The pressure for survival and the need for additional food supplies are causing the
rapid expansion of irrigation throughout the world (Michael, 2002). The area of
land irrigated in the world is more than 248 million hectares. Nine countries—China,
India, the US, Pakistan, Indonesia, Mexico, Iran, Thailand and Uzbekistan—have the
largest irrigation areas, amounting to almost 70% of the world total irrigation area
(FAO, 2001).
The oceans occupy about 70.8% of the earth’s surface and land occupies only 29.2%.
About 97.5% of the world water resource is in the oceans and is saline, implying that
it may not be good for agricultural purposes (FAO, 2001). Of the remaining 2.5% of the
global water resource, about 2% is in ice caps and glaciers, which is generally not
available for the requirement of mankind. About half the volume of the groundwater lies
in water-bearing formations more than 800 m below ground surface and is not
ordinarily available for economical development. The water available for development by man is mainly from streams, rivers, freshwater lakes, and about half of the quantity
of groundwater which occurs at depths less than 800 m from ground surface (Benami,
1993).
Water being a limited resource, its efficient use is basic to the survival of the
ever-increasing population of the world. In the comprehensive strategy needed for the
conservation and development of water resources, several factors are to be kept in view.
These include the availability of water, its quality, location, distribution and variation in
its occurrence (Adedeji and Kola, 2008). The objective of efficient irrigation is to increase
agricultural production per unit volume of water per unit of cropped land in a unit of
time. |
