Function of Sulfur:

Plants acquire sulfur from the growing medium as sulfate (SO₄=). Sulfate is readily soluble and subject to loss by leaching. Plant metabolism reduces sulfate and sulfur dioxide to forms that can be used to build organic molecules. Sulfur is a vital part of all plant proteins, and certain plant hormones. It is also used in the formation of certain oils and volatile compounds found in the onion and garlic family.

Sulfur Deficiency:

Since sulfur is associated with the formation of proteins and chlorophyll, its deficiency symptoms resemble those of nitrogen. Sulfur is moderately mobile within the plant, therefore deficiency symptoms usually start on the younger leaves and progress over time to the older leaves, resulting in plants becoming uniformly chlorotic. While sulfur deficiency symptoms on an individual leaf look like those of nitrogen, nitrogen deficiency begins in the lowest leaves, not the newest.