الفهرس 
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Abstract
A field experiment was carried out at the Agronomy Department Experimental Farm, Faculty of Agriculture, Assiut University during 2017 and 2018 seasons, to study the effect of plant densities and splitting nitrogen fertilizer on sunflower yield and its components. The experiment was laid out in randomized complete block design using split- plot arrangement with four replications. The three densities were arranged in whole units. Plant densities namely (46666, 28000 and 20000 plants / fed) resulted by sowing in ridges 60 cm in width and hill spacing 15, 25 and 35 cm on sunflower Sakaha-53 variety. Three treatments of splitting nitrogen fertilizer were examined at recommended dose (30 kg N/ fed.), applied in 2 or 3 equal splits at different stages, which occupied the sub- plots. Sowing was done on the 6 and 11 June in 2017 and 2018 seasons, respectively, using seeds obtained from the Agriculture Center. All other recommended cultural practices for sunflower crop were done in both seasons. The obtained results are summarized as follows:
A- Agronomic characters:
1- Plant height (cm):
The data reveal that the interaction between plant density and splitting nitrogen fertilizer had non- significantly effect on plant height in both seasons. The tallest plants were recorded by plant density 46666 plants /fed when received nitrogen at three doses in both seasons.
2- Stem diameter (cm):
The results show that the interaction between plant density and splitting nitrogen fertilizer had non- significantly effect on stem diameter in both seasons. The thickest stem were obtained by plant density 20000 plants /fed when received nitrogen at three doses in both seasons.
3- Head diameter (cm):
The interaction between plant density and splitting nitrogen fertilizer had significantly effect on head diameter in the first season only. Plant density 20000 plants /fed which were received by (N1) gave the highest mean values of head diameter (18.95 and 17.85 cm) in the first and second seasons, respectively.
B- Yield and yield component:
1- Head weight per plant (g):
The results show that the interaction between plant density and splitting nitrogen fertilizer had significantly effect on head weight per plant in both seasons. Plant density 20000 plants /fed when received nitrogen at three doses recoded the highest head weight per plant (105.53 and 103.32 g) in the first and second seasons, respectively.
2- Seed weight per plant (g):
Data indicated that the interaction between plant density and splitting nitrogen fertilizer had significantly effect on seed weight per plant in both seasons. Plant density 20000 plants /fed when received nitrogen at three doses recoded the highest seed weight per plant (74.38 and 71.63 g) in in the first and second seasons, respectively.
3- Seed index (g):
Data showed that the interaction between plant density and splitting nitrogen fertilizer had significantly effect on seed index in both seasons. Plant density 20000 plants /fed when received nitrogen at three doses gave the highest mean values of seed index (6.85 and 7.19 g) in the first and second seasons, respectively.
4- Number of seeds per head:
The results reveal that the interaction between plant density and splitting nitrogen fertilizer had non- significantly effect on plant height in both seasons. The highest mean values were obtained by plant density 20000 plants /fed when received nitrogen at three doses in the first and second seasons, respectively.
5- Shelling%:
The results reveal that the interaction between plant density and splitting nitrogen fertilizer had non- significantly effect on plant height in both seasons.
6- Husk%:
Data showed that the interaction between plant density and splitting nitrogen fertilizer had significantly effect on husk percentage in both seasons. Plant density 20000 plants /fed when received nitrogen at three doses in both seasons gave the highest mean values of husk percentage (76.85 and 75.70%) in the first and second seasons, respectively.
7- Seed yield per feddan (kg):
It evident from the data that interaction between plant density and splitting nitrogen fertilizer had significantly effect on Seed yield per fed in both seasons. Plant density 20000 plants /fed when received nitrogen at three doses gave the highest mean values Seed yield per fed (2833.33 and 2728.58 kg /fed) in the first and second seasons, respectively.
C- Oil content:
1- Seed oil percentage (%):
Data showed that the interaction between plant density and splitting nitrogen fertilizer had significantly effect on oil percentage in both seasons. Plant density 46666 plants /fed when received nitrogen at three doses in both seasons gave the highest mean values of oil percentage (41.48and 41.16 %) in the first and second seasons, respectively.
2- Oil yield per feddan(kg):
Data revealed that the interaction between plant density and splitting nitrogen fertilizer had significantly effect on oil yield per fed in both seasons. Plant density 20000 plants /fed when received nitrogen at three doses gave the highest mean values of oil yield per fed (1084.73kg /fed) in the first season, while in the second season the highest mean values of oil yield (990.69 kg /fed) was recorded from 20000 plants /fed when received nitrogen at two doses of nitrogen.