The most important fertilizer for producing food is nitrogen.

But, as is obvious with any fertilizer or pesticide or anything else, the dose makes the poison. DDT became a problem when it was used improperly, by people who assumed more would work better, and the same thing happens with people who use too much fertilizer, including the organic kind.

Chemical compounds containing reactive nitrogen are major drivers of air and water pollution worldwide, and hence of diseases like asthma or cancer. If overused, nitrogen pollution could rise by 20 percent by 2050, according to a paper by scientists of the Potsdam Institute for Climate Impact Research.

Mitigation efforts could decrease the pollution by 50 percent without sacrificing yield, they write.

"Nitrogen is an irreplaceable nutrient and a true life-saver as it helps agriculture to feed a growing world population – but it is unfortunately also a dangerous pollutant," says Benjamin Bodirsky, lead-author of the study.

In the different forms it can take through chemical reactions, it can contribute to respirable dust, to the formation of aggressive ground-level ozone, and it can destabilize water ecosystems. Damages in Europe have been estimated at between 1-4 percent of economic output.

Half of that nitrogen pollution damage is from agriculture so the scholars ran extensive computer simulations to explore the effects of different mitigation measures.

Same food, less nitrogen pollution

There is one way to substantially reduce the risks - farmers can more carefully target fertilizer application to plants' needs, using soil measurements.  Currently, every second ton of nitrogen put on the fields is not taken up by the crops but blown away by the wind, washed out by rain or decomposed by microorganisms.

Farmers can also make an effort to efficiently recycle animal dung used as fertilizer.

"Mitigation costs are currently many times lower than damage costs," says co-author Alexander Popp. "For consumers in developed countries, halving food waste, meat consumption and related feed use would not only benefit their health and their wallet. Both changes would also increase the overall resource efficiency of food production and reduce pollution."

And there is biology. Products that require less fertilizer, because they have been genetically optimized to grow in difficult climates, mean less pollution. But before those can be cost-effective in poor countries, they need uptake in rich ones, which means cultural issues, such as anti-science crusades by environmentalists against GMOs, would have to be resolved.

"Health effects of nitrogen pollution more important than climate effects"

"The nitrogen cycle is interwoven with the climate system in various ways," Hermann Lotze-Campen points out, co-author of the study and co-chair of PIK's research domain Climate Impacts and Vulnerabilities.

Nitrous oxide, or laughing gas, on the one hand is one of the major greenhouse gases. On the other hand, nitrogen containing aerosols scatter light and thereby cool the climate. And as fertilizing nutrient, nitrogen enhances the growth of forests which binds CO2.

"Currently the health effects of nitrogen pollution are clearly more important, because the different climate effects largely cancel out," says Lotze-Campen. "But this may change – hence limiting nitrogen would have the double benefit of helping our health today and avoiding climate risks in the future."

Citation: Bodirsky, B.L., Popp, A., Lotze-Campen, H., Dietrich, J.P., Rolinski, S., Weindl, I., Schmitz, C., Müller, C., Bonsch, M., Humpenöder, F., Biewald, A., Stevanovic, M. (2014), 'Reactive nitrogen requirements to feed the world in 2050 and potentials to mitigate nitrogen pollution', Nature Communications, DOI:10.1038/ncomms4858