Sulphur is classified as a secondary nutrient, and is often referred to as the ‘fourth major plant nutrient’. Sulphur is frequently a limiting nutrient in plant quality and yield, largely due to increasing yields from crops and lack of awareness of the importance of sulphur.
Sulphur is necessary for the utilisation of nitrogen, and is a key component of protein. As a result, the formation of enzymes, vitamins, and chlorophyll, are dependent on its availability. Insufficient sulphur will limit the use of nitrogen and prevent protein from forming. In order for legumes to fix nitrogen, sulphur must be available to form the nodules necessary for nitrogen fixation.
Sulphur is contained in organic material and small amounts in soil minerals. This means organic, heavier soils can supply more sulphur than lighter, sandier soils. It is taken up by the plant in the form of sulphur ions- they are converted from organic sulphur by a series of processes (the sulphur cycle) which are influenced by microbial action. This requires warmth, moisture and time.
Sulphur Levels Vary
Sulphur levels vary greatly in the soil, throughout the profile and dependent on weather conditions. Levels can vary greatly month by month. This is partly because sulphur can be easily lost through leaching, particularly in light, sandy soils and wet weather, as it moves out of reach of plant roots. Therefore application of sulphur during spring is advisable to ensure it is taken up during active growth of the plant and not lost from the soil.
Solid manure has slow release of sulphur- apply in autumn to ensure available for spring
Liquid applications available rapidly, should be cautious of leaching
Because of its role in protein formation, sulphur is important in sward quality and yield.
Soil Sulphur Deficiency
Similarly to calcium, sulphur is immobile in the plant and therefore deficiency symptoms appear on the younger leaves first. One of the main signs of a sulphur deficiency is pale green young leaves, with latter stages of deficiency resulting in a yellow-coloured appearance. Generally, plants will be small and have stunted growth with pale leaf veins.
Sulphur can improve the winter hardiness of plants, and therefore a slight deficiency could present itself as an overall weak sward.
Take a Test
If you are unsure of your soil sulphur levels, a soil test would be advisable to ensure optimal fertiliser application whilst avoiding leaching.