Terra Preta
La primera descripción de Terra Preta (do
Indo), o tierra negra, es de Hartt en 1871, que la denominó «terra cotta».
Estos suelos se hallaron por primera vez en la Cuenca del Amazonas en
Brasil, luego se encontraron en otros lugares de Ecuador y Perú, como también
en África Occidental (Benin y Liberia) y en la Sabana de Sudáfrica.
Muchos de estos suelos se consideran estériles, por lo tanto Terra Preta, con
su fertilidad enriquecida por el alto contenido de materia orgánica y
nutrientes, como nitrógeno, fósforo, potasio y calcio, es una anomalía.
Enclavada en un paisaje de tierra árida, Terra Preta está dividida en
parcelas que promedian las 20
ha, aunque también existen registros de sitios que
tienen hasta 350 ha. ¿Cómo se formó Terra Preta? La historia que se esconde detrás de Terra
Preta recién comienza a develarse. Además de su marcada fertilidad, otro
rasgo característico es la presencia de cerámica, carbón y sustancias ácidas
muy aromáticas. Con esta evidencia, los investigadores creen que los suelos
tienen un origen antropogénico y los estudios de carbono 14 revelaron una
antigüedad que oscila entre los 1 780 y 2 260 años. La teoría actual dice que los suelos de Terra
Preta se encuentran sobre antiguos asentamientos indígenas, aunque no se sabe
con certeza si los indios eligieron estos sitios por su fertilidad o si ellos
mismos la formaron. Las evidencias sugieren que los indios modificaron la
fertilidad del suelo con la quema de troncos, ramas, malezas, rastrojos, capa
vegetal de los bosques cercanos y también con el carbón de las cocinas y las
cenizas de las casas. Una fertilidad que persistió a través de los tiempos.
El hallazgo de cerámicas ornamentales, de bosques de bambú, los vestigios de
cultivos, de caminos, pozos y canales asociados con los suelos negros
corroboran esta teoría, que también se confirma con la documentación de los
europeos a su llegada al Brasil, cuando pudieron observar que estas prácticas
aún se realizaban (McCann 2001). ¿Un nuevo modelo para la agricultura sostenible
de hoy? Hoy en día, el acceso a estas tierras negras
está limitado por los reclamos de tierras y por los cambiantes sistemas de
tenencia de la tierra que hacen que estas prácticas de enriquecimiento de la
fertilidad del suelo ya no existan. Sin embargo, las investigaciones actuales
apuntan a reproducir la formación de estos suelos en nuevas zonas sin agotar
los recursos del entorno y en términos de décadas en lugar de siglos. Si esto
es posible, los científicos creen que Terra Preta podría servir de modelo
para el desarrollo de prácticas agrícolas intensivas en el trópico, de alto
rendimiento pero sustentables.
Fuente: W. Sombroek (comunicación personal);
Bechtold, 2001
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Terra Preta
Terra preta (“dark soil” in Portuguese) refers to expanses of very
dark, fertile anthropogenic soils found in the AmazonBasin.
It owes its name to its very high charcoal content. It is also known as
“Amazonian dark earth” or “Indian black earth”. In Portuguese its full name
is “Terra preta do índio” or “Terra preta de índio”.
Terra preta is characterized by the presence of low-temperature
charcoal in high concentrations; of high quantities of pottery shards; of
organic matter such as plant residues, animal faeces, fish and animal bones
and other material; and of nutrients such as nitrogen (N), phosphorus (P),
calcium (Ca), zinc (Zn), manganese (Mn). It also shows high levels of microorganic
activities and other specific characteristics within its particular
ecosystem. It is less prone to leaching than surrounding soils. Terra preta
zones are generally surrounded by terra comum, or "common soil";
these are infertile soils, mainly acrisols, but also ferralsols, and
arenosols.
Terra preta soils are of pre-Columbian nature and were created by man
between 700o and 500 BP ("Before Present"). Thousands of years
after its creation it is so well known by local farmers and caboclos in Brazil's
Amazonian basin, that they seek it out for use and for sale as compost. Its
depth can reach 2 metres
(6 feet).
It is reputedly known by the locals as self-regenerating at the rate of 1 centimetre per
year.
History For a long time, the origins of the Amazonian dark earths were not
immediately clear and several theories were considered. One idea was that
they resulted from ashfall from volcanoes in the Andes,
since they occur more frequently on the brows of higher terraces. Another
theory considered its formation as a result of sedimentation in Tertiary
lakes or in recent ponds. However, because of their elevated charcoal content
and the common presence of pottery remains, it is now widely accepted that
these soils are a product of indigenous soil management involving a labor
intensive technique termed slash-and-char. The technique is differentiated
from slash and burn by a lower temperature burn (thus producing more charcoal
than ashes) and in being a tool for soil improvement.
The Spanish explorer Francisco de Orellana, the 16th C explorer who
was the first European to transverse the Amazon River,
reported densely populated regions running hundreds of kilometers along the
river, suggesting population levels exceeding even those of today. The only
reason this population left no lasting monuments was simply that they happened
to use local wood as their construction material, which unfortunately 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 were once
more settled and agrarian but after the demographic collapse of the 16th and
17th century due to European introduced diseases they reverted to less
complex modes of existence but maintained certain traditions. Moreover, many
indigenous people were forced to adapt to a more mobile lifestyle in order to
protect themselves against colonialism. This might have made the benefits of
terra preta, such as its self-renewing capacity, less attractive — farmers
would not have been able to enjoy the use of renewed soil because they would
have been forced to move for safety. Slash-and-burn might have been an
adaptation to these conditions.
For 350 years after the European arrival by Vicente Yáñez Pinzón, the
Portuguese portion of the basin remained an untended former food gathering
and planned agricultural landscape occupied by the Indigenous peoples who
survived the arrival of European diseases. There is ample evidence for
complex large-scale, pre-Columbian social formations, including chiefdoms, in
many areas of Amazonia (particularly the
inter-fluvial regions) and even large towns and cities. For instance the
pre-Columbian culture on the island
of Marajo may have
developed Social stratification and supported a population of 100,000 people.
The Native Americans of the Amazon rain forest may have used Terra preta to
make the land suitable for the large scale agriculture needed to support
large populations and complex social formations such as chiefdoms.
Location The Terra Preta soils are found mainly in Amazonia,
where Sombroek et al. estimate that this covers at least 0.1- 0.3%, or 6,300
to 18,900 km²s of low forested Amazonia (cited by Denevan and Woods); but others
estimate this surface at 1.0% or more (twice the surface of Great-Britain).
Plots of Terra preta exist in small surfaces averaging 20 hectares, but near-900 acres' surfaces
have also been reported. They are found among various climatic, geological
and topographical situations. Their distribution mainly follows the water
courses, from East Amazonia to the central basin of Amazonia.
Williams W. Woods (soil biologist at Southern Illinois University) estimates
that around 10% of the original terra comum appears to have converted to
Terra preta. According to William Balée (anthropologist at Tulane
University in New Orleans),
the spreads of tropical forest between the savannas could be mainly
anthropogenic – a notion with dramatic implications world-wide for
agriculture and conservation. Terra preta sites are also known in other South
American areas (Ecuador, Peru, Guyana),
in West Africa (Benin, Liberia), and
on the South African savannas.[1] Similar soil, dark earth, was found in late
Roman Britain. Source:
W. Sombroek (comunicación personal); Bechtold, 2001
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