Meredith Albright Rande Kamolz Wade Grewe Introduction Climate, Biomes, and African Soils Great Crisis in Africa: Desertification Fire and soil degradation Introduction Soil Moisture Characterized by soil moisture stress Over 86% of Africa is moisture stressed Precipitation Soil type Introduction Primary Soil Types Aridisols - 26.4% 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 Soils Climates 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 Human-Induced Desertification Areas of Vulnerability Natural occurrence in savanna and grasslands Create/maintain agricultural areas Dr. Michael D. King, NASA Earth observatory Soil degradation concerns Focus: South African soil Fine, sandy loam www.kirkanddonna.com/rtw/pics/0713Savannah.jpg Compaction 1. • Mechanical impact of raindrops break down aggregates Clay dispersion 2. • Fire-induced low-salt environments Flocculation Clay dispersion High salt concentration Low salt concentration in soil solution •Flocculation creates macro-pores •Clay dispersion clogs pores •High water infiltration •Low infiltration macro-pore no macro-pores _ --------++++++ _ ++++++ __ ----------+++++++ clay _ +++++++ _ + + + - + ++ - - - + + + -+ - + - + _ ++ + - + + - _ + + - Decreased water infiltration Decreased organic matter Decreased aggregation Decreased water storage capacity 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 Decrease soil quality – natural vegetation Reduced long-term agricultural stability Reduced food security Solution – termites may control crust formation www.kirkanddonna.com/rtw/pics/0713Savannah.jpg images.jupiterimages.com/common/detail/72/51/22565172.jpg •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 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