Sulphur, a vital nutrient optimising productivity and crop quality on both arable and grassland farms, is fast becoming increasingly important and new forms of sulphur fertiliser are gaining popularity.

Professor Steve McGrath, head of sustainable agricultural sciences at Rothamsted Research, told delegates to a conference at Grantham, that sulphur was an ‘essential’ element for all plants and animals to make essential amino acids.

The event was organised by ICL UK Fertilisers, the company which is now operating the only mine in the world extracting polyhalite, which is marketed as Polysulphate, from beneath the North Sea, at Boulby, North Yorkshire.

Marketed for fertiliser use, this complex mineral supplies a readily spreadable product supplying sulphur along with a range of other important nutrients. In the past four years, several agronomy companies have been testing the product in a range of crops.

Overall, results show clear benefits from sulphur and often improvements in yield and quality from Polysulphate compared to traditional sources of the nutrient.

While at one time adequate supplies came from atmospheric deposition, today’s cleaner air means sulphur needs to be applied for yield and quality crops. In 1970, it was estimated that 8m tonnes of sulphate were deposited from industrial emissions.

Today, that is less than 500,000 tonnes, while fertiliser application on UK farms is only around 220,000 tonnes of sulphate. “Where sulphur is deficient, expensive nitrogen is wasted,” said Prof McGrath.

Cereals are most likely to respond to sulphur treatment on lighter and medium soils, whereas oilseed rape will respond to an application on all mineral soils. Deficiency can be detected by soil, leaf tissue and grain analysis.

Even in legumes, which fix nitrogen in root nodules, sulphur is essential for nodule formation.

The shortage of sulphur was highlighted by Jonathan Telfer, of Lancrop Laboratories, which provides soil and plant tissue testing and holds some 73m data points. Sulphur deficiency has increased from 60% in 1995, to 97% in 2017 across all soils.

For wheat and potatoes, the element can play an important part in quality. Dr Tanya Curtis, of Curtis Analytics, outlined how food processing and retailing industries are increasingly concerned about acrylamide, a neurotoxin that can form at high temperatures in baking, roasting and frying. An inadequate sulphur supply can lead to free asparagine (an amino acid) and sugars in crops which are precursors of acrylamide.

“In wheat trials, sulphur deprivation causes a massive accumulation of free asparagine in the bread,” she said. “When baked, this can lead to levels of acrylamide that are unacceptable in bread.”

Peter Scott, technical director of Origin Fertiliser, told delegates of his firm’s trials on maize, grassland and lucerne – a programme that included independent trials with Galway University. Grassland trials showed significant improvements in dry matter and protein in grass from treatment with Polysulphate.

Yield improvement in one Irish trial was worth an extra £100, allowing for cost of treatment. Similar improvements were seen in forage maize.

Mr Scott questioned why so little sulphur, in any form, was applied to grassland when it had the potential to boost volume and quality of comparatively low cost feed.

Compared to ammonium sulphate, Polysulphate releases sulphur more slowly and speakers believed this was the reason for improved performances, a view confirmed by Scott Garnett, ICL’s UK agronomist.

Mr Garnett told of the wide range of crops being tested by ICL and work on application timing. There is increasing evidence that autumn application is giving benefits due to enabling the crop to make more efficient use of residual soil nitrogen.

“In the field we are seeing stronger root development and significant increases in biomass early in the season. This is an effect we will continue to research in the coming season,” he added.