A new study shows that there has been a real fall in fertiliser footprint across the EU, even when imports are taken into account. One reason for this shift could be our changing tastes, from "meat and two veg" to "stir fry" or "quinoa salad".

Thomas Nesme from the University of Bordeaux in France and his colleagues assessed the changes in European fertiliser footprint by estimating the amount of mineral phosphorus fertilisers applied to soils in both EU and non-EU countries, and calculating how much mineral phosphorus was used to grow the food imported into the EU.

Within the EU the team showed that 1.87 Tg of mineral phosphorus was used in 1995, falling to 1.09 Tg per year by 2005. As expected, this reflects the environmental regulations to limit fertiliser overuse, and perhaps also the high levels of phosphorus already residing in the soil.

"Since farmers applied phosphorus fertiliser in great excess in the 1970s and 1980s there was a large legacy of phosphorus in the soil, making it easy to reduce fertiliser application," said Nesme.

But did this reduction also reflect a greater dependence on imported food? To their surprise, Nesme and his colleagues found that the EU imported a virtual flow of phosphorus of 0.55 Tg per year in 1995, but that this fell to 0.50 Tg per year by 2009.

"These results were contrary to our hypothesis that trade increases would be used to help the EU reduce its domestic phosphorus fertiliser use by outsourcing its phosphorus footprint abroad," they write in Environmental Research Letters (ERL). But looking at the figures in detail revealed a more complex picture.

Over the same time period the countries that the EU sources most of its imports from have changed dramatically. In 1995 imported food was dominated by trade from North America and South East Asia. By 2009 the dominant importing countries became South America and South East Asia.

Globally there has been a general trend in reducing mineral fertiliser use in these exporting countries. In some of the emergent countries – Brazil and Argentina in particular – fertiliser is used very efficiently.

"Exporters of 2009 have lower phosphorus fertilisation rates than exporters of 1995," said Nesme. Though he cautions that this isn't the case everywhere, and countries such as China have seen huge increases in fertiliser use over the same period.

Changing tastes are also likely to have played a role. Animal products require large amounts of mineral phosphorus fertiliser in their production chain, so a trend towards eating less meat in EU countries will also have helped to reduce the fertiliser footprint.

"This has to be nuanced, however, by the fact that many livestock farms in the EU now rely on imported soybean – a commodity with a significant phosphorus fertiliser footprint – whereas many livestock farms were using pastures in the past, with much lower mineral phosphorus fertiliser demand," said Nesme.

Looking ahead, Europe's legacy of excess phosphorus from previous over-application should help to keep fertilisation rates low across the EU, but other countries may find that intensive farming starts to leave their soils impoverished.

"If these exporting countries want to keep their soil fertile they will have no choice but to increase their phosphorus fertiliser use," said Nesme. But potentially this need can be better managed through greater recycling of phosphorus by applying animal manure to fields and recycling of urban waste. Meanwhile, continued trends of eating less meat are likely to help drive down fertiliser footprints too.

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