Biochar(Agrichar)
Soil Biogeochemistry
Johannes Lehmann
 

 

 

Biochar: the new frontier


Inspired by the fascinating properties of Terra Preta de Indio, biochar was identified as a soil amendment that has the potential to revolutionize concepts of soil management. While "discovered" may not be the right word, as biochar or bio-char (also called charcoal or biomass-derived black carbon, in the context of agricultural application sometimes called agrichar or agri-char, which we do not adopt due to the wider applicability of biochar for environmental management beyond agriculture) has been used in traditional agricultural practices as well as in modern horticulture, never before has evidence been accumulating that demonstrates so convincingly that biochar has very specific and unique properties that make it stand out among the opportunities for sustainable soil management.

The benefits of biochar rest on two pillars:
1- The extremely high affinity of nutrients to biochar (adsorption)
2- The extremely high persistence of biochar (stability)
(beneficial effects of biochar on both soil microbial functions and soil water availability are highly likely but not yet sufficiently quantified to be effectively managed)

These two properties (which are truly extraordinary - see details below) can be used effectively to address some of the most urgent environmental problems of our time:
1- Soil degradation and food insecurity
2- Water pollution by agro-chemicals
3- Climate change
Biochar is not a silver bullet that will solve environmental problems without a much wider and far reaching strategy. But it can provide an important tool that contributes to a comprehensive approach that must include policy guidance.

"Soils with biochar additions are typically more fertile, produce more and better crops for a longer period of time."

Reading:
Lehmann J 2007 Bio-energy in the black. Frontiers in Ecology and the Environment 5, 381-387.
Lehmann J and Rondon M 2006 Bio-char soil management on highly weathered soils in the humid tropics. In Uphoff N (ed.) Biological Approaches to Sustainable Soil Systems. CRC Press, Boca Raton , FL. pp.517-530.
Lehmann, J., Gaunt, J. and Rondon, M.: 2006, 'Bio-char sequestration in terrestrial ecosystems – a review', Mitigation and Adaptation Strategies for Global Change 11, 403-427

 

 

THE TWO PILLARS OF BIOCHAR PROPERTIES

Nutrient Affinity
All organic matter added to soil significantly improves various soil functions, not the least the retention of several nutrients that are essential to plant growth. What is special about biochar is that it is much more effective in retaining most nutrients and keeping them available to plants than other organic matter such as for example common leaf litter, compost or manures. Interestingly, this is also true for phosphorus which is not at all retained by 'normal' soil organic matter (Lehmann, 2007).

Reading:
Lehmann J 2007 Bio-energy in the black. Frontiers in Ecology and the Environment 5, 381-387.
Lehmann, J., da Silva Jr., J.P., Steiner, C., Nehls, T., Zech, W. and Glaser, B.: 2003a, ‘Nutrient availability and leaching in an archaeological Anthrosol and a Ferralsol of the Central Amazon basin: fertilizer, manure and charcoal amendments', Plant and Soil 249 , 343-357.
Liang, B. , Lehmann, J., Solomon, D., Kinyangi, J., Grossman, J., O'Neill, B., Skjemstad, J.O., Thies, J., Luizão, F.J., Petersen, J. and Neves, E.G.: 2006, 'Black carbon increases cation exchange capacity in soils', Soil Science Society of America Journal 70: 1719-1730.
Mikan, C.J. and Abrams, M.D.: 1995, 'Altered forest composition and soil properties of historic charcoal hearths in southeastern Pennsylvania', Canadian Journal of Forestry Research 25, 687-696.
Sombroek, W., Nachtergaele, F.O. and Hebel, A.: 1993, ‘Amounts, dynamics and sequestering of carbon in tropical and subtropical soils', Ambio 22, 417-426.

Persistence
It is undisputed that biochar is much more persistent in soil than any other form of organic matter that is commonly applied to soil. Therefore, all associated benefits with respect to nutrient retention and soil fertility are longer lasting than with alternative management. The long persistence of biochar in soil also makes it a prime candidate for the mitigation of climate change as a potential sink for atmospheric carbon dioxide. The success of effective reduction of greenhouse gases depends on the associated net emission reductions through biochar sequestration. A net emission reduction can only be achieved in conjunction with sustainable management of biomass production. During the conversion of biomass to biochar about 50% of the original carbon is retained in the biochar, which offers a significant opportunity for creating such a carbon sink (Lehmann, 2007). This promises biochar to become an appropriate tool to contribute a significant wedge in a wider strategy for the mitigation of the anthropogenic greenhouse effect.

Reading:
Baldock JA and Smernik RJ. 2002, 'Chemical composition and bioavailability of thermally altered Pinus resinosa (Red pine) wood',Organic Geochemistry 33 : 1093-109.
Cheng CH, Lehmann J, Thies JE and Burton S 2008 Stability of black carbon in soils across a climatic gradient. Journal of Geophysical Research (Biogeosciences) in press. 10.1029/2007JG000642

Lehmann, J.: 2007, 'A handful of carbon',Nature 447, 143-144.
Lehmann, .J, Gaunt, J. and Rondon, M.: 2006, 'Bio-char sequestration in terrestrial ecosystems – a review',Mitigation and Adaptation Strategies for Global Change 11, 403-427.
Pessenda, L.C.R., Gouveia, S.E.M. and Aravena, R.: 2001, ‘Radiocarbon dating of total soil organic matter and humin fraction and its comparison with 14 C ages of fossil charcoal', Radiocarbon 43 , 595-601.
Schmidt, M.W.I. and Noack, A.G.: 2000, ‘Black carbon in soils and sediments: analysis, distribution, implications, and current challenges', Global Biogeochemical Cycles 14 , 777-794
.Seifritz, W.: 1993, ‘Should we store carbon in charcoal?', International Journal of Hydrogen Energy 18 , 405-407.
Shindo, H.: 1991, ‘Elementary composition, humus composition, and decomposition in soil of charred grassland plants', Soil Science and Plant Nutrition 37 , 651-657.

 

LAND-USE SYSTEMS AND BIOCHAR USE

Biochar research and development has experienced a meeting of interests by different scientific communities and stakeholders that allow an exciting perspective on how to handle biomass in a future economy. The potential to combine bio-energy production, sustainable agriculture and waste management into one approach using biochar offers in many cases significant synergism for a combined strategy.

 

Bio-energy production through low-temperature pyrolysis

(read more about Biochar and Bio-energy)

 

Sustainable agriculture

In both industrialized and developing countries, in mechanized and large-scale or subsistence agriculture, lack of carbon is constraining ecosystem health. Biochar may in many cases be an appropriate approach to make this valuable commodity last longer, be more efficient in soil, and in combination with energy production, carve out carbon that would otherwise be wasted and even harmful to environment and human health. Intelligent solutions tailored to local opportunities and constraints are required.

Waste management

Biochar production offers an exciting perspective on managing green or brown wastes. A combination of waste management (recognizing that biomass "wastes" are unlikely to remain untapped indefinitely, and that wastes of today may become valuable commodities of tomorrow), bioenergy production and sustainable soil management can succeed by an approach involving biochar. Several technologies of pyrolysis bioenergy are able to utilize biomass streams that are diffcult to handle by other currently available bioenergy concepts (e.g., if they have too high mineral contents and contain little sugar), and produce biochar that is typically easier and less expensive to transport than the original material. Careful consideration needs to be paid to the type of feedstock, if the biochar is to be used as a soil amendment, and sufficient testing has to precede implementation to avoid environmental contamination.

Reading:
Laird D 2008 The charcoal vision: A win–win–win scenario for simultaneously producing bioenergy, permanently sequestering carbon, while improving soil and water quality. Agronomy Journal 100, 178-181.
Lehmann, J.: 2007, 'A handful of carbon',Nature 447, 143-144.
Lehmann J 2007 Bio-energy in the black. Frontiers in Ecology and the Environment 5, 381-387.
Lehmann, .J, Gaunt, J. and Rondon, M.: 2006, 'Bio-char sequestration in terrestrial ecosystems – a review', Mitigation and Adaptation Strategies for Global Change 11, 403-427.
Mathews JA 2008 Carbon-negative biofuels. Energy Policy 36, 940-945.