Two experiments were conducted at Water Studies and Research Complex (WSRC), Station, National Water Research Center, Toshka – Abu Simbel, during the two growing seasons of 2018 and 2019 to compare available reference ET equations (Hargreaves, Makkink, Priestley–Taylor and Turc) to the FAO-56 method to determine suitable alternatives for use in Toshka region, and to evaluation effects of drought stress and filter mud cake on physiological traits of two maize hybrids, three regulated deficit irrigation levels of available water content depletion (AWCD) I1, 13 %, I2, 25% and I3, 50% AWCD were combination with three levels of filter mud cake (FMC) F1: 4 kg m2 , F2 : 2 kg m2 and F3 : 0 kg m2.
The results showed that the Hargreaves equation is suitable for estimating ETo for the study area. Also, the results of this study showed that grain yield and water use efficiency in fineseeds and pioneer varieties were greatly improved by 80.8 , 74.7, 74.7 , 79.6 , 77.2 , 74.1 , 69.8 and 75.7% respectively, under (I1F1) compared to (I3F3).
The study was carried out at the experimental farm of the Water Studies and Research Center, Toshka, Abu simbel City, Egypt, which is located at 22o, 24`.11` N longitude of 31o, 35`.43` E longitude. The altitude of the area is 188m above sea level.