Role of Sulfur in Onion Production

Sulfur is an important component of enzymes and other proteins, and is required for chlorophyll formation.

It has a marked effect on the pungency of the onion through increasing the pyruvic acid content of the bulb – a key quality characteristic.

USA trials show that sulfur is important for bulb weight.

Sulfur is also important for yield and it helps to improve crop's utilization of nitrogen. Between 45-90 lb/ac of sulfur can be commonly used. However, high rates particularly on S-rich soils can have a detrimental effect on yield.

Because sulfur has a marked effect on onion pungency and sugar content, it is important to exploit the right soil and use an appropriate rate and timing of sulfur that satisfies market requirements and tastes.

Sulfur effect at growth stages

Stage Sulfur effect
Pre-Planting Encourage plant growth
Bulb Fill Depending upon the desired pungency of the onion

See more on Onion Growth Stages.

General Guidelines for Sulfur Application

Most sulfur uptake occurs in late season during bulb growth. Sulfur helps to improve the crop's utilization of nitrogen. Plants with a high sulfur content have greater tolerance to pest and disease attack. Sulfur has also been linked to increasing skin strength and color.

Sulfur Deficiencies in Onion

Leaf production is affected and the plant produces fewer leaves. Younger leaves are uniformly yellow in color.