1. Soils of Africa Meredith Albright Rande Kamolz Wade Grewe
Africa is a continent of diverse soil types. It straddles the equator with terrain ranging from semiarid shrublands near the Mediterranean, broad deserts, vast grasslands and savannas, and deep rainforest jungles.
Meredith Albright
Rande Kamolz
Wade Grewe

2. Introduction Climate, Biomes, and African Soils
Great Crisis in Africa: Desertification
Fire and soil degradation
Map courtesy:

3. Introduction Soil Moisture
Characterized by soil moisture stress
Over 86% of Africa is moisture stressed
Precipitation
Soil type
The amount of soil moisture present plays a great role in African soil formation. Over 86% of the land in Africa is characterized by some degree of soil moisture stress. The main factors deciding soil moisture are the amount of precipitation and the soil type’s ability to absorb and retain moisture.
- University of Minnesota, Unit 10 – Soils of Africa. -

4. Introduction Primary Soil Types Aridisols - 26.4% Entisols – 24.5%
Sahara and Kalahari deserts
Entisols – 24.5%
Lightly weathered – dry areas
Oxisols – 14.3%
Sombic horizon (OM accumulation) in Rwanda and Burundi
Alfisols – 10.5%
Argillic horizon
Relatively higher fertility
Ultisols – 6.2%
Argillic horizon, deep, well- drained soil
Low fertility
There are 5 major soil types in Africa. The great African deserts of the Sahara and Kalahari are composed of primarily Aridisols and Entisols and make up over 50% of the continent’s landmass.
20% of the landmass is Oxisols and Ultisols in the tropical and equitorial jungles with Alfisols making up the majority of soil in the vast savanna grasslands.
- Map courtesy:
- University of Minnesota, Unit 10 – Soils of Africa.

5. Climate and Soil Relationship
Soils
Climates
Africa lacks major mountain ranges and other large moderating features which results in latitude north and south of the equator and ocean currents being the main factors in deciding climate. There is a general trend of climates and soils being mirrored across the equator but there are several interesting exceptions. One example of anomaly are the vertisols of Sudan, Ethiopia, and Chad. This soil is made up of montmorillonite clay caused by the volcanic activity of the nearby Rift Valley. Another exception are the climates of southern Africa. - - -

6. Currents
Climates
Warm currents in the ocean off the eastern coast bring moist air inland to encounter the escarpment of the Drakensburg Mountains and cause a borderline subtropical marine climate. The soils in this area (as illustrated by the earlier soil moisture map) are udic (they get a decent amount of rain). This contrasts with the aridisols of the Kalahari desert on the western shore caused by the cold Benguela current that does not give up much moisture to the coastline. The cold Canary current of the North Atlantic plays a similar role in the formation of the vast northern deserts. -

7. Desertification of Soil
Degradation of land and soil in arid, semi-arid, and dry sub-humid environments
Causes
Poor land management
Climatic variation
Salinization
Became mainstream during the Sahelian Drought that began in 1968
Led to the deaths of more than 100,000 people and millions of livestock by 1973
There are natural causes such as climatic variation, drought but I’m going to focus on the anthropogenic influences. Overgrazing is the most harmful, as well as poor crop rotation, slash and burn clearing-deforestation.

8. Human-Induced Desertification
Areas of Vulnerability
Veg. degradation leads to soil being exposed to erosion, loss of humus and nutrients, further loss of plant cover, severe loss of soil, lost depth and water storage capacity. -

9. Fire-induced soil changes
Natural occurrence in savanna and grasslands
Create/maintain agricultural areas
Soil degradation concerns
Focus: South African soil
Fine, sandy loam
Dr. Michael D. King, NASA Earth observatory
(King, 2007; Mills and Fey 2004a,b; Mando et al. 1996)

10. Crust Formation Compaction Clay dispersion
Mechanical impact of raindrops break down aggregates
Clay dispersion
Fire-induced low-salt environments
(Mills and Fey, 2004a; Mills and Fey, 2004b; Snyman, 2003)

11. Flocculation Clay dispersion
High salt concentration
Flocculation creates macro-pores
High water infiltration
Low salt concentration in soil solution
Clay dispersion clogs pores
Low infiltration
macro-pore
no macro-pores _
(Mills and Fey 2004a)
(Brady and Weil, 2008) _ _ _
clay _ _ _ _

12. Soil Consequences Decreased water infiltration
Decreased organic matter
Decreased aggregation
Decreased water storage capacity
(Mills and Fey, 2004a) (Mills and Fey, 2004b) (Francis et al. 2007) (Valentin et al, 2004)

13. Environmental and Social Consequences
Decrease soil quality – natural vegetation
Reduced long-term agricultural stability
Reduced food security
Solution – termites may control crust formation
(Mando et al. 1996)
images.jupiterimages.com/common/detail/72/51/ jpg

14. Summary Where and Why Broad spectrum of soil types Biomes Weathering
Desertification is a rapidly growing concern due to intensive land use and increasing demand for crop production.
Unnaturally frequent fires degrade soil
Decrease agricultural stability
Reduce food security
The growing population in Africa is leading to increased demand for agriculture which is leading to land clearing with fires…This is causing widespread concerns about soil fertility and food security due to soil crusting.

15. References
Brady, N.C., R. Weil, The Nature and Properties of Soils, Fourteenth edition. Pearson Prentice Hall, Columbus, Ohio, pp
King, Michael, Nasa Earth Observatory -
Mando, A., L. Stroosnijder, L. Brussaard, Effects of termites on infiltration into crusted soil. Geoderma 74:
Mills, A.J., M.V. Fey, 2004a. Frequent fires intensify soil crusting: physiochemical feedback in the pedoderm of long-term burn experiments in South Africa. Geoderma 121:
Mills, A., M. Fey, 2004b. Transformation of thicket to savanna reduces soil quality in the Eastern Cape, South Africa. Plant and Soil 265:
Snyman, H.A., Short-term response of rangeland following an unplanned fire in terms of soil characteristics ina semi-arid climate of South Africa. Journal of Arid Environments 55:
Valentin, C., J.L. Rajot, D. Mitja, Responses of soil crusting, runoff and erosion to fallowing in the sub-humid and semi-arid regions of West Africa. Agriculture, Ecosystems and Environment 104:
University of Minnesota, Unit 10 – Soils of Africa.