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.
