Comparison of bulb and leaf quality, and antioxidant compounds of intermediate-day onion from organic and conventional systems

Abstract

This study aimed to compare bulb and leaf characteristics, leaf diseases, physiological disorder, bulb nutritional quality, and storage loss of onion from both organic and conventional farms in southeastern Korea during the 2011/2012 growing season. Soil and plant samples were collected from 8 certified organic fields managed organically for more than 5 years and 8 conventional fields adjacent to the organic fields. Onion bulb fresh weight and marketable bulb yield were significantly higher in the conventional field than in the organic field. At harvest, tops-down and leaf yellowing were 15.0 and 16.9%, respectively, lower in organic onions compared to conventional onions. Total phenolic compounds were significantly higher in conventional than organic onions, while there were no significant differences in pyruvic acid, soluble solid and flavonoids content between conventional onions and organic onions. In principal component analysis, highly weighted variables under PC1 included the number of scales, leaf yellowing, soluble solids, pyruvic acid, flavonoids, phenolics and storage loss in organic onions, but bulb weight and leaf weight in conventional onions. In organic onions, leaf yellowing correlated positively with flavonoids (p = 0.015), but negatively with soluble solids (p = 0.040); soluble solids were negatively correlated with flavonoids (p = 0.049). By contrast, conventional onions showed a positive correlation between bulb weight and leaf weight (p = 0.038), and between soluble solids and phenolics (p = 0.019), but a negative correlation between leaf weight and leaf yellowing (p = 0.016).