Yield and nutritional quality of different short-day onion cultivars as affected by nitrogen application

Abstract

Onion is one of the most important vegetable crops in the world, cultivated and consumed for its flavour-enhancing and medicinal properties; hence, comprehensive understanding of crop responses to N application is of immense importance. To determine the effects of different nitrogen (N) levels on yield, quality and mineral content of onion, four short-day onion cultivars (‘Mata Hari’ [red onion], ‘Mikado’ [brown onion], ‘Cristalina’ [white onion] and ‘Star 5516’ [brown onion]) were subjected to six different N levels (0, 30, 60, 90, 120 and 180 kg ha−1). Application of 180 kg N ha−1 significantly increased total yield (46.51 t ha−1), whereas no N application resulted in poor yield (15.35 t ha−1). ‘Star 5516’ produced the highest marketable and total yield compared with the other cultivars, and ‘Mata Hari’ had the lowest marketable yield, possibly due to higher bolting percentage. An increase in N application resulted in an elevation of N, magnesium, manganese, zinc and sulphur concentrations in bulbs. Bulbs of the red onion cultivar had higher N, phosphorus, calcium, sodium, iron, zinc and sulphur levels than those of the other cultivars, with a significantly higher percentage total soluble solids and sulphur concentration than the white and brown onion cultivars. The results of this study show that increasing N fertilisation up to 180 kg N ha−1 increases the concentration of certain minerals in bulbs, as well as marketable yield, with ‘Star 5516’ yielding highest and ‘Mata Hari’ showing the best quality.