Sulfur fertiliser use increased as air pollution dropped

Research by the University of Colorado at Boulder has found a correlation between increased use of the chemical in agriculture as atmospheric levels decline. 

Ambient concentrations of sulfur, an essential nutrient plants need to survive, were particularly high during the 1980s, and farmers could rely on particles drifting from the sky onto their land, helping fertiliser their crops. 

But while flora relies on sulfur, for many other life forms it is considered toxic. Regulations were introduced to limit the amount deemed acceptable in the air, driven in part by concerns over acid rain, which it causes, and resulting rising mercury levels in fish — with sulfur known essentially capable of making a number of heavy metals ‘mobile’, helping them find a way into rivers and other water sources.

Now a team of scientists has compiled the first ever assessment of fertiliser use data for the Midwestern US between 1985 and 2019, and identified that as sulfure levels fell due to new laws, farmers have increasingly looked to sulfur-rich fertiliser to plug the gap between what their crops need and what can is present in the atmosphere. This adoptive behaviour again presents major problems for nature, with heavy metals more likely to find their way to livestock through run off.

‘We find a clear increase in sulfur fertilizer use commensurate with a decline in atmospheric deposition,’ said Eve-Lyn Hinckley, a Cooperative Institute for Research in Environmental Sciences (CIRES) fellow, University of Colorado Boulder ecologist and lead author of a new assessment of sulfur fertilizer use. ‘It’s the same form of sulfur as was going on with acid rain. However, that was diffuse, widespread atmospheric deposition, and this is intense, targeted applications in much larger amounts.’

Hinckley has pointed out that despite the significant risks, farmers do need fertilisers rich in sulfur, and therefore prohibition is not possible. Instead, the goal now is to follow what others have achieved with other nutrients that potentially pose an environmental threat — for example nitrogen and phosphorous: understanding how selective timing and application can help mitigate the negative impacts.  

Last year, Air Quality News reported on research that synthetic nitrogen-based compounds, often used to spray and fertilise crops, accounted for 2% of global emissions. You can read more on the study here.

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