Driving his tractor through a windy field at the feet of western Canada's Rocky Mountains, Doug McBain spreads small white pellets and canola seed into the freshly turned soil.

This is no ordinary farming process. McBain is testing a new form of fertiliser that could help rejuvenate crops by returning sulphur - one of the biggest by-products of oil and gas production - back to the earth.

Sulphur is essential for healthy crop growth and occurs naturally in food such as onions and eggs. Yet its combination with other elements can create dangerous compounds such as hydrogen sulphide.

Companies helping to meet rising energy demand are tapping into oil and gas fields with higher levels of the bright yellow chemical. Tighter regulations also mean more sulphur must be removed from transport fuel before it can be burned.

Putting sulphur to use

Nearly 60 million tonnes of sulphur are extracted globally each year. Much of this goes into the production of sulphuric acid, which is used globally in numerous sectors, including metals and phosphate mining.

But there are questions over what to do with what's left. One answer lies in agriculture. Farmers in some parts of the world are struggling with a sulphur shortage. Large areas of Asia, Africa, Brazil and the western USA lack enough to produce crops.

In India, where intensive farming has led to a lack of nutrients in the ground, almost half the soil tested around the country suffers from sulphur deficiency, according to the US-based non-profit The Sulphur Institute.

"Energy companies are removing more sulphur from their hydrocarbons at a time when crops are crying out for it," says Shell Technical Services Manager Rafael Garcia.

In 2004, Shell developed Thiogro, a technology combining sulphur with phosphate, another commonly used fertiliser. The sulphur is incorporated into the phosphate fertiliser in the form of microscopic particles that break down over time in the soil to provide a longer-lasting, more stable source of sulphur nutrition with less chance of run-off. Farmers now buy more than 150,000 tonnes of the product each year, helping to boost harvests from soybeans in Brazil, to rice in China and clover for animal fodder in Australia.

Boosting harvests

The latest variation of the product plans to go further. Urea-ES combines two crucial plant nutrients: nitrogen held inside granules of urea - the chemical made from ammonia - and the microscopic particles of elemental sulphur recycled from Shell's oil and gas refineries. With field trials underway in Brazil and North America, Shell intends to license the technology globally to fertiliser manufacturers.

For farmers like McBain, the new fertiliser is a way of boosting harvests. Surveying the soil first ploughed by his grandfather over a century ago, McBain reflects on fertiliser's role in modern farming. "Since I started working the fields with my dad, our crop yield has just about doubled," he says.

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