Biochar: Potential for countering land degradation and for improving agriculture

Applied Geography 34 (2012) 21e28

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Biochar: Potential for countering land degradation and for improving agriculture C.J. Barrow Geography Department, College of Science, Swansea University, Singleton Park, Swansea, Wales SA2 8PP, UK

a b s t r a c t Keywords: Biochar Amazonian dark earths Doubly green revolution Soil enhancement Terra preta Slash-and-char

Biochar is attracting attention as a means for sequestering carbon and as a potentially valuable input for agriculture to improve soil fertility, aid sustainable production and reduce contamination of streams and groundwater. This study reviews biochar potential and problems and argues for adequate research before hasty application leads to environmental and socio-economic damage and discourages application. There is also a need for broad overview because research is conducted by a diversity of specialist fields including soil chemistry, archaeology, farming extension and so forth. Research on biochar-rich Amazonian dark earths may help identify the best raw materials (feedstock) and ways for producing biochar for agricultural use and countering land degradation. Ó 2011 Elsevier Ltd. All rights reserved.

Introduction Biochar may prove a key and accessible input for agriculture, it could help rehabilitate degraded land, and play a major role in sequestering atmospheric carbon dioxide. The UN Convention to Combat Desertification has been promoting biochar for countering land degradation and many other bodies have enthusiastically backed its use. However, without adequate research and caution in application there could be problems, which might discredit or delay biochar development. Since the 1940s agriculture has shifted from using locally produced manure and compost to purchased, often imported, chemical fertiliser. With oil and phosphate supplies dwindling fertiliser is increasingly costly and insecure, use leads to dependency, causes pollution and does little to maintain soil organic carbon. Alternatives are manure and compost but for many farmers these are difficult to get and if used can cause serious groundwater and stream nutrient pollution. Manures and composts can contain pathogens, heavy metals and pharmaceuticals and usage may lead to ammonia and methane releases adding to global warming. Biochar could be a way of disposing of agricultural wastes, human sewage, livestock manure, industrial wastes, refuse, etc., with less greenhouse gas emissions and when applied to the land perhaps even a reduction of pre-existing groundwater and stream contamination (plus some carbon sequestration). Agriculture over the last 40 years has fed a growing population, but this green revolution is widely seen to be unsustainable, environmentally damaging and unlikely to keep up with demand.

E-mail address: [email protected]. 0143-6228/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.apgeog.2011.09.008

So, there is a call for a new doubly green revolution: increased yields, reduced negative impacts, better sustainability, and all this accessible to poorer farmers as well as commercial producers. Biochar could be a key input for raising and sustaining production and simultaneously reducing pollution and dependence on fertilisers, it could also improve soil moisture availability and sequester carbon (Lal, 2006; 2008a: 7; Marris, 2006; Sohi, Krull, Lopez-Capel, & Bol, 2010; Verheijen, Jeffery, Bastos, van der Velde, & Diafas, 2010, 166 pp.; Woods, Falcão, & Teixeira, 2006). Biochar could also be a valuable soil amendment for rehabilitating degraded land and bringing poor soils into production, which would help cut further land clearance. Biochar research is underway but is conducted by a diversity of specialisms and there is limited thorough impartial interdisciplinary overview (although no shortage of websites enabling discussion). Applied geographers could help to make such overviews to assess potential and problems.

Amazonian dark earths Amazonian dark earths occur as patches of a darker colour than surrounding and underlying soils. The colouration is due to high biochar content and they generally have elevated soil organic matter content, pH and nutrient levels. Amazonian dark earths are subdivided into: terra preta and terra mulata (black earths and brown earths respectively). It is now generally accepted that humans have formed these, (Glaser & Woods, 2004; Lehmann, Kern, Glaser, & Woods, 2003). ‘Formed by humans’ could mean anthropic - unintentionally formed, or anthropogenic e intentionally formed. Some studies suggest terra preta may be a ‘midden deposit’ resulting from village waste and fire ash slowly accumulating around dwellings

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(Denevan, 2008; Kern et al., 2003; Nakamura, Hiraoka, Matsumoto, Tamura, & Higashi, 2007). Others argue South American preConquest farmers deliberately and rapidly created the dark earths to sustain semi-intensive farming lasting for many centuries on very poor soils. If the latter proves the case and it is possible to copy (perhaps improve) and spread the techniques around the world it could be a huge benefit for modern agriculture. Interest in terra preta (syn. Anthropogenic black earths, black carbon soils, anthrosols) was largely pioneered by the late Wim Sombroek (see also Eden, Bray, Herrera, & McEwan, 1984) and more recently by Sohi, Woods, Glaser, and Lehmann (Lehmann et al., 2003; Sohi et al., 2010; Sombroek, 1966; Sombroek, Ruivo, Fearnside, Glaeser, & Lehmann, 2003; Woods et al., 2009). Terra preta typically has three- or more times the total soil organic carbon than soils it lies on (a 14% organic matter content is common) and it usually contains far more P, Ca and humus than surrounding soils. It often includes abundant potsherds but it is unclear whether these are just midden debris or (I suggest) might indicate transport and deliberate addition of material as well as biochar. Terra preta deposits can be very fertile and robust if cultivated even centuries after the peoples who formed them diedout. In surrounding acidic, nutrient-poor Oxisols compost, fertiliser or manure quickly breakdown and leach away. Terra preta soils are often highly aromatic and are thought to mainly date from between 450 BC and AD 950 although some may be older, even as much as 6000 years. These soils have a distinctive soil biota, which may be one reason why they have sustainable fertility after centuries of abandonment and the ability to ‘regenerate’ if quarried (provided enough is left in-situ). The key to dark earths’ qualities is thought to be biochar, which may increase beneficially the microbial biomass (bacteria and arbuscular mycorrhizal fungi) and the amount of larger organisms, especially earthworms. Similar dark deposits are reported outside Amazonia, in Peru, Colombia, Bolivia, Guyana, Ecuador, the USA (Skjemstad, Reicosky, Wilts, & McGowan, 2002), Benin, Liberia, S. Africa, Europe (especially Germany, the UK and Russia). Sussex University (UK) was granted research funding in 2010 to investigate dark earths in West Africa. If terra preta is as beneficial as claimed and can be made today relatively quickly using local materials and techniques that small and larger farmers could adopt it would have huge agricultural value, plus potential for atmospheric carbon sequestration. Currently a number of questions need attention: 1) Were dark earths deliberately made and if so how? If formed quite rapidly using accessible wastes to make biochar that was added to soil as an amendment there could be huge potential. 2) If terra preta results from biochar enhanced with inputs that are not cheaply and widely available it may have less to offer. If rich riverine ecosystem inputs were used to enhance the biochar it could be more difficult to develop away from flood lands. 3) Do dark earths sequester carbon long-term, can they continue to capture carbon once formed, and are they capable of rapid ‘re-growth’ if dug and part-removed? 4) Could one element of manufacturing these soils today be the development of suitable microorganism cultures for seeding biochar? 5) What are the optimum way(s) to form the biochar in terms of raw materials and techniques? 6) How is it best developed/applied by farmers and are there risks? To address question 1); accidental formation might be ruled-out because these soils are rather uniform and occur as extensive deposits of often over 400 ha, with some patches 6 km by 0.5 km

(Denevan & Woods, undated, 11 pp.). With respect to question 2), many terra preta deposits lie close to várzeas (rich flood lands) (Denevan, 1996a,b; Lima, Shaefer, Mello, Gilkes, & Ker, 2002). However, this might be a misimpression because until recently travel was easier by rivers so riverside deposits could be overrepresented. Hecht and Heckenburger reported Kurikuro Indians (upper Rio Xingu, Amazonian Brazil) still burnt vegetable waste and mixed it deliberately with soil in planting areas (Hemming, 2008: 283). There are reports of similar modern practices by the Kayapó in western Amazonia (Hecht, 2003). Since the 1990s evidence has accumulated for very extensive pre-Conquest (ca. 2000 BC to AD 1400) field systems in seasonally flooded areas like the Llanos of northern Bolivia (in the de Mojos area of Beni Department) and western Brazil, French Guyana, Venezuela, Belize, Ecuador, Surinam and Mexico (Anathaswamy, 2010; Caesar, 2010; Geddes, 2009; Mann, 2008). Along with these fields are habitation mounds up to 20 m high providing platforms for villages connected by long, straight causeways built by throwing up soil to leave a canal. These sites supported large populations with sustained agriculture in areas now un-farmed (Paz-Rivera & Putz, 2009; Woods et al., 2009). The causeways were possibly used during floods and the canals for canoe travel and irrigation during the lower water periods (Conry, 1974; Denevan, 1966a,b, 2001; Erickson, 2003; Hecht, 2003; Mann, 2000). Hemming (2008: 285) noted explorers in AD 1620 report such cultivation by large sedentary populations. A possibility is that this culture may have developed slash-and-char biochar production that can be re-invented and adopted by poorer farmers. There are widespread traditions of slash-and-burn cultivation and soil amendment with charcoal and ash. For example, Japan has long experience of tilling charcoal into farmland. Much of the farmland of Africa, Latin America, Austral Asia, Southeast Asia and Asia is acidic and infertile, often with high levels of iron and aluminium. Biochar applications could make it easier to farm such soils and reduce the impact of doing so. Slash-and-char strategies should be easy for those used to slash-and-burn to adopt (The African Biodiversity NetworkBiofuels Network and Gaia Foundation, 2009: 3). Deliberate biochar production in Amazonia might have used grass from várzeas and brushwood from forest areas. Such slashand-char would be less of a challenge, given the people had only stone tools of little use for clearing forest trees. Today there are huge amounts of ‘capim’ grass produced on flood lands and as floating mats, which could be dragged to shore (Barrow, 1985). However, some are sceptical of the value of non-woody material for producing biochar, claiming it has poor yield of vital bio-oils. Many modern peoples practice slash-and-burn: for example, there is the chitamene strategy of Zambia and Zimbabwe and similar practices elsewhere in the tropics (and forms of slash-and-burn beyond the tropics). These involve cutting grass and brush on very poor and often seasonally dry soils from an area 5- to 8-times the size of the planting plot on which the material is heaped in wind-rows or mounds to be burnt just before the rains and planting (some variants rely on termites to break down the trash) (Allan, 1965; Kleinman, Pimmentel, & Bryant, 1995). These systems enable reasonable crops from poor (often dry) soils but the burn produces more ash and charcoal than biochar. Ash and charcoal probably have a much shorter residence time in soil than biochar (perhaps less than 100 years) so soil amendment is comparatively short-lived (Nguyen et al., 2009). Slash-and-burn seldom contributes more than 3% of the carbon from the cut biomass to the soil, whereas slash-and-char is reputed to contribute up to 50% in a highly stable form (biochar) (Glaser et al., 2002; Lehmann, Gaunt, & Rondon, 2006). Slash-andburn planting plots are soon abandoned, thus it demands much land and commonly breaks-down if there is a growing population.

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However, slash-and-char should enable planting plots to be sedentary, sustainable and highly productive. Could terra preta (and other Amazonian dark earths) require more than slash-and-char? Potshards might indicate transport of material to enhance biochar. Pre-Conquest Indians trapped and poisoned huge hauls of fish and reared vast numbers of river turtles in enclosures. Historians also report they harvested large quantities of turtle eggs, which were largely converted to oil. Was so much oil, used in lamps, for cooking or as a food reserve? Or was oil taken to the farm plots? If so, successful biochar farming might require an input of something like turtle-egg oil. This might be substituted today using urine, night soil, refuse, or an initial dose of chemicals. Amazonian brown earths probably formed through preConquest agriculture (Woods & Mann, 2000; Woods et al., 2009; Erickson, 2003: 483). There have been suggestions that they have a distribution fringing terra preta. There is disagreement over extent of brown earths, some place it as high as 10% of Amazonia. Others estimate there is between 6300 km2 and 18,900 km2 (0.1e0.3%) in lowland Amazonia. Maps of dark earths (preta and mulata) have been published by Smith (1980: 557), Glaser, Balashov, Haumaier, Guggenberger, and Zech (2000: 5) and Lima et al. (2002: 2). In pre-Conquest Latin America it is possible that palm fronds and nut husks, brushwood, aquatic weeds and domestic wastes were charred (Piperno & Pearsall, 1998). Charring could be achieved by earthing-over fires or simply burning green vegetation under frequent rainfall may have formed biochar rather than charcoal/ash (Steiner, 2007). Slash-and-char (a term suggested by Lehmann to indicate a lower temperature form of slash-and-burn that leaves more biochar than ash and charcoal) may have sustained large populations without demanding access to new clearances every few years. If these methods can be rediscovered they could be a valuable innovation for many parts of the world (Lehmann et al., 2002). One possibility is that pre-Conquest peoples used babassu (babaçu) palms (Orbignya spp.) as a raw material for biochar. Cutting the palms would be easy with stone-axes and the plants resprout enabling sustained production. Babassu flourishes over more than 200,000 km2 of Amazonia today and it readily colonises deforested areas accumulating nutrients from deep below ground. The fruit yields oil and the palm is also widely used today as a source of fronds for building, palm-heart for food, and the nut husks are burnt for cooking charcoal. Anderson, May, and Balick (1991: 114) describe how, after oil has been pressed from the fruit, modern settlers start a fire in a hole about 1 m-deep, heap in the husks and cover the pit with damp leaves and a layer of sand. The slow combustion produces biochar rich in oily aromatic carbons (which they add to their plots). Attempts to recreate terra preta Researchers are exploring the potential for copying and improving dark earth production (Glaser, 2007; Lehmann, 2009; Mann, 2002; Steiner, 2008a). In Brazil the agricultural research and extension agency EMBRAPA has been active (Steiner et al., 2007) and the Terra Preta Nova Group, an international network of scholars, has also undertaken the quest since 2001. So far, there has been limited success. The research has mainly focused on warmer environments and there is a need to establish the potential for cooler (including temperate) environments (see: Atkinson, Fitzgerald, & Hipps, 2010). Biochar research and development groups have been established at many institutions, including: Cornell University, Bayreuth University, Edinburgh University, Massey University, Swansea University, Iowa State University, Georgia State University (USA),

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Delaware State University, University of Hawaii at Manoa, University of New South Wales, and in Thailand, India, Vietnam, Mongolia, China and Indonesia. The USA made provision in a recent Farm Bill to support biochar research and development. UN agencies have started to support biochar studies and companies are active, including: the Biochar Energy Corporation; Eprida; Best Energies. The character and potential of biochar Lehmann and Joseph (2009) define biochar as the carbon-rich product when biomass, such as wood, manure or leaves, is heated in a closed container with little or no available air. In more technical terms, biochar is produced by so-called thermal decomposition of organic material with limited supply of oxygen, and at relatively low temperatures (<700  C) (Stockmann, 2011: 39e41, 55 pp.). This process often mirrors the production of charcoal, which is one of the most ancient industrial technologies developed by mankind (Anon. Reviewer). However, biochar can be distinguished from charcoal and similar materials in that it is produced with the intent it be applied to soil as a means of improving soil productivity, carbon (C) storage and possibly filtration of percolating soil water (to try and cut pollution of surface and groundwater bodies). The production process and the intended use, forms the basis for distinguishing biochar (Lehmann et al., 2006). Biochar is the appropriate term where charred organic matter is applied to soil in a deliberate manner, with the intent to improve soil properties. This distinguishes biochar from charcoal that is used as fuel for heat, as a filter, as a reductant in iron making or as a colouring agent in industry or art (Lehmann et al., 2006). Commercial suppliers have developed various trade names already, such as AgricharÒ. Biochar is the most widely used and arguably the best term. Biochar is very variable in quality, depending on raw material, pyrolysis conditions, whether it is enriched with other compounds and how finely it is ground. The problem is that biochar is a generic term and standards have not been established but are much needed. Slow pyrolysis is said to minimize the risk of producing dioxins and harmful polyaromatic hydrocarbons, which could contaminate biochar and/or escape with exhaust gases and solid or liquid wastes. Low temperature pyrolysis gives a material with more desirable soil improvement properties than charcoal or ash that is also richer in aromatic carbon and humic substances. The pyrolysis can generate useful heat, biofuel or syngas as by-products. It may be possible to sequester more carbon dioxide in the soil than is liberated to the atmosphere during biochar pyrolysis: making it a carbon negative activity, which can enhance profitability (Fowles, 2007; Lal, 2007; Lehmann & Joseph, 2009; Matthews, 2008b). Sohi, Loetz-Capel, Krull, and Boll (2009, 65 pp.) noted biochar seems capable of remaining in soil without releasing carbon for centuries, even millennia and it enhances microbial activity. The mean soil carbon residence time for buried biochar is likely to be at least 1000 years, possibly longer (Nguyen & Lehmann, 2009). Some burnt materials like ash can be hydrophobic; so if added to soil they reduce moisture storage and enhance runoff resulting in poorer crops and even erosion; care needs to be exercised to ensure biochar does not have these qualities (Renner, 2007). So far the indications are that it enhances soil moisture. Beneficial applications might not need to be very frequent (compared with fertilisers, compost or manures). Ideally, biochar should have a long residence time in soil and actively support beneficial soil microorganisms. More research is needed to check these qualities. Also, successful biochar programmes will require more than technical know-how if they are to avoid unwanted socio-economic impacts; there must be political will, farmer support, organisational skills and the ability to cover the costs of raw material transportation and application to the land.

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NGOs, research bodies and green activists worldwide are very interested in biochar for: soil improvement; waste management; energy production; rehabilitation of degraded land and mitigation of climate change (Table 1 lists possible benefits). Some have been undertaking biochar production and usage trials (Rumpel et al., 2006). But there is a threat that biochar might be tightly controlled by commercial bodies, hindering wider adoption, especially by poorer people. There are already fears that biochar feedstock production could compete with food growing so a number of initiatives seek raw materials from land unsuitable for crops (and

Table 1 Possible benefits from biochar.  Enhance plant growth. Raise and sustain crop yields. Help improve good and problematic nutrient-poor soils, including acidic tropical humid and drier environment soils.  Help compensate for greenhouse gas emissions associated with agricultural development.  Store carbon in soil. Compost and manures are subject to rapid microbial breakdown.  Biochar may bind agrochemicals and help reduce phosphate and nitrate and agrochemicals pollution of streams and groundwater. Thus helping resolve major problems hindering sustained and improved agriculture.  Enable production of useful materials from uncropped land making use of unused wastes.  Reduce the need for fertiliser/manure/compost.  Reduce costs of sewage and animal waste treatment and cut emissions that they would otherwise cause if held in lagoons or heaps. Experimental sewage conversion to biochar is already underway in Bingen (Germany). Animal manures/soiled bedding/litter in many countries present a costly waste disposal problem and are a source of methane, ammonia and other greenhouse gases if left in heaps or lagoons. Application of manure or compost to the soil may stimulate bacteria and cause methane and N2O to the atmosphere. Composting also releases greenhouse gases and compost may have a limited residence time in soil. Pyrolysis destroys microorganisms and some veterinary pharmaceuticals.  Offer a more environmentally-friendly way of processing plastics and refuse e if biochar is too contaminated for agricultural use for growing non-food crops or send to landfill to sequester carbon.  Store carbon in soil. Sequestration in biochar is likely to be centuries, possibly thousands of years. Ash tends to be lost by wind and water erosion and leaches out of soil.  Reduce plant uptake of pesticides from contaminated soils (Xiang-Yang Yu. et al., 2009). A form of bioremediation.  Nutrient affinity i.e. retention of plant nutrients, notably retention of N on permeable soils under rainy conditions.  Reduce soil acidity/raise pH.  Reduce aluminium toxicity.  Increase cation exchange capacity  By improving moisture retention biochar may reduce the demand for irrigation and make cropping more secure.  Support biofuel production e reduce its carbon footprint and even enable it to move toward being carbon neutral.  Increase soil microbial biomass. And support other beneficial organism like earthworms.  Support nitrogen fixation.  Increase arbuscular mycorrhizal fungi in soil.  Suppress methane and N2O (nitrous oxide gas) emission from cultivated soil (helping slow global warming).  If biochar supports intensive sustainable agriculture it could help cut pressure for new forest clearances (biodiversity conservation benefits).  Reduce dependency of farmers on input suppliers.  Increase adaptability to environmental change by making production more resilient.  Opportunities for poor to benefit from carbon offset market.  Periurban/urban agriculture: biochar may be a useful input to counter harmful compounds like heavy metals, dioxins, PAHs (polycyclic aromatic hydrocarbons) present in sewage or refuse inputs.  Biochar may improve soil moisture retention, increasing agricultural resilience against climatic change effects like increased drought and floods.

hopefully with no other value that will be disrupted) or seek to use agricultural wastes (Demirbas, 2006; Hooda & Rawat, 2006; McHenry, 2009; Pan, Zhang, Zou, Li, & Zhang, 2010; Stamatov & Rocha, 2007). Ideally, biochar feedstock production should help prevent erosion, rehabilitate degraded land and/or improve the habitat for conservation of wildlife. Potentially almost any organic material and some plastics can be used as feedstock, including: rural wastes, agro-industrial waste, sewage, animal manure, aquatic algae, aquatic plants, etc. In India work is in progress to expand a National Biomass Resource Atlas to check what potential feedstocks are currently being used for and assess how much there is available (Ministry of New and Renewable Energy: National Biomass Resource Atlas http://www.mnes.nic.in accessed June 2009). Studies on potential global feedstock supply and logistics have been conducted by Woolf (2008, 31 pp.). Brazil alone might be able to produce large amounts of bio fuel using land that has been cleared, degraded and abandoned, by growing elephant grass e Miscanthus spp. and get biochar as a byproduct (Strezov, Evans, & Hayman, 2008). Another possibility would be to produce algae as biochar feedstock in lagoons or bioreactors using poor quality water and effluent or exhaust gases from industry or power generation for nutrients. In the Maldives there are plans to produce biochar from crop wastes and mix it with fish processing effluent using community-size pyrolysis units. These will produce syngas and ‘enhanced’ biochar for soil improvement, reduce fertiliser import costs (currently over UK£60 per tonne) and earn carbon credits (The Sunday Times UK 30/08/09: 9) (see Table 2). Agriculture contributes significantly to global warming because it liberates soil organic carbon and methane (Franzluebbers & Doraiswamy, 2007). So, sequestering carbon in farmland by soil Table 2 Promising biochar feedstocks.  Cattle, poultry and pig manure, aquaculture waste- presently often costly to dispose of.  Wood waste from forestry, paper pulp manufacture, packaging or carpentry (provided it is not treated with fungicides if it to be used for agriculture).  Biochar as a by-product: from biofuel or biogas production (biodiesel, alcohol, hydrogen, syngas) or local heat/electricity generation. This is attractive because it may make the bioenergy enterprise more cost effective and possibly closer to being carbon neutral. However, this may not encourage production of biochar of optimum quality for soil improvement.  Farm crop and agricultural product processing wastes. Materials that might otherwise be landfilled or composted (liberating greenhouse gases). For example, rice husks, straw, maize stover and stripped-cobs, oil-seed husks after oil extraction.  Plants specifically grown for biochar. This could be problematic if plantations displace food production or marginalize farmers who then clear new land and destroy biodiversity. There may be opportunities to grow raw material on degraded land or poorly vegetated areas without serious biodiversity or groundwater impacts (perhaps even providing better wildlife habitats) (Packer, 2009). Elephant grass (Miscanthus spp.) might be grown on road verges, rail cuttings or land taken out of farm production because of agrochemical contamination; salt-tolerant plants might be used on areas affected by salinization and sodification (alkalinisation). This may help rehabilitate the areas by removing some salts in the harvested plants and by trapping more rainfall. In some environments nuisance exotics (e.g. Jatropha spp., Prosopsis spp. eucalyptus spp., or Albizia spp.) may be a useful feedstock. Various palms may have promise, for example babassu, providing oil-seed from poor degraded land with biochar as a by-product.  Effluent, sewage and poor quality surface or groundwater, which are unusable for irrigating food crops is used to grow algae, Azolla, water hyacinth, etc. Using waste lagoons or bioreactors to yield biochar feedstock would reduce competition with food production.

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amendment with biochar, or by rehabilitating degraded land with biochar would be welcome (Johnson, Franzluebbers, Weyers, & Reicosky, 2007; Lal, 2004; Leake, 2008). Where feedstock produces contaminated biochar unsuitable for improving food crops it could simply be land-filled, a less technically challenging strategy than pumping CO2 down oil-wells or mines or seeding oceans with chemicals (Lovett, 2008). Preliminary calculations suggest that if 2.5% of the world’s agricultural land produced biochar (ideally from wastes) that was added to topsoil then atmospheric carbon dioxide levels might be reduced to pre-AD 1752 quantities by 2050 (Jacquot, 2008). Biochar production could be possible at village scale and if suitablestoves could be rapidly spread it may enable impressive levels of carbon lock-up and soil improvement (Whitman & Lehmann, 2009). There have been trials of cheap pyrolysis stoves in India by NGOs like Social Change and Development (in Tamil Nadu) and Action for a Global Climate Community but results are not conclusive. A point, which should not be overlooked, is that farmers often burn crop residue, weeds and wastes on their fields, which releases carbon dioxide to the atmosphere and does little to help sustain fertility, rehabilitate degraded land or bring infertile areas into production. To establish and support small-scale biochar production and biochar soil amendment on a significant scale will be a challenge The African Biodiversity Network et al. (2009: 6e8) tested small-scale production and was sceptical that it will work. Perhaps small companies or town/city authorities could gather waste and sell or distribute biochar of consistent quality more effectively (something applied geographers might explore)? Saline or polluted water that is unsuitable for food crops may support algae production or salt-tolerant higher plants (palms, reeds, mangroves, various halophytes, etc.) for biochar feedstock. Use of contaminated wastes as feedstock may not lead to harmful compounds in biochar e but more research is needed to check (Shinogi, Yoshida, Koizumi, Yamaoka, & Saito, 2003). The rapidly growing aquatic plant Azolla spp., might be assessed as a raw materials for biochar. There is palaeoecological evidence that Azolla sequestered atmospheric carbon dioxide so effectively that it was one of the main causes of the global cooling from tropical and high atmospheric carbon dioxide conditions of the mid-Eocene before the Quaternary (Speelman et al., 2009). Azolla could be cultured in lagoons using sewage. Another possible feedstock is Prosopis spp., which has become a common introduced plant on degraded land in many salinized and semiarid areas. In India Jatropha spp. plantations are being explored for biodiesel, alcohol and biochar (Hooda & Rawat, 2006). If not carefully controlled, biochar could be in competition with food production and drive small farmers driven off their land (George Monbiot, The Guardian newspaper, UK 24/03/09). Biofuel production and carbon credits speculation by business will happen anyway and biochar as a by-product might at least help improve soil as well as sequester carbon (Matthews, 2008a). Such possibilities have prompted a few bodies like the NRDC to make assessments of the promise and risks (Brick, 2010, 17 pp.). Care is also needed to ensure biochar production does not use non-food materials that people already exploit for building or other household uses (Clapp, Hayes, & Ciavatta, 2007). However, huge quantities of usable wastes are presently disposed of in ways that are costly and have negative impacts. James Lovelock recently argued in the UK media that the only hope for mitigating catastrophic climate change is biochar production from waste biomass cooked by pyrolysis and buried. Discussion websites devoted to biochar and the literature is expanding rapidly. For some years the International Biochar Initiative (IBI) has served as a platform for the exchange of information on biochar research and development as a means of carbon

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sequestration. To ensure biochar sequestration of carbon has better support the IBI has encouraged studies and lobbying for more recognition and ideally cash payment or carbon credits. In the EU the European Biochar network is also active. In May 2009 the UN Framework Convention on Climate Change (UNFCC) included biochar in its proposals for ‘Enhanced Action on Mitigation’, recognising it has a dual role in countering climate change and combating land degradation. Interest in biochar was taken forward by the 18th World Congress of Soil Science in 2006 in Philadelphia, the 2007 International Agrichar Initiative 2007 Conference and the 2008 Conference of the IBI: “Biochar, Sustainability and Security in a Changing Climate” In May 2009 the 1st Asia Pacific Biochar Conference was held in Australia. There have been encouraging studies of biochar, which suggest it is beneficial and that applications may not need to be especially frequent. In Australia there have been promising trials with biochar for improving poor soils (Quayle, 2010, 24 pp.). Application to upland rice fields in Laos reportedly raised yields, and improved response to N and NP fertiliser; however, in this case it is not clear the commercially supplied ‘biochar’ was the product of low temperature pyrolysis and the feedstock was not closely monitored (Asai et al., 2009). Biochar plus NPK fertiliser gave double the yields of grain when applied to a Brazilian Oxisol compared with NPK alone (Christoph et al., 2007). Kimetu et al. (2008) reported applications to degraded soils in Kenya doubled maize yields, but they failed to prove why, although there were indications it had raised soil CEC and pH. In this case the biochar was made from eucalyptus at 400e500  C with oxygen deprivation, it was then crushed to peasize and hoed-in. Applied to sandy acidic soils in southwestern USA biochar is reported to have increased SOC and to have improved overall fertility (Novak et al., 2009). Rondon, Lehmann, Ramirez, and Hurtado (2007) reported applications (30e90 g per kg 1 soil) improved biological nitrogen fixation by bean crops, and may have improved B and Mo availability. In June 2009 long-term field trials with biochar to assess its beneficial effect on soil structure and water retention were started at Rothamstead Experimental Station (UK). The value of biochar for soil improvement seems promising and is probably partly related to the huge surface area of its particles and their many micropores, which provide a microhabitat for beneficial soil microorganisms and enable moisture retention and adsorption of nutrients (Lehmann & Joseph, 2009; Sohi et al., 2009, 65 pp.). There are indications that biochar added to soil prompts beneficial arbuscular mycorrhizal fungi activity (Warnock, Lehmann, Kuyper, & Rilling, 2007). There are a few cases where ‘biochar’ reportedly had a negative impact on soil it was added to (Lal, 2008b). Possibly those unpromising trials used high temperature charcoal or biochar of poor quality; what is needed is more dispassionate and scientifically rigorous testing and established standards for biochar. Great differences in biochar performance are likely, depending on how it is produced and whether or not it is enhanced with additives. It also remains to be established whether it is best: tilledin, top-dressed, spread around plants or between rows, whether it should be pulverized or buried as coarser material and at what rate and frequency of application. Research is needed to assess how and for what time biochar can be stored. The indications are that commonly used fertiliser spreaders or simple implements can be used so it could be an innovation that is easy to use. There have trials of various pyrolysis units, including microwave pyrolysis (The Sunday Times -UK 24/01/10: 10). But many of these are more focused on production of heat and syngas or liquid fuels than biochar quality. More research is needed on biochar quality and the establishment of reliable standards. Studies of the value of biochar for soil improvement so far mainly focus on the humid tropics, although NGOs are active in some non-tropical environments

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(Glaser, Haumaier, Guggenburger, & Zech, 2001; Lehmann & Rondon, 2006; Sohi et al., 2009, 65 pp.; Woolf, 2008, 31 pp.). There are many rather ad hoc, sometimes not very scientific trials. Consequently, there is a risk that agencies, NGOs or governments will get projects underway before enough has been done to establish actual benefits and risks and best practice; poor results might then greatly hinder future progress. Even small failures can set off distrust and discourage efforts on a wide front. There is a need for broader interdisciplinary study of the type undertaken by applied geographers to check the innovation ‘package’ successful biochar usage involves. Biochar and the doubly green revolution World population is increasing, there is likely to be environmental change as a consequence of global warming and current agriculture often causes pollution and degrades soil. The challenge is to boost and sustain food production and do this while coping with environmental change in ways that avoid further land degradation (a doubly green revolution). When fertiliser, manure, or compost is applied it is often rapidly lost committing the farmer to recurrent costs and the phosphate, potash and nitrate escape and cause stream and groundwater contamination. This contamination, together with pesticides, herbicides and heavy metals can be severe enough to ruin streams; lakes, groundwater and inshore marine environments and may threaten the continuation of farming. Trials in China with biochar applied at up to 1.0% by weight to agrochemicals contaminated soils reportedly resulted in the sequestration or breakdown of pollutants and their reduced uptake by plants (Xiang-Yang Yu., Guang-Guo Ying, & Kookana, 2009). It is important to get more from fertilisers, manure or compost because much of the world’s food production is in the hands of smallholders with poor access to such inputs and also supplies of phosphate are dwindling so future access could become problematic. Biochar application has the potential to ease these problems in an accessible way (Atkinson et al., 2010; Bruges, 2010, 128 pp.; Glaser et al., 2002; Steiner, 2008b; Whitman & Lehmann, 2009). If biochar can be produced regionally or locally it offers a way to reduce dependency (for many countries fertiliser imports are a serious cost to their economies). Biochar for land rehabilitation and improvement The United Nations Convention to Combat Desertification (UNCCD) supports biochar as a means for combating land degradation, improving farmland and combating climate change. There are two ways in which biochar use can counter land degradation: 1) biochar use to make farming more sustainable and productive with less harmful pollution. This would reduce pressure for clearing new land (Abend, 2008, 4 pp.). 2). Biochar use to rehabilitate degraded or naturally poor land e also helping to reduce pressures for clearing new areas. One vital question is ‘how will degraded or desertified regions produce sufficient biochar to effectively support land rehabilitation when there is only sparse plant cover to use for feedstock?’ One solution would be to grow hardy vegetation on unfarmed biodiversity-poor areas, perhaps irrigated with water too poor to be used for food crops. Other possibilities are algae, reeds, grasses or aquatic weeds grown in lagoons using poor quality water and effluents. Waste from towns and agricultural waste might also be used if transport were cost effective. Strezov et al. (2008) suggest un-irrigated elephant grass grown on degraded (non-agricultural) land could produce biofuel and biochar even where growth rates are less than 40 metric tons of dry biomass per hectare per annum. Land ruined by salts or soda, might produce biomass for biochar production and the removal of the contaminants with the biomass

could help rehabilitate it as well as providing material to improve soils elsewhere. This has been explored in Australia (Bartle, Olsen, Cooper, & Hobbs, 2007), where dry, salty land yields coppiced eucalyptus feedstock and in Sumatra where forestry and paper pulp waste has been used (Ogawa, Okimori, & Takahashi, 2006). Urban brown field sites could be rehabilitated with biochar to support amenity planting or biofuel and timber production and at the same time lock-up carbon. Linked to refuse treatment biochar could have much potential. Modern urban refuse in developed countries (and increasingly in developing nations) is likely to be contaminated with toxic materials and so may not make good compost; however, some studies suggest uncontaminated biochar may be produced with it. The contribution of biochar to mitigating global warming Biochar production does emit carbon dioxide and other greenhouse gases but combined with waste disposal or biofuel production it appears to offer a practical way to mitigate global warming. Understandably biochar potential is attracting much attention as a safe, practical, technically simple, and affordable methods of sequestration, which has a chance of spreading fast enough to have real effect. If enough farmers, larger agricultural enterprises, biofuel producers, and waste treatment plants a are established it could become an important means of carbon sequestration. This potential is a little better researched than biochar agricultural value; although, there is insufficient data on biochar-burial soil carbon mean residence times. Some key questions relating to biochar sequestration of carbon are:  Is buried biochar stable, will it lock up carbon and not release it (might it even take up more carbon after burial)?  Is biochar production and burial cost-effective?  Is biochar production efficient enough to sequester sufficient carbon to make it worthwhile?

Conclusions Interest in biochar has ‘taken-off’ and projects are being implemented. It is clear that biochar particles have an enormous surface area and an intricate internal structure, which provide a potentially valuable adaptive niche for microorganisms and the subsequent production of biofilms. It also looks likely that biochar can improve soil cation exchange capacity. However, without adequate research into biochar potential, risks and best ways to produce and apply it there is a danger that unexpected problems and failures will hinder and discourage progress. One difficulty already apparent is that researchers sometimes fail to establish the exact nature of their biochar, which makes it difficult to interpret results. There needs to be more study of biochar qualities and the establishment of standards. Biochar production from wastes could be a very good way to reduce demand for fertilisers (cutting dependency, costs and pollution), sequester carbon and enable relatively cheap and lasting amelioration of degraded land and sustainable and improved agriculture. But there are risks, commerce may use biochar for profit and in the process reduce food production and drive smaller farmers off the land and destroy biodiversity (The African Biodiversity Network et al., 2009). Another risk is that national bodies or companies will fail to make findings widely available or patent biochar know-how and make it difficult for poorer farmers to adequately access the innovation.

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Slash-and-char techniques may hold out promise for more sustainable production and reduced land degradation without discouraging costs suitable for even relatively remote areas. Study of Amazonian dark earths prompted interest in biochar but there should not be the assumption that pre-Conquest soil improvement was just through biochar production. If inputs of fish, animal or vegetable oils were used to ‘enhance’ the biochar, then modern initiatives may fail or need inputs that could make them more costly and less accessible, especially for poor farmers in areas away from rivers or the sea. Biochar could be a key component for a doubly green revolution; it could also be one of the best practical ways to counter global warming and it might be an effective way to rehabilitate degraded land and counter pollution of streams and groundwater. However, enthusiasm needs to be backed with adequate research to establish the qualities of biochar and to develop the best usage and ways to promote optimum innovation. There is a need for a broad overview of the diverse research. If biochar is found to have the potential its supporters claim its use must be carefully controlled to reduce problems. Acknowledgements I am most grateful to the Swansea University Biochar Research Team, especially Professor A. Street-Perrott, for their support. References Abend, L. (2008). Carbon: The biochar solution. Time online. http://www.time.com/ time/magazine/article/0,9171,1864279,00.html Accessed June 2009, 4 pp. Allan, P. (1965). The African husbandman. Edinburgh: Oliver and Boyd. Anathaswamy, A. (2010). Amazon life owes a thing or two to us. New Scientist, 17 April 2010 page 10. Anderson, A. B., May, P. H., & Balick, M. J. (1991). The subsidy from nature: Palm forests, peasantry, and development on an Amazon frontier. New York: Columbia University Press. Asai, H., Samson, B. K., Stephan, H. M., Songyikhangsuthor, K., Homma, K., Kiyono, Y., et al. (2009). Biochar amendment techniques for upland rice production in Northern Laos 1. Soil physical properties, leaf SPAD and grain yield. Field Crops Research, 111(2009), 81e84. Atkinson, C. J., Fitzgerald, J. D., & Hipps, N. A. (2010). Potential mechanisms for achieving agricultural benefits from biochar application to temperate soil: a review. Plant Soil, 337(1e2), 1e18. Barrow, C. J. (1985). The development of the várzeas (floodlands) of the Brazilian Amazon. In J. Hemming (Ed.), Change in the Amazon basin. Man’s impact on forests and rivers, Vol. 1 (pp. 108e128). Manchester: Manchester University Press. Bartle, J., Olsen, G., Cooper, D., & Hobbs, T. (2007). Scale of biomass production from new woody crops for salinity control in dryland agriculture in Australia. International Journal of Global Energy Issues, 27(2), 115e137. Brick, S. (2010). Biochar: Assessing the promise and risks to guide U.S. policy. NRDC Issue Paper November 2010. New York: Natural Resources Defense Council. 17 pp. Bruges, J. (2010). The biochar debate: Charcoal’s potential to reverse climate change and build soil fertility. Cachan (France): Lavoesier. 128 pp. Caesar, E. (2010). A glint of El Dorado in the Amazon jungle. UK: The Sunday Times. 10/01/10: 7. Christoph, G. T., Wenceslau, L., Johannes, N., Thomas, M., deVasconcelos, J. L., Winfried, E. H. B., et al. (2007). Long-term effects of manure, charcoal and mineral fertilization on crop production and fertility on a highly weathered central Amazonian upland soil. Plant and Soil, 291(2007), 275e290. Clapp, C. E., Hayes, M. H. B., & Ciavatta, C. (2007). Organic wastes in soils: biogeochemical and environmental aspects. Soil Biology and Biochemistry, 39(6), 1239e1243. Conry, M. J. (1974). Plaggen soils, a review of man-made raised soils. Soils and Fertilizers, 37, 319e326. Demirbas, A. (2006). Production and characterization of bio-chars from biomass via pyrolysis. Energy Sources, 28(5), 413e422. Denevan, W. M. (1966a). The aboriginal cultural geography of the Llanos de Mojos of BoliviaIn Ibero-Americano, Vol. 48. Berkeley: University of California Press. Denevan, W. M. (1996b). A bluff model of riverine settlement in prehistoric Amazonia. Annals of the Association of American Geographers, 86(4), 654e681. Denevan, W. M. (2001). Cultivated landscapes of native Amazonia and the Andes. Oxford: Oxford University Press. Denevan, W. M. (2008). Comments on prehistoric agriculture in Amazonia. Culture & Agriculture, 20(2e3), 54e59.

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