There is strong evidence that plant active sulphur should be included in all crop and grassland fertiliser programmes.
This is a clear message that has been endorsed by all agricultural research and development organisations operating within the UK and Ireland.
This reflects the fact that the heavy rains of the past three months have washed this key nutrient well down soil profiles or removed it entirely from cropping locations.
Some nutrients have higher mobility levels within soils than others. Sulphur (S) is one of the higher profile culprits, alongside nitrogen.
Low S levels
Last year’s wet conditions showed visibly in fields where nitrogen inputs were delayed due to ground conditions, or in trials where nitrogen was not applied.
Data collected over the past two years has confirmed the increase in crops with low S levels, either through tissue analysis or grain analysis.
This work has shown that low S samples more than doubled in 2024 from the previous year, presumably down to the wet conditions.
Whilst slurries, manures, and digestates all contain sulphur, the quantities and form of sulphur can vary considerably, depending on feeding and storage practices.
Variations of between 5-55% availability have been identified in availability of sulphur from cattle slurry.
Conversions of plant-available inorganic sulphur to organic sulphur or reduced to sulphide may be part of the reason for this variation.
With high levels of uncertainty, it is difficult to rely on this source alone to meet a crop’s sulphur requirement, unless soils have had regular applications of manures over a long period of time.
Role of sulphur
Therefore, in one form or another, it is very likely that sulphur will be required in 2025 by most crops, and this should be planned in early when making nutrient management plans this season.
The major role of sulphur in all plants is in support of nitrogen in protein production which is hugely important for high crop yields.
In brassicas, (veg, oilseed rape, kale etc), sulphur is also in glucosinolate compounds, which give them their hot taste.
Sulphur also reduces the likelihood of immature rapeseed which faces penalty pricing in the market.
This explains the greater requirement and importance of sulphur applications to brassicas.
In grass, sulphur is probably more important for improving the quality of grazing and silage, in terms of protein, than the yield increase achieved.
Deficiency symptoms
Deficiency symptoms in cereals, grass and brassicas show up in the younger leaves first.
Symptoms are a pale yellow appearance (chlorosis) and, later on, stunting. Much later, OSR flowers will have pale yellow, or almost white, petals.
Symptoms in some crops are easily missed, or confused with nitrogen deficiency, and may not be noticed at all, especially in cereals and grass.
Because routine soil analysis cannot be used to predict sulphur deficiency, plant tissue testing is often used.
For oilseed rape and cereals there is the Malate Sulphate test which can be done early in the crop’s life, but it may need to be repeated later at stem extension.