Yield and bulb quality of storage onion cultivars as affected by farming system and nitrogen dose

The need of sustainable management system is connected both to environmental safeguarding and to the increasing consumers’ demand for safety and premium-quality food. A research was carried out to assess the interactions between 2 farming systems (organic, conventional), 4 nitrogen doses (100, 133, 166.5, 200 kg•ha⁻¹ N) and 11 cultivars on yield, quality, antioxidants, elemental composition and heavy metals content of storage onion bulbs. The bulb yield of six out of eleven cultivars was significantly greater in the conventional farming than in the organic one, with Ramata di Montoro and Rossa di Tropea showing the best performances, even in terms of plant dry weight, under both farming systems; Tosca reached the highest leaf area index. The conventional farming system also led to higher bulb yield, dry weight, nitrate content and ascorbic acid compared to the organic one for most cultivars, whereas quercetin was better affected by the organic management. The 166.5 and 200 kg•ha⁻¹ N doses resulted in the highest yield as well as Leaf Area Index (LAI), and 200 kg•ha⁻¹ N also enhanced dry weight, nitrate content and ascorbic acid. The 100 kg•ha⁻¹ N supply elicited the highest bulb storability, whereas 166.5 kg•ha⁻¹ N led to the highest bulb dry matter, soluble solids, total sugars, macroelements and most microelements. The 133 kg•ha⁻¹ N dose resulted in the highest monosaccharides, titratable acidity, quercetin, polyphenols, and Antioxidant Activity (AOA). The cultivar Ramata di Montoro showed the highest values of soluble solids, total sugars, monosaccharides and pungency. The cultivar Rosies des Aries displayed the lowest bulb storability, along with Rossa di Tropea, and the highest dry matter together with Grenada, Tosca and Zolotnichek. Polanowska attained the highest levels of antioxidants, AOA and macroelements. The highest bulb accumulation of microelements and heavy metals differed with the cultivar, though Ramata di Montoro showed the lowest accumulation of most heavy metals. Based on the outcome of the present research, the conventional farming system is recommendable in terms of yield, for the 55% of the storage onion cultivars examined, whereas the organic management improves the overall bulb quality, and the 166.5 kg•ha⁻¹ N represents the most effective dose for achieving the best compromise between yield and quality.