Outstanding Features

The formerly called “Terra Preta”, now called Amazonian Dark Earths (ADE), in the Amazon Basin are dark coloured, highly fertile soils. Their origin was not clear for a long time and several conflicting theories have been presented. It is now widely accepted that these soils were not only used by local populations, but are a product of indigenous soil management. Since the peopling of the Amazon reaches back to 10,000 before present, some of these soils were formed very long ago. Many of the soils were created 500-1500 years ago, but dates reaching back to 2500 before present or beyond are not uncommon.

ADE are usually highly fertile; in one example, at Açutuba (Central Amazon, Brazil), the land had been continuously cultivated for 40 years without fertilization. This is an extraordinarily long period of time since most upland soils in Amazonia can not be used for more than one cropping season without nutrient inputs.

Diverse organic nutrient sources were identified such as fish residues, turtle shells, weeds and sediment from the rivers, manures, and kitchen waste other than fish. It appears that the “Terra Preta management” which produced the Amazonian Dark Earths was a sophisticated combination of organic soil management and burning, using locally available nutrient and carbon sources. The burning is used not to produce ash such as in conventional slash-and-burn techniques, but to produce incompletely combusted organic material, or charcoal, and can therefore be understood as a type of ”slash-and-char” technique. The key to the fertility is the high nutrient retention ensuring high nutrient availability and at the same time very low nutrient losses by leaching. The abundance of black carbon has been proposed as the likely reason for the stability of organic carbon and consequent carbon-enrichment in these soils

This combination of organic additions which produced the observed highly resilient soil fertility, persisting over centuries and millennia until today, is remarkable in a soil environment that is so severely constrained by low inherent fertility as it is the case in the Amazon Basin.

The system is very adaptive as it is found on a large variety of soil types and regions. The key elements of the system (pyrogenic carbon and organic phosphorus and calcium) are ingenious and innovative. Its existence over long periods of time proves its sustainability. The Terra Preta system supports a high biodiversity (vegetation and soil biodiversity) and ecosystem functioning as it builds the natural resource capital “soil” with long-term benefits and extraordinarily high resilience towards external and internal shocks. This resilience creates a remarkable livelihood security. The knowledge systems and culture linked to the Terra Preta management are unique; ADE and the Terra Preta management are of utmost archaeological value.

The indigenous populations and the cultural practices that led to the creation of these soils have long since died out. The survivors and immigrant communities may have shifted from the labor-intensive Terra Preta system to shifting cultivation due to the introduction of steel axes that enabled them to slash forests and utilize the nutrients in the above ground biomass after burning as a fertilizer.

Vegetational and pollen analyses also show an unusually high diversity of crops that were grown on ADE. The cultivars still found among the vegetation reflects an advanced domestication process, like for example the spineless pupunha (Bactris gasipaes). Agrobiodiversity was probably an important aspect of the sustainability of the Terra Preta system. Because of the fertility of the soils and the centuries of agricultural practices by indigenous peoples, a special ecosystem has developed at ADE sites.

The patterns of ADE use today vary depending on proximity to urban areas. Current populations “riberinhos or caboclos” (settled at these sites starting in 19^th century) recognize the value of the ADEs as a natural resource. However, the understanding that these soils were created through management may have been lost

Goods and Services Provided

Soils, and particularly the highly fertile ADE, represent an important livelihood resource. The high levels of inherent fertility of ADE ensure sustained agricultural production, particularly when compared to crops grown on soils made available through slash and burn. The resilience of these soils is important in ensuring sustainability of production and reducing vulnerability of the livelihoods for those using this resource. In some situations, particularly close to urban centres the use of the land to produce cash crops such as papaya and banana which grow exceptionally well on ADE can create valuable cash economies in smallholder agriculture.

At a national level the social and cultural services represented by ADE are recognized as an important part of Brazil's national heritage. It is recognized that ADEs represent part of the country's cultural identity that has been lost. ADE bear testimony to an ancient civilization and its adoption to a nutrient-poor environment and open the door to our understanding of pre-Columbian history in the Amazon Basin.

Within the Amazon the fertility of the ADEs and the centuries of agricultural practices by indigenous peoples created new ecological niches where special ecosystem developed. High stands of cultivated plants among the vegetation can still be found like the Brazil nut (Bertholletia excelsa), kapok or sumauma (Ceiba pentandra), babaçu (Attalea speciosa), peachpalm or pupunha (Bactris gasipaes) and tucumã (Astrocaryum aculeatum). Many plant species can be found that are specific to ADE. At some sites a dense liana or bamboo forest developed. This special ecosystem attracts various animal species like the recently discovered Titi monkey Callicebus bernhardi.

The biodiversity of the soil itself appears to be unique as well. Recent evidence revealed a distinct and unique microbiological diversity associated with ADE. The specific habitat in ADE supported and preserved microorganisms that are absent in surrounding ecosystems.

Threats and Challenges

Except perhaps in some very remote locations the indigenous practices that led to the creation have died out. A key threat now is the over exploitation of ADE sites by agriculture and the lack of knowledge to maintain the fertility of the sites. Where ADE are cultivated the degradation progresses much slower than in adjacent non-ADE soils. However, also ADE degrades, and it appears from the limited data currently available that after 10-40 years ADE soils lose their high nutrient availability and some of its organic carbon and become unproductive. In its most extreme form recognition of the inherent fertility of ADE has lead to ‘mining' with soil being removed to provide a product for local horticulture in the vicinity of urban regions.

Other threats include the physical destruction by building projects (roads, urban housing). The loss of knowledge of the processes for their creation means that as ADE are being destroyed the productive potential of this region declines. Not only does this threaten livelihoods and national as well as global cultural heritage but also our opportunity to 'learn' from these soils. This is a tragedy that does not only deprive local farmers of sustainable agricultural technologies but also other regions in the world where Terra Preta systems could be adopted.

Policy and Development Relevance

The challenge is to learn from these ADEs in an appropriate way, to explore whether lessons from the past may contribute towards the formulation of sustainable forms of agriculture, thereby giving the local farmers alternatives for the slash-and-burn agriculture practiced today, whilst creating the opportunity to maintain, preserve and recuperate the fertility of the over-exploited ADE sites.

Many urban settlements and current cities such as Santarem, Belem and Manaus are situated on major ADE sites. Converting all ADE sites into protected National Heritage Sites does not appear to be a feasible approach. The challenge is to find appropriate ways of balancing conservation, current use and future development.

ADEs offer the opportunity to learn from cultural practices (that were developed at a time in history when lack of access to steel, and techniques for its utilization, required people to practice highly intensive agriculture on fixed areas of land.) This knowledge from past and present indigenous populations (in very remote situations) may offer prospects to current populations as again we are challenged to increase levels of production. Immigration into the Amazon Region and regional as well as global population growth forces the development of permanent agriculture. Permanent agriculture in turn demands the development of sustainable and resilient as well as affordable soil amendments.

ADEs appear to reflect the outcome of quite unique management strategies, which contrast with current management practices –possibly offering a route to new forms of organic agriculture that can provide high yields (competitive or even superior to the use of mineral/commercial fertilizers) with low impact on the environment. Terra Preta management has the potential to maintain the natural resource capital instead of exploiting and degrading the environment in such fragile ecosystems as those in the Amazon Basin. It provides a new development perspective for the humid tropical lowlands locally, regionally and world-wide.

Global Importance

At an international level, researchers of virtually all disciplines have recently highlighted the importance of ADE and the Terra Preta management system not only for Brazil, but as a global heritage that must be preserved

Highly weathered soils and tropical climatic conditions as they are found in the Amazon are representative of many locations in the world, thus findings from the study of ADE will potentially inform strategies to manage many agro-ecosystems world-wide. The soil types where ADE are found today range from sandy (up to 90 % sand) to clayey (up to 90 % clay) soils and therefore include all textures that can potentially be encountered in agricultural soils.

The potential for carbon sequestration of ADE does not only benefit local farmers or farming communities once the Kyoto protocol is applied to agricultural soils. It also benefits global climate. Soils are the single largest pool of organic carbon in terrestrial ecosystems. Even small changes in the total carbon stocks in soils provide a huge source or sink for carbon dioxide in the atmosphere. ADE soils contain up to 10 times more organic carbon than adjacent sites. This is an enormous carbon sequestration potential in comparison to other contemporary efforts such as reduced tillage or afforestation, which typically result in increases of carbon stocks by 20 to 50 %. Additionally, the carbon in ADE has proven to be much more resilient to microbial decomposition and has therefore a much higher longevity in soil than organic carbon added by afforestation or manuring.

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