PRETIC - The new WRB A new diagnostic horizon in WRB for ... · ‘Terra Preta de Indio’ or...
Transcript of PRETIC - The new WRB A new diagnostic horizon in WRB for ... · ‘Terra Preta de Indio’ or...
PRETIC - The new WRB diagnostic horizon for Amazonian Dark Earths
A new diagnostic horizon in WRB for anthropic topsoils in Amazonian Dark Earths (SouthAmerica)
Anjos, Lúcia Helena C. dos, UFRRJ;
Teixeira, Wenceslau .G., Embrapa Soils;
Schad, Peter, Technische Universitaet Muenchen;
Fontana, Ademir, Embrapa Soils
Introduction Characteristics ADEs Rationale Pretic Horizon Anthrosols
Why a new horizon for Amazonian Dark Earths?
The Amazonian Dark Earths (ADE), also called “Terra Preta de
Índio”, are classified according to WRB as Anthrosols (IUSS Working
Group WRB, 2006)
Different studies attribute to them the hortic, plaggic or terric horizon
according to base saturation, extractable P content, amount of artefacts,
animal activity, and other soil diagnostic criteria.
However they do not fit the central concept of any of them:
- deep cultivation, intensive fertilization and/or long-continued
application of human and animal wastes and other organic residues
(hortic horizon);
- addition of sods (topsoil layers together with vegetation) and animal
manure (plaggic horizon);
- addition of earthy manures, compost, beach sands or mud (terric
horizon).
Introduction Characteristics ADEs Rationale Pretic Horizon Anthrosols
Characteristics of the ADEs?
The ADEs are associated to pre-Columbian
Amerindian settlements and have been reported
mainly in the Amazon region.
They are variable in terms of depth of the
diagnostic horizon, physical and chemical properties,
but mostly have dark colors, high stocks of organic
carbon, extractable and total phosphorus, calcium,
magnesium, micronutrients (mainly zinc and
manganese) and other metals as strontium and
barium.
Contrasting with natural soils in the surrounding
area, the surface horizons influenced by human
activities have extraordinarily high CEC and nutrient
availability.
Artefacts TPI Rio Preto da Eva
TPI Rosa de Fogo Rio Preto da Eva - AM
Introduction Characteristics ADEs Rationale Pretic Horizon Anthrosols
Characteristics of the ADEs?
Artefacts of ceramic, stones and
bones and pieces of charcoal are
frequently found mixed into the soil.
Clear evidences of past human
occupation in the landscape
(constructions, gardens), shell mounds
(“sambaquis”), earthworks (geoglyphs)
are identifiable.
Sambaqui
fluvial Miracatu
Sambaqui –
Camacho 05_2007 154
Caldeirão, 2010 - P1050695
Introduction Characteristics ADEs Rationale Pretic Horizon Anthrosols
Rationale for a new Horizon!
Amazon Dark Earths Distribution (Teixeira, Wenceslau G.)
Introduction Characteristics ADEs Rationale Pretic Horizon Anthrosols
Rationale for a new Horizon!
The ADEs may not show the evidences of animal activity required for the
hortic horizons, and they were not influenced by manuring, as required for the
hortic horizons, since this activity was not part of the pre-Columbian Amerindian
culture.
Additionally, the surface anthropic horizons typical for the ADE show a high
base saturation (BS); the base cations were added from bones (Ca), ashes, and
many other organic materials (i.e. kitchen middens, palm leaves, human feces).
Horizons,
depth (cm)Color Corg
g/kg
Clay
g/kgCa+Mg
Base cations
cmolc/kgCEC
BS
%
P
mg/kg
A1 0-31 2.5Y 2.5/1 56.1 189 13.7 13.8 17.6 78 216
A2 31-43 2.5Y 3/1 22.5 203 5.5 5.5 9.2 60 66
AB 43-57 2.5Y 4/1 10.0 203 2.7 2.7 5.8 50 32
B2 130-190 2.5Y 7/6 1.9 320 1.2 1.2 2.3 52 15
Ferralsol, P18 (TB11-00), Humaita – Apuí, Amazon; 7º 51’ 29,6’’ S and 61º 17’ 52,8’’ WGr (Cunha, 2005)
Introduction Characteristics ADEs Rationale Pretic Horizon Anthrosols
Pretic Horizon (2014, update 2015)Pretic (from Portuguese preto, black)
General description
A pretic is a mineral surface horizon that results from human activities including the addition of charcoal. It
is characterized by its dark colour, the presence of artefacts (ceramic fragments, lithic instruments, bone
or shell tools etc.) and high contents of organic carbon, phosphorus, calcium, magnesium and
micronutrients (mainly zinc and manganese), usually contrasting with natural soils in the surrounding
area. It typically contains visible remnants of charcoal.
Pretic horizons are for example widespread in the Amazon Basin, where they are the result of pre-
Columbian activities and have persisted over many centuries despite the prevailing humid tropical
conditions and high organic matter mineralization rates.These soils with a pretic horizon are known as
‘Terra Preta de Indio’ or ‘Amazonian Dark Earths’. They generally have high organic carbon stocks. Many
of them are dominated by low-activity clays.
Diagnostic criteria:
A pretic horizon is a surface horizon consisting of mineral material and has:
1. a Munsell colour value of ≤ 4 and a chroma of ≤ 3, both moist; and
2. ≥ 1% organic carbon; and
3. a base saturation (by 1 M NH4OAc, pH 7) of ≥ 50%; and
4. exchangeable Ca plus Mg (by 1 M NH4OAc, pH 7) of ≥ 2 cmolc kg-1 fine earth; and
5. ≥ 30 mg kg-1of extractable P (Mehlich-1); and
Introduction Characteristics ADEs Rationale Pretic Horizon Anthrosols
Pretic Horizon (2014, update 2015)
Pretic (from Portuguese preto, black)
6. one or more of the following:
a. ≥ 1% artefacts (by volume, by weighted average); or
b. ≥ 1% charcoal (by volume, by weighted average); or
c. evidences of past human occupation in the surrounding landscape, e.g. constructions,
gardens, shell mounds (‘sambaquis’), or earthworks (geoglyphs); and
7. < 25% (by volume) of animal pores, coprolites or other traces of soil animal activity; and
8. one or more layers with a combined thickness of ≥ 20 cm.
Additional characteristics
Charcoal is an artefact only if it is intentionally manufactured by humans.
Relationships with some other diagnostics
Pretic horizons do not show the animal activity required for hortic and irragric horizons. The
diagnostic criteria for P concentrations in pretic and hortic horizons are based on different analytical
methods with a lower requirement for the pretic horizon.
The high base saturation sets the pretic horizon apart from plaggic horizons. It cannot be excluded
that a pretic horizon fulfils also the criteria of the plaggic horizon. In this case, the soil scientist
should use historical knowledge for making the final decision, whether the horizon is called plaggic
or pretic. Some pretic horizons may qualify as mollic or umbric horizons.
Introduction Characteristics ADEs Rationale Pretic Horizon Anthrosols
Anthrosols
Perfil Terra Preta Indio,
Lago do Limão, Ago 2004
Introduction Characteristics ADEs Rationale Pretic Horizon Anthrosols
Introduction Characteristics ADEs Rationale Pretic Horizon Anthrosols
Argissolo Amarelo Distrófico A antrópico,
Caldeirão, Iranduba, AM
Hor cm %C P mg kg-1 Ca1 Mg1 Zn2 Mn2
Au1 0-40 2.4 56 6.44 0.58 12 50
Au2 40-71 2.1 138 3.41 0.39 12 38
Au3 71-90 1.9 124 2.27 0.32 14 31
Bt2 165-200 0.2 84 1.95 0.29 6 8
1cmolc kg-1, 2 mg kg-1
Introduction Characteristics ADEs Rationale Pretic Horizon Anthrosols
Other classes
Perfil XI RCC Roraima, Rorainópolis
Lixic Pretic Xanthic Ferralsol
(Hypereutric, Amphiloamic, Vetic)
ARGISSOLO AMARELO Distrófico
antrópico plintossólico
Hor cm %C P mg kg-1 Ca* Mg*
Aup 0-14 1.07 47 3.8 0.6
Au1 14-41 0.79 36 3.6 0.5
Au2 41-63 0.53 25 1.8 0.5
*cmolc kg-1
Introduction Characteristics ADEs Rationale Pretic Horizon Anthrosols
What is the next step?
Database of soils identified as Amazonian Dark Earths (ADE), and their
classification;
To test properties and limits of diagnostic criteria (WRB, updated 2015);
Studies on different environments, beyond Amazon region; are this soils
limited to this area of Brazil?
How about other regions of the world? How widespread are the Dark
Earths?
IntroductionCharacteristics ADEs Rationale Pretic Horizon Anthrosols
Acknowledgement
Photos, courtesy from Wenceslau Geraldes
Teixeira <[email protected]> and
colleagues from different Institutions
Analytical data from: Cunha, T.J.F., 2005. Ácidos húmicos de solos
escuros da Amazônia (TPI). Thesis UFRRJ – CPGA-CS. 138p.