Download Soils of Africa - University of Colorado Boulder

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
_
+++++++
_
+
+
+
- + ++
-
- - + + +
-+
-
+ -
+
_
++
+
- + + -
_
+ +
-

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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
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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