الفهرس 
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Abstract
Two field experiments were carried out at the experimental Farm of Sakha Agriculture Research Station, Kafr EL-Sheikh Governorate, Egypt, during the two successive summer seasons of 2014 and 2015. This research was carried out to determine the growth, yield and some yield components of three sunflower genotypes (Helianthus annuus L.) at different nitrogen fertilizer levels and hill spacing The experiments were designed in split-split plots in a randomized complete block design with three replications. The main plot treatments were allocated of three sunflower genotypes. The sub-sub plots were allocated with the three hill spacing. The referent examination of seed germination was conducted in seed technology laboratory Agronomy Department of the Agriculture Faculty, Mansoura University, Egypt during April 2016.Plant height, stem diameter, number of leaves/plant, leaf area/plant, number of seeds/head, head diameter, thousand seeds weight, seed yield/fed, germination percentage, percentage of abnormal seedling, mean germination time, coefficient of velocity, percentage of dead seed and the value of the vigourThe results showed that plant height (cm), leaves number/plant, leaf area (cm2), number of seeds/head, head diameter (cm), thousand seeds weight (g), seed yield/fed, abnormal seedling percentages, mean germination time, coefficient velocity percentage and value of the vigour percentage significantly affected by studied sunflower genotypes. However, stem diameter (cm), germination percentage and dead seed percentages insignificantly affected by studied sunflower genotypes. The results clearly revealed that plant height (cm), stem diameter, leaves number/plant, leaf area (cm2), number of seeds/head, head diameter (cm), thousand seeds weight (g), seed yield/fed, mean germination time, coefficient velocity percentage and value of the vigour percentage significantly affected by nitrogen fertilization levels. However, germination percentage, abnormal seedling percentages and dead seed percentages insignificantly affected by nitrogen fertilization levels. The tallest plants (cm), leaves number/plant, leaf area (cm2), number of seeds/head, head diameter (cm), thousand seeds weight (g), seed yield/fed, was recorded with nitrogen fertilization 70 Kg/fed. In addition, the lowest mean germination time and the highest percentages of coefficient velocity and the highest value of the vigour percentage was recorded from nitrogen fertilization at the rate of 50 Kg /fed.The results clearly indicated that plant height (cm), stem diameter (cm), leaves number/plant, leaf area (cm2), number of seeds/head, head diameter (cm), thousand seeds weight (g), seed yield/fed, germination percentage, coefficient velocity percentage, abnormal seedling percentages and dead seed percentages and value of the vigour percentage significantly affected by different hill spacing. However,number of leaves/plant and dead seed percentages not affected significantly by different hill spacing. The interaction between genotypes and nitrogen fertilizer levels significantly affected on plant height, leaf area (cm2), head diameter, 1000 seeds weight, abnormal seedlings percentages, mean germination time and value of the vigour percentage. The interaction between studied sunflower genotypes and hill spacing significantly affected on plant height, leaf area (cm2), number of seeds/head, head diameter, 1000 seeds weight, seed yield/fed, germination percentages, abnormal seedling percentages, mean germination time, coefficient velocity percentage and value of the vigour percentage. However, the interaction between studied sunflower genotypes and nitrogen fertilizer levels insignificantly affected on stem diameter, number of leaves/plant and number of seeds/head. from obtained results it could be concluded that the optimal seed yield/fed and germination characters could be obtained from sown Nsovak genotype at hill spacing of 20 cm nitrogen fertilization at a rate of 50 Kg /fed.