Growth, N-uptake and Yield Attributes of Sunflower Plants Grown on an Aridisols in Response to N-fertilizer

A field experiment was conducted to study the impact of different nitrogen fertilizer rates (0, 50, 100 and 150 kg N/ha as urea) on dry matter yield, nitrogen uptake (N), seed yield, seed oil content and properties of sunflower using the 15N labeling technique. Sunflower plants responded to increasing N supply with respect to growth performance. Dry matter yield (DM) and total N uptake were significantly increased with increasing N-supply. Regardless of N-fertilizer rates, partitioning of N yield in different plant parts showed that capitulum was the principle sink of N (60%) followed by leaves (30%) and stem (10%). Seed yield was significantly increased at higher N-supply. However, seed oil content was reduced in the N-fertilized treatments. Decreasing of seed oil content due to N addition was overcompensated by the seed yield increase. Consequently, oil yield was almost the same amongst all treatments. No clear trend of the effect of N supply on oil quality parameters was observed. Nitrogen derived from fertilizer (Ndff) was significantly increased with increasing N-supply. Regardless of N fertilizer rate, mean value of the %15NUE was 64%. This efficiency was less pronounced in stem and leaves than that in capitulum which had a greater value (69%) at higher N-supply.