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Résumé :
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Irrigated agriculture is by far the greatest user of water on earth.The limits to the availability of water and land for irrigated agriculture necessitate the careful use of these resource.Nevertheless,an increased efficiency in the use of irrigation water can have negative as well as positive effects.The aims of this study have been: -to present data on actual irrigation efficiencies worldwide, -to illustrate how these data can be used in the design and management of irrigation systems,and -to show when improvements are useful or not.The study therefore evaluates relationships between measured irrigation efficiencies and caracteristics of the environment,of the infrastructure of irrigation systems,and of their operation.Irrigation efficiencies are basically ratios of volumes in the water balance of an irrigation scheme.This study concentrates mainly on the relationships between the components of the water balance of irrigation systems and the factors that might influence these relationships.Other factors that are related to irrigation (e.g. the management of crops,the socio-economic and legal environment of irrigation systems,or the quality of water) were not the direct subjet of this study.This does not mean that their importance is not recognized.Those factors,together with the conclusions of this study,should be taken into account when final decisions are being made on the use of water.
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