Following one of the wettest starts to any year on record for many UK regions, growers are being urged to pay particular attention to the effectiveness of sulphur applications this spring.
Solubility, duration of nutrient release and accuracy of rates are of particular importance with many applications potentially going on to very wet soils, says Richard Ward of ICL Growing Solutions.
“Sulphur fertilisation is essential to drive optimum levels of nitrogen utilisation efficiency (NUE), crop quality and yield,” he points out.
But with many different sulphur products on the market, understanding how the different forms work is key to achieving the best results. “The term solubility is often misused. Plant-manufactured and granulated sulphur-containing fertiliser products, including ammonium sulphate (AS) and other nitrogen sulphur (NS) products, break down in the soil and release nutrients relatively rapidly.
“This is especially the case in wet conditions, with nutrients available more quickly and over a shorter period of time for crops to take them up. As a result, the likelihood of nutrient losses and potential environmental problems is increased.”
Polysulphate (48% SO3, 14% K2O, 17% CaO and 6% MgO), in contrast, is a natural granule mined from under the North Sea with minimal subsequent processing, he says.
“This separates polysulphate from all other types of sulphate, with its raw granular form meaning it simply takes longer to dissolve into the soil than industrially manufactured or re-constituted fertilisers.
“Polysulphate is a fully water soluble fertiliser, but with an extended release of nutrients, making it ideal for the UK.”
Trials data
University of Nottingham trials have shown that about 50% of the sulphur contained in polysulphate is available in the first 12 days after application, with the remainder released in the following 6 – 8 weeks. He says this gives crops the best chance of utilising the sulphur as its release is more precisely matched to crop needs through the growing cycle.
Polysulphate also has a wider application window and can be applied early, Richard notes. There is also the flexibility of being able to de-couple nitrogen and sulphur applications if needed, which is not possible with traditional NS products, he adds.
“This is particularly beneficial for legumes that fix their own nitrogen and also in crops like oilseed rape, for example, where a different N:S ratio to a cereal crop is required.
“Whether applied as a straight product or as part of a blended fertiliser, polysulphate offers the flexibility to match the sulphur needs to those of the specific crop.”
“At the same time, it provides valuable calcium, magnesium and potash and all in a low chloride form, making it suitable across all crop types.”
