The substances added to soil to increase its productivity — from the manure and composted matter of ancient agriculture through the guano trade of the 19th century to the synthetic nitrogen fertilizers of the 20th century whose invention is estimated to have made possible the lives of roughly half the people alive today — one of the most consequential technologies in human history and one whose environmental costs are now among the most serious challenges facing planetary agriculture.
Fritz Haber won the Nobel Prize in Chemistry in 1918. He also directed Germany’s chemical weapons program in World War I, overseeing the first use of chlorine gas at Ypres in 1915. His wife, Clara Immerwahr — the first woman to earn a doctorate from the University of Breslau — killed herself in protest at his work. He died in 1934 as a Jewish refugee from the Nazi Germany he had served. And his most consequential achievement was neither gas nor prize but the Haber-Bosch process — the industrial fixation of atmospheric nitrogen into ammonia — which made synthetic fertilizer possible. The process that enabled industrial-scale chemical warfare is the same process that feeds roughly half the people alive today.