Here There and Everywhere

The biggest reason the children are so robust: fertilizer.

Ms. Nha, her face weathered beyond its 51 years, said her growth was stunted by a childhood of hunger and malnutrition. Just a few decades ago, crop yields here were far lower and diets much worse.

Then the widespread use of inexpensive chemical fertilizer, coupled with market reforms, helped power an agricultural explosion here that had already occurred in other parts of the world. Yields of rice and corn rose, and diets grew richer.

Now those gains are threatened in many countries by spot shortages and soaring prices for fertilizer, the most essential ingredient of modern agriculture.

Some kinds of fertilizer have nearly tripled in price in the last year, keeping farmers from buying all they need. That is one of many factors contributing to a rise in food prices that, according to the United Nations’ World Food Program, threatens to push tens of millions of poor people into malnutrition.

Protests over high food prices have erupted across the developing world, and the stability of governments from Senegal to the Philippines is threatened.

In the United States, farmers in Iowa eager to replenish nutrients in the soil have increased the age-old practice of spreading hog manure on fields. In India, the cost of subsidizing fertilizer for farmers has soared, leading to political dispute. And in Africa, plans to stave off hunger by increasing crop yields are suddenly in jeopardy.

The squeeze on the supply of fertilizer has been building for roughly five years. Rising demand for food and biofuels prompted farmers everywhere to plant more crops. As demand grew, the fertilizer mines and factories of the world proved unable to keep up.

Some dealers in the Midwest ran out of fertilizer last fall, and they continue to restrict sales this spring because of a limited supply.

“If you want 10,000 tons, they’ll sell you 5,000 today, maybe 3,000,” said W. Scott Tinsman Jr., a fertilizer dealer in Davenport, Iowa. “The rubber band is stretched really far.”

Fertilizer companies are confident the shortage will be solved eventually, noting that they plan to build scores of new factories. But that will probably create fresh problems in the long run as the world grows more dependent on fossil fuels to produce chemical fertilizers. Intensified use of such fertilizers is certain to mean greater pollution of waterways, too.

Agriculture and development experts say the world has few alternatives to its growing dependence on fertilizer. As population increases and a rising global middle class demands more food, fertilizer is among the most effective strategies to increase crop yields.

“Putting fertilizer on the ground on a one-acre plot can, in typical cases, raise an extra ton of output,” said Jeffrey D. Sachs, the Columbia University economist who has focused on eradicating poverty. “That’s the difference between life and death.”