ABSTRACT
Semi arid zones are generally characterised by rainfall amounts not exceeding 500
mm a-1 or whose potential annual evaporation easily exceeds the annual precipitation.
Communities in the arid and semi-arid zones of the world are faced with food deficits
almost on an annual basis due to crop failure. This has seen millions of people
surviving on food relief measures to avert starvation disasters. Food relief measures
create a huge burden on governments and relief organisations. In arid and semi-arid
regions, crop failure is closely related to a strong imbalance between effective rainfall
and high potential evaporation (Hatibu et al., 2006). The resultant sub-optimal yields
obtained fall way below the annual food requirements for the ever-increasing world
population. The situation has been exacerbated by the general environmental
degradation where soil and nutrient loss continue without strict control.
