Soils of Africa are less fertile compared to those in the rest of the world, according to a paper presented by Columbia University during the African Fertilizer Summit. This is because the terrain of Africa is very old and has experienced no volcanic rejuvenation. Other factors like weathering, erosion and leaching also contribute towards this. The soils are not rich in nutrients, making almost 55 percent of the total land of Africa unsuitable for cultivation, according to the paper. The soils in Africa are classified based on their age, parent material, physiography and climatic conditions.
Ferralsol is mostly found in major portions of central Africa, Liberia, Sierra Leone and eastern parts of Madagascar. Ferrasols are deeply weathered, graveled and acidic in nature and also have low nutrient supplying and retention capabilities. They are well drained, have a good structure and a deep profile. Cash crops like coffee, rubber, cocoa, coconut, oil palm and plantain are grown in newly cleared land, but after two or three crops, nutrients in the soil are depleted, forcing the farmers to move towards freshly cleared lands.
Acrisols are present in the southern part of sub-humid zone of West Africa, southern Guinea, most parts of Cote d’Ivoire, southern Ghana, Togo, Benin, Nigeria and central Cameroon. They have high water holding capacity, but less biological activity and inhibit root penetration. They are less weathered, have low mineral reserves and have leaching problems. Lime and organic matter should be added to get a good yield for longer periods.
Nitosols are present in limited areas like Ethiopia, Kenya, Tanzania, east DRC and in the Rift Valley Zone. Nitosols have clay-rich sub soil, good soil structure and high fertility level. The clay retains the nutrients in the soil making it fertile. They have high water holding capacity and deep root penetration.
Lixisols occur in a belt in West Africa, southeast Africa and Madagascar. They have high clay content reducing its nutrition holding capacity. Lixisols have a medium to high pH and they lose fertility due to continual agricultural use. Their physical characteristics are however better than acrisols.
Arenosols are found in regions of West Africa that includes - northern Senegal, Mauritania, central Mali, southern Niger, Chad and eastern Sudan. Arenosols are also found in patches in Botswana, Angola, southwest DRC and North African countries. Quartz is the main composition of this type of soil, and they have a low nutrient content and retaining capacity and water retention capacity. Arenosols are affected by leaching and have a weak structure, making them less productive.
Vertisols are found in the semi-arid and sub-humid zones of Sudan, Ethiopia and in Tanzania. This particular type of soil contains clay that swells and shrinks depending on the water content. During the rainy season, it swells causing flooding, and during the dry season it shrinks causing deep cracks. Tilling is difficult because it is sticky when wet and hard when dry. Nitrogen is lost heavily during floods.