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1.4.2 Deficit Irrigation
Deficit or minimum irrigation is the deliberate under-irrigation
of a crop. The technique is employed in areas where water is very limited.
In some cases, water is only applied at the critical stages of crop
growth. Applying minimum quantities of water at these critical stages
sustains the crop so that it continues to develop and to yield reasonable
quantities of produce - the alternative being no crop at all. For dryland
farming, the technology is practised in conjunction with water harvesting.
The harvested water being enough for "critical stage"
Extent of Use
The technology is employed by large-scale commercial farmers in Zimbabwe
and South Africa for growing winter wheat. It is successfully done using
sprinkler and drip irrigation systems.
Operation and Maintenance
The operation of this technology requires minimum skills once the
systems are installed. However, the installation of piping requires some
training, and the maintenance of pumps requires artisans.
Level of Involvement
Trials are being carried out in Zimbabwe to establish the applicability
of the technique for use in small rural irrigation schemes. It is usually
farmer-managed with external technical advice.
Experiments carried out in Mutoko, Zimbabwe, show that applying 86% of
the optimum irrigation water results in net returns of $100/ha. The
operational cost was $130/ha.
Effectiveness of the Technology
The method is effective in sustaining crops with very little water.
Reasonably high yields of winter crops have been recorded in Southern
Africa, under conditions where there was little irrigation water
This technology is suitable for use where water is limited (e.g., by
drought) and a reduction in volume of irrigation waters is necessary.
There are positive benefits to using this technique as it conserves
water and enables plants and crops to be grown under adverse conditions.
The technique saves on water. Because of the limited volumes of water
used, there is also a resultant saving on electricity and labour. Also, if
practised where the rains have failed, farmers will at least harvest
The crop yields will progressively reduce depending on the percentage
deficit applied. The yield will always be less than the optimum.
Further Development of the Technology
There is need for further research on how this technology could best be
combined with water harvesting techniques.
English, M. and Stoutjeskdyk 1994. Consideration of Deficit Irrigation
in the Communal Lands of Zimbabwe. In: R. Owen, K. Verbeek, J. Jackson and
T. Steenhuis (Editors), Dambo Farming In Zimbabwe: Water Management,
Cropping and Soil Potentials for Smallholder Farming in the Wetland.
Conference Proceedings. University of Zimbabwe, CIIFAD. 193 p.