Meredith Albright Rande Kamolz Wade Grewe
Jan 03, 2016
Meredith AlbrightRande KamolzWade Grewe
Introduction
Climate, Biomes, and
African Soils
Great Crisis in Africa:
Desertification
Fire and soil
degradation
Characterized by soil moisture stress Over 86% of
Africa is moisture stressedPrecipitatio
nSoil type
IntroductionSoil Moisture
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 horizonRelatively higher fertility
Ultisols – 6.2%Argillic horizon, deep, well-
drained soilLow fertility
IntroductionPrimary Soil Types
Climates
Degradation of land and soil in arid, semi-arid, and dry sub-humid environments
CausesPoor land managementClimatic variationSalinization
Became mainstream during the Sahelian Drought that began in 1968Led to the deaths of more than 100,000 people
and millions of livestock by 1973
Areas of
Vulnerabilit
y
Human-Human-InducedInducedDesertificatiDesertificationon
Natural occurrence in savanna and grasslands
Create/maintain agricultural areas
Soil degradation concerns
Focus: South African soilFine, sandy loam
Dr. Michael D. King, NASA Earth observatory
www.kirkanddonna.com/rtw/pics/0713Savannah.jpg
1. Compaction• Mechanical impact of
raindrops break down aggregates
2. Clay dispersion• Fire-induced low-salt
environments
+ + + + + + + - - - - - - - - - - -
+ + + + + + +
High salt concentration
•Flocculation creates macro-pores
•High water infiltration
+ + + + + + - - - - - - - - -
+ + + + + +
_ _
__
_
clay
macro-pore
+ - + + - -
+ - + + + - + + + +
- - - - + -
+ + + - + + -
+ + -
Low salt concentration in soil solution
•Clay dispersion clogs pores
•Low infiltration
_
_
_
no macro-pores
Flocculation Clay dispersion
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 vegetationReduced long-term agricultural stabilityReduced 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