How modern fertilizer, and the nitrogen in it, have led to bountiful harvests with a larger environmental cost. Scientists are trying to find a balance:

“The nitrogen dilemma is most starkly visible in China, a country that loves its food and worries that supplies might run out. To the casual visitor, that anxiety seems misplaced. There’s a feast, it seems, on every street. In a restaurant called San Geng Bi Feng Gang, on the outskirts of Nanjing, I watch with wonder as dishes parade by: steamed fish, fried mutton chops, chrysanthemum-leaf-and-egg soup, a noodle dish made from sweet potatoes, fried broccoli, Chinese yams, steaming bowls of rice.

“‘Did you always eat this well?’ I ask Liu Tianlong, an agricultural scientist who’s introducing me to farmers nearby.

“His boyish smile fades, and for a second he looks grim. ‘No,’ he says. ‘When I was young, you were lucky to get three bowls of rice.’”