Nitrogen and Sulfur Influence Nutrient Usage and Accumulation in Onion

To study the effects of nitrogen (N) and sulfur (S) fertility on onion (Allium cepa L.) bulb pungency, bulb fresh and dry weight, nutrient uptake and accumulation in the bulb, “Granex 33” onions were greenhouse grown using nutrient solution culture. A factorial arrangement of solutions containing 1.7, 15.0, and 41.7 mg L^-1 S and 10, 50, 90, and 130 mg L^-1 N were used. Bulb pungency and bulb fresh and dry weight were affected by both S and N treatments. Depletion patterns for most of the macronutrients from the nutrient solutions during plant growth were affected by N and S levels, and differed depending on the N and S combination. In certain N and S combinations, magnesium (Mg) and calcium (Ca) usage were unaffected over time. Bulb N levels increased with N fertility and decreased slightly with S availability, while bulb phosphorous levels responded linearly to N fertility. Overall changes in bulb Ca and Mg levels were minor, but were influenced by N and S fertility. Bulb S content was affected by low S and N fertility, decreasing with each. Boron levels in onion bulbs decreased with increasing N and S fertility, while bulb manganese, iron, and zinc concentrations tended to increase with increasing N availability and decrease with increasing S. Potassium, copper, and molybdenum bulb concentrations were unaffected by N or S fertility. These results have the potential of being used as a reference in developing nutritional programs designed for optimal onion performance having specific flavor intensities.