The major thrust of this publication is to promote greater awareness of the concepts and practices that underlie the efficient use of water. The aim is to apply these principles towards improving small-scale farming and ultimately food security in Africa. Just how to apply these principles in various locations depends on site-specific condi-tions affecting the economics of land, water, labour, machinery, energy and the choice of crops to be grown. It also depends on social factors and on long-term environ-mental effects. No simple universal prescription or panacea can be offered on how to design and implement irrigation systems to provide high efficiency, social benefits and resource conservation all at once. None of the available technologies guarantees success everywhere: each can be used with greater or lesser efficiency, and each may fail if poorly managed.
If efficiency of land and water use is to be more than just an abstract
concept, it must become the explicit goal of institutional or governmental sponsors as
well as of workers in the field. Irrigation systems should be tailored from the outset to
provide the owner-operators with motivation, knowledge, responsibility, opportunity to
improvise and access to credit.
Irrigation units in developing countries are highly variable in scale and organization,
and they will undoubtedly continue to be so. On the one hand are huge government-sponsored
or commercial projects, ranging in size from a few hundred to perhaps tens of thousands of
hectares. In extreme contrast are the numerous small family units on the scale of 0.1 to
10 hectares. Some of the latter may each have direct access to an independent water source
(such as a dug well), while others may be in associations (such as village cooperatives)
sharing access to a joint water source.
Quite obviously, irrigation methods suitable for one scale of operation can be quite
unsuitable for another. High-pressure sprinkler systems, for example, may be suitable for
commercial growers of industrial crops, but far too expensive for small-scale farming. The
technology of choice should be the one that fits the size of each type of operation.
What is needed in the area of irrigation development is not so much technology transfer
per se, but an awareness of the need for, and the principles of, improving the efficiency
of land and water use. The inefficient use of these vital resources is not confined to any
particular group of countries: the malady is universal. No technology will succeed
automatically, though some have a greater potential than others. Ultimately, the job must
be done by people working in separate locations, endowed with the necessary incentives,
knowledge and means. Rather than viewing irrigation development merely as a supply
problem, the time has come to emphasize the demand side of the water balance. More
specifically, the problem is how to manage the demand for water so as to ensure efficiency
and sustainability. More and better water can be had by conserving the resource and
protecting its quality, and greater economic returns can be obtained by improving its
utilization.
Overall, the best chance for improving the efficiency of water use in small-scale farming
is embodied in systems that convey water in closed conduits to crops of high potential
yields. Ideally, such systems should provide water on demand, at a rate calibrated to meet
continuous crop needs while preventing waste, salinization and water-table rise. The
high-frequency, low-volume, partial-area (or partial-volume), low-cost irrigation methods
described here provide but a few relevant examples.