Keywords: TXRF; Spatial variation; Soil nutrients; Total element composition; Africa soil; Soil-forming factors; Acrisols; Lixisols; Plinthosols; Vertisols; Arenosols; Nitisols; Ferralsols; Leptosols; Fluvisols; Calcisols; Cambisols; Luvisols; Alisols; Gleysols;