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. http://commons.wikimedia.org/wiki/Image:Africa_satellite_orthographic.jpg Meredith Albright Rande Kamolz Wade Grewe

Introduction Climate, Biomes, and African Soils Great Crisis in Africa: Desertification Fire and soil degradation Map courtesy: http://soils.usda.gov/use/worldsoils/mapindex/order.html

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, 2004. Unit 10 – Soils of Africa. http://www.soils.umn.edu/academics/classes/soil4505/doc/unit10af.htm - http://soils.usda.gov/use/worldsoils/mapindex/smr.html

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: http://soils.usda.gov/use/worldsoils/mapindex/order.html - University of Minnesota, 2004. Unit 10 – Soils of Africa. http://www.soils.umn.edu/academics/classes/soil4505/doc/unit10af.htm

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. - http://soils.usda.gov/use/worldsoils/mapindex/order.html - http://www.worldbook.com/wb/Students?content_spotlight/climates/african_climate - http://www.africanculturalcenter.org/2_2climates.html

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. - http://www.physicalgeography.net/fundamentals/8q_1.html

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.

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. - http://soils.usda.gov/use/worldsoils/mapindex/dsrtrisk.html

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) www.kirkanddonna.com/rtw/pics/0713Savannah.jpg

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)

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 + + + + + + + + + + + + + _ _ _ _

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) http://www.geography.learnontheinternet.co.uk/images/ecosystems/savanna.jpg http://www.ciat.cgiar.org/africa/images/f_afnet3.jpg http://www.nigeldennis.com/stock/images/landscapes/sa/kalahari/65000.jpg

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) www.kirkanddonna.com/rtw/pics/0713Savannah.jpg images.jupiterimages.com/common/detail/72/51/22565172.jpg

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.

References Brady, N.C., R. Weil, 2008. The Nature and Properties of Soils, Fourteenth edition. Pearson Prentice Hall, Columbus, Ohio, pp 420-423. King, Michael, 2007. Nasa Earth Observatory - http://earthobservatory.nasa.gov/ Mando, A., L. Stroosnijder, L. Brussaard, 1996. Effects of termites on infiltration into crusted soil. Geoderma 74: 107-113 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: 45-64. Mills, A., M. Fey, 2004b. Transformation of thicket to savanna reduces soil quality in the Eastern Cape, South Africa. Plant and Soil 265: 153-163. Snyman, H.A., 2003. 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: 160-180. Valentin, C., J.L. Rajot, D. Mitja, 2004. 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: 287-302. University of Minnesota, 2004. Unit 10 – Soils of Africa. http://www.soils.umn.edu/academics/classes/soil4505/doc/unit10af.htm