A. A Sulphur deficiency is indicated by yellowing of the younger leaves. It occurs mainly on sandy free draining soils with a low organic matter content. There is no reliable soil test for sulphur and deficiency is diagnosed by means of herbage analysis. If you expect a sulphur deficiency you can confirm it by applying a sulphur containing fertilizer to the affected fields and leave a small area spread with the equivalent fertilizer without sulphur to see if there is a difference.