Total sulfur and sulfate accumulation in onion is affected by sulfur fertility

Abstract

Because sulfate (SO₄ ^‐2) accumulation patterns were unknown in onion, a study was conducted to determine how three onion varieties accumulated total bulb‐sulfur (S) and bulb‐SO₄ ^‐2 in response to increasing S‐fertility. Plants were greenhouse grown in pots containing washed river sand and fertilized with five different nutrient solutions possessing SO₄ ^‐2 concentrations of 5, 25, 50, 75, or 150 mg liter¹ until the plants were mature. Bulbs were harvested and analyzed for total‐S, SO₄ ^‐2, and pungency, as measured by enzymatically developed pyruvic acid (EPY). Bulbs accumulated significant levels of SO₄ ^‐2 and S. The amount of bulb‐SO₄ ^‐2 and bulb‐S increased linearly as S‐fertility increased. The three varieties differed in total bulb‐S, bulb‐SO₄ ^‐2, the percent of total bulb‐S accumulated as SO₄ ^‐2, and EPY. Bulb‐SO₄ ^‐2 ranged from 0.047 to 0.318 % dry mass in response to S‐fertility level and variety, while total bulb‐S ranged from 0.154 to 0.535% dry mass. Diverse S and SO₄ ^‐2 accumulation and utilization patterns denoted complex S metabolism for onion in relation to flavor development.