38 Soil and its Impact on Culture: A Case Study in the Sudanese Sahel.
38 Soil and its Impact on Culture: A Case Study in the Sudanese Sahel.
Soil and its Impact on Culture: A Case Study in the Sudanese Sahel.
Soil is the basis of human survival and adaptations to it occur in a multitude of ways. Soils are created by nature through the processes of the breakup of rocks, climate, living organisms and time. This is referred to as “weathering.” When these different processes combine, a multitude of soil types are produced. Humans have learned to survive, using their soils for food production, building materials, medicine, and art.
Major soil types of Sudan, Sudanese Soil Information (SUSIS) 2016 Free map from Sudanese Land and Water Research Center. Vertisols are represented by color red designated as Vertic Haplocambids.
The focus of this treatise is to examine the relationship the people of the Sudanese Sahel have with their difficult to manage vertisol. This soil shrinks and cracks when dry, when wet it expands and bulges. It does not hold much water and once wet, seals the ground to any downward percolation of water.
Vertisol, a soil order described in the (7th Approximation of Soils 1960) that occupies 16% of the area of Sudan, is better known as black cracking clay, occurring in many countries and is known by local names such as “black earth” in Australia,” black gumbo” in East Texas, “vioi soil” in South Africa, and bentonite clay in the USA. In the Great Soil Groups classification, it is known as montmorillonite. In Sudan, they are known as “black cotton clays”. Chemically it is made up of hydrated aluminum silicate. Science taxonomy divides the vertisols into sub-categories depending on the size of the cracks that occur and the length of time between shrinking and swelling periods. The Sudanese vertisols are labeled “usterts.”
Climatically, vertisol occur where there are pronounced wet and dry seasons. In the Sudanese Sahel, the dry season lasts August to April when the water evaporates and the soil shrinks, leaving cracks up to a half inch wide.
My keys provide a sense of crack size of a vertisol sample. Photo by Rick Bein 1977
When the rains come, the soil swells and tries to close up again, but the cracks are now already full of debris and instead, the swelling process expands upward leaving chunks of soil protruding over the flat landscape. The dead plant material trapped inside decomposes, and over centuries of time, darkens the soil.
A stabilized sand dune is perched on top the dry-season black cotton clay plain. Clumps of soil (gilgai) protrude over the clay plain and a primitive road has compacted the slightly dampened clay. Surface water on the clay evaporates quickly while the dune holds enough water to sustain the sparse vegetation
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Once the wet vertisol closes its cracks there is no more downward seepage and water is trapped on the surface.
After each rainstorm, this volatile landscape becomes a quagmire, and any travel is hampered by slippery mud clinging to feet and motor vehicle tires. Dirt roa