''Terra preta'' (, locally , literally "black soil" in

Portuguese Portuguese may refer to: * anything of, from, or related to the country and nation of Portugal ** Portuguese cuisine, traditional foods ** Portuguese language, a Romance language *** Portuguese dialects, variants of the Portuguese language ** Portu ...

) is a type of very dark, fertile

anthropogenic Anthropogenic ("human" + "generating") is an adjective that may refer to: * Anthropogeny, the study of the origins of humanity Counterintuitively, anthropogenic may also refer to things that have been generated by humans, as follows: * Human im ...

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...

(

anthrosol An anthrosol (or anthropogenic soil) in the World Reference Base for Soil Resources (WRB) is a type of soil that has been formed or heavily modified due to long-term human activity, such as from irrigation, addition of organic waste or wet-field cul ...

) found in the

Amazon Basin The Amazon basin is the part of South America drained by the Amazon River and its tributaries. The Amazon drainage basin covers an area of about , or about 35.5 percent of the South American continent. It is located in the countries of Bolivi ...

. It is also known as "Amazonian dark earth" or "Indian black earth". In Portuguese its full name is or ("black soil of the

Indian Indian or Indians may refer to: Peoples South Asia * Indian people, people of Indian nationality, or people who have an Indian ancestor ** Non-resident Indian, a citizen of India who has temporarily emigrated to another country * South Asia ...

", "Indians' black earth"). ''Terra mulata'' ("mulatto earth") is lighter or brownish in color. Terra preta HC1

''Terra preta'' owes its characteristic black color to its weathered

charcoal Charcoal is a lightweight black carbon residue produced by strongly heating wood (or other animal and plant materials) in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, cal ...

content, and was made by adding a mixture of charcoal, bones, broken pottery, compost and manure to the low fertility Amazonian soil. A product of indigenous

soil management Soil management is the application of operations, practices, and treatments to protect soil and enhance its performance (such as soil fertility or soil mechanics). It includes soil conservation, soil amendment, and optimal soil health. In agricult ...

and

slash-and-char Slash-and-char is an alternative to slash-and-burn that has a lesser effect on the environment. It is the practice of charring the biomass resulting from the slashing, instead of burning it. The resulting residue matter charcoal can be utilized ...

agriculture, the charcoal is 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 tiny pottery shards; of organic matter such as plant residues, animal

feces Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...

, fish and animal bones, and other material; and of

nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...

s such as

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...

zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...

and

manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...

. Fertile soils such as ''terra preta'' show high levels of microorganic activities and other specific characteristics within particular

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...

s. ''Terra preta'' zones are generally surrounded by ''terra comum'' ( or ), or "common soil"; these are infertile soils, mainly

acrisol An Acrisol is a Reference Soil Group of the World Reference Base for Soil Resources (WRB). It has a clay-rich subsoil and is associated with humid, tropical climates, such as those found in Brazil, and often supports forested areas. In the USDA so ...

s, but also

ferralsol Oxisols are a soil order in USDA soil taxonomy, best known for their occurrence in tropical rain forest within 25 degrees north and south of the Equator. In the World Reference Base for Soil Resources (WRB), they belong mainly to the ferralsols ...

s and

arenosol In USDA soil taxonomy, a Psamment is defined as an Entisol which consists basically of unconsolidated sand deposits,nutrient leaching because of its high concentration of charcoal, microbial life and organic matter. The combination accumulates nutrients, minerals and microorganisms and withstands leaching. ''Terra preta'' soils were created by farming communities between 450 BCE and 950 CE. in Soil depths can reach . It is reported to regenerate itself at the rate of per year.

History

Early theories

The origins of the Amazonian

dark earth Dark earth in geology is a substratum, up to 1 meter (3.1 feet) thick, that indicates settlement over long periods of time. The material is high in organic matter, including charcoal, which gives it its characteristic dark colour; it may also co ...

s were not immediately clear to later settlers. One idea was that they resulted from ashfall from volcanoes in the

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

, since they occur more frequently on the brows of higher terraces. Another theory considered its formation to be a result of

sedimentation Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the ...

tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...

lakes or in recent ponds.

Anthropogenic roots

Soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...

s with elevated

content and a common presence of

pottery Pottery is the process and the products of forming vessels and other objects with clay and other ceramic materials, which are fired at high temperatures to give them a hard and durable form. Major types include earthenware, stoneware and por ...

remains can accrete accidentally near living quarters as residues from food preparation, cooking fires, animal and fish

bone A bone is a Stiffness, rigid Organ (biology), organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red blood cell, red and white blood cells, store minerals, provid ...

s, broken pottery, etc., accumulated. Many ''terra preta'' soil structures are now thought to have formed under kitchen

midden A midden (also kitchen midden or shell heap) is an old dump for domestic waste which may consist of animal bone, human excrement, botanical material, mollusc shells, potsherds, lithics (especially debitage), and other artifacts and ecofact ...

s, as well as being manufactured intentionally on larger scales. Farmed areas 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. This type of soil appeared between 450 BCE and 950 CE at sites throughout the

. Recent research has reported that ''terra preta'' may be of natural origin, suggesting that pre-Columbian people intentionally utilized and improved existing areas of soil fertility scattered among areas of lower fertility.

Amazonia

Amazonians formed complex, large-scale social formations, including

chiefdom A chiefdom is a form of hierarchical political organization in non-industrial societies usually based on kinship, and in which formal leadership is monopolized by the legitimate senior members of select families or 'houses'. These elites form a ...

s (particularly in the inter-fluvial regions) and even large towns and cities. For instance, the culture on the island of

Marajó Marajó () is a large coastal island in the state of Pará, Brazil. It is the main and largest of the islands in the Marajó Archipelago. Marajó Island is separated from the mainland by Marajó Bay, Pará River, smaller rivers (especially ...

may have developed

social stratification Social stratification refers to a society's categorization of its people into groups based on socioeconomic factors like wealth, income, race, education, ethnicity, gender, occupation, social status, or derived power (social and political). As ...

and supported a population of 100,000. Amazonians may have used ''terra preta'' to make the land suitable for large-scale agriculture.

Spanish Spanish might refer to: * Items from or related to Spain: **Spaniards are a nation and ethnic group indigenous to Spain **Spanish language, spoken in Spain and many Latin American countries **Spanish cuisine Other places * Spanish, Ontario, Cana ...

explorer

Francisco de Orellana Francisco de Orellana Bejarano Pizarro y Torres de Altamirano (; 1511 – November 1546) was a Spanish explorer and conquistador. In one of the most improbably successful voyages in known history, Orellana managed to sail the length of the Amaz ...

was the first European to traverse the

Amazon River The Amazon River (, ; es, Río Amazonas, pt, Rio Amazonas) in South America is the largest river by discharge volume of water in the world, and the disputed longest river system in the world in comparison to the Nile. The headwaters of t ...

in the 16th century. He reported densely populated regions extending hundreds of kilometres along the river, suggesting population levels exceeding even those of today. Orellana may have exaggerated the level of development, although that is disputed. The evidence to support his claim comes from the discovery of

geoglyph A geoglyph is a large design or motif (generally longer than 4 metres) produced on the ground by durable elements of the landscape, such as stones, stone fragments, gravel, or earth. A positive geoglyph is formed by the arrangement and alignmen ...

s dating between 0–1250 CE and from ''terra preta''. Beyond the geoglyphs, these populations left no lasting monuments, possibly because they built with wood, which would have rotted in the humid climate, as stone was unavailable. Whatever its extent, this civilization vanished after the demographic collapse of the 16th and 17th century, due to European-introduced diseases such as smallpox and ''

bandeirante The ''Bandeirantes'' (), literally "flag-carriers", were slavers, explorers, adventurers, and fortune hunters in early Colonial Brazil. They are largely responsible for Brazil's great expansion westward, far beyond the Tordesillas Line of 1494 ...

'' slave-raiding. The settled agrarians again became nomads, while still maintaining specific traditions of their settled forbears. Their semi-nomadic descendants have the distinction among tribal indigenous societies of a hereditary, yet landless,

aristocracy Aristocracy (, ) is a form of government that places strength in the hands of a small, privileged ruling class, the aristocracy (class), aristocrats. The term derives from the el, αριστοκρατία (), meaning 'rule of the best'. At t ...

, a historical anomaly for a society without a sedentary, agrarian culture. Moreover, many

indigenous people Indigenous peoples are culturally distinct ethnic groups whose members are directly descended from the earliest known inhabitants of a particular geographic region and, to some extent, maintain the language and culture of those original people ...

s adapted to a more mobile lifestyle to escape

colonialism Colonialism is a practice or policy of control by one people or power over other people or areas, often by establishing colonies and generally with the aim of economic dominance. In the process of colonisation, colonisers may impose their relig ...

. This might have made the benefits of ''terra preta'', such as its self-renewing capacity, less attractive: farmers would not have been able to cultivate the renewed soil as they migrated.

Slash-and-char Slash-and-char is an alternative to slash-and-burn that has a lesser effect on the environment. It is the practice of charring the biomass resulting from the slashing, instead of burning it. The resulting residue matter charcoal can be utilized ...

agriculture may have been an adaptation to these conditions. For 350 years after the European arrival, the Portuguese portion of the basin remained untended.

Location

''Terra preta'' soils are found mainly in the

Brazilian Amazon Brazilian commonly refers to: * Something of, from or relating to Brazil * Brazilian Portuguese, the dialect of the Portuguese language used mostly in Brazil * Brazilians, the people (citizens) of Brazil, or of Brazilian descent Brazilian may also ...

, where Sombroek ''et al.'' in estimate that they cover at least 0.1 to 0.3%, or of low forested Amazonia; but others estimate this surface at 10.0% or more (twice the area of

Great Britain Great Britain is an island in the North Atlantic Ocean off the northwest coast of continental Europe. With an area of , it is the largest of the British Isles, the largest European island and the ninth-largest island in the world. It is ...

). Recent model-based predictions suggest that the extent of ''terra preta'' soils may be of 3.2% of the forest. ''Terra preta'' exists in small plots averaging , but areas of almost have also been reported. They are found among various climatic,

geological Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Eart ...

, and

topographical Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary sci ...

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 , (see distribution map of ''terra preta'' sites in Amazon basin The spreads of

tropical forest Tropical forests (a.k.a. jungle) are forested landscapes in tropical regions: ''i.e.'' land areas approximately bounded by the tropic of Cancer and Capricorn, but possibly affected by other factors such as prevailing winds. Some tropical fores ...

between the

savannas A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to ...

could be mainly anthropogenic—a notion with dramatic implications worldwide for

agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people to ...

and

conservation Conservation is the preservation or efficient use of resources, or the conservation of various quantities under physical laws. Conservation may also refer to: Environment and natural resources * Nature conservation, the protection and manageme ...

. Archaeological 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. ''Terra preta'' sites are also known in the

Llanos de Moxos The Beni savanna, also known as the Llanos de Moxos or Moxos plains, is a tropical savanna ecoregion of the Beni Department of northern Bolivia. Setting The Beni savanna covers an area of in the lowlands of northern Bolivia, with small portio ...

of Bolivia,

Ecuador Ecuador ( ; ; Quechua: ''Ikwayur''; Shuar: ''Ecuador'' or ''Ekuatur''), officially the Republic of Ecuador ( es, República del Ecuador, which literally translates as "Republic of the Equator"; Quechua: ''Ikwadur Ripuwlika''; Shuar: ''Eku ...

Peru , image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = Seal (emblem), National seal , national_motto = "Fi ...

and

French Guiana French Guiana ( or ; french: link=no, Guyane ; gcr, label=French Guianese Creole, Lagwiyann ) is an overseas departments and regions of France, overseas department/region and single territorial collectivity of France on the northern Atlantic ...

, and on the African continent in

Benin Benin ( , ; french: Bénin , ff, Benen), officially the Republic of Benin (french: République du Bénin), and formerly Dahomey, is a country in West Africa. It is bordered by Togo to the west, Nigeria to the east, Burkina Faso to the north ...

Liberia Liberia (), officially the Republic of Liberia, is a country on the West African coast. It is bordered by Sierra Leone to Liberia–Sierra Leone border, its northwest, Guinea to its north, Ivory Coast to its east, and the Atlantic Ocean ...

, and the

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...

savanna A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to ...

Pedology

In the international soil classification system

World Reference Base for Soil Resources The World Reference Base for Soil Resources (WRB) is an international soil classification system for naming soils and creating legends for soil maps. The currently valid version is the fourth edition 2022. It is edited by a working group of the Inte ...

(WRB) ''Terra preta'' is called Pretic

Anthrosol An anthrosol (or anthropogenic soil) in the World Reference Base for Soil Resources (WRB) is a type of soil that has been formed or heavily modified due to long-term human activity, such as from irrigation, addition of organic waste or wet-field cul ...

. The most common original soil before transformed into a terra preta is the

Ferralsol Oxisols are a soil order in USDA soil taxonomy, best known for their occurrence in tropical rain forest within 25 degrees north and south of the Equator. In the World Reference Base for Soil Resources (WRB), they belong mainly to the ferralsols ...

. ''Terra preta'' has a

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

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. ''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 * Growth of microorganisms and animals in the soil

Wood charcoal

The transformation of biomass into charcoal produces a series of charcoal derivatives known as pyrogenic or

black carbon Chemically, black carbon (BC) is a component of fine particulate matter (PM ≤ 2.5 µm in aerodynamic diameter). Black carbon consists of pure carbon in several linked forms. It is formed through the incomplete combustion of fossil fue ...

, the composition of which varies from lightly charred organic matter, to

soot Soot ( ) is a mass of impure carbon particles resulting from the incomplete combustion of hydrocarbons. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolysed ...

particles rich in

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on large ...

formed by recomposition of

free radical A daughter category of ''Ageing'', this category deals only with the biological aspects of ageing. Ageing Ailments of unknown cause Biogerontology Biological processes Causes of death Cellular processes Gerontology Life extension Metabo ...

s. 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 In chemistry, a dehydration reaction is a chemical reaction that involves the loss of water from the reacting molecule or ion. Dehydration reactions are common processes, the reverse of a hydration reaction. Dehydration reactions in organic che ...

with an oxygen/carbon (O/C) ratio less than 60; smaller values have been suggested. Cited in . Because of possible interactions with minerals and organic matter from the soil, it is almost impossible to identify charcoal by determining only the proportion of O/C. The hydrogen/carbon percentage Cited in . or molecular markers such as benzenepolycarboxylic acid, Cited in are used as a second level of identification. 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). Cited in Other measurements found carbon levels 70 times greater than in surrounding

ferralsols Oxisols are a soil order in USDA soil taxonomy, best known for their occurrence in tropical rain forest within 25 degrees north and south of the Equator. In the World Reference Base for Soil Resources (WRB), they belong mainly to the ferralsol ...

, with approximate average values of 50 Mg/ha/m. Cited in 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 Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...

materials) has an internal layer of biological

petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...

condensates that the bacteria consume, and is similar to cellulose in its effects on microbial growth. Charring at high temperature consumes that layer and brings little increase in soil fertility. The formation of condensed aromatic structures depends on the method of manufacture of charcoal. in The slow

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

of charcoal creates

carboxylic group In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with substituent, R referring to the alkyl, alkenyl, aryl, or other group. ...

s; these increase the

cation exchange capacity Cation-exchange capacity (CEC) is a measure of how many cations can be retained on soil particle surfaces. Negative charges on the surfaces of soil particles bind positively-charged atoms or molecules (cations), but allow these to exchange with ot ...

of the soil. Cited in . 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 are higher proportions of forms of

carboxyl In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...

ic and

phenol Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it req ...

ic 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 Specific definitions of sustainability are difficult to agree on and have varied in the literature and over time. The concept of sustainability can be used to guide decisions at the global, national, and individual levels (e.g. sustainable livi ...

of ''terra preta''. Amending

with wood charcoal greatly increases productivity. Globally, agricultural lands have lost on average 50% of their carbon due to intensive cultivation and other damage of human origin. Fresh charcoal must be "charged" before it can function as a

biotope A biotope is an area of uniform environmental conditions providing a living place for a specific assemblage of plants and animals. ''Biotope'' is almost synonymous with the term "habitat", which is more commonly used in English-speaking countrie ...

. Several experiments demonstrate that uncharged charcoal can bring a temporary depletion of available nutrients when first put into the soil, that is 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.).

Organic matter and nutrients

Charcoal's porosity brings better retention of organic matter, of water and of dissolved nutrients, Cited in . as well as of pollutants such as

pesticide Pesticides are substances that are meant to control pests. This includes herbicide, insecticide, nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, microbicide, fungicide, and lampri ...

s and aromatic poly-cyclic hydrocarbons. Cited in .

Organic matter

Charcoal's high absorption potential of organic molecules (and of water) is due to its porous structure. ''Terra preta'''s high concentration of charcoal supports a high concentration of organic matter (on average three times more than in the surrounding poor soils), Cited in . up to 150 g/kg. Organic matter can be found at deep. Bechtold proposes to use ''terra preta'' for soils that show, at 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

s regenerate in spite of these tropical conditions' prevalence and their fast mineralisation rates. The stability of organic matter is mainly because the biomass is only partially consumed.

Nutrients

''Terra preta'' soils also show higher quantities of nutrients, and a better retention of these nutrients, than surrounding infertile soils. The proportion of P reaches 200–400 mg/kg.Lehmann, Johannes.som
Site Terra Preta de Índio - Soil Biogeochemistry
, Cornell University. 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. Anthrosol's availability of P, Ca, Mn and Zn is higher than 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 Rice is the seed of the grass species ''Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima ''Oryza glaberrima'', commonly known as African rice, is one of the two domesticated rice species. It was first domesticated and grown i ...

and ''

Vigna unguiculata The cowpea (''Vigna unguiculata'') is an annual herbaceous legume from the genus ''Vigna''. Its tolerance for sandy soil and low rainfall have made it an important crop in the semiarid regions across Africa and Asia. It requires very few inputs, ...

'') increased by 38–45% without fertilization ( P < 0.05), compared to crops on fertilized ferralsol. Amending with charcoal pieces approximately in diameter, instead of ground charcoal, did not change the results except for manganese (Mn), for which absorption considerably increased. Nutrient leaching 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 Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

) 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.) lack the mineral matter to provide those nutrients. The clay matter that exists in those soils is capable of holding only 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

excrement Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...

s (rich in P and N); * Kitchen refuse, such as animal bones and

tortoise Tortoises () are reptiles of the family Testudinidae of the order Testudines (Latin: ''tortoise''). Like other turtles, tortoises have a turtle shell, shell to protect from predation and other threats. The shell in tortoises is generally hard, ...

shells (rich in P and Ca); *

Ash Ash or ashes are the solid remnants of fires. Specifically, ''ash'' refers to all non-aqueous, non- gaseous residues that remain after something burns. In analytical chemistry, to analyse the mineral and metal content of chemical samples, ash ...

residue from incomplete combustion (rich in Ca, Mg, K, P and charcoal); * Biomass of terrestrial plants (e.g.

compost Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical and biological properties. It is commonly prepared by decomposing plant, food waste, recycling organic materials and manure. The resulting m ...

); and * Biomass of

aquatic plant Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes to distinguish them from algae and other microphytes. A macrophyte is a plant that ...

s (e.g.

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

). Saturation in pH and in base is more important than in the surrounding soils.

Microorganisms and animals

The peregrine

earthworm An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. Th ...

Pontoscolex ''Pontoscolex'' is a genus of earthworms in the family Glossoscolecidae, or alternatively, in the family Rhinodrilidae. General characteristics The type species ''Pontoscolex corethrurus'' has a circumtropical distribution, although it originat ...

corethrurus'' (

Oligochaeta Oligochaeta () is a subclass of animals in the phylum Annelida, which is made up of many types of aquatic and terrestrial worms, including all of the various earthworms. Specifically, oligochaetes comprise the terrestrial megadrile earthworm ...

Glossoscolecidae The Glossoscolecidae are a large family of earthworms (annelids) which has native representatives in South and Central America. The species '' Pontoscolex corethrurus'' has a circumtropical distribution. They are found mostly in forest, but one ...

) ingests charcoal and mixes it into a finely ground form with the mineral soil. ''P. corethrurus'' is widespread in Amazonia and notably in clearings after

burning Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combusti ...

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''. Some

ant Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of 22 ...

s are repelled from fresh ''terra preta''; their density is found to be low about 10 days after production compared to that in control soils.

Modern research on creating ''terra preta''

Synthetic ''terra preta''

A newly coined term is 'synthetic ''terra preta''’.Chia, C., Munroe, P., Joseph, S. and Lin, Y. 2010. Microscopic characterisation of synthetic Terra Preta. Soil Research, 48 (7), pp. 593—605 STP is 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

ped Peds are aggregates of soil particles formed as a result of pedogenic processes; this natural organization of particles forms discrete units separated by pores or voids. The term is generally used for macroscopic (visible; i.e. greater than 1 mm i ...

s and aggregates over a viable time frame. Such a 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 soil fertility is carbon, thought to have been gradually incorporated 4 to 10 thousand years ago. Biochar is capable of decreasing soil

acidity In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...

and if soaked in nutrient rich liquid can slowly release nutrients and provide habitat for

microbes A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

in soil due to its high

porosity Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...

surface area. The goal is an economically viable process that could be included in modern agriculture. Average poor tropical soils are easily enrichable to ''terra preta nova'' by the addition of charcoal and condensed smoke. ''Terra preta'' may be an important avenue of future

carbon sequestration Carbon sequestration is the process of storing carbon in a carbon pool. Carbon dioxide () is naturally captured from the atmosphere through biological, chemical, and physical processes. These changes can be accelerated through changes in land ...

while reversing the current worldwide decline in

soil fertility Soil fertility refers to the ability of soil to sustain agricultural plant growth, i.e. to provide plant habitat and result in sustained and consistent yields of high quality.

and associated

desertification Desertification is a type of land degradation in drylands in which biological productivity is lost due to natural processes or induced by human activities whereby fertile areas become increasingly arid. It is the spread of arid areas caused by ...

. Whether this is possible on a larger scale has yet to be proven. Tree Lucerne (tagasaste or ''

Cytisus proliferus ''Cytisus proliferus'', tagasaste or tree lucerne, is a small spreading evergreen tree that grows high. It is a well known fertilizer tree. It is a member of the Fabaceae (pea) family and is indigenous to the dry volcanic slopes of the Canary ...

'') is one type of

fertilizer tree Fertilizer trees are used in agroforestry to improve the condition of soils used for farming. As woody legumes, they capture nitrogen from the air and put it in the soil through their roots and falling leaves. They can also bring nutrients fro ...

used to make ''terra preta''. Efforts to recreate these soils are underway by companies such as

Embrapa The Brazilian Agricultural Research Corporation (Embrapa - pt, Empresa Brasileira de Pesquisa Agropecuária) is a state-owned research corporation affiliated with the Brazilian Ministry of Agriculture. Since its inception on April 26, 1973, it ha ...

and other organizations in Brazil. Synthetic ''terra preta'' is produced at the Sachamama Center for Biocultural Regeneration in High Amazon, Peru. This area has many ''terra preta'' soil zones, demonstrating that this anthrosol was created not only in the Amazon basin, but also at higher elevations. A synthetic ''terra preta'' process was developed by Alfons-Eduard Krieger to produce a high humus, nutrient-rich, water-adsorbing soil.

''Terra preta'' sanitation

''Terra preta'' sanitation (TPS) systems have been studied as an alternative

sanitation Sanitation refers to public health conditions related to clean drinking water and treatment and disposal of human excreta and sewage. Preventing human contact with feces is part of sanitation, as is hand washing with soap. Sanitation systems ...

option by using the effects of lactic-aid conditions in

urine-diverting dry toilet A urine-diverting dry toilet (UDDT) is a type of dry toilet with urine diversion that can be used to provide safe, affordable sanitation in a variety of contexts worldwide. The separate collection of feces and urine without any flush water has m ...

s and a subsequent treatment by

vermicomposting Vermicompost (vermi-compost) is the product of the decomposition process using various species of worms, usually red wigglers, white worms, and other earthworms, to create a mixture of decomposing vegetable or food waste, bedding materials, and ...

Notes

References

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External links

* * * * * * * * ABC Science Online. * {{DEFAULTSORT:Terra Preta Amazon basin Types of soil Indigenous topics of the Amazon Pre-Columbian indigenous peoples of the Amazon