Growers of bread-making wheat may need to apply selenium fertilisers to ensure the grain meets human dietary needs.

Researcher Fangjie Zhao pointed out that while the element was not required by the crop, it played an important anti-cancer, anti-virus and male-fertility role in foods.

But UK consumers’ daily intake of selenium had halved over the past quarter century, mainly because millers were relying more on home-grown wheat than imports from North America and Canada, Dr Zhao explained.

There soils contained about 10 times as much selenium. Waitrose was already selling selenium-enriched bread, which, he suspected, was made from imported wheat.

Millers and bakers were prevented by law from adding selenium to flour and bread, so the search was on to find the correct levels that needed to be applied to UK crops.

“We need to know the appropriate amounts. They are tiny, and we don’t want to apply too much, as the range between toxicity and sufficiency is narrow.”

In the second year of trials rates of 5-200g/ha were being assessed. One complication was that there was clearly an interaction between sulphur and selenium.