الفهرس 
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Abstract
To explore the yield potential of the newly released cultivars, practically, under unfavorable conditions. Further, enhancing tolerance ability of some rice cultivars throughout appropriate potassium requirements and identify the more critical phases for water stress which has to be avoided. Three field experiments were conducted at E- l¬Sirw Agricultural Research Station of the ARC, Ministry of Agriculture located in Damietta prefecture during the three succiessive seasons of 1999, 2000 and 2001.
The field experiments were laid out in a split-¬split plot design with four replications. The main plots were devoted to four irrigation treatments, i.e. :
(1) continuous flooding throughout all the seasons and it referred as (I1).
(2) water withholding for 12 days at 15 days after transplanting (DAT) it referred as (I2).
(3) water withholding for 12 days at 25 15 days after transplanting ( DAT) it referred as (I3).
(4) water withholding for 12 days at 35 15 days after transplanting (DAT) it referred as (I4).when water water withholding were ended as per treatments, common practies were followed throughout the rest of the growing season.
The sub plots were allocated to three rice cultivars viz., Sakha 101, Sakha 102 and Giza 178 while the sub¬-sub plots were occupied by the potassium rats; 0, 20 and 40 kg K2O/fed.