Темные земли Амазонии: Антропогенные почвы и древнее земледелие.

Very dark, fertile Amazonian anthropogenic soil

Terra preta (ˈtɛʁɐ ˈpɾetɐ, literally "black soil" in Portuguese) is a type of very dark, fertile anthropogenic soil (anthrosol) 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, 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; 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 (ˈtɛʁɐ koˈmũ, ku ), or "common soil"; these are infertile soils, mainly acrisols, Terra preta is less prone to 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. Soil depths can reach It is reported to regenerate itself at the rate of per year.

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 formed under kitchen middens, 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 Amazon Basin.

Amazonians formed complex, large scale social formations, including chiefdoms (particularly in the inter fluvial regions) and even large towns and cities. For instance, the culture on the island of Marajó may have developed social stratification and supported a population of 100,000. Amazonians may have used terra preta to make the land suitable for large scale agriculture. Spanish explorer Francisco de Orellana was the first European to traverse the Amazon River 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 geoglyphs 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 The settled agrarians again became nomads, while still maintaining specific traditions of their settled forebears. Their semi nomadic descendants have the distinction among tribal indigenous societies of a hereditary, yet landless, aristocracy, a historical anomaly for a society without a sedentary, agrarian culture. Moreover, many indigenous peoples adapted to a more mobile lifestyle 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 cultivate the renewed soil as they migrated. Slash and char agriculture may have been an adaptation to these conditions. For 350 years after the European arrival, the Portuguese portion of the basin remained untended.

Terra preta soils are found mainly in the Brazilian Amazon, where Sombroek et al. estimate that they cover at least 0.1–0.3%, or of low forested Amazonia; 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, and topographical situations. 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 between the savannas could be mainly anthropogenic—a notion with dramatic implications worldwide for agriculture and conservation. Terra preta sites are also known in the Llanos de Moxos of Bolivia, Ecuador, Peru and French Guiana, and on the African continent in Benin, Liberia, and the South African savannas. 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. 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; 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 or molecular markers such as benzenepolycarboxylic acid, 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). Other measurements found carbon levels 70 times greater than in surrounding ferralsols, with approximate 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. Charring at high temperature consumes that layer and brings little increase in soil fertility. The slow oxidation of charcoal creates carboxylic groups; these increase the cation 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 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. Amending ferralsol with wood charcoal greatly increases productivity. 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, worm tea, etc. ).

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

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), up to 150 g/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 peregrine earthworm Pontoscolex corethrurus (Oligochaeta: Glossoscolecidae) 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 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 ants are repelled from fresh terra preta; their density is found to be low about 10 days after production compared to that in control soils.

A newly coined term is 'synthetic terra preta'. STP is a fertilizer consisting of materials thought to replicate the original materials, including crushed clay, blood and bone meal, manure and biochar 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 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. 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 underway by companies such as Embrapa 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 (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.