The extent and distribution of salt-affected soils in Sub-Saharan Africa from 1970 to the present: A review of the current state of knowledge

Finias Mwesige ^*

• Mwalimu Julius K. Nyerere University of Agriculture and Technology, Mara, Tanzania

Salt-affected soils are a global issue, affecting 1 billion hectares worldwide, including 80 million hectares in Africa. In Sub-Saharan Africa (SSA), these soils originate from marine, geological, and hydrogeological sources, as well as human activities and arid climatic conditions-induced salinization. This systematic review, conducted using the PRISMA framework, provides an in-depth analysis of salt-affected soils in SSA from 1970 to the present. It highlights historical trends and emerging patterns of salinization in the region. The review estimates that 65.6 million hectares of land in SSA are salt-affected, with key hotspots in coastal zones, river deltas like the Nile Delta, and arid and semi-arid areas with intensive irrigation. Generally, the coastal areas of Eastern Africa, Southwest Africa, and the West African and inland areas of the Nile Delta and Lake Chad Basin are the most vulnerable. Ethiopia is the most affected country, with 11 million hectares impacted, primarily due to poor irrigation and drainage infrastructure. The study also highlights research gaps, revealing that coastal countries such as Senegal, Tanzania, and Kenya are better studied than inland areas like Chad and Mali. The review identifies that available estimates of salt-affected soils heavily rely on the FAO report of 1988, based on Solonchaks (saline soils) and Solonetz (sodic soils). This report was produced from the FAO Soil Map of the World at a scale of 1:5,000,000, which was created between 1970 and 1981. Due to its coarse resolution, high generalization, and environmental changes that have occurred over the decades, it may be considered outdated, stressing the need for updated assessments using modern techniques. The creation of digital fine-scale maps by integrating field and laboratory data, soil databases like WoSIS and HWSD, and remote sensing is suggested. To mitigate salt-affected soils in SSA, improving irrigation, using brackish water, salt-tolerant crops, gypsum, organic amendments, drainage systems, and phytoremediation with halophytes are recommended. Generally, the review stresses the need for updated research, modern technologies, and sustainable land management practices to combat salt-affected soils, with projections suggesting these efforts could double agricultural yields in affected areas, improving food security and economic resilience.