INTEGRATED SOIL
FERTILITY
IMPROVEMENT IN SEMI ARID AREAS
Introduction
Moisture stress affects over two thirds of all soils in semi arid areas while soil fertility
degradation has been described as the second most important constraint to food security in
Africa. Despite proposals for a diversity of solutions and the investment of time and resources
by a wide range of institutions it continues to prove a substantially intransigent problem.
Inadequate management has exacerbated these problems to an alarming extent. The
population is thus trapped in a vicious poverty cycle between land degradation, and the lack of
resources or knowledge to generate adequate income and opportunities to overcome the
degradation.
Why soil fertility improvement?
The rural poor cannot expand land holdings because the frontier is limited and the
availability of arable land has shrunk dramatically per capita over the past 20 years.
Compared to other areas, a large proportion of soils in semi arid areas has low inherent
fertility and exhibits a variety of constraints, among them: nutrient deficiency, low organic
matter, moisture stress, and high erodibility.
Nutrients are commonly not replaced to the degree that they are removed in crop
harvesting and other losses, resulting in high negative nutrient balances e.g. net loss of
over 100 kg per hectare per year in south west of Zimbabwe.
Millions of hectares of land are physically degraded each year, due principally to water and
wind erosion. These processes have led to the semi arid areas being characterised by
declining per capita food production.
How do farmers lose nutrients
The causes of soil infertility include shortage of manure, tillage practices, continuously
cropping the same land, limited crop rotation, indiscriminate cutting of trees, burning of crop
residues and bush fires.
Picture 1: A field in a semi-arid area of Gwanda, Zimbabwe. Picture by Douglas Gumbo: Practical
Action
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