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Wageningen Universiteit (1994)

Soil salinity and acidity : spatial variability and effects on rice production in West Africa’s mangrove zone

Sylla, M.

Titre : Soil salinity and acidity : spatial variability and effects on rice production in West Africa’s mangrove zone

Auteur : Sylla, M. 

Université de soutenance : Wageningen Universiteit

Grade : PhD thesis 1994

Résumé partiel
In the mangrove environment of West Africa, high spatial and temporal variability of soil constraints (salinity and acidity) to rice production is a problem for the transfer and adoption of new agronomic techniques, for land use planning, and for soil and water management. Recently, several National and International Agricultural Centers have initiated research programs to characterize environments where their newly developed technologies have to be applied. However, the mangrove agro- ecosystems in West Africa have not been characterized in a detailed way. Most of the soils in this environment are potential or actual saline acid sulfate soils. The spatial and temporal variability of soil salinity and acidity in these coastal lowlands results from complex interactions between climate, coastal morphology, river hydrology, vegetation, landform and tidal flooding. Diagnosing the occurrence of both potential and actual acid sulfate soils is the first step in land use planning for such areas. But to cope with the intricacies of these soils, understanding the processes of soil salinization and acidification at different scales should be formalized to properly characterize mangrove environments.

The main objectives of this thesis were : 1) to give a comprehensive characterization framework for the West African mangrove environments with emphasis on the possibilities of and constraints for rice cultivation ; 2) to determine the various causal factors for soil salinization and acidification ; 3) to test whether temporal variability of soil chemistry is sufficient to provide a time window of minimum stress during the rice growing period ; 4) to relate the response of rice to improved agronomic practices in specific environments and to provide a means to characterize specific rice growing locations, and 5) to test rice varietal responses to saline and acid sods under different agronomic practices and to relate yields and yield components to the nutrient contents in leaves, in order to diagnose physiological disorders.

First, a multi-scale approach was developed involving a range from Macro to Micro level based on the pre-conditions of acid sulfate soil formation. The main factors for classification are climate and coastal morphology at Macro scale ; hydrology, physiography and vegetation complexes at Meso level ; and topography (catena), vegetation species, tidal flooding and sedimentation rate at Micro level. Information from previous process-based studies on acid sulfate soil formation and data from secondary sources were used. Different environments were then distinguished and their characteristics were summarized by ecological zone. Constraints to rice production and potentials for agricultural development were matched with environmental conservation issues.

Mots clés : acid soils / acid sulfate soils / soil / sodium / improvement / salinization / rice / oryza sativa / land evaluation / land capability / soil suitability / west africa / geostatistics

Présentation et version intégrale

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