The alkali soils of the middle Niger Valley Origins, formation and present evolution

Laurent Barbiero (1) , Brigitte van Vliet-Lanoë (2, 3)

1 LMTG - Laboratoire des Mécanismes et Transfert en Géologie
2 PBDS - Processus et bilan des domaines sédimentaires
3 LDO - Domaines Océaniques

In Niger Republic, the regional development of irrigation along the river Niger is confronted with an large extension of alkali soils. The study of one of these areas, on the Liptako bedrock, reveals a concentric soil distribution: in a zone of brown soil with abrupt textural change and alkaline in depth (stagnic Solonetz), appears a ring of brown steppe soils (cambic Calcisol), and zones of alkali soils (Solonetz). These alkali soils are not saline but their soil solution is more concentrated than in brown steppe soils. The study of the abrupt contact between brown steppe soils and alkali soils shows morphological and geochemical changes, due to calcite and fluorite precipitation. The detailed study of this contact demonstrates a present transformation of alkali soils into brown steppe soils. Therefore, it appears that soil alkalization is no longer in process on the terraces of the river Niger. The formation of brown steppe soils and alkali soils may be explained by the existence of a former pond. This hypothesis is supported by aerial pictures and microscopic observations. It is also consistent with a recent study of the hydrology of sahelian ponds and with considerations on the chemical quality of the runoff.

Mots clés: non-saline alkali soils; sodic soils; soil genesis; de-alkalization; Sahel; Niger

Domaines: Sciences de la Terre

Laurent Barbiero, Brigitte van Vliet-Lanoë. The alkali soils of the middle Niger Valley Origins, formation and present evolution. Geoderma, 1997, 84, pp.323-343. ⟨hal-00364728⟩