Use of Stable Isotopes to Determine Evaporation, Transpiration and Efficiency of Irrigation Water Use in Cultivated Areas in Egypt

Abstract

The largest consumptive use of water resources in Egypt is for agricultural purposes.  The water balance and 
efficiency of irrigation water use in agricultural fields is greatly affected by loss of water to the atmosphere 
through evapotranspiration. The present work is devoted to partition evapotranspiration discharge (ET) into 
evaporation (E) and crop evapotranspiration (ETc) and to explore irrigation water use efficiency and how it is 
improved by using modern  irrigation techniques in the newly reclaimed zones in Egypt; stable isotopes 
(Oxygen-18 and Deuterium) as being differently affected by evaporation and transpiration, have been employed 
for that. The evaporation loss (E) has been determined (5% - 6%) using heavy isotopes enrichment factor of a 
drying pan, as well as the slope of Oxygen 18 vs Deuterium evaporation trend of collected groundwater 
samples. The eastern zone of the study area shows a water use efficiency of about 33% where flooding 
techniques are applied for irrigation using Nile water. In the western zone, groundwater is used for irrigation 
with spray techniques, the crop transpiration domains, the water loss to atmosphere and water use efficiency is 
highly improved. The soil infiltration of evaporated return water in the eastern and western zones has been 
discussed.