The breakthrough came in 1909, when Fritz Haber, a German-Jewish chemist, developed a technique for synthesizing ammonia, a nitrogen compound. By 1914, the experimental technique had become industrially viable, and in that year Haber’s method, called the Haber–Bosch process, yielded as much reactive nitrogen as the entire Peruvian guano trade. The

Haber’s nitrogen allowed the European conflict to drag on for two more years, raising the casualties on each side by several millions.

The night gardener told me that the man who invented modern-day nitrogen fertilizers—a German chemist called Fritz Haber—was also the first man to create a weapon of mass destruction, namely chlorine gas, which he poured into the trenches of the First World War. His green gas killed thousands and made countless soldiers claw at their throats as the