land. They no longer had to keep moving and could establish more permanent settlements and infrastructures. Over generations large amounts of organic waste blended into the soil with the biochar—maize stover; undug potatoes, yams and cassava; overripe melons; acrid groundnuts; bean shells; huge stashes of shellfish (sambaquis) remains along with phosphorus-rich; fish tails, heads and bones; slash piles of tropical vegetation removed from gardening areas; carcasses of mostly consumed tapirs, capybaras, various types of tropical monkeys, and dead dogs; and rotted and discarded hut thatching.
It swirled and mixed in piles and pieces across the cultivated landscape. It was desiccated and then rained on, and desiccated and rained on again. Some of it fermented. It was oxidized, aerated, volatilized, and mineralized. A fantastic number of potsherds were buried in it.
It was crushed and broken and incorporated in the soil with the footsteps of the people going to and fro, by the hoes wielded by the tropical agriculturalists, by ever-seeking roots breaking apart the charcoal in search of its tightly held nutrients, and by charcoal-loving worms, Pontoscolex corethrurus, (a species of earthworm widespread throughout the Amazonian Basin and which can ingest and break apart biochar into tiny pieces rich in humus saturating it in a nexus of beneficial intestinal excretions, and blend it up well with the mineral soil in nice little chunks called soil aggregates).
Surely it was urinated on. Feces were incorporated into it. The dead were probably buried into it. Vast orgies of spawning microbial flourished and died in it. Enormous fractal reefs of arbuscular mycorrhizal fungi spread across it, the hyphae and spores of which produced a super sticky glycoprotein called “glomalin” that capture even more carbon. All the while more and more biochar was added to the soil.
It was dug and planted into and dug and planted into again and again. Piles of fish bones, half eaten tapirs, and thatch roofing were added again and again. The soils grew rich and black with the soot and decay of centuries.
Generations passed. The societies transformed. The Terra Preataians made love, had children, and died. They taught their children how to manage the soil as the generation before them had taught them to do. In the end, they had accomplished a remarkable feat. They had generated an exceeding rich soil capable of continuously supporting dense populations from a soil which was previously so poor and devoid of nutrients that it could only support a few years of agricultural production before it was complete worn out.
Then the conquistadors came. The bearded Europeans admired, disdained, made slaves out of, reproduced with, and wielded steel against the natives. It was the zoonotic germs, however, that killed most of natives off—upwards of 95 to 99% by many estimates—and caused later European explorers to conclude the New World was a largely uninhabited, untamed wilderness just waiting to be exploited. And the Terra Pretaean’s long tradition of teaching their children how to make the black soil ceased.
Only now have we rediscovered the potential of recreating these soils. We’ve also discovered, coincidentally enough, in the process of recreating these rich soils we may also be able to generate clean, renewable energy, produce food more sustainably, and begin to start tackling some of the most significant threats that have ever faced humanity including global climate change.
We have much work to do and but little time to do it in. I remain hopeful that humanity has the intelligence, compassion, and wisdom to start solving these momentous challenges. Whether and how biochar will assist this effort remains to be seen. However, I believe the emerging science will corroborate initial findings that biochar is among the most important tools we now have to counteract some of the most significant threats now facing us including global climate change, food insecurity, water scarcity, and energy depletion.