Natural transformation of alkaline soils into sub-arid soils on a Sahelian valley bottom in Niger

alkaline soils bottomland soils calcita calcite estructura del suelo geochemistry geochimie niger pedogenese sahel soil genesis soil morphological features soil structure sol alcalin structure du sol suelo alcalino suelo de hondonada trait morphologique du sol tropical zones xerosol xerosoles xerosols zona tropical zone tropicale