The increasing global demand for food and other agricultural products
calls for urgent measures to increase water use efficiency which is,
with plant nutrient availability, one of the two main limiting factors
in crop production. Although only 20% of all cultivated land in the
world is under irrigation, it provides 35-40% of all crop production.
Because of higher yields under irrigated agriculture, investments for
irrigation are usually a top priority. However, it has become a matter
of serious concern in recent years that, despite their high co ts, the
performance of many irrigation projects has fallen short of expectations
as a result of inadequate water management at both farm and system
levels. Crop production increase has been well below the project
targets. The greatest potential for increasing food and other
agricultural products is the more efficient use of naturally occurring
precipitation in conjunction with improved soil fertility management.
Until recently, regardless of the amounts and distribution of rainfall,
irrigation practices were used almost exclusively to supplement the
amount of soil water stored in the root zone to such an extent that the
available soil water never allowed the crop to suffer from water stress
throughout the growing season. As a result, even today farmers still
tend to over-irrigate to ensure a bountiful amount of water stored.