Organically Fertilized Onions (Allium cepa L.): Effects of the Fertilizer Placement Method on Quercetin Content and Soil Nitrogen Dynamics

Abstract

Field-cured onions cv. Hyskin ( Allium cepa L.) supplied with organic nitrogen fertilizer were studied. The fertilizer was applied by broadcasting and harrowing, broadcasting and rotary cultivation, or placement between rows. Nitrogen dynamics were monitored throughout the growing season by soil sampling. Variation in quercetin content in the onion scales was analyzed by HPLC. The organically fertilized onions were compared with inorganically fertilized onions grown in the same field. Inoculation with arbuscular mycorrhizal fungi (AMF) in the row at sowing or during commercial transplant production was tested but did not significantly affect mycorrhizal root colonization levels in the field. Onions that received no fertilizer at all or that had fertilizer placed between rows had better establishment, probably due to more favorable soil nitrogen concentrations for seedling emergence. Broadcast application led to higher nitrogen concentration in the root zone, resulting in fewer but larger individual onions. Quercetin levels were not significantly altered as a result of nitrogen fertilizer source (inorganic or organic), application method, or mycorrhizal inoculation. However, variation between years was significant, with quercetin levels in 2004 almost twice as high as those in 2005.

Handbook of Plant Food Phytochemicals

“…Some studies report higher levels of flavonols and anthocyanins in smaller onion bulbs, however in other studies bulb size had no significant effect on quercetin glycoside content [113,128]. In a study to evaluate the antioxidant potential of wild Allium species (A. neapolitanum, A. roseum, A. subhirsutum and A. sativum) growing in Italy, Nencini and colleagues report significantly higher levels of antioxidant activity as measured by FRAP test and a DPPH assay in the flowers or leaves, with lowest antioxidant capacity consistently reported for the bulbs [121].…”

“…Levels of quercetin in onion were shown to be unaffected by either the type or amount of nitrogen fertilization [113]. Sulphur application can increase yield and bulb size, and as might be expected, led to increased levels of the S containing alk(en)yl sulfoxides and increased pungency (measured as pyruvate content in macerated tissue) [52].…”

Onions: A Source of Flavonoids

“…Mogren et al [80] did not ind signiicant diferences on quercetin glucoside levels between onions organically produced and onion treated with chemical fertilizers. The conclusion could be that the nitrogen source, organic or inorganic, and the absence of chemical fungicides seemed to have no efect on quercetin biosynthesis.…”

Effect of Bioinoculants on the Quality of Crops

“…The beneficial effects derived from onion consumption depend on two groups of chemical compounds: the flavor precursors alkenyl sulfoxides and flavonoids (Griffiths et al 2002;Mogren et al 2008). Yellow onions contain high concentration of flavonols, and the main flavonol glycosides have been shown to be quercetin 4-0 -monoglucoside and quercetin 3,4 0 -diglucoside (Price and Rhodes 1997).…”