Nitrogen and sulphur have a lot in common. They complement each other as they are tied together due to several common physiological processes with a central role in the synthesis of proteins. In proteins for every 15 parts of nitrogen there is one part of sulphur which implies that the N:S ratio is commonly 15:1 for most crops but can be much higher for some crops (e.g. rape seed).
Corresponding to the ‘Theory of Minimum’, too much nitrogen induces a sulphur deficiency and equally, a sulphur deficiency limits the uptake of nitrogen. Therefore, an adequate sulphur supply increases nitrogen use efficiency.
As nitrogen and sulphur have common physiological processes, they show common deficiency symptoms. Yellowing of the plants is the main symptom, which starts from the leaf tip to the base down on lower (older) leaves when nitrogen is deficient, whereas sulphur deficiency is shown on the young leaves first.