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 different 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 performance (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 Mediterranean environment where weather conditions are unpredictable and inconsistent. 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. [ABSTRACT FROM AUTHOR]