Aspects de la pédogenèse des sols halomorphes de la basse Rusizi (Burundi) / Raymond P. Frankart ; Adrien J. Herbillon

Public ISBD Titre : Aspects de la pédogenèse des sols halomorphes de la basse Rusizi (Burundi) : présence et genèse de l'analcime Type de document : texte imprimé Auteurs : Raymond P. Frankart, Auteur ; Adrien J. Herbillon, Auteur Editeur : Bruxelles [Belgique] : Institut national pour l'Étude agronomique au Congo (INEAC) Année de publication : 1971 Collection : Publications Sous-collection : Scientifique num. 71 Importance : xiii, 125 p. Présentation : ill. Format : 27 cm Langues : Français (fre) Catégories : Burundi -- Sols -- Pédogenèse ; Ruzizi, plaine de la (Sud-Kivu, Congo, République démocratique) -- Sols -- Pédogenèse ; Sediments (Géologie) -- Burundi ; Sols -- Burundi Index. décimale : 631 Techniques spécifiques, équipement Résumé : Typical soils of the Rusizi plain (Tanganyika graben, Burundi) are described in relation to ecoclimatic conditions of formation. The solonetz-vertisol sequence has been recognized on the old lacustrine alluvium level while the solonchak-solonetz-vertisol association is characteristic for the recent river deposits level. It is shown that the distribution and genesis of these different soils are governed by topographic and pedoclimatic factors (more especially the possibilities of external drainage as well as the level and the quality of the ground waters). Generally speaking, the older soils located on the lacustrine alluvium are poorly salted (conductivity less than 2 mmhos/cm) and are saturated with Mg2+ for 30-40 % of their cation exchange capacity. On the other hand, the recent alluvial soils, often very salted (conductivity up to 20 mmhos/cm), are saturated with Na+. By way of an experimental leaching (dialysis), it is shown that the presence of a high amount of Mg2+ on the exchangeable sites of soils previously salted is an intermediate stage in the evolution of these soils. In this case, the magnesium is due to the dissolution of poorly soluble magnesium salts (carbonates and perhaps silicates) and is not related to the destruction of the clay minerals. All the Rusizi soils show the same general trend as far as the evolution of their clay mineralogy is concerned: the montmorillonites, present in the parent material, progressively disappear in the upper part of the profile. In the alkaline sodic soils located on recent and present river deposits, the montmorillonite is replaced by analcite and the conditions of formation of this zeolitic mineral are discussed. When analcite is present, the general rules of solubility and cation exchange do not apply any more so that an important amount of sodium can be very firmly retained by the soil material. The presence of "zeolitic sodium" has also been suspected in the natric horizon of older solonetzic soils located on the lacustrine alluvia but analcite has never been detected in this case Aspects de la pédogenèse des sols halomorphes de la basse Rusizi (Burundi) : présence et genèse de l'analcime [texte imprimé] / Raymond P. Frankart, Auteur ; Adrien J. Herbillon, Auteur . - Bruxelles (Belgique) : Institut national pour l'Étude agronomique au Congo (INEAC), 1971 . - xiii, 125 p. : ill. ; 27 cm. - (Publications. Scientifique; 71) . Langues : Français (fre) Catégories : Burundi -- Sols -- Pédogenèse ; Ruzizi, plaine de la (Sud-Kivu, Congo, République démocratique) -- Sols -- Pédogenèse ; Sediments (Géologie) -- Burundi ; Sols -- Burundi Index. décimale : 631 Techniques spécifiques, équipement Résumé : Typical soils of the Rusizi plain (Tanganyika graben, Burundi) are described in relation to ecoclimatic conditions of formation. The solonetz-vertisol sequence has been recognized on the old lacustrine alluvium level while the solonchak-solonetz-vertisol association is characteristic for the recent river deposits level. It is shown that the distribution and genesis of these different soils are governed by topographic and pedoclimatic factors (more especially the possibilities of external drainage as well as the level and the quality of the ground waters). Generally speaking, the older soils located on the lacustrine alluvium are poorly salted (conductivity less than 2 mmhos/cm) and are saturated with Mg2+ for 30-40 % of their cation exchange capacity. On the other hand, the recent alluvial soils, often very salted (conductivity up to 20 mmhos/cm), are saturated with Na+. By way of an experimental leaching (dialysis), it is shown that the presence of a high amount of Mg2+ on the exchangeable sites of soils previously salted is an intermediate stage in the evolution of these soils. In this case, the magnesium is due to the dissolution of poorly soluble magnesium salts (carbonates and perhaps silicates) and is not related to the destruction of the clay minerals. All the Rusizi soils show the same general trend as far as the evolution of their clay mineralogy is concerned: the montmorillonites, present in the parent material, progressively disappear in the upper part of the profile. In the alkaline sodic soils located on recent and present river deposits, the montmorillonite is replaced by analcite and the conditions of formation of this zeolitic mineral are discussed. When analcite is present, the general rules of solubility and cation exchange do not apply any more so that an important amount of sodium can be very firmly retained by the soil material. The presence of "zeolitic sodium" has also been suspected in the natric horizon of older solonetzic soils located on the lacustrine alluvia but analcite has never been detected in this case

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