In evaluating technology development in Sub-Saharav Africa, the constraint of seasonallabour availability has frequently been emphasised. However, the most pressing constraint for most regions is the availability of quality land. To respond to this constraint in semi-arid regions, we need to focus on the combination of water availability and soil fertility. After discussing the high-potential/low-potential issue, two critical research problems are examined: 1. The effect of structural adjustment on agricultural intensification. With a lag higher purchased input use became more profitable than prior to devaluation in a field study in the Sahel. 2. The potential effects of the introduction of improved water retention techniques in semi-arid regions. Important differences in techniques depend upon soil characteristics and the degree of mechanisation. The water retention then makes the higher use of inorganic fertiliser more profitable and less risky.