Meredith Albright Rande Kamolz Wade Grewe. Introduction Climate, Biomes, and African Soils Great Crisis in Africa: Desertification Fire and soil degradation.

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