الفهرس 
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Abstract
The present study was conducted during 2006 and 2007at the Crop Water Requirements Research Field, Sakha Agricultural 31o 07’ N latitude, 30o 57’ E longitude with an elevation of about 6 meters above mean sea level. The location represents the conditions of northern middle Nile Delta region. The aim of this work was to study the effect of both amount and intervals of irrigation water on crop yield of sunflower (Helianthus annuus L. cv. Sakha 53), some water relations as well as the contribution of groundwater table to crop-water needs. The design of the experiment was split-plot. Irrigation intervals (main plots) were one, two and three weeks; designated as A, B and C, respectively. While four irrigation levels was assigned in sub-plot as:
I1: Irrigation according to fill the root zone at field capacity + 10%.
I2: Irrigation according to Ibrahim equation.
I3: Irrigation according to Hargraves equation.
I4: Irrigation according to FAO Penman-Monteith equation.
The main results in this study can be summarized as follows:
5.1. Amount of water applied:
The highest value of water applied 45.8 cm was recorded with irrigation every one week. The lowest value of water applied 40.32 cm was obtained with irrigation interval every three weeks . The mean values in the two seasons for water applied under different levels can be arranged in descending order as: I2 > I3 > I4 > I1. The corresponding values are 44.52 > 44.37 > 43.74 > 38.88 cm, respectively.