Quality and nitrogen use efficiency of sunflower grown at different nitrogen levels under Mediterranean conditions

A two-year field experiment (during 1998 and 1999) was carried out in a Mediterranean environment to study the effects of different nitrogen (N) fertilizer rates on N uptake, N remobilization, N use efficiency, and yield performance of sunflowers grown in Southern Italy. Two sunflower genotypes (one commercial standard line and one selected genotype) and three N fertilization levels (0, 50, and 100 kg ha(-1) as ammonium nitrate) were compared in this experiment. N uptake (N content x biomass dry weight) of the leaves and stems, hand-held chlorophyll meter (SPAD readings), and leaf area index (LAI) were measured at flowering time; yield and its components, percentage of oil content, and plant N uptake were determined at physiological maturity. Nitrogen use efficiency parameters and N remobilization were also calculated. The results indicated a significant difference in yield, percentage of oil content, total N uptake, and N use efficiency parameters between the years, indicating greater limits imposed by the environment on sunflower potential. In the year with irregular rainfall (1998), higher N uptake at the flowering stage was found, thus determining higher N translocated, whereas in the year with normal rainfall distribution (1999), a higher total N uptake at the maturity phase was recorded. The intermediate N fertilization treatment (50 kg N ha(-1)) showed a better utilization of applied N, reducing the possibility of pollution. In fact, in both years, yield, LAI, total N uptake, and N use efficiency were statistically unaffected by the two N fertilization treatments. The differences between sunflower genotypes in yield performance and N use efficiency were observed during 1999, when the climate did not limit sunflower growth. In contrast, during 1998 N fertilization rates showed a significant response to the N fertilizer treatments in yield and in most measured parameters. Finally, the significant correlation between N uptake and N use efficiency parameters with yield indicate the importance of N nutrition in sunflowers grown in Mediterranean conditions, whereas the negative correlation between yield and oil content confirms that higher seed production is associated with lower oil content.