PRODUCTIVITY OF IRRIGATION TECHNOLOGIES IN THE WHITE VOLTA SUB-BASIN - Sustainable Irrigation Development in the White Volta Sub-Basin - page 149

that manual abstraction technologies are more productive than motorised
abstraction (pumps). This is perhaps because manual application of water by
bucket is more precise and closer to the roots, which enhances crop
production.
6.4.2 Water productivity
Water productivity is a measure of performance generally defined as the
physical quantity or economic value generated from the use of a given
quantity of water (Molden et al., 2003). Increasing water productivity to
obtain higher output or value for each drop of water use is key to the
efficient use of water in the sub-basin and therefore a very important factor
in the comparative analysis of irrigation technologies. The productivity of
the various irrigation technologies in the sub-basin is an important variable
for decision on up-scaling irrigation technologies: the higher the productivity
of a technology, the more efficient the scarce water will be used.
Water productivity equals the crop yield divided by the volume of water
applied. The average water productivity can then be computed for each
technology (Figure 6.4a). This water productivity approach helps to compare
the water management weaknesses of the various technologies and gives an
idea of the improvement required to make the irrigation technology water
efficient.
Figure 6.4: a) Water productivity for tomatoes in 2008; b) Value of water
for tomato production in 2008.
Figure 6.4a shows that the temporal and permanent shallow wells (producing
60 kg of tomatoes per m 3 of water applied), and riverine alluvial dugouts (45
kg/m 3 ) are the most water productive technologies in the Upper East Region
of Ghana. However the same cannot be said of permanent shallow wells in
Southern Burkina Faso. Water productivity of permanent shallow wells and
small reservoirs in Southern Burkina Faso are about 50% and 30% of that in
the Upper East Region. The large reservoir irrigation scheme is the
technology with the lowest water productivity (9 kg/m 3 ). This confirms the