Sulfur distribution in five Ethiopian Rift Valley soils under humid and semi-arid climate

The Rift Valley has diverse soil types with different fertility potential. The climate of the Rift Valley is also diverse. Five major soil types that lie in the humid, sub-humid, and semi-arid parts of the Rift Valley were studied. Total sulfur (S) in the subsoil of the Solonetz and Andosol approximates total S contents of similar soils in other parts of the world. Organic matter is the major source of total sulfur for the soils in the humid parts (Nitisol, Andosol and Vertisol), whereas gypsum is the major source for the soils in the drier parts (Fluvisol and Solonetz). The Nitisol has the lowest soluble sulfate, which is below the critical level for crop production. All other soils contain soluble sulfate which is adequate for crop production. Land degradation, crop residue removal, clearing and burning of forests and other vegetation, crop uptake, and use of non-S fertilizers are major causes of sulfur deficiency in the Rift Valley. Maintenance of the soil organic matter, utilization of subsurface inorganic S and proper management of soils should maintain the S status of the soils in the future.