New FAO publication aims to bring small-scale irrigation to farmers in sub-Saharan Africa

Irrigation is a key tool for agricultural intensification. Although only 16 percent of the world's fields are irrigated, they yield 36 percent of global harvests. In developing countries, irrigation increases yields of most crops by 100 to 400 percent. Despite this, some of the world's most needy farmers are still unable to water their land effectively.

The use of porous jars buried up to the neck is one of the oldest irrigation methods and is practised by traditional farmers throughout North Africa and the Near East.

Professor Daniel Hillel, expert in soil/water relations, was asked by FAO Director-General Jacques Diouf to write an irrigation book specifically for one major group of vulnerable agriculturists - the small-scale farmers of sub-Saharan Africa. Hillel is irrigation advisor to the Oversight Committee for FAO's Special Programme on Food Security, spearhead of the Organization's work to promote food self-sufficiency in the world's poorest countries. As a retiree, he was contracted under FAO's Programme for the use of retired experts.

"Small-scale irrigation for arid zones: Principles and options" promotes HELPFUL (High-frequency, Efficient, Low-volume, Partial-area, Farm-Unit, Low-cost) irrigation techniques. Hillel, who has a lifetime's experience of irrigation, points out that "Elaborate and expensive systems ... imported and installed in the grand hope of achieving instant modernization, typically fail for lack of expert maintenance and spare parts. Such installations can quickly become white elephants - idle monuments to hasty 'progress' relying on ill-adapted technology."

When they do work, poorly managed irrigation systems cause a range of environmental problems. Rising water tables, caused by excessive applications, leakage from drainage channels and inadequate drainage, lead to salinization and waterlogging, which reduces crop yields. Conversely, overpumping of groundwater depletes supplies and threatens long-term viability of the irrigation schemes and the crop yields they support.

Drip irrigation - the slow, localized application of water, literally drop by drop.

"Just enough is best"

"It is the universal fallacy of humans to assume that if a little of something is good, then more must be better. In irrigation (as indeed in many other activities), just enough is best." says Hillel.

The irrigation techniques described in Hillel's paper are the result of combining revolutionary developments that have taken place in recent decades in the science of irrigation with traditional technologies used successfully for centuries. It is now possible to maintain nearly optimal soil moisture conditions - thus eliminating problems of waterlogging and salinization, as well as saving water - throughout the growing season, responding continually to varying weather and developing stages of crop growth.

Although these methods are applied on a large scale in industrial countries, they need not depend on expensive manufactured equipment and high-energy inputs. Hillel explains how simple jars of porous clay, perforated plastic pipes and other low-cost equipment can be used to regulate water flow to crops (see Box below).

Hillel's paper advocates development "based on the best principles of efficient irrigation, insofar as possible using indigenous skills and materials. The best principles of efficient irrigation should be disseminated, not necessarily the most elaborate machinery." It is written for decision-makers and the general public. Believing that "ready-made prescriptions tend to be specific and inflexible, and hence rarely apply as new problems arise in changing circumstances", Hillel's aim has been to explain the principles of modern irrigation so that farmers and their advisors will be able to modify their approaches and actions when new conditions arise.

Summary of small-scale irrigation methods

Methods based entirely on local materials and workmanship

  • Low-fired porous ceramic pots are placed on the surface or embedded in the soil within the root zone. When filled with water and dissolved fertilizers, the permeable clay receptacles ooze water and nutrients into the soil.
  • Sectioned ceramic pipes constitute line sources that feed elongated beds.

Methods based on imported materials but local fabrication

  • Moulded plastic pipes or extruded plastic tubing are perforated manually and laid over the ground to simulate drip irrigation.
  • Vertical sections of plastic pipes (or even discarded plastic containers such as bottles) are embedded in the ground.
  • Thin-walled plastic vessels are filled with sand or gravel to provide mechanical resistance to crushing.
  • Slit plastic sleeves cover the perforated sections of the tubes to prevent root penetration into the outlet holes.
  • Sand filters prevent suspended particles or algae from clogging the outlets.
  • Auxiliary containers are used to dissolve and inject fertilizer into the irrigation water.
  • Vertical standpipes are used to deliver water from an underground pipe to small basins.

Methods based on imported components*

  • Manufactured drip emitters and microsprayer assemblies are carefully supervised and maintained.
  • Ancillary equipment such as screen and media filters, metering valves, pressure regulators and fertilizer injectors are used in various combinations.

* These options will be justified only for cash crops in a stable market economy.

15 July 1997

Related links:

 FAO Home page 

 Search our site 

Comments?: [email protected]