Effects of transplanting time and plant density on yield, quality andantioxidant content of onion (Allium cepa L.) in southern Italy

tThe aim of this research was to evaluate the effects of four transplanting times (1 February, 16 February,3 March, 18 March) and three plant densities (21.2, 27.2 and 38.1 pt m−2) on the growth, productivity andbulb quality indicators (size, dry weight, soluble solids content, sugars, acids, amino acids, antioxidants,mineral composition) of long-day onion crops, cultivar “Ramata di Montoro”.Crop yield, bulb mean weight and calibre decreased significantly from the earliest to the latest trans-planting time. Plant density did not affect production significantly but the most spaced crop (21.2 pt m−2)produced bulbs of the biggest size.The bulb quality indicators responded differently to transplanting time: dry weight, glucose, fructose,raffinose, citric and malic acids and vitamin C content did not change; soluble solids content, sucrose, andoxalic acid increased from the 1 February to the 18 March transplanting time, while pyruvic acid, calcium,chlorides and nitrates content decreased. The sequence of transplanting times resulted in complex patternof variations of the mineral composition and of the free amino acid content of the bulbs. The bulb totalpolyphenol content did not vary with the transplanting time and it was about 7 mg g−1dry weight, withthe outer skins containing more than double polyphenols compared to the inner fresh scales.This research on “Ramata di Montoro” onion has shown that early transplanting increases bulb yieldand size, whereas some aspects of bulb quality improve with late transplants.