Sulphur fertilisers can reduce the level of the acrylamide carcinogen in cereals and potato crops, delegates to last week’s ICL Fertilisers technical and agronomists conference in Grantham heard last week.

Tanya Curtis of Curtis Analytics explained that acrylamides, which are formed by cooking – baking, roasting and frying – starchy foods at high temperatures have been linked to lung cancer. The European Food Safety Agency (EFSA) is sufficiently concerned to be working on maximum limits and is due to introduce legislation from March 2020 requiring significant reductions in acrylamide levels in foodstuffs.

Work at Rothamsted Research has found high levels of acrylamide in sulphur-deprived wheats – the lower the grain sulphur content, the higher the acrylamide levels. There is also a link to the amino acid asparagine – stressed plants have higher levels of this amino acid, and sulphur deprivation is a stress factor.

While the acrylamide reducing response to sulphur varies by variety, Dr Curtis said adding the plant nutrient to avoid deficiency will mitigate the problem, while plant breeding could offer a longer-term solution.

A research project funded by the AHDB and crisp maker Pepsico found a correlation between increasing levels of sulphur crop fertilisation and reduced acrylamide in potato food products. Dr Curtis said the McDonalds chain has already taken action to cut acrylamide in fried potato products served in its restaurants.

Peter Scott, technical director at Origin Fertilisers, warned that sulphur applications to forage crops are at less than optimum rates. Just 10% of UK grassland received a dose of sulphur in 2017, compared to over 70% of the winter oilseed rape area and just under that figure for winter wheat. And yet it is well documented that sulphur helps increase the dry matter yield of both grass and maize silages, leading to greater nutrient intake and milk and meat yields.

The optimal level is a 12:1 nitrogen to sulphur plant nutrient ratio, and an average grass silage should be at least 0.25% sulphur, he advised. However, the average UK silage has just 0.19% sulphur- a 25% shortfall on that recommended.

Mr Scott attributed this disparity to a mixture of ignorance and inertia – farmers were reluctant to change from their traditional blend; tended to over-estimate the sulphur content of organic manures; didn’t have an integrated nutrient management plan; were concerned that it was an antagonist to selenium and copper uptake; or simply failed to understand the importance of sulphur as a plant nutrient.

Origin’s trials work on grass, maize and lucerne crops showed that compound NPK or DAP fertilisers plus ammonium sulphate increased yields in all three crops compared to controls without a sulphur fertiliser, and that switching ammonium sulphate for Polysulphate increased yield again.

ICL’s Polysulphate fertilisers, made from polyhalite extracted from beneath the North Yorkshire moors, is now available in three forms – Polysulphate, PotashpluS and PKpluS. November saw the mine produce a record 75,000 tonnes of polyhalite, “putting it on track towards a target of a million tonnes next year and up to three million tonnes by 2030,” says the company.

“Our first year of PotashpluS sales exceeded our expectations, and the feedback from customers and farmers has been really positive,” noted ICL UK sales and marketing director Howard Clark. “Our agronomy trials programme, including our own and independent trials, shows all polysulphate products performed as well and often better than traditional products.”