Nitrogen (N) - fertilisers

Nitrogen is a crucial ingredient in fertilisers. And thanks to a pair of clever Germans, the Haber-Bosch process of fixing nitrogen from the air ensures that the planet's burgeoning population can still feed itself. But does it also threaten the planet with an environmental disaster more calamitous than climate change? And could the solution be provided by genetic engineers? (Picture: Legume root nodules; Credit: Ninjatacoshell/Wikicommons)