Difference between revisions of "Biochar: Effects on Soil and Crops"

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==Biochar's effects on soil fertility and quality==  
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==Soil fertility and quality==  
  
 
Organic matter added to soil helps it retain nutrients that are essential to plant growth. Proponents of biochar say that it is much more effective than other organic matter in retaining nutrients and keeping them available to plants. A study by Johannes Lehmann says this is also true for phosphorus, which is not retained by 'normal' soil organic matter.<ref>Lehmann, J., 2007 Bio-energy in the black. Frontiers in Ecology and the Environment 5, 381-387.</ref>  
 
Organic matter added to soil helps it retain nutrients that are essential to plant growth. Proponents of biochar say that it is much more effective than other organic matter in retaining nutrients and keeping them available to plants. A study by Johannes Lehmann says this is also true for phosphorus, which is not retained by 'normal' soil organic matter.<ref>Lehmann, J., 2007 Bio-energy in the black. Frontiers in Ecology and the Environment 5, 381-387.</ref>  
  
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Researchers who have tested the impact of charcoal on soil fertility say that much of the benefit may derive from charcoal’s vast surface area and complex pore structure, which is hospitable to the bacteria and fungi that plants need to absorb nutrients from the soil. Christoph Steiner, a research scientist at the University of Georgia, says, "We believe that the structure of charcoal provides a secure habitat for microbiota, which is very important for crop production." Steiner and coauthors noted in their 2003 book Amazonian Dark Earths that the charcoal addition to soil caused a 280-400% increase in plant uptake of nitrogen.<ref>Tenenbaum, David J., Biochar: carbon mitigation from the ground up, Environmental Health Perspectives, Feb 2009 v117 i2 pA70–74.</ref>  
+
Researchers who have tested the impact of charcoal on soil fertility say that much of the benefit may derive from charcoal’s vast surface area and complex pore structure, which is hospitable to the bacteria and fungi that plants need to absorb nutrients from the soil. Christoph Steiner, a research scientist at the University of Georgia, says, "We believe that the structure of charcoal provides a secure habitat for microbiota, which is very important for crop production." Steiner and coauthors noted in their 2003 book ''Amazonian Dark Earths'' that the charcoal addition to soil caused a 280-400% increase in plant uptake of nitrogen.<ref>Tenenbaum, David J., Biochar: carbon mitigation from the ground up, Environmental Health Perspectives, Feb 2009 v117 i2 pA70–74.</ref>  
  
 
A report for Biofuelwatch, however, says that over-reliance on biochar to create soil fertility is dangerously reductionist. It says the farmers who created terra preta added different types of biomass the soil, thus building up humus as well as charcoal. Biochar advocates, on the other hand, “promote stripping the land of ‘agricultural and forestry residues’, which would greatly reduce humus.” Done on a large scale, the report warns, this would “replace at least some humus with biologically dead charcoal, an untested but potentially very dangerous strategy.”<ref>Almuth Ernsting and Rachel Smolker, “[http://www.biofuelwatch.org.uk/docs/biocharbriefing.pdf Biochar for Climate Change Mitigation: Fact or Fiction?]”, Biofuelwatch, February 2009, p. 4</ref>
 
A report for Biofuelwatch, however, says that over-reliance on biochar to create soil fertility is dangerously reductionist. It says the farmers who created terra preta added different types of biomass the soil, thus building up humus as well as charcoal. Biochar advocates, on the other hand, “promote stripping the land of ‘agricultural and forestry residues’, which would greatly reduce humus.” Done on a large scale, the report warns, this would “replace at least some humus with biologically dead charcoal, an untested but potentially very dangerous strategy.”<ref>Almuth Ernsting and Rachel Smolker, “[http://www.biofuelwatch.org.uk/docs/biocharbriefing.pdf Biochar for Climate Change Mitigation: Fact or Fiction?]”, Biofuelwatch, February 2009, p. 4</ref>
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 +
==Water retention of soil==
 +
 +
A survey of published studies showed that only sandy soils had higher available moisture after charcoal additions. Clay soils (which are naturally good at retaining water) showed decreased moisture content with increasing charcoal additions.<ref>Glaser B, Lehmann J, Zech W (2002) Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal—a review. Biol Fertil Soils 35:219–230</ref>
 +
 +
==Crop yield==
 +
According to Cornell University Department of Soil and Crop Sciences, “Soils with biochar additions are typically more fertile [and] produce more and better crops for a longer period of time.”<ref>“[http://www.css.cornell.edu/faculty/lehmann/research/biochar/biocharmain.html Biochar: The new frontier],” Cornell University Department of Soil and Crop Sciences, Cornell University website</ref>
 +
 +
This is largely confirmed by studies examining the effects on crop yield of added charcoal. Most show positive results in the short term, though in a few cases, either no difference or negative results have been found. Longer-term studies are lacking.
 +
 +
Here are the results of studies on the impact on yield of adding charcoal to soil:
 +
*Research on peas and mung beans in India showed an 160% and 122% biomass increase respectively<ref>Iswaran V, Jaiuhri KS, Sen A (1980), “Effect of charcoal, coal and peat on the yield of moong, soybean and pea”, Soil Biol Biochem 12:191–192</ref>
 +
*Research in Japan on soybeans grown on volcanic ash loam showed an 151% biomass increase at an application rate of 0.5 Mgha-1 (megagrams per hectare, a megagram being a metric ton). However, higher rates of application decreased yield: 5 Mgha-1 of char decreased yield to 63% and 15 Mgha-1 char decreased yield to 29%<ref>Kishimoto S, Sugiura G (1985), “Charcoal as a soil conditioner”, Int. Achieve Future 5:12–23</ref>
 +
*Research in Japan on sugi trees (the national tree of Japan, often grown near temples) on clay loam with addition of charcoal from different sources at an application rate of 0.5 Mgha-1 found:<ref>Kishimoto S, Sugiura G (1985), “Charcoal as a soil conditioner”, Int. Achieve Future 5:12–23</ref>
 +
::wood charcoal increased biomass 249%
 +
::bark charcoal increased biomass 324%
 +
::activated charcoal increased biomass 244%
 +
*Research on bauhinia trees found increased biomass by 13% and height by 24%<ref>Chidumayo E.N. (1994), “Effects of wood carbonization on soil and initial development of seedlings in miombo woodland, Zambia,” Forest Ecological Management 70: 353–357</ref>
 +
*Research on cowpeas found 150% biomass increase from application rates of 67 Mgha-1 and 200% biomass increase from application rates of 135 Mgha-1<ref>Glaser, B., Lehmann, J., Zech, W., 2002. Ameliorating physical and chemical properties of
 +
highly weathered soils in the tropics with charcoal – a review. Biology and Fertility of Soils 35, 219-230.</ref>
 +
*Research on cowpeas and rice at the Embrapa Amazonia Ocidental, Manaus, Brazil found a 38-45% increase in biomass (no yield reported)<ref>Lehmann, J., da Silva Jr, J.P., Steiner, C., Nehls, T., Zech, W., Glaser, B., 2003. Nutrient availability and leaching in an archaeological Anthrosol and a Ferralsol of the Central Amazon basin: fertilizer, manure and charcoal amendments. Plant & Soil 249, 343-357.</ref>
 +
*Research in Ghana on maize grown on disused charcoal production sites and adjacent fields found a grain yield 91% higher and biomass yield 44% higher on the charcoal site than the control<ref>Oguntunde, P.G., Abiodun, B.J., Ajayi, A.E., van de Giesen, N., 2008. Effects of charcoal production on soil physical properties in Ghana. Journal of Plant Nutrition and Soil Science 171, 591-596.</ref>
 +
*Research on maize, cowpea and peanuts on low fertility soil found acacia bark charcoal plus fertilizer increased maize and peanut yields (but not cowpea)<ref>Yamato, M., Okimori, Y., Wibowo, I.F., Anshori, S., Ogawa, M., 2006. Effects of the application of charred bark of Acacia mangium on the yield of maize, cowpea and peanut, and soil chemical properties in South Sumatra, Indonesia. Soil Science and Plant Nutrition 52, 489 - 495.</ref>
 +
*Research on radishes on heavy soil using commercial greenwaste biochar at three different rates of application showed increased yield only in combination with nitrogen fertilizer<ref>Chan, K.Y., Van Zwieten, L., Meszaros, I., Downie, A., Joseph, S., 2007. Agronomic values of greenwaste biochar as a soil amendment. Australian Journal of Soil Research 45, 629-634.</ref>
 +
*Research on common beans in Colombia found increased nitrogen fixation through charcoal additions, resulting in increased bean yield by 46% and biomass production by 39%<ref>Rondon, M.A., Lehmann, J., Ramirez, J., Hurtado, M., 2007. Biological nitrogen fixation by common beans (Phaseolus vulgaris L.) increases with bio-char additions. Biology and Fertility of Soils 43, 699-708.</ref>
 +
*Research over four cropping cycles with rice and sorghum found that charcoal amended with chicken manure resulted in the highest cumulative crop yield<ref>Steiner, C., Teixeira, W.G., Lehmann, J., Nehls, T., MacêDo, J.L.V., Blum, W.E.H., Zech, W., 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, 275-290.</ref>
 +
*In a study part-funded by the [[Rockefeller Foundation]], research on maize on degraded soil in Kenya showed that charcoal doubled crop yield.<ref>Kimetu J, Lehmann HJ, Ngoze S, Mugendi D, Kinyangi J, Riha S, Verchot L, Recha J and Pell A 2008 Reversibility of soil productivity decline with organic matter of differing quality along a degradation gradient. Ecosystems, in press. Summary here: [http://www.css.cornell.edu/faculty/lehmann/research/biochar/biocharproject.html Mitigation of Soil Degradation with Biochar], Field Experiment, Western Kenya, 2008.</ref>
 +
 +
Preliminary findings of an industry study by biomass companies [[Dynamotive Energy Systems]] Corporation and [[BlueLeaf]] Inc. indicated an overall increase in crop yield that ranged from 6% to 17% in soils where charcoal was applied compared to control plots. In addition, plots with biochar yielded higher plant density and greater root depth.<ref>“[http://www.dynamotive.com/2009/05/12/blueleaf-inc-and-dynamotive-announce-biochar-test-results-cquest-biochar-enriched-plots-exhibit-overall-higher-crop-yield/ BlueLeaf Inc. and Dynamotive Announce Biochar Test Results CQuest Biochar Enriched Plots Yield Crop Increase Ranging From Six to Seventeen Percent vs. Control Plots]”, Dynamotive website, May 12 2009</ref> 
 +
 +
A combination of higher biochar application rates alongside NPK fertilizer increased crop yield on tropical Amazonian soils<ref>Steiner, C., Teixeira, W.G., Lehmann, J., Nehls, T., MacêDo, J.L.V., Blum, W.E.H., Zech, W., 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, 275-290.</ref> and semi-arid soils in Australia.<ref>Ogawa, M., Okimori, Y., Takahashi, F., 2006. Carbon sequestration by carbonization of biomass and forestation: three case studies. Mitigation and adaptation strategies for
 +
global change 11, 429-444.</ref>
 +
 +
Bruno Glaser reviewed studies on yield conducted during the 1980s and 1990s and found marked positive impacts on yield of low applications of charcoal to soil. However, in some cases, higher rates seemed to inhibit plant growth.<ref>Glaser, B., Haumaier, L., Guggenberger, G., Zech, W., 2001. The 'Terra Preta' phenomenon: a model for sustainable agriculture in the humid tropics. Naturwissenschaften, 37-41.</ref> 
 +
 +
The varying effects on yield appear to depend on such factors as quantities added, soil type, and crop tested.
 +
 +
Longer-term field studies are ongoing.
 +
 +
==Nutrient content of plants==
 +
A field study carried out in Brazil on highly weathered soil looked at the effect of different fertilizers on nutrient content of the plants grown. The plants fertilized with chicken manure had the highest nutrient content followed by plants that received compost and/or mineral fertilizer. Chicken manure significantly improved the potassium and phosphorus nutrition in comparison to all other treatments. Charcoal applications did not show a significant influence on nutrient levels.<ref>Christoph Steiner et al., Long term effects of manure, charcoal and mineral fertilization on crop production and fertility on a highly weathered Central Amazonian upland soil, Plant Soil (2007) 291: 275–290.</ref>
 +
 +
==The synthetic fertilizer question==
 +
 +
Some of the claims for charcoal’s beneficial effects on the carbon cycle are based on the assumption that less synthetic fertilizer could be used if it were mixed with charcoal. Synthetic fertilizer creates huge greenhouse gas emissions in production and use, so if less were needed to grow as many crops, this would make a significant contribution to efforts to combat climate change.
 +
 +
One study that made a detailed assessment of the overall carbon balance of a charcoal strategy assumed a 10% reduction in the fertilizer required to maintain current crop yield.<ref>Gaunt, J.L., Lehmann, J., 2008. Energy balance and emissions associated with biochar sequestration and pyrolysis bioenergy production. Environmental Science & Technology 42, 4152-4158.</ref> This assumption makes up an important part of the net carbon benefit claimed in the paper.
 +
 +
It’s important to bear in mind that such claims for charcoal are based on data from short-term localized studies that may not be supported in long-term studies, on all soils, or in general farming practice.
 +
 +
In addition, Biofuelwatch suspects that energy and agribiz companies view charcoal as a way of sustaining fundamentally unsustainable synthetic fertilizer use. Biofuelwatch says, “much of the industry and research focus is on producing fertilizer made from a combination of charcoal and synthetic nitrogen fertilizer (ammonium bicarbonate),” a technology pioneered by the US energy technology company [[Eprida]].<ref>Almuth Ernsting and Rachel Smolker, “[http://www.biofuelwatch.org.uk/docs/biocharbriefing.pdf Biochar for Climate Change Mitigation: Fact or Fiction?]”, Biofuelwatch, February 2009, p. 4</ref> Thus charcoal, in the hands of industry, could become a way of perpetuating chemically-based farming.
  
 
==Resources==
 
==Resources==
 +
 +
*[[Biochar]]
 +
*[[Biochar: Carbon Sequestration]]
 +
*[[Biochar Lobby]]
  
 
==Notes==
 
==Notes==

Latest revision as of 15:10, 1 December 2009

Soil fertility and quality

Organic matter added to soil helps it retain nutrients that are essential to plant growth. Proponents of biochar say that it is much more effective than other organic matter in retaining nutrients and keeping them available to plants. A study by Johannes Lehmann says this is also true for phosphorus, which is not retained by 'normal' soil organic matter.[1]

Researchers who have tested the impact of charcoal on soil fertility say that much of the benefit may derive from charcoal’s vast surface area and complex pore structure, which is hospitable to the bacteria and fungi that plants need to absorb nutrients from the soil. Christoph Steiner, a research scientist at the University of Georgia, says, "We believe that the structure of charcoal provides a secure habitat for microbiota, which is very important for crop production." Steiner and coauthors noted in their 2003 book Amazonian Dark Earths that the charcoal addition to soil caused a 280-400% increase in plant uptake of nitrogen.[2]

A report for Biofuelwatch, however, says that over-reliance on biochar to create soil fertility is dangerously reductionist. It says the farmers who created terra preta added different types of biomass the soil, thus building up humus as well as charcoal. Biochar advocates, on the other hand, “promote stripping the land of ‘agricultural and forestry residues’, which would greatly reduce humus.” Done on a large scale, the report warns, this would “replace at least some humus with biologically dead charcoal, an untested but potentially very dangerous strategy.”[3]

Water retention of soil

A survey of published studies showed that only sandy soils had higher available moisture after charcoal additions. Clay soils (which are naturally good at retaining water) showed decreased moisture content with increasing charcoal additions.[4]

Crop yield

According to Cornell University Department of Soil and Crop Sciences, “Soils with biochar additions are typically more fertile [and] produce more and better crops for a longer period of time.”[5]

This is largely confirmed by studies examining the effects on crop yield of added charcoal. Most show positive results in the short term, though in a few cases, either no difference or negative results have been found. Longer-term studies are lacking.

Here are the results of studies on the impact on yield of adding charcoal to soil:

  • Research on peas and mung beans in India showed an 160% and 122% biomass increase respectively[6]
  • Research in Japan on soybeans grown on volcanic ash loam showed an 151% biomass increase at an application rate of 0.5 Mgha-1 (megagrams per hectare, a megagram being a metric ton). However, higher rates of application decreased yield: 5 Mgha-1 of char decreased yield to 63% and 15 Mgha-1 char decreased yield to 29%[7]
  • Research in Japan on sugi trees (the national tree of Japan, often grown near temples) on clay loam with addition of charcoal from different sources at an application rate of 0.5 Mgha-1 found:[8]
wood charcoal increased biomass 249%
bark charcoal increased biomass 324%
activated charcoal increased biomass 244%
  • Research on bauhinia trees found increased biomass by 13% and height by 24%[9]
  • Research on cowpeas found 150% biomass increase from application rates of 67 Mgha-1 and 200% biomass increase from application rates of 135 Mgha-1[10]
  • Research on cowpeas and rice at the Embrapa Amazonia Ocidental, Manaus, Brazil found a 38-45% increase in biomass (no yield reported)[11]
  • Research in Ghana on maize grown on disused charcoal production sites and adjacent fields found a grain yield 91% higher and biomass yield 44% higher on the charcoal site than the control[12]
  • Research on maize, cowpea and peanuts on low fertility soil found acacia bark charcoal plus fertilizer increased maize and peanut yields (but not cowpea)[13]
  • Research on radishes on heavy soil using commercial greenwaste biochar at three different rates of application showed increased yield only in combination with nitrogen fertilizer[14]
  • Research on common beans in Colombia found increased nitrogen fixation through charcoal additions, resulting in increased bean yield by 46% and biomass production by 39%[15]
  • Research over four cropping cycles with rice and sorghum found that charcoal amended with chicken manure resulted in the highest cumulative crop yield[16]
  • In a study part-funded by the Rockefeller Foundation, research on maize on degraded soil in Kenya showed that charcoal doubled crop yield.[17]

Preliminary findings of an industry study by biomass companies Dynamotive Energy Systems Corporation and BlueLeaf Inc. indicated an overall increase in crop yield that ranged from 6% to 17% in soils where charcoal was applied compared to control plots. In addition, plots with biochar yielded higher plant density and greater root depth.[18]

A combination of higher biochar application rates alongside NPK fertilizer increased crop yield on tropical Amazonian soils[19] and semi-arid soils in Australia.[20]

Bruno Glaser reviewed studies on yield conducted during the 1980s and 1990s and found marked positive impacts on yield of low applications of charcoal to soil. However, in some cases, higher rates seemed to inhibit plant growth.[21]

The varying effects on yield appear to depend on such factors as quantities added, soil type, and crop tested.

Longer-term field studies are ongoing.

Nutrient content of plants

A field study carried out in Brazil on highly weathered soil looked at the effect of different fertilizers on nutrient content of the plants grown. The plants fertilized with chicken manure had the highest nutrient content followed by plants that received compost and/or mineral fertilizer. Chicken manure significantly improved the potassium and phosphorus nutrition in comparison to all other treatments. Charcoal applications did not show a significant influence on nutrient levels.[22]

The synthetic fertilizer question

Some of the claims for charcoal’s beneficial effects on the carbon cycle are based on the assumption that less synthetic fertilizer could be used if it were mixed with charcoal. Synthetic fertilizer creates huge greenhouse gas emissions in production and use, so if less were needed to grow as many crops, this would make a significant contribution to efforts to combat climate change.

One study that made a detailed assessment of the overall carbon balance of a charcoal strategy assumed a 10% reduction in the fertilizer required to maintain current crop yield.[23] This assumption makes up an important part of the net carbon benefit claimed in the paper.

It’s important to bear in mind that such claims for charcoal are based on data from short-term localized studies that may not be supported in long-term studies, on all soils, or in general farming practice.

In addition, Biofuelwatch suspects that energy and agribiz companies view charcoal as a way of sustaining fundamentally unsustainable synthetic fertilizer use. Biofuelwatch says, “much of the industry and research focus is on producing fertilizer made from a combination of charcoal and synthetic nitrogen fertilizer (ammonium bicarbonate),” a technology pioneered by the US energy technology company Eprida.[24] Thus charcoal, in the hands of industry, could become a way of perpetuating chemically-based farming.

Resources

Notes

  1. ↑ Lehmann, J., 2007 Bio-energy in the black. Frontiers in Ecology and the Environment 5, 381-387.
  2. ↑ Tenenbaum, David J., Biochar: carbon mitigation from the ground up, Environmental Health Perspectives, Feb 2009 v117 i2 pA70–74.
  3. ↑ Almuth Ernsting and Rachel Smolker, “Biochar for Climate Change Mitigation: Fact or Fiction?”, Biofuelwatch, February 2009, p. 4
  4. ↑ Glaser B, Lehmann J, Zech W (2002) Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal—a review. Biol Fertil Soils 35:219–230
  5. ↑ “Biochar: The new frontier,” Cornell University Department of Soil and Crop Sciences, Cornell University website
  6. ↑ Iswaran V, Jaiuhri KS, Sen A (1980), “Effect of charcoal, coal and peat on the yield of moong, soybean and pea”, Soil Biol Biochem 12:191–192
  7. ↑ Kishimoto S, Sugiura G (1985), “Charcoal as a soil conditioner”, Int. Achieve Future 5:12–23
  8. ↑ Kishimoto S, Sugiura G (1985), “Charcoal as a soil conditioner”, Int. Achieve Future 5:12–23
  9. ↑ Chidumayo E.N. (1994), “Effects of wood carbonization on soil and initial development of seedlings in miombo woodland, Zambia,” Forest Ecological Management 70: 353–357
  10. ↑ Glaser, B., Lehmann, J., Zech, W., 2002. Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal – a review. Biology and Fertility of Soils 35, 219-230.
  11. ↑ Lehmann, J., da Silva Jr, J.P., Steiner, C., Nehls, T., Zech, W., Glaser, B., 2003. Nutrient availability and leaching in an archaeological Anthrosol and a Ferralsol of the Central Amazon basin: fertilizer, manure and charcoal amendments. Plant & Soil 249, 343-357.
  12. ↑ Oguntunde, P.G., Abiodun, B.J., Ajayi, A.E., van de Giesen, N., 2008. Effects of charcoal production on soil physical properties in Ghana. Journal of Plant Nutrition and Soil Science 171, 591-596.
  13. ↑ Yamato, M., Okimori, Y., Wibowo, I.F., Anshori, S., Ogawa, M., 2006. Effects of the application of charred bark of Acacia mangium on the yield of maize, cowpea and peanut, and soil chemical properties in South Sumatra, Indonesia. Soil Science and Plant Nutrition 52, 489 - 495.
  14. ↑ Chan, K.Y., Van Zwieten, L., Meszaros, I., Downie, A., Joseph, S., 2007. Agronomic values of greenwaste biochar as a soil amendment. Australian Journal of Soil Research 45, 629-634.
  15. ↑ Rondon, M.A., Lehmann, J., Ramirez, J., Hurtado, M., 2007. Biological nitrogen fixation by common beans (Phaseolus vulgaris L.) increases with bio-char additions. Biology and Fertility of Soils 43, 699-708.
  16. ↑ Steiner, C., Teixeira, W.G., Lehmann, J., Nehls, T., MacêDo, J.L.V., Blum, W.E.H., Zech, W., 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, 275-290.
  17. ↑ Kimetu J, Lehmann HJ, Ngoze S, Mugendi D, Kinyangi J, Riha S, Verchot L, Recha J and Pell A 2008 Reversibility of soil productivity decline with organic matter of differing quality along a degradation gradient. Ecosystems, in press. Summary here: Mitigation of Soil Degradation with Biochar, Field Experiment, Western Kenya, 2008.
  18. ↑ “BlueLeaf Inc. and Dynamotive Announce Biochar Test Results CQuest Biochar Enriched Plots Yield Crop Increase Ranging From Six to Seventeen Percent vs. Control Plots”, Dynamotive website, May 12 2009
  19. ↑ Steiner, C., Teixeira, W.G., Lehmann, J., Nehls, T., MacêDo, J.L.V., Blum, W.E.H., Zech, W., 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, 275-290.
  20. ↑ Ogawa, M., Okimori, Y., Takahashi, F., 2006. Carbon sequestration by carbonization of biomass and forestation: three case studies. Mitigation and adaptation strategies for global change 11, 429-444.
  21. ↑ Glaser, B., Haumaier, L., Guggenberger, G., Zech, W., 2001. The 'Terra Preta' phenomenon: a model for sustainable agriculture in the humid tropics. Naturwissenschaften, 37-41.
  22. ↑ Christoph Steiner et al., Long term effects of manure, charcoal and mineral fertilization on crop production and fertility on a highly weathered Central Amazonian upland soil, Plant Soil (2007) 291: 275–290.
  23. ↑ Gaunt, J.L., Lehmann, J., 2008. Energy balance and emissions associated with biochar sequestration and pyrolysis bioenergy production. Environmental Science & Technology 42, 4152-4158.
  24. ↑ Almuth Ernsting and Rachel Smolker, “Biochar for Climate Change Mitigation: Fact or Fiction?”, Biofuelwatch, February 2009, p. 4
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