XUAN CANH, Vietnam — Truong Thi Nha stands just four and a half feet tall. Her three grown children tower over her, just as many young people in this village outside Hanoi dwarf their parents.

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.