ENVIRONMENTAL AND ECONOMIC IMPACTS OF SOIL EROSION
AND FERTILITY MINING IN NORTHERN TANZANIA
Ephraim Nkonya, Andrew Barkley, Steve Hamilton, and Daniel Bernardo
Research Assistant, Professor, Assistant Professor, and Professor
Department of Agricultural Economics, Kansas State University
342 Waters Hall, Manhattan Kansas 66506-4011
Telephone: 785-532-6702, Fax: 785-532-6925
Contact author: Ephraim Nkonya, e-mail nkonya@ksu.edu
Selected Paper, American Agricultural Economics Association Annual Meetings
Nashville, Tennessee, August 8 – 11, 1999
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ENVIRONMENTAL AND ECONOMIC IMPACTS OF SOIL EROSION AND
FERTILITY MINING IN NORTHERN TANZANIA
Introduction
Soil erosion, and soil fertility mining, the practice of growing crops with insufficient
replacement of nutrients taken up by the crops, are among the major factors causing agricultural
production stagnation in Sub-Saharan Africa (SSA). The incidence of soil erosion and
degradation in SSA is higher than in any other part of the world (Lal; Cleaver and Donovan).
The major factor contributing to soil degradation has been rapid population growth that has
undermined the traditionally sustainable practices of shifting cultivation and transhumant
pastoralism. The pressure on land has led to shorter fallows, cultivation on fragile land and
overgrazing, which in turn have all accelerated soil erosion. It is estimated that soil erosion
affects 65% of cropland in SSA (Dejene, et al.).
Many soils in SSA are inherently of low fertility because the continent is dominated by a
geologically old and deeply weathered landscape, making African soils some of the poorest in
the world. Chemical fertilizer use has not proved to be a practical solution to the low fertility
problem, due in part to poor infrastructure and inefficient input and agricultural product
marketing systems, which have resulted in high fertilizer prices that are unaffordable to the
resource-poor farmers (Bumb and Baanante). Additionally, the traditional crop varieties used by
a majority of farmers in SSA have a lo