The Potash Development Association (PDA) is recommending that sulphur (S) be included within all fertiliser programmes for 2025.
This reflects the fact that the heavy rains of the past 12 months or so have washed the key nutrient well down soil profiles or removed it entirely from cropping locations.
Some nutrients have higher mobility levels within soils than others. S is one of the higher profile culprits, alongside nitrogen (N).
Last year’s wet conditions showed very visibly in fields where nitrogen (N) inputs were delayed due to ground conditions, or in trials where N 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.
While slurries, manures and digestates all contain S, the quantities and form of S can vary considerably, depending on feeding and storage practices.
Variations of between 5-55% availability have been identified in availability of S from cattle slurry.
Conversions of plant available inorganic S to organic S 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 S requirement, unless soils have had regular applications of manures over a long period of time.
Fertiliser programmes
Therefore, in one form or another, it is very likely that S will be required in 2025 by most crops, and this should be planned early when making nutrient management plans this season.
The major role of S in all plants is in support of N in protein production, which is hugely important for high crop yields.
In brassicas, (veg, oilseed rape, kale etc.) S is also in glucosinolate compounds, which give them their hot taste. S also reduces the likelihood of immature rapeseed which faces penalty pricing in the market.
This explains the greater requirement and importance of S applications to brassicas.
In grass, S is probably more important for improving the quality of grazing and silage, in terms of protein, than the yield increase achieved.
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, particularly in cereals and grass.
Because routine soil analysis can not be used to predict S deficiency, plant tissue testing is often used.
For oilseed rape and cereals there is the Malate S test which can be done early in the crop’s life, but it may need to be repeated later at stem extension.
