Two experiments were conducted at Water Studies and Research Complex (WSRC), Station, National Water Research Center, Toshka -Abu Simbel, during two growing seasons of 2018 and 2019 to compare available reference evapotranspiration (ET • ) equations (Hargreaves-Samani (HS), Makkink (MK), Priestley-Taylor (PT) and Turc (TC)) 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) I 1 , 13 %, I 2 , 25% and I 3 , 50% AWCD were combined with three levels of filter mud cake (FMC) F 1 : 4 kg m 2 , F 2 : 2 kg m 2 and F 3 : 0 kg.The data revealed that the individual influence of used 13% AWCD and FMC 4 kg m 2 , caused increases of the plant height (m), leaf area (cm 2 ), no. grains/cob, grain yield (ton/fed.) and water use efficiency (WUE) (Kg/m 3 ).The data also, revealed that the average seasonal values of the actual evapotranspiration (Eta) decreased as the percentage of soil moisture depletion increased (more available water extracted) . The Eta values were 1012.5, 853.1 and 712.7mm at 13, 25 and 50% AWCD, respectively.The data also, revealed that the grain yield in the first season (2017/2018) were 1.70, 1.32 and 0.77 ton/fed. While in the second season (2018/2019) were 1.85, 1.53 and 0.75 ton/fed for 13, 25 and 50% AWCD, respectively.The data revealed that increased regime treatment from 13 to 50% AWCD decreased WUE by maize plants from (0.45 to 0.29 kg/m 3 ) and (0.48 to 0.27 kg/m 3 )in 2017/2018 and 2018/2019, respectively.The results showed that the Hargreaves -Samani (HS) equation is suitable for estimating ETo for the studied area.

Upper Egypt is characterized by high temperatures in summer and low temperatures in winter, which has a significant impact on the dates of planting maize in this region. The productivity of the maize crop as well as the efficiency of the use of water can be severely affected by planting dates and drought. Consequently, the optimum irrigation level and planting date must be determined based on local conditions. Two irrigation schemes were used: (1) control (full irrigation water applied), (2) 70% of irrigation water. Field experiments were conducted at the water studies and research complex station, National Water Research Center in Toshka to evaluate two irrigation levels (full irrigation water applied and 70% of irrigation water requirements) under five planting dates (early seeding (mid-February and March), normal (mid- June) and late planting (mid- August and September) in 2019 and 2020) to determine the optimum planting date and irrigation level. Early SD has increased the days between seeding and plant emergence. Late SD reduced the number of days until the plant matured and had higher grain yields and water use efficiency (WUE). The planting date in September under the irrigation level of 70% achieved the best productivity and the best water use efficiency, where the productivity was 7.01 Mg ha−1 and the water use efficiency was 0.72 kg/m3 The data confirm the general perception of farmers that the September sowing date under 70% irrigation levels is the best within the experimentation area.