FOUR-YEAR FIELD EXPERIMENT ON NITROGEN APPLICATION TO SUNFLOWER GENOTYPES GROWN IN SEMIARID CONDITIONS

A four-year field experiment was carried out to study the effects of differ-ent N levels on yield, yield components, N uptake and seed quality of sunflower genotypes grown in semiarid Mediterranean conditions. Five genotypes (four commercial hybrids and one newly selected genotype) and three N fertilization levels (0, 50 and 100 kg N ha-1) were compared over four years (1996, 1997, 1998 and 1999). Sunflower plants were taken at flowering time and their dry weight, leaf area index and total N content were determined. At maturity stage, yield, yield components, oil content, protein content, N uptake and seed quality were determined. The obtained results indicated significant differences in yield perform-ance (seed, oil and protein production) throughout the years (from 2.52 t ha-1 in 1996 to 3.81 in 1999), confirming the need to use recommended genotypes and adjust fertilizer rates to crops requirements, especially in the Mediterra-nean environment where weather conditions are unpredictable and inconsist-ent. In fact, the genotypes showed different behavior in all years regarding total N uptake, seed, oil and protein production, indicating that the sunflower crop is responsive to agronomic management. The highest level of N fertilizer resulted in the best sunflower performance although, due to variations in year and genotype, fertilizer N could be applied according to total annual N uptake. Finally, the N uptake and the diameter of head were the most important parameters that influenced sunflower yield performance. Key words: nitrogen fertilization, N uptake, seed quality, sunflower, yield component