الفهرس 
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Abstract
A field experiment was established at the experimental farm of Water Studies and Research Complex (WSRC), Station National Water Research Center, Toshka – Abu Simbel City, Egypt, during two growing seasons of 2018/2019 and 2019/2020. A split split plot arrangement of a randomized design with three replications was used with irrigation levels as main plots and maize varieties as subplots and filter mud as sub-subplots. Each of studied sites was divided into two divisions to studied two sowing date and maize seeds were planted at two dates namely the second week of August and February, respectively.
The objectives of this study are:
- Determining the water requirements for maize grown on the Toshka soils under the different sowing dates.
- Studing the individual and combined influence of irrigations levels, filter mud cake (FMC) of production, water use efficiency and crop water requirements of maize grown in Toshka under different sowing dates.
- Investigating the response of two maize hybrids maturities for later than traditional planting sowing date in terms of yield, yield components, ET, and WUE.
- comparing available reference ET equations (Hargreaves, Makkink, Priestley–Taylor and Turc) to the FAO-56method to determine suitable alternatives for use in Toshka region,
The obtained results could be summarized as follows: -
Actual evapotranspiration (Eta)
• The highest average values of Eta were recorded under irrigation level (I1) 13% of AWD with 1003 and 856 mm in first and second sowing date respectively, while, (I3) 50% of AWD were recorded the lowest average values with 706 and 551 mm in first and second sowing date, respectively.
• The results indicated that the average values ETa 1003, 845 and 706 mm in the first sowing date under the irrigation levels (I1) 13%, (I2) 25%, and (I3) 50% of AWD, respectively. The corresponding Eta were 859, 682 and 551 mm in the second sowing date .
• The results indicated that the average values of ETa were 850, 735 and 621 mm in the first sowing date under irrigation levels (I1) 13%, (I2) 25%, and (I3) 50% of AWD, respectively, with FMC applications at rate (4kg/m2). While it were 684, 579 and 489 mm in the second sowing dates under the same corresponding irrigation levels.
• ETa affected significantly by planting date. It was responded very differently to the second sowing date. The ETa reduction was 14.36% in second sowing date compared with first sowing date
• The total amount of ETa decreased with an increment in the proportionate doses of FMC. The highest ETa was recorded under F3 (0kg/m2) FMC treatment, whereas, F1(4kg/m2)FMC treatment accounted the least water use.
Irrigation water applied
• The results indicated that the average values of irrigation water applied were 1114, 939 and 784 mm in the first sowing date at (control treatment) under irrigation levels (I1) 13%, (I2) 25%, and (I3) 50% of AWD, respectively.
• The average corresponding values were 954, 757 and 612 mm in the second sowing date at (control treatment)
• The results indicated that the average values of irrigation water applied were 945, 816 and 690 mm in the first sowing dateat (I1F3) under the three irrigatin levels (I1), (I2) and (I3),respectively.
• They were 760, 643 and 543 mm in the second sowing date at the same treatment under the corresponding irrigation levels.
• It can be noticed that applying FMC application at rate 4kg/m2, under each irrigation level gave the lowest irrigation water applied in both sowing date.
Water use efficiency (WUE)
• The highest WUE was recorded under irrigation level I1 (13% of AWD). The lowest irrigation level (I3) 50% of AWD resulted in the lowest WUE.
• The results indicated that the average values of WUE were 0.47, 0.44 and0.28 kg/m3 in the first sowing irrigation levels (I1) 13%, (I2) 25%, and (I3) 50% of AWD, respectively. While they were 0.32, 0.32 and 0.21 kg/m3 in the second sowing date at same treatment under the corresponding irrigation levels.
• The results indicated that the average values WUE were 0.52, 0.39 and 0.27 kg/m3 in the first sowing date under the irrigation levels (I1)13%,(I2) 25% and (I3) 50%of AWD,, respectively, with FMC applications at rate (4kg/m2). While they were 0.41, 0.28 and 0.19 kg/m3 in the second sowing date at under the corresponding irrigation levels.
• WUE significantly affected by planting date. It was responded very differently to second sowing date. The WUE reduction was 31.91% in second sowing date compared with the first sowing date.
• The total value of WUE decreased with an increment in the doses of FMC. The highest ETa was recorded under F3 (0kg/m2) FMC treatment, whereas, F1(4kg/m2) FMC treatment accounted the least water use.
Maize yield and productivity of water applied.
• In general, the results indicated that maize grain yields were increased in the first sowing date compared to the second sowing date under high irrigation level (I1) and applying FMC at rate of 4Kg/m2, while under low irrigation level(I3) without FMC the maize yield was low.
• The results indicated that the total average values of Fine seeds and Pioneer hybrids yield in the first sowing date were1.28 and1.36 ton/fed., respectively. While, they were 0.71 and0.84 ton/fed. in the second sowing date at same treatment under the same corresponding irrigation levels.
• Planting date has highly significant for grain yield. It was responded very differently in the second sowing date. The grain yield reduction was 44.5 and 38.24% for Fin seeds and Pioneer, respectively in second sowing date compared with first sowing date.
• When the combinations of high irrigation level and 4kg/m2 FMC application (I1F1) were considered, recorded higher grain yield, while, low irrigation level and 0kg/m2 (I3F3) resulted in lower grain yield as compared to all the other treatments.
• Also the results indicated that the influence of using FMC application caused increases in the average maize yield between sowing date by 64.8 % at (4Kg/m2FMC) and 43.9% at (2Kg/m2FMC), respectively.
• In general, the results indicated that the mean productivity of water applied to maize increased in the first sowing date than the seconds owing date.
• Finally, the data revealed that using 100% of available water + filter mud cake in rate(4Kg/m2) under the first sowing date caused increases of maize grain yield more than the same treatment under the second sowing date
Evaluation of ETo Estimation methods
• Four ETo methods were evaluated relative to the FAO56- PM under arid conditions are prevalent in the Toshka region. The Food and Agriculture organization Penman-Monteith FAO56- PM equation was used as the basis for comparison with four methods (Hargreaves-Samani, Makkink, Priestley and Taylor and Turc). The Hargreaves-Samani method ranked first among methods evaluated .
• The Hargreaves–Samani model, the only temperature-based equation, performed second best since it considers the second influential parameter which is maximum temperature in evapotranspiration for hyper arid environment – based on its statistical analysis – with a moderate underestimation of 21%. Turc model had the worst performance compared with other models, with a 59% underestimation of the measured ETo since it considers relative humidity which is insignificant parameter in hyper arid environments.
Conclusions
• According to the obtained results for the interactions among the studied treatments (planting maize seeds in the second week of August, water regimes at depletion by13% of available water and use filter mud cake in rate (16,800Kg/fed.), it might be recommended for achieving the best maize production and productivity of water applied.
• Among the four methods, the Hargreaves method provided the best ET estimations based on the lowest error statistics MBE , RMSE , PE and R2
Recommendations
• In many regions of the world, the meteorological stations do not have enough data to use Penman-Monteith FAO56- PM equation. Therefore, it becomes necessary to develop procedures for realizing regional and temporal adjustments to Hargreaves-Samani obtain the best estimations of ETo. The most accurate of the easily applied models for estimating crop evapotranspiration was the calibrated HS.
• Since the FAO-56 PM model proved to be superior on estimating reference crop evapotranspiration, it is recommended to calibrate the selected models for long period to obtain the average of calibrated coefficients.