Terra preta

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Left - a nutrient-poor oxisol; right - an oxisol transformed into fertile terra preta

Terra preta (“dark earth” in Portuguese) refers to expanses of very dark, fertile anthropogenic soils found in the Amazon Basin. It owes its name to its very high charcoal content. It is also known as “Amazonian dark earth” or “Indian black earth”. In Portuguese its full name is “Terra preta do índio” or “Terra preta de índio”. Terra mulata is lighter or brownish in color.[1]

Terra preta is characterized by the presence of low-temperature charcoal in high concentrations; of high quantities of pottery sherds; of organic matter such as plant residues, animal faeces, fish and animal bones and other material; and of nutrients such as nitrogen (N), phosphorus (P), calcium (Ca), zinc (Zn), manganese (Mn)[2]. It also shows high levels of microorganic activities and other specific characteristics within its particular ecosystem. It is less prone to nutrient leaching, which is a major problem in most rainforest soils. Terra preta zones are generally surrounded by terra comum, or "common soil"; these are infertile soils, mainly acrisols[2], but also ferralsols and arenosols[3].

Terra preta soils are of pre-Columbian nature and were created by humans between 450 BC and AD 950 [4] [5]. The soil's depth can reach 2 metres (6 feet). Thousands of years after its creation it has been reported to regenerate itself at the rate of 1 centimetre per year[6] by the local farmers and caboclos in Brazil's Amazonian basin, and they seek it out for use and for sale as valuable compost.

Contents

[edit] History

For a long time, the origins of the Amazonian dark earths were not immediately clear and several theories were considered. One idea was that they resulted from ashfall from volcanoes in the Andes, since they occur more frequently on the brows of higher terraces. Another theory considered its formation as a result of sedimentation in Tertiary lakes or in recent ponds.

However, because of their elevated charcoal content and the common presence of pottery remains, it is now widely accepted that these soils are a product of indigenous soil management involving a labor intensive technique termed slash-and-char. The technique is differentiated from slash and burn by a lower temperature burn (thus producing more charcoal than ashes) and in being a tool for soil improvement.

This type of soil appeared between 450 BC and AD 950 at sites throughout the Amazon Basin.[5]

The Spanish explorer Francisco de Orellana, the 16th Century explorer who was the first European to transverse the Amazon River, reported densely populated regions running hundreds of kilometers along the river, suggesting population levels exceeding even those of today. These populations left no lasting monuments, possibly because they used local wood as their construction material, which would have rotted in the humid climate (stone was unavailable). While it is possible Orellana may have exaggerated the level of development among the Amazonians, their semi-nomadic descendants have the odd distinction among tribal indigenous societies of a hereditary, yet landless, aristocracy, a historical anomaly for a society without a sedentary, agrarian culture. This suggests they once were more settled and agrarian but became nomadic after the demographic collapse of the 16th and 17th century due to European-introduced diseases and maintained certain traditions. Moreover, many indigenous people were forced to adapt to a more mobile lifestyle in order to protect themselves against colonialism. This might have made the benefits of terra preta, such as its self-renewing capacity, less attractive — farmers would not have been able to enjoy the use of renewed soil because they would have been forced to move for safety. Slash-and-burn might have been an adaptation to these conditions.

For 350 years after the European arrival by Vicente Yáñez Pinzón, the Portuguese portion of the basin remained an untended former food gathering and planned agricultural landscape occupied by the Indigenous peoples who survived the arrival of European diseases. There is ample evidence for complex large-scale, pre-Columbian social formations, including chiefdoms, in many areas of Amazonia (particularly the inter-fluvial regions) and even large towns and cities[7]. For instance the pre-Columbian culture on the island of Marajo may have developed Social stratification and supported a population of 100,000 people[7]. The Native Americans of the Amazon rain forest may have used Terra preta to make the land suitable for the large scale agriculture needed to support large populations and complex social formations such as chiefdoms[7].

[edit] Location

Terra Preta soils are found mainly in Amazonia, where Sombroek et al.[8] estimate that they cover at least 0.1 to 0.3%, or 6,300 to 18,900 km² of low forested Amazonia (cited by Denevan and Woods[1]); but others estimate this surface at 1.0% or more (twice the surface of Great-Britain)[6]. Plots of Terra preta exist in small surfaces averaging 20 hectares, but near-900 acres' surfaces have also been reported. They are found among various climatic, geological and topographical situations[1]. Their distribution either follows main water courses, from East Amazonia to the central basin of Amazonia[9], or are located on interfluvial sites (mainly of circular or lenticular shape and of a smaller size averaging some 1.4 ha), see also distribution map of Terra Preta sites in Amazon basin[10]. William I. Woods (soil biologist/archaeologist at the University of Kansas) estimates that around 10% of the original terra comum appears to have been converted to Terra preta[11]. According to William Balée (anthropologist at Tulane University in New Orleans), the spreads of tropical forest between the savannas could be mainly anthropogenic – a notion with dramatic implications worldwide for agriculture and conservation[12].

Terra preta sites are also known in other South American areas (Ecuador, Peru, Guyana)[13], in West Africa (Benin, Liberia), and on the South African savannas[2]. Similar soil was found in late Roman Britain - see dark earth.

[edit] Pedology

Terra Preta is defined as a type of latosol, having a carbon content ranging from high to very high (more than 13-14% organic matter) in its A horizon, but without hydromorphic characteristics[14]. The composition of Terra preta presents important variants. For instance, the gardens close to dwellings received more nutrients than fields farther away[15]. The variations in Amazonian dark earths prevent from establishing a clear separation line on whether they were intentionally created for soil improvement or whether the lightest variants are a by-product of habitation. The varied features of the dark earths throughout the Amazon Basin suggest the existence of an extensive ancient native civilization dating back 500 to 2500 years bp.

Terra preta's capacity to increase its own volume – thus to sequester more carbon – was 'discovered' by pedologist William I. Woods of the University of Kansas[6]. This central mystery of Terra preta, is actively studied by many researchers from various disciplines.

The processes responsible for the formation of Terra preta soils are[3]:

  1. Incorporation of wood charcoal
  2. Incorporation of organic matter and of nutrients
  3. Role of micro-organisms and animals in the soil

[edit] Wood charcoal

The transformation of biomass into charcoal produces a series of charcoal derivates covered under the name of pyrogenic or black carbon, the composition of which varies; from lightly charred organic matter, up to soot particles rich in graphite formed by recomposition of free radicals (Hedges et al. 2000)[16]. Here, all types of charbonated materials are called charcoal. By convention, charcoal is considered to be any natural organic matter thermically transformed with an O/C percentage less than 0.6[16] (smaller values have been suggested[17]). Because of possible interactions with minerals and organic matter from the soil, it is almost impossible to identify charcoal with any certainty by determining only the proportion of O/C. The H/C percentage[18] or molecular markers such as benzenepolycarboxylic acid[19], are therefore used as second level of identification[3].

Charcoal was added to poor soils, as wood charcoal processed at low temperature and with a limited supply of oxygen (i.e., with smothered fires). William I. Woods (University of Kansas, Lawrence), expert on (ancient) abandoned living sites, has measured in Terra preta up to 9% black carbon (against 0.5% in surrounding soils)[20]. B. Glaser et al have found up to 70 times more carbon than in surrounding Ferralsols[3], with approximative average values of 50 Mg ha-1 m-1[21].

Amending the soil with low temperature charcoal produced from a mix of wood and leafy biomass (termed biochar) has been observed to increase the activity of arbuscular mycorrhizal fungi. Finnish researcher Janna Pietikäinen has tested high porosity materials such as zeolite, activated carbon and charcoal; these tests show – contrary to her expectations - that microbial growth is substantially improved with charcoal. It may be so that these small pieces of charcoal tend to migrate within the soil, providing a habitat for bacteria that decompose the biomass in the surface ground cover[22]. It is theorized that this process may have an essential role in Terra preta soils' self-propagation; a virtuous cycle would be established as the fungus spreads from the charcoal, fixing additional carbon, stabilizing the soil with glomalin, and increasing nutrient availability for nearby plants[23][24]. Many other agents contribute, from earthworms to humans and the charring process.

The chemical structure of charcoal in Terra preta soils is characterized with poly-condensed aromatic groups, providing prolonged biological and chemical stability that sustains the fight against microbial degradation; it also provides, after partial oxydation, the highest nutrient retention[3][21]. Wood charcoal (but not that from grasses or high cellulose made at low temperature), thus has an internal layer of biological oil condensates that the bacteria consume, and that is similar to cellulose in its effects on microbial growth (Christoph Steiner, EACU 2004). Charring at high temperature loses that layer and brings little increase in the soil fertility[6]. Glaser et al. (1998[19] and 2003[25]) and Brodowski et al. (2005[26]) have proved that the formation of condensed aromatic structures depends on the manufacture of charcoal. It is the slow oxidation of charcoal that creates carboxylic groups; these increase the cations' exchange capacity in the soil[27][28]. Lehmann et al have studied the nucleus of black carbon particles produced by the biomass. They have found it highly aromatic even after thousands of years in the soil and presenting spectral characteristics of fresh charcoal. Around that nucleus and on the surface of the black carbon particles, there were higher proportions of forms of carboxylic and phenolic Cs spatially and structurally distinct from the particle's nucleus. Analysis of the groups of molecules provides evidences both for the oxydation of the black carbon particle itself, as well as for the adsorption of non-black carbon[29].

This charcoal is thus decisive for the sustainability aspect of Terra preta soils[30][27]. Amendements of Ferrasol with wood charcoal greatly increases vegetal productivity[9]. Note that agricultural lands have lost in average 50% of their carbon due to the practice of intensive cultivation and other degradations of human origin[6].

It is important to note that the fresh charcoal must first be “charged” before it can function as a biotope[31]. Several experiments demonstrate that uncharged charcoal can bring a provisional depletion of available nutrients when first put into the soil - until its pores fill up with nutrients. This is overcome by soaking the charcoal for a few weeks (2 to 4 weeks) in any liquid nutrient (urine, plant tea. ...).

[edit] Organic matter and nutrients

Charcoal's porosity brings a better retention of organic matter, of water and of dissolved organic nutrients[27], as well as of pollutants such as pesticides and aromatic poly-cyclic hydrocarbons[32].

Organic matter

The high absorption potential of organic molecules (and of water) is due to the porous structure of charcoal[3]. The Terra preta soils, containing great quantities of charcoal, are equally characterized by a high concentration of organic matter (on average three times more than in the surrounding poor soils[3][21][28][33]), up to 150 g/kg[9]. Organic matter can be found at 1 to 2 metre deep[14].

Gerhard Bechtold proposes to call "Terra Preta" the soils that show, at 50 cm depth, a minimum proportion of organic matter superior to 2.0 or 2.5%. The accumulation of organic matter in moist tropical soils is a paradox, because of optimum conditions for degradation[21]. It is remarkable that anthrosols regenerate in spite of these tropical conditions' prevalence and the fast mineralisation rates[9]. It has been demonstrated that the stability of organic matter is mainly due to the biomass being only partially consumed[21].

Nutrients

Terra preta soils also show higher quantities of nutrients, and a better retention of these nutrients, than the surrounding infertile soils[21]. The proportion of P reaches 200-400 mg/kg[34]. The quantity of N is also higher in anthrosol, but that nutrient is immobilized because of the high proportion of C over N in the soil[9].

The anthrosol's availability of P, Ca, Mn, and Zn is clearly higher than the neighbouring Ferrasol. The absorption of P, K, Ca, Zn, and Cu by the plants increases when the quantity of available charcoal increases. The production of biomass for two crops (rice and Vigna unguiculata (L.) Walp.) increased by 38-45% without fertilization (P < 0.05), compared to crops on fertilized Ferrasol[9].

Amending with pieces of charcoal approximately 20 mm in diameter, instead of ground charcoal, did not change the results of experience except for manganese (Mn), for which absorption considerably increased[9].

Nutrient drainage is minimal in this anthrosol, despite their abundant availability, resulting in high fertility. When inorganic nutrients are applied to the soil, however, the nutrients' drainage in anthrosol exceeds that in fertilized Ferralsol[9].

As potential sources of nutrients, only C (via photosynthesis) and N (from biological fixation) can be produced in situ. All the other elements (P, K, Ca, Mg, a.s.o.) must be present in the soil. In Amazonia the approvisionning in nutrients from composting in situ is excluded for natural soils heavily washed-out (Ferralsols, Acrisols, Lixisols, Arenosols, Uxisols, ...) that do not contain these elements in high concentration. In the case of Terra preta, the only possible nutrient sources are primary and secondary. The following components have been found[21]:

  1. Human and animal excrements (rich in P and N);
  2. Kitchen refuse, such as animal bones and tortoise shells (rich in P and Ca);
  3. Ash residue from incomplete combustion (rich in Ca, Mg, K, P and charcoal);
  4. Biomass of terrestrial plants (e.g. compost); and
  5. Biomass of aquatic plants (e.g. algae).

Saturation in pH and in base is more important than in the surrounding soils (Sombroek, 1966; Smith, 1980; Kern and Kämpf, 1989; Sombroek et al., 1993; Glaser et al., 2000; Lehmann et al., 2003; Liang et al., 2006)[34].

[edit] Microorganisms and animals

Bacteria and fungi (myco-organisms) live and die within the porous media, thus increasing its carbon content. Johannes Lehman and W. Zech, Bruno Glaser à l'Universite de Bayreuth (Allemagne), Embrapa (Manaus, Brazil) and many others, are studying these phenomena.

Until now there is no scientific evidence for a particular micro-organism to be responsible for the formation of Terra Preta, but a significant production of biological black carbon has recently been identified, especially under moist tropical conditions. It is possible that the fungus Aspergillus niger is mainly responsible for it[22]. Topoliantz and Ponge's work, summarized in a synthetic article in “Soil Biology & Biochemistry”[35], shows that the peregrine earthworm Pontoscolex corethrurus (Oligochaeta: Glossoscolecidae), widespread in all Amazonia and notably in clearings after burning processes thanks to its high tolerance of a low content of organic matter in the soil, has been shown to ingest pieces of charcoal and to mix them in a finely ground form with the mineral soil. The authors, who experimentally verified this process, point at this as an essential element in the generation of Terra preta soils, associated with agronomic knowledge involving layering the charcoal in thin regular layers favourable to its burying by Pontoscolex corethrurus. Some ants are repelled from fresh Terra Preta soils, their density of appearance is found to be low after about 10 days as compared to control soils – see Terra Preta Experiments.

[edit] Modern research to recreate Terra preta

Efforts to recreate these soils are being undertaken by companies such as Biochar Energy Corporation, Eprida and Best Energies . Research efforts are underway at Cornell University, the University of Georgia, Iowa State University and Geoecology Energy Organisation. Biochar is the main (and likely key) ingredient in the formation of terra preta. One focus of these researchers is the prospect that if biochar becomes widely used for soil improvement, it will involve globally significant amounts of carbon sequestration, remediating global warming.

[edit] See also

[edit] Notes

  1. ^ a b c [1] “Discovery and awareness of anthropogenic amazonian dark earths (terra preta)”, by William M. Denevan, University of Wisconsin-Madison, and William I. Woods, University of Kansas.
  2. ^ a b c Glaser, Bruno. "Terra Preta Web Site". http://www.geo.uni-bayreuth.de/bodenkunde/terra_preta/. 
  3. ^ a b c d e f g Glaser, Bruno (27 February 2007). "Prehistorically modified soils of central Amazonia: a model for sustainable agriculture in the twenty-first century". Philosophic Transactions of the Royal Society B 362 (1478): 187–196. doi:10.1098/rstb.2006.1978. http://www.journals.royalsoc.ac.uk/(xquef445kynlbt3pti5kdsr0)/app/home/contribution.asp?referrer=parent&backto=issue,3,14;journal,5,231;linkingpublicationresults,1:102022,1. Retrieved on 2008-05-04. 
  4. ^ E.G. Neves, R.N. Bartone, J.B. Petersen & M.J. Heckenberger (2001). The timing of Terra Preta formation in the central Amazon: new data from three sites in the central Amazon. p. 10. 
  5. ^ a b “Historical Ecology and Future Explorations” in “Amazonian Dark Earths: origin, properties, and management” http://www.css.cornell.edu/faculty/lehmann/terra_preta/Book/TerraPreta_book_publication.htm] by J. Lehmann, N. Kaampf, W.I. Woods, W. Sombroek, D.C. Kern, T.J.F. Cunha et al., Chapter 23, 2003. (Clark Erickson), pp. 484
  6. ^ a b c d e "Carbon negative energy to reverse global warming". http://www.eprida.com/hydro/yahoo2004.htm. 
  7. ^ a b c Mann, C, C., ed. (2005). 1491: New Revelations of the Americas Before Columbus. University of Texas. ISBN 1400032059.  page 296
  8. ^ “Classification of Amazonian Dark Earths and other Ancient Anthropic Soils” in “Amazonian Dark Earths: origin, properties, and management” http://www.css.cornell.edu/faculty/lehmann/terra_preta/Book/TerraPreta_book_publication.htm] by J. Lehmann, N. Kaempf, W.I. Woods, W. Sombroek, D.C. Kern, T.J.F. Cunha et al., Chapter 5, 2003. (eds J. Lehmann, D. Kern, B. Glaser & W.I. Woods); cited in Lehmann et al., 2003, pp. 77-102
  9. ^ a b c d e f g h [2] “Nutrient availability and leaching in an archaeological Anthrosol and a Ferralsol of the Central Amazon basin: fertilizer, manure and charcoal amendments”, by J. Lehmann, J. Pereira da Silva Jr., C. Steiner, T. Nehls, W. Zech & Bruno Glaser. Plant and Soil 249: 343–357, 2003.
  10. ^ [3] “TP Sites Known in Literature and by Surveys”, by G. Bechtold
  11. ^ Cited by Charles C. Mann in [“1491” http://www.theatlantic.com/doc/200203/mann], citation extract quoted [here http://www.ecoworld.com/blog/2007/11/27/terra-preta/].
  12. ^ [4] “Earthmovers of the Amazon” by Charles C. Mann. Article in the series “News Focus” in SCIENCE, February 4, 2000, vol. 287: 786-789. This article presents archeological researches in the Beni area, directly linked with the recent renewal of interest on Terra preta, as well as photographs of experimental reconstructions of that mode of agriculture.
  13. ^ [5] “Vivre en Guyane” - compte rendu succint de découverte de sites de Terra preta en Guyane.
  14. ^ a b [6] Terra Preta - Homepage about Anthrohumox in Brazilian Lowland - Research by Gerhard Bechtold.
  15. ^ “Smouldered-earth policy – Created by ancient Amazonian natives, dark soils retain abundant carbon.” Article by B. Harder in Science News[www.sciencenews.org], 4 March 2006, vol. 169, p. 133.
  16. ^ a b “The molecularly uncharacterized component of nonliving organic matter in natural environments.” by J.I. Hedges et al., 2000 Org. Geochem. 31, 945–958. (doi:10.1016/S0146-6380(00)00096-6). Cited by B. Glaser in “Prehistorically modified soils of central Amazonia: a model for sustainable agriculture in the twenty-first century”.
  17. ^ “The identification of black carbon particles with the analytical scanning electron microscope: methods and initial results.” P. Stoffyn-Egli, T.M. Potter, J.D. Leonard & R. Pocklington. 1997. Sci. Total Environ. 198, 211–223. (doi:10.1016/S0048-9697(97)05464-8). Cited by B. Glaser in “Prehistorically modified soils of central Amazonia: a model for sustainable agriculture in the twenty-first century”.
  18. ^ “Hydrogen-deficient molecules in natural riverine water samples—evidence for the existence of black carbon in DOM.” by S. Kim, L.A. Kaplan, R. Benner & P.G. Hatcher. 2004. Mar. Chem. 92, 225–234. (doi:10.1016/j.marchem.2004.06.042). Cited by B. Glaser in “Prehistorically modified soils of central Amazonia: a model for sustainable agriculture in the twenty-first century”.
  19. ^ a b “Black carbon in soils: the use of benzenecarboxylic acids as specific markers”, by B. Glaser, L. Haumaier, G. Guggenberger & W. Zech. 1998. Org. Geochem. 29, 811–819. (doi:10.1016/S0146-6380(98)00194-6). Cited by B. Glaser in “Prehistorically modified soils of central Amazonia: a model for sustainable agriculture in the twenty-first century”
  20. ^ W.I. Woods & J.M. McCann in Yearbook Conf. Latin Am. Geogr. Vol. 25 (ed. Caviedes, C.) 7–14. (Univ. Texas, Austin, 1999). Cited in “Putting the carbon back: Black is the new green” [7], article in Nature 442, 624-626, 10 August 2006. Link to article in the Biopact site: “Terra Preta: how fuels can become carbon-negative and save the planet”.
  21. ^ a b c d e f g “The ‘Terra Preta’ phenomenon: a model for sustainable agriculture in the humid tropics.” by B. Glaser, L. Haumaier, G. Guggenberger and W. Zech, 2001. Naturwissenschaften 88, 37–41 (doi:10.1007/s001140000193). Cited in “Weed composition and cover after three years of soil fertility management in the central Brazilian Amazon: Compost, fertilizer, manure and charcoal applications”, by J. Major et al.
  22. ^ a b B. Glaser & K.-H. Knorr, not yet published as to early 2007, cited in “Prehistorically modified soils of central Amazonia: a model for sustainable agriculture in the twenty-first century”, by Bruno Glaser
  23. ^ [8] Controls on production, incorporation and decomposition of glomalin -- a novel fungal soil protein important to soil carbon storage. By Sara Wright, Soil Microbial Systems Laboratory. In “Summaries of FY 2000 Activities, Energy Biosciences, September 2001.
  24. ^ [9] Plant-fungal interactions via Glomalin: A fungal protein that affects soil ecosystem cycling of C, N, P & S. By Jude Maul and Laurie Drinkwater (Cornell University, Ithaca, NY). ESA Annual Meeting 2005, Palais des congrès de Montréal, Contributed Oral Session 89: Soil Ecology: Plant - Soil Relationships., August 10, 2005.
  25. ^ “Organic chemistry studies on Amazonian Dark Earths”, by G. Guggenberger and W. Zech. Chapter 12 of [“Amazonian Dark Earths: origin, properties, and management” http://www.css.cornell.edu/faculty/lehmann/terra_preta/Book/TerraPreta_book_publication.htm] by J. Lehmann, B. Glaser, N. Kaampf, W.I. Woods, W. Sombroek, D.C. Kern, T.J.F. Cunha et al. (eds J. Lehmann, D. Kern, B. Glaser & W. Woods 2003), pp. 227–241. Dordrecht, The Netherlands: Kluwer.
  26. ^ “Black carbon assessment using benzenepolycarboxylic acids: revised method”, by S. Brodowski, A. Rodiodec, L. Haumaier, B. Glaser & W. Amelung. 2005. Org. Geochem. 36, 1299–1310. (doi:10.1016/j.orggeochem.2005.03.011).
  27. ^ a b c [10] “Stability of soil organic matter in Terra Preta soils” by Bruno Glaser, Ludwig Haumaier,Georg Guggenberger and Wolfgang Zech, Institut de Sciences des Sols, University of Bayreuth, D-95440 Bayreuth, Germany.
  28. ^ a b “Ecological aspects of soil organic matter in tropical land use. In Humic substances in soil and crop sciences. Selected readings”, by W. Zech, L. Haumaier et R. Hempfling. 1990 (eds P. McCarthy, C. E. Clapp, R. L. Malcolm & P. R. Bloom), pp. 187–202. Madison, WI: American Society of Agronomy and Soil Science Society of America. Cited by B. Glaser in “Prehistorically modified soils of central Amazonia: a model for sustainable agriculture in the twenty-first century”.
  29. ^ “Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy for mapping nano-scale distribution of organic carbon forms in soil: Application to black carbon particles”, by Johannes Lehmann, Biqing Liang, Dawit Solomon, Mirna Lerotic, Flavio Luizao, James Kinyangi, Thorsten Schafer, Sue Wirick, and Chris Jacobsen. Global Biogeochemical Cycles, vol. 19, GB1013, doi:10.1029/2004GB002435, published 16 February 2005.
  30. ^ “Slash-and-char: a feasible alternative for soil fertility management in the Central Amazon?”, by Johannes Lehmann, Jose Pereir Da Silva Jr., Marco Rondon, Cravo Manoel Da Silva, Jacqueline Greenwood, Thomas Nehls, Christoph Steiner and Bruno Glaser. Symposium no. 13, Paper no. 449. 17e WCSS, 14-21 August 2002, Thailand.
  31. ^ “Everyone’s carbon sequestration: decrease atmospheric carbon dioxide, earn money and improve the soil.” By Folke Günther[11], Holon Ecosystem Consultants, Lund, Sweden. Presented at the International Institute for Industrial Environmental Economics – IIIEE), 26 March 2007.
  32. ^ “Biodegradation of two commercial herbicides (Gramoxone and Matancha) by the bacteria Pseudomonas putida”, par M. Kopytko, G. Chalela & F. Zauscher. 2002. Elec. J. Biotechnol. 5, 182–195. Cited by B. Glaser in “Prehistorically modified soils of central Amazonia: a model for sustainable agriculture in the twenty-first century”.
  33. ^ “Amazon soils. A reconnaissance of the soils of the Brazilian Amazon region”, by W. G. Sombroek, 1966. vol. 672, p. 283. Wageningen, The Netherlands: Verslagen van Landbouw-kundige Onderzoekingen. Cited by B. Glaser in “Prehistorically modified soils of central Amazonia: a model for sustainable agriculture in the twenty-first century”.
  34. ^ a b [12] Site “Terra Preta de Indio - Soil Biogeochemistry” by Johannes Lehmann, Cornell University.
  35. ^ "Ingestion of charcoal by the Amazonian earthworm Pontoscolex corethrurus: a potential for tropical soil fertility" by Jean-François Ponge, Stephanie Topoliantz, Sylvain Ballof, Jean-Pierre Rossi, Patrick Lavelle, Jean-Marie Betsch and Philippe Gaucher. Soil Biology & Biochemistry, Volume 38, Issue 7, July 2006, Pages 2008-2009.

[edit] References

[edit] External links

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