Terra preta (Portuguese pronunciation: [ˈtɛʁɐ ˈpɾetɐ], locally [ˈtɛha ˈpɾeta], literally "black soil" in Portuguese) is a type of very dark, fertile manmade (anthropogenic) soil found in the Amazon Basin. 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 ("black soil of the Indian", "Indians' black earth"). Terra mulata ("mulatto earth") is lighter or brownish in color.
Terra preta owes its characteristic black color to its weathered charcoal content, and was made by adding a mixture of charcoal, bone, and manure to the otherwise relatively infertile Amazonian soil. A product of indigenous soil management and slash-and-char agriculture, the charcoal is very stable and remains in the soil for thousands of years, binding and retaining minerals and nutrients.
Terra preta is characterized by the presence of low-temperature charcoal residues in high concentrations; of high quantities of potsherds; of organic matter such as plant residues, animal feces, fish and animal bones and other material; and of nutrients such as nitrogen (N), phosphorus (P), calcium (Ca), zinc (Zn), manganese (Mn). Fertile soils such as terra preta show high levels of microorganic activities and other specific characteristics within particular ecosystems.
Terra preta zones are generally surrounded by terra comum ([ˈtɛhɐ koˈmũ] or [ˈtɛhɐ kuˈmũ]), or "common soil"; these are infertile soils, mainly acrisols, but also ferralsols and arenosols. While deforested arable soils in the Amazon are productive for just a short period of time, and farmers are constantly moving to new areas and clearing more land, the terra preta soil is less prone to nutrient leaching caused by heavy rains and floods because of its high concentration of charcoal, microbial life and organic matter; accumulating nutrients, minerals, and microorganisms.
Terra preta soils are of pre-Columbian nature and were created by humans between 450 BCE and 950 CE. The soil's depth can reach 2 meters (6.6 ft). Thousands of years after its creation, it has been reported to regenerate itself at the rate of 1 centimeter (0.39 in) per year by the local farmers and caboclos in Brazil's Amazonian basin, who seek it for use and for sale as valuable potting soil.
- 1 History
- 2 Location
- 3 Pedology
- 4 Modern research on creating terra preta
- 5 See also
- 6 Notes
- 7 References
- 8 External links
The origins of the Amazonian dark earths were not immediately clear to later settlers. 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 to be a result of sedimentation in tertiary lakes or in recent ponds.
Soils with elevated charcoal content and a common presence of pottery remains can accrete accidentally near living quarters as residues from food preparation, cooking fires, animal and fish bones, broken pottery, etc., accumulated. Many terra preta soil structures are now thought to have been formed under kitchen middens. However, due to the immense demand for valuable charcoal the intentional creation of terra preta is undisputed.
Areas used for growing crops around living areas are referred to as terra mulata. Terra mulata soils are more fertile than surrounding soils but less fertile than terra preta, and were most likely intentionally improved using charcoal.
The Spanish explorer Francisco de Orellana, the 16th century explorer who was the first European to traverse 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, while still maintaining certain traditions. Moreover, many indigenous peoples adapted to a more mobile lifestyle in order to escape 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 employ the renewed soil as they migrated for safety. Slash-and-char might have been an adaptation to these conditions.
The BBC's Unnatural Histories presents evidence that Orellana, rather than exaggerating his claims as previously thought, was correct in his observations that an advanced civilization was flourishing along the Amazon in the 1540s. It is believed that the civilization was later devastated by the spread of diseases from Europe, such as smallpox. The evidence to support this claim comes from the discovery of numerous geoglyphs dating between 0–1250 CE and terra preta.
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 those who survived the epidemics. 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. For instance the pre-Columbian culture on the island of Marajó may have developed social stratification and supported a population of 100,000 people. Amazonians 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.
Terra preta soils are found mainly in the Brazilian Amazon, where Sombroek et al. estimate that they cover at least 0.1 to 0.3%, or 6,300 to 18,900 square kilometres (2,400 to 7,300 sq mi) of low forested Amazonia; but others estimate this surface at 10.0% or more (twice the area of Great Britain).
Terra preta exists in small plots averaging 20 hectares (49 acres), but areas of almost 360 hectares (890 acres) have also been reported. They are found among various climatic, geological, and topographical situations. Their distributions either follow main water courses, from East Amazonia to the central basin, or are located on interfluvial sites (mainly of circular or lenticular shape) and of a smaller size averaging some 1.4 hectares (3.5 acres), (see distribution map of terra preta sites in Amazon basin The spreads of tropical forest between the savannas could be mainly anthropogenic — a notion with dramatic implications worldwide for agriculture and conservation.
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. Terra preta presents important variants. For instance, gardens close to dwellings received more nutrients than fields farther away. The variations in Amazonian dark earths prevent clearly determining whether all of them 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.
Terra preta's capacity to increase its own volume—thus to sequester more carbon—was first documented by pedologist William I. Woods of the University of Kansas. This remains the central mystery of terra preta.
The processes responsible for the formation of terra preta soils are:
- Incorporation of wood charcoal
- Incorporation of organic matter and of nutrients
- Role of micro-organisms and animals in the soil
The transformation of biomass into charcoal produces a series of charcoal derivatives known as pyrogenic or black carbon, the composition of which varies from lightly charred organic matter, to soot particles rich in graphite formed by recomposition of free radicals. Here, all types of carbonized materials are called charcoal. By convention, charcoal is considered to be any natural organic matter transformed thermally or by a dehydration reaction with an Oxygen/Carbon (O/C) ratio less than 60 smaller values have been suggested. 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 Hydrogen/Carbon percentage or molecular markers such as benzenepolycarboxylic acid, are therefore used as a second level of identification.
The indigenous people added low temperature charcoal to poor soils. Up to 9% black carbon has been measured in some terra preta (against 0.5% in surrounding soils). Other measurements found carbon levels 70 times greater than in surrounding Ferralsols, with approximative average values of 50 Mg/ha/m.
The chemical structure of charcoal in terra preta soils is characterized by poly-condensed aromatic groups, that provide prolonged biological and chemical stability against microbial degradation; it also provides, after partial oxidation, the highest nutrient retention. Low temperature charcoal (but not that from grasses or high cellulose materials) has an internal layer of biological petroleum condensates that the bacteria consume, and is similar to cellulose in its effects on microbial growth. Charring at high temperature loses that layer and brings little increase in soil fertility. The formation of condensed aromatic structures depends on the method of manufacture of charcoal. The slow oxidation of charcoal creates carboxylic groups; these increase the cations' exchange capacity of the soil. The nucleus of black carbon particles produced by the biomass remains aromatic even after thousands of years and presents the spectral characteristics of fresh charcoal. Around that nucleus and on the surface of the black carbon particles, there are higher proportions of forms of carboxylic and phenolic carbons spatially and structurally distinct from the particle's nucleus. Analysis of the groups of molecules provides evidences both for the oxidation of the black carbon particle itself, as well as for the adsorption of non-black carbon.
This charcoal is thus decisive for the sustainability of terra preta. Soil amendment to ferralsol with wood charcoal greatly increases productivity. Note that agricultural lands have lost on average 50% of their carbon due to intensive cultivation and other damage of human origin.
Fresh charcoal must first be "charged" before it can function as a biotope. Several experiments demonstrate that uncharged charcoal can bring a provisional depletion of available nutrients when first put into the soil - until its pores fill with nutrients. This is overcome by soaking the charcoal for two to four weeks in any liquid nutrient (urine, plant tea, etc.).
Biochar is charcoal produced at relatively low temperatures from a biomass of wood and leafy plant materials in an environment with very low or no oxygen. Amending soil with biochar has been observed to increase the activity of arbuscular mycorrhizal fungi. Tests of high porosity materials such as zeolite, activated carbon, and charcoal show that microbial growth substantially improves with charcoal. It may be that small pieces of charcoal migrate within the soil, providing a habitat for bacteria that decompose the biomass in the surface ground cover. This process may have an essential role in terra preta's self-propagation; a virtuous cycle develops as the fungus spreads from the charcoal, fixing additional carbon, stabilizing the soil with glomalin, and increasing nutrient availability for nearby plants. Many other agents contribute, from earthworms to humans as well as the charring process.
If biochar becomes widely used for soil improvement, it will involve globally significant amounts of carbon sequestration, helping remediate global warming. "Bio-char soil management systems can deliver tradable C emissions reduction, and C sequestered is easily accountable, and verifiable."
Biochar is shown to have increased soil cation exchange capacity leading to improved plant nutrient uptake. Along with this it was particularly useful in the acidic tropical soils as it is capable of raising pH due to its slightly alkaline nature. Biochar also shows that, in relation to a soil, productivity of oxidised residue is particularly stable, abundant and entirely capable of increasing soil fertility levels.
Biochar stability as a form of charcoal is due to its formation. The process of pyrolysis, the burning of organic material at high temperatures, and very low oxygen levels results in a porous char rich and ash poor product. This through application to soil has potential to be a nutrient dense long term addition to soil fertility.
Organic matter and nutrients
Charcoal's high absorption potential of organic molecules (and of water) is due to its porous structure. Terra preta's great quantity of charcoal supports a high concentration of organic matter (on average three times more than in the surrounding poor soils), up to 150 g/kg. Organic matter can be found at 1 to 2 metres (3 ft 3 in to 6 ft 7 in) deep.
Gerhard Bechtold proposes to use terra preta for soils that show, at 50 centimeters (20 in) depth, a minimum proportion of organic matter over 2.0-2.5%. The accumulation of organic matter in moist tropical soils is a paradox, because of optimum conditions for organic matter degradation. It is remarkable that anthrosols regenerate in spite of these tropical conditions' prevalence and their fast mineralisation rates. The stability of organic matter is mainly due to the biomass being only partially consumed.
Terra preta soils also show higher quantities of nutrients, and a better retention of these nutrients, than the surrounding infertile soils. The proportion of P reaches 200–400 mg/kg. 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.
The anthrosol's availability of P, Ca, Mn, and Zn is clearly higher than the neighboring 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 Ferralsol.
Amending with pieces of charcoal approximately 20 millimeters (0.79 in) in diameter, instead of ground charcoal, did not change the results except for manganese (Mn), for which absorption considerably increased.
Nutrient leeching is minimal in this anthrosol, despite their abundance, resulting in high fertility. When inorganic nutrients are applied to the soil, however, the nutrients' drainage in anthrosol exceeds that in fertilized Ferralsol.
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, etc.) must be present in the soil. In Amazonia, the provisioning of nutrients from the decomposition of naturally available organic matter fails as the heavy rainfalls wash away the released nutrients and the natural soils (ferralsols, acrisols, lixisols, arenosols, uxisols, etc.) do not contain the mineral matter to provide those nutrients. The clay matter that exists in those soils is incapable of holding but a small fraction of the nutrients made available from decomposition. In the case of terra preta, the only possible nutrient sources are primary and secondary. The following components have been found:
- Human and animal excrements (rich in P and N);
- Kitchen refuse, such as animal bones and tortoise shells (rich in P and Ca);
- Ash residue from incomplete combustion (rich in Ca, Mg, K, P and charcoal);
- Biomass of terrestrial plants (e.g. compost); and
- Biomass of aquatic plants (e.g. algae).
Microorganisms and animals
Bacteria and fungi (myco-organisms) live and die within the porous media of charcoal, thus increasing its carbon content.
A significant biological production of black carbon has recently been identiﬁed, especially under moist tropical conditions. It is possible that the fungus Aspergillus niger is mainly responsible.
The peregrine earthworm Pontoscolex corethrurus (Oligochaeta: Glossoscolecidae) ingests pieces of charcoal and mixes them in a finely ground form with the mineral soil. P. corethrurus is widespread in all Amazonia and notably in clearings after burning processes thanks to its tolerance of a low content of organic matter in the soil. This as an essential element in the generation of terra preta, associated with agronomic knowledge involving layering the charcoal in thin regular layers favorable to its burying by P. corethrurus.
Modern research on creating terra preta
Synthetic terra preta
A newly coined term is ‘synthetic terra preta’. A fertilizer consisting of materials thought to replicate the original materials, including crushed clay, blood and bone meal, manure and biochar is of particulate nature and capable of moving down the soil profile and improving soil fertility and carbon in the current soil peds and aggregates over a viable time frame. This mixture provides multiple soil improvements reaching at least the quality of terra mulata. Blood, bone meal and chicken manure are useful for short term organic manure addition. Perhaps the most important and unique part of the improvement of the soil fertility is carbonized biomass (pyrogenic carbon), thought to have been gradually incorporated 4 to 10 thousand years ago. Biochar is capable of decreasing soil acidity and if soaked in nutrient rich liquid can slowly release nutrients, and provide habitat for microbes in soil due to its high porosity surface area.
The goal is an economically viable process that could be included in modern agriculture practices. Average poor tropical soils are easily enrichable to terra preta nova by the addition of crumbled charcoal and condensed smoke. Terra preta may be an important avenue of future carbon sequestration while reversing the current worldwide decline in soil fertility and associated desertification. Whether this is possible on a larger scale has yet to be proven. Tree Lucerne (tagasaste or Cytisus proliferus) is one type of Fertilizer tree used to make Terra preta. Efforts to recreate these soils are being undertaken by State owned companies such as Embrapa and other organizations in Brazil. Academic research efforts continue.
Terra preta is being produced successfully at the Sachamama Center for Biocultural Regeneration in High Amazon, Peru. This area has many remaining terra preta soil zones, demonstrating that this anthrosol was created not only in the Amazon basin, but also at higher elevations.
Terra preta sanitation
Terra preta sanitation (TPS) systems have been studied as an alternative sanitation option by using the effects of lactic-aid conditions in urine-diverting dry toilets and a subsequent treatment by vermicomposting.
- 1491: New Revelations of the Americas Before Columbus
- Archaeological horizon
- Black Dirt Region
- Ukrainian Chernozem
- Lost City of Z
- Terramare culture
- "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.
- Mao, J.-D.; Johnson, R. L.; Lehmann, J.; Olk, J.; Neeves, E. G.; Thompson, M. L.; Schmidt-Rohr, K. (2012). "Abundant and stable char residues in soils: implications for soil fertility and carbon sequestration". Environmental Science and Technology. 46: 9571–9576. doi:10.1021/es301107c.
Terra Preta soils consist predominantly of char residues composed of ~6 fused aromatic rings.
- The influence of human alteration has been generally underestimated, reports Darna L. Dufour: "Much of what has been considered natural forest in Amazonia is probably the result of hundreds of years of human use and management." "Use of Tropical Rainforests by Native Amazonians," BioScience 40, no. 9 (October 1990):658. For an example of how such peoples integrated planting into their nomadic lifestyles, see Rival, Laura, 1993. "The Growth of Family Trees: Understanding Huaorani Perceptions of the Forest," Man 28(4):635–652.
- Kleiner, Kurt (2013). "The bright prospect of biochar : article : Nature Reports Climate Change". nature.com. Retrieved February 2, 2013.
- Cornell University (1 March 2006). "Amazonian Terra Preta Can Transform Poor Soil Into Fertile". Science Daily. Rockville, MD. Retrieved 22 July 2014.
- Glaser, Bruno. "Terra Preta Web Site".
- Glaser, Bruno (27 February 2007). "Prehistorically modified soils of central Amazonia: a model for sustainable agriculture in the twenty-ﬁrst century". Philosophical Transactions of the Royal Society B. 362 (1478): 187–196. PMC . PMID 17255028. doi:10.1098/rstb.2006.1978. Retrieved 4 May 2008.
- Watkins and Griffiths, J. (2000). Forest Destruction and Sustainable Agriculture in the Brazilian Amazon: a Literature Review (Doctoral dissertation, The University of Reading, 2000). Dissertation Abstracts International, 15–17
- Williams, M. (2006). Deforesting the Earth: From Prehistory to Global Crisis (Abridged ed.). Chicago, IL: The University of Chicago Press. ISBN 0-226-89947-0.
- 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.
- "Historical Ecology and Future Explorations" in "Amazonian Dark Earths: origin, properties, and management" by J. Lehmann, N. Kaampf, W.I. Woods, W. Sombroek, D.C. Kern, T.J.F. Cunha et al., Chapter 23, 2003. (Clark Erickson), p. 484
- Day, Danny (2004). "Carbon negative energy to reverse global warming". Eprida.
- Nicholas C. Kawa Amazonia in the Anthropocene: People, Soils, Plants, Forests, University of Texas Press, 2016 p,59.
- Pollmer, Udo (4 January 2014). "Die Wundererde vom Amazonas" [The miracle soil from the Amazon] (in German). Deutschlandradio Kultur.
- "Unnatural Histories - Amazon". BBC Four.
- Simon Romero (14 January 2012). "Once Hidden by Forest, Carvings in Land Attest to Amazon’s Lost World". The New York Times.
- Mann, C. C., ed. (2005). 1491: New Revelations of the Americas Before Columbus. University of Texas. p. 296. ISBN 1-4000-3205-9.
- Mann, C, C., ed. (2005). 1491: New Revelations of the Americas Before Columbus. University of Texas. ISBN 1-4000-3205-9.
- "Classification of Amazonian Dark Earths and other Ancient Anthropic Soils" in "Amazonian Dark Earths: origin, properties, and management"  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.
- 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. Cited by Charles C. Mann in "1491", citation extract quoted here.
- "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.
- ). "TP Sites Known in Literature and by Surveys", by G. Bechtold
- William Balée (anthropologist at Tulane University in New Orleans) " Earthmovers of the Amazon" by Charles C. Mann. Article in the series "News Focus" in SCIENCE, 4 February 2000, vol. 287: 786–789. This article presents archeological research 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.
- Mandin, Marie-Laure (January 2005). "Vivre en Guyane" - compte rendu succint de découverte de sites de Terra preta en Guyane." [Living in Guyana - summary report discovery of Terra preta sites in Guyana] (PDF) (in French). Archived from the original (PDF) on 23 July 2013. Retrieved 12 November 2015.
-  Terra Preta - Homepage about Anthrohumox in Brazilian Lowland - Research by Gerhard Bechtold.
- "Smouldered-earth policy – Created by ancient Amazonian natives, dark soils retain abundant carbon." Article by B. Harder in [www.sciencenews.org Science News], 4 March 2006, vol. 169, p. 133.
- "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".
- "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".
- "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".
- "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"
- 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" , 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".
- "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.
- Christoph Steiner, EACU 2004
- "Organic chemistry studies on Amazonian Dark Earths", by G. Guggenberger and W. Zech. Chapter 12 of "Amazonian Dark Earths: origin, properties, and management" 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.
- "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).
- "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.
- "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".
- "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.
- "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.
- "Everyone’s carbon sequestration: decrease atmospheric carbon dioxide, earn money and improve the soil." By Folke Günther, Holon Ecosystem Consultants, Lund, Sweden. Presented at the International Institute for Industrial Environmental Economics – IIIEE), 26 March 2007.
- 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
- 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.
- 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., 10 August 2005.
- JOHANNES LEHMANN, JOHN GAUNT, and MARCO RONDON; BIO-CHAR SEQUESTRATION IN TERRESTRIAL ECOSYSTEMS – A REVIEW; Mitigation and Adaptation Strategies for Global Change (2006) 11: 403–427
- [Mao,. J., Johnson, R, Lehmann, J., Olk, D., Neves, E., Thompson, M. and Schmidr-Rohr, K. 2012. Abundant and stable char residues in soils: Implications for soil fertility and carbon sequestration. Environmental science \& technology, 46 (17), pp. 9571—9576]
- Adrados, A., Lopez-Urionabarrenechea, A., Solar, J., Requies, J., De Marco, I. and Cambra, J. 2013. Upgrading of pyrolysis vapors from biomass carbonization. Journal of Analytical and Applied Pyrolysis.
- "Charcoal as a habitat for microbes and its effect on the microbial community of the underlying humus", by J. Pietikainen, O. Kiikkila & H. Fritze. 2000. Oikos 89, 231–242. doi:10.1034/j.1600-0706.2000.890203.x. Cited by B. Glaser in "Prehistorically modiﬁed soils of central Amazonia: a model for sustainable agriculture in the twenty-ﬁrst century".
- "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".
- "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".
- "Site Terra Preta de Índio - Soil Biogeochemistry" by Johannes Lehmann, Cornell University.
- Sombroek, 1966; Smith, 1980; Kern and Kämpf, 1989; Sombroek et al., 1993; Glaser et al., 2000; Lehmann et al., 2003; Liang et al., 2006)
- Jean-François Ponge, Stéphanie Topoliantz, Sylvain Ballof, Jean-Pierre Rossi, Patrick Lavelle, Jean-Marie Betsch and Philippe Gaucher (2006). "Ingestion of charcoal by the Amazonian earthworm Pontoscolex corethrurus: a potential for tropical soil fertility" (PDF). Soil Biology and Biochemistry. 38 (7): 2008–2009. doi:10.1016/j.soilbio.2005.12.024.
- Reddy, N. Sai Bhaskar. "Terra Preta Roof-Top Experiments".
- Chia, C., Munroe, P., Joseph, S. and Lin, Y. 2010. Microscopic characterisation of synthetic Terra Preta. Soil Research, 48 (7), pp. 593—605
-  Jauss, J. 2013. Terra Preta de Indio.
- Adams, M., 2013. Securing soil through carbon. Sydney, University of Sydney.
- Rahman, M. 2013. Nutrient use and Carbon Sequestration Efficiencies in Soils from different Organic. Wastes in Rice and Tomato Cultivation. Communications in Soil Science and Plant Analysis.
- Madari, B. E., Cunha, T. J. F. & Soares, R., 2011. Organic matter of the anthropogenic dark earths of Amazonia. Dynamic Soil, Dynamic Plant, 5(1), pp. 21-28.
- Mao, J., Johnson, R., Lehmann, J., Olk, D., Neves, E., Thompson, M. and Schmidt-Rohr, K. 2012. Abundant and stable char residues in soils: Implications for soil fertility and carbon sequestration. Environmental science \& technology, 46 (17), pp. 9571—9576.
- Mann, Charles C. (September 2013). "Our Good Earth - National Geographic Magazine". ngm.nationalgeographic.com. Retrieved February 2, 2013.
- Embrapa Amazônia Ocidental, Embrapa Solos
- Cornell University, University of Georgia, Universität Bayreuth, University of Florida, Iowa State University, Geoecology Energy Organisation
- Factura, H.; Bettendorf, T.; Buzie, C.; Pieplow, H.; Reckin, J.; Otterpohl, R. (2010): Terra Preta Sanitation: re-discovered from an ancient Amazonian civilisation - integrating sanitation, bio-waste management and agriculture. In: Water Science and Technology, 61.10, p. 2673
- "1491"., by Charles Mann.
- "Eprida Home Page". Retrieved 8 May 2006.
- "Programme Summary: The Secret of El Dorado". BBC Two, 9 pm, Thursday 19 December 2005. Retrieved 10 July 2008.
- "Terra Preta". Hypography discussion forum. Archived from the original on 8 April 2008. Retrieved 8 May 2006.
- "Putting the carbon back: Black is the new green" (PDF). Nature. Retrieved 10 July 2008.
- "Terra Preta Discussion List". Retrieved 10 July 2008.
- Bechtold, G.: "Research work, homepage and thesis about Terra Preta with maps of TP sites and TP field work in Belterra, Pará".
- Michael Tennesen (2007). "Black Gold of the Amazon", in Discover Magazine Vol. 28 No. 04, April 2007. Last accessed March 2007.
- "Terra Preta Home Page". Retrieved 20 April 2007.
- David Haywood (2007). "Could the Mysterious Agricultural Techniques of an Ancient Amazonian Civilization Make New Zealand Farming More Competitive?", on Public Address Radio 5 May 2007. Last accessed May 2007.
- Casselman, Anne (May 2007). "Special Report: Inspired by Ancient Amazonians, a Plan to Convert Trash into Environmental Treasure". Scientific American. Retrieved 10 July 2008.
- Manuel Arroyo-Kalin (2007) 
|Wikimedia Commons has media related to Terra preta.|
- Putting the carbon back: The hundred billion tonne challenge, Nature 442, 620-623 ( 10 August 2006 ), doi:10.1038/442620a
- Salleh, Anna (28 June 2007). "Charred farm waste could gobble up carbon". News in Science. Australian Broadcasting Corporation. Retrieved 10 July 2008. ABC Science Online.
- Horstman, Mark (23 September 2007). "Agrichar – A solution to global warming?". ABC TV Science: Catalyst. Australian Broadcasting Corporation. Retrieved 10 July 2008.
- Terra Preta Amazonian Earth Interview with Dr. Bruno Glaser in META magazine
- Website of the Terra Preta Program of Wageningen University
- Geoarchaeological approaches to the study of Terras Pretas. Archived 30 October 2008 at the Wayback Machine.