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.