Sulphur is critical to the taste and pungency of the bulb. Supplies need to be tailored to suit the desired market requirement. Sulphur can also improve skin strength and colour, and has a marked effect on the pungency of the onion through increasing the pyruvic acid content of the bulb. Therefore, it is important to use the right soil and an appropriate rate and timing of sulphur that satisfies market demands.
Sulphur also has a marked effect on bulb sugar content, so soil type and use of sulphur as part of a nutritional program have to be carefully considered in order to meet market requirements. For example, sweet onions benefit from being grown in low sulphur soils and should have low S-nutrition regimes with most of the S applied early season to minimise uptake into the onion bulb.