Geochemical characteristics of soils in Fezzan, Sahara desert : implications for environment and agriculture

An investigation was conducted to geochemically characterize the soils in Fezzan of the Sahara desert in order toassess (a) the role of the soils as a carbon store, (b) the potential risk of the fine-grained soil fraction as a dustsource, and (c) the potential soil constraints for the development of irrigation agriculture. The results showthat, on average, there was about 0.7% of carbon stored in the topsoil with approximately 1/3 being inorganiccarbon and 2/3 being organic carbon. The fine-grained soil fraction contained 2.13% of Fe and 252 mg/kg of phosphorus,indicating that the Fezzan area could be an important source of ocean iron and phosphorus. Manganeseand strontium were identified as the major chemical pollutants potentially present in the dusts. The soils weregenerally alkaline and saline. Sodium dominated the soluble basic cations with a mean sodium adsorptionratio N16. Calcium dominated the exchangeable basic cations with a mean exchangeable sodium percentage of6.52, suggesting thatmost of the topsoils were not sodic. However, there was a tendency that sodicity increasedwith depth for some soils. Different strategies are proposed for reclaiming the soils using the groundwater fromthe Great Man-made River Project