Nitrogen is the bringer of life and death to mankind on a massive scale, but it may also threaten us with a potential environmental disaster as frightening as climate change.

Justin Rowlatt gets the chemical lowdown - replete with the inevitable bangs - from professor Andrea Sella of University College London. He travels to home of the Haber-Bosch process - which first cracked open nitrogen's explosive potential a century ago - at BASF's gigantic chemical works in Ludwigshafen.

We send our Washington DC correspondent Rajini Vadyanathan to a sewage works, while Justin heads for the John Innes Centre to meet Giles Oldroyd - a genetics researcher hoping to break man's nasty nitrogen addiction. Show less