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A mixed blessing Part I

N. Nitrogen. Atomic number seven. Unnoticed, untasted, it nevertheless fills our stomachs. It is the engine of agriculture, the key to plenty in our crowded, hungry world.

Without this independent-minded element, disinclined to associate with other gases, the machinery of photosynthesis cannot function-no protein can form and no plant can grow. Corn, wheat, and rice, the fast-growing crops on which humanity depends for survival, are among the most nitrogen hungry of all plants. They demand, in fact, than nature alone can provide.

Enter modern chemistry. Giant factories capture inert nitrogen gas from the vast stores in our atmosphere and force in into a chemical union with the hydrogen in natural gas, creating the reactive compounds that plants crave. That nitrogen fertilizer-more than a hundred million tons applied worldwide every year-fuels bountiful harvest. Without it, human civilization in its current form could not exist. Our planet’s soil simply could now grow enough food to provide all seven billion of us our accustomed diet. In fact, almost half of the nitrogen found in our bodies’ muscles and organ tissues started out in a fertilizer factory.

Yet this modern miracle exacts a price. Runaway nitrogen is suffocating wildlife in lakes and estuaries, contaminating groundwater, and even warming the globe’s climate. As a hungry world looks ahead to billions more mouths needing nitrogen-rich protein, how much clean water and air will survive our demand for fertile fields?

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.”

Liu grew up in the aftermath of China’s great famine, which lasted from 1959 to 1961 and killed an estimated 30 million people. The famine passed, but scarcity continued until the late 1970s, when farmers regained control of their own harvests. “Within two years, almost overnight, food was in surplus,” recalls Deli Chen, who witnessed those reforms as a boy in a small rice-growing village in Jiangsu Province.

Yet China’s newly entrepreneurial farmers ran into another barrier: the limits of their land. As the country’s population grew by an astounding 300 million people between 1970 and 1990, China’s traditional agriculture struggled to keep up.

Song Linyuan, an elderly but spry farmer in a village northwest of Nanjing, recalls how he once keprt his 1.3 acre of cropland as fertile as possible, composting household waste and spreading manure from his pigs and chickens. In all, his efforts added perhaps a hundred pounds of nitrogen per acre of land each year. He harvested 2,600 to 3,300 pounds of rice per acre.

That’s respectable harvest, a better yield than in many parts of the world. But now he gets more than twice that: 7,200 pounds per acre. It’s a harvest many farmers can only dream of.

The difference? “Better fertilizer,” he says. We’re sitting in a shop surrounded by farmers. Song’s answer provokes a loud discussion. Some agree that fertilizer was key; others say better seeds were more important. In reality the two technologies are intertwined. The high-yielding varieties of rice and wheat that breeders created in the 1950s and 1960s could reach their full

potential only if they got more nitrogen.
The Chinese government made sure those crops were well fed. Between 1975 and 1995 it built hundreds of nitrogen factories, quadrupling the country’s manufacture of fertilizers and turning China into the world’s biggest producer. Song now spreads about five times as much nitrogen as before, saturating his fields with urea-a diary of nitrogen-by casting handfuls of the snow-white granules across green shoots. This adds up to 530 pounds of nitrogen per acre. Farmers who grow vegetables use even more; some spread a ton of nitrogen, or even two, on each hectare. Few of them think they are doing anything harmful. “No, no pollution,” says Song, when asked about the environmental effects of fertilizer.

Scientists tell different story. “Nitrogen fertilizer is overused by 30 to 60 percent” in intensively managed fields, says Xiaotang Ju, of the China Agricultural University of Beijing. “It’s misuse!” Once spread on fields, nitrogen compounds cascade through the environment, altering our world, often in unwelcome ways. Some of the nitrogen washes directly from fields into streams or escapes into the air. Some is eaten, in the form of grain, by either humans or farm animals, but is then released back into the environment as sewage or manure from the world’s growing number of pig and chicken farms.

Deli Chen recalls catching fish as a boy. “The river was clean. You could see right through it”, he says. By 1980 “you couldn’t see the fish anymore.” The cloudiness came in part from proliferating phytoplankton, a symptom of water that’s eutrophic, or overloaded with nutrients.

Our demand for food, to be sure, isn’t solely to blame. The combustion that drives cars and electric generators releases nitrogen oxides into the atmosphere, and when those compounds return to earth in drops of rain, they also act as fertilizers. (This accounts for about a quarter of the nitrogen load in Lake Tai). But worldwide, commercial fertilizer adds up to 70 percent of the nitrogen that human activity produces every year.

Dan Charles  Source: DIJEST, January 2014

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