ABSTRACT
Grain yields have been noted to oscillate below 1 t ha-1 in many sub-Saharan
smallholder rainfed farming systems (Bhatt et al., 2006; Rockström et al., 2007;
Rockström et al., 2004), yet there is potential to double or even quadruple current
yields (Rockström et al., 2007) if soil moisture retention can be enhanced as a
mitigation strategy against the impacts of dry spells. A common measure of the
efficiency of farming systems is the obtained yield per season. For the common
farmer, this can simply mean the number of grain bags obtained at the end of the
season. If more harvests are required, the solution would be to simply increase the
land under cultivation. This approach is more applicable where land and water
resources are not limited. However, under the existing challenges of water scarcity in
the sub-Saharan region water productivity would be a more appropriate measure of
the efficient utilisation of cropping systems. Water productivity (WP) measures the
biomass produced from a unit of water or, inversely, WP is a measure of the amount
of water required to produce a given amount of biomass. Where WP values are
extremely low, it may be more efficient to import rather than to cultivate crops in
areas where the opportunity costs of using water for other purposes are very high
(Dabrowski et al., 2009).
