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Modelling of bulk density as related to aggregate size distribution in clayey Ferralsols

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Submitted on 14 Jun 2006

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Modelling of bulk density as related to aggregate size

distribution in clayey Ferralsols

Nathalie Volland-Tuduri, Ary Bruand, Michel Brossard, Luíz Carlos Balbino,

Maria Inês Lopes de Oliveira, Éder de Souza Martins

To cite this version:

Nathalie Volland-Tuduri, Ary Bruand, Michel Brossard, Luíz Carlos Balbino, Maria Inês Lopes de Oliveira, et al.. Modelling of bulk density as related to aggregate size distribution in clayey Ferralsols. Eurosoil, 2004, Freiburg, Germany. �hal-00079880�

(2)

Modelling of bulk density as related to aggregate size distribution in clayey

Ferralsols

Nathalie Volland-Tuduri

(1)

, Ary Bruand

(1)

, Michel Brossard

(2)

, Luíz Carlos

Balbino

(3)

, Maria Inês Lopes de Oliveira

(4)

, Éder de Souza Martins

(4)

.

1

ISTO, Institut des Sciences de la Terre d'Orléans (ISTO), Université d'Orléans, Géosciences, BP 6759, 45067 Orléans Cedex 2, France, Nathalie.Volland@univ-orleans.fr; Ary.Bruand@univ-orleans.fr.

2

IRD, BP 64501, 34394 Montpellier Cedex 5, France, brossard@ird.mpl.fr.

3

EMBRAPA Arroz e Feijão, CP 179, 75375-000, Santo Antônio de Goiás-GO, Brazil, balbino@cnpaf.embrapa.br.

4

EMBRAPA Cerrados, CP 08223, 73301-970 Planaltina-DF, Brazil, eder@cpac.embrapa.br.

Among microaggregated soils, there are Ferralsols that show little or no distinct horizonation. Their macrostructure is weak to moderate and they have typically a strong microstructure. In most Brazilian clayey Ferralsols, physical properties are closely related to the development of microstructure that consists of subrounded microaggregates 50 to 500 µm in diameter. They correspond to the pseudosand, micropeds, granules which were described earlier. Our objective was to show that in these soils bulk density (Db) can be modelled according to

microaggregation development and clay content.. The soils studied are located in the Central Plateau in Brazil. We measured the bulk density, aggregate size distribution, particle size distribution, and main chemical properties from the surface down to 160 cm depth in two soils under native vegetation and three others under pasture. Backscattered electron scanning images (BESI) of microaggregation were recorded using polished thin sections. BESI showed that microaggregates were either in loose assemblage or close assemblage. Aggregates size distribution enabled the measurement of the proportion of microaggregates in loose (ΦL) and

close assemblage (ΦC) in every soil with respect to depth. Our results also showed that a

linear relationship between the reciprocal of Db and ΦL or ΦC can be established. Finally, in

order to avoid Db variation because of texture variation alone, a linear positive relationship

between Db and ΦL that takes clay content into account is proposed. The latter enables the

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