In plants, sulphur is a building block of amino acids (e.g. cystine), proteins, vitamins, enzymes and some volatile compounds such as mustard oil. It is needed for chlorophyll formation. It gives many vegetables their flavour. It increases the development and activity of enzymes and vitamins. It helps improve root growth and seed production, and contributes to the plant’s strength and resistance to cold. Rainwater can contain sulphur, and plants can also take up sulphur from rainwater. Sulphur is part of the structure of organic substances, so it can be found in the soil in both organic and inorganic forms; however, a large part of the sulphur in the soil is organic sulphur.
Plants take up sulphur through their roots in the form of sulphate ions (SO4²⁻); they can also take it in as sulphur dioxide (SO2) through their stomata. Within the plant, sulphur moves mainly upwards; downward transport is very limited. Sulphur in old tissues is not transported to young tissues. Sulphur can be leached from the soil by irrigation, and irrigation water may also contain sulphur.
Symptoms of Sulphur Deficiency
The symptoms of sulphur deficiency in plants are very similar to those of nitrogen deficiency: a uniform yellowing, with light green leaves. The difference is that with sulphur deficiency the yellowing appears first on the young leaves, whereas with nitrogen deficiency it starts on the old leaves. This is because sulphur cannot be transported from the old leaves to the young leaves.
