Splitting of nitrogen application through growth stages in various sunflower cultivars to improve their vegetative growth and seed yield

A field experiment was carried out in spring seasons of 2012 and 2013 to increase the efficiency of nitrogen application in spite of that no splitting nitrogen has practiced for the studied cultivars. Five splitting treatments (T1, T2, T3, T4, and T5) of nitrogen application were studied in three sunflower cultivars (Shumos, Akmar, and Zehrat Al-Iraq). The results showed that Shumos cultivar, T4 treatment of nitrogen application and their interaction gave the highest seed yield (6.3 and 6.43), (5.78 and 6) and (6.62 and 6.9 ton ha-1), respectively, on both seasons. The highest significant correlation value belonged to the correlation between seed yield and leaf area (0.85 and 0.87) for both seasons. It can be concluded that splitting of nitrogen fertilizer during growth stages is effective to increase the efficiency of nitrogen application and lead to increase seed yield. Also, leaf area could be a selection criterion to improve seed yield.