Rice Farmers Adapt to Global Warming by Reviving Hardy Seed Breeds and Nimbly Adjusting Planting Rotations

(p. A1) Rice is in trouble as the Earth heats up, threatening the food and livelihood of billions of people. Sometimes there’s not enough rain when seedlings need water, or too much when the plants need to keep their heads above water. As the sea intrudes, salt ruins the crop. As nights warm, yields go down.

These hazards are forcing the world to find new ways to grow one of its most important crops. Rice farmers are shifting their planting calendars. Plant breeders are working on seeds to withstand high temperatures or salty soils. Hardy heirloom varieties are being resurrected.

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The climate crisis is particularly distressing for small farmers with little land, which is the case for hundreds of millions of farmers in Asia. “They have to adapt,” said Pham Tan Dao, the irrigation chief for Soc Trang, a coastal province in Vietnam, one of the biggest rice-producing countries in the world. “Otherwise they can’t live.”

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(p. A10) “We now accept that fast-rising salty water is normal,” said Mr. Pham, the irrigation chief. “We have to prepare to deal with it.” Where saltwater used to intrude 30 kilometers or so (about 19 miles) during the dry season, he said, it can now reach 70 kilometers inland.

Climate change brings other risks. You can no longer count on the monsoon season to start in May, as before. And so in dry years, farmers now rush to sow rice 10 to 30 days earlier than usual, researchers have found. In coastal areas, many rotate between rice and shrimp, which like a bit of saltwater.

But this requires reining in greed, said Dang Thanh Sang, 60, a lifelong rice farmer in Soc Trang. Shrimp bring in high profits, but also high risks. Disease sets in easily. The land becomes barren. He has seen it happen to other farmers.

So, on his seven acres, Mr. Dang plants rice when there’s freshwater in the canals, and shrimp when seawater seeps in. Rice cleans the water. Shrimp nourishes the soil. “It’s not a lot of money like growing only shrimp,” he said. “But it’s safer.”

Elsewhere, farmers will have to shift their calendars for rice and other staple grains, researchers concluded in a recent paper. Scientists are already trying to help them.

The cabinet of wonders in Argelia Lorence’s laboratory is filled with seeds of rice — 310 different kinds of rice.

Many are ancient, rarely grown now. But they hold genetic superpowers that Dr. Lorence, a plant biochemist at Arkansas State University, is trying to find, particularly those that enable rice plants to survive hot nights, one of the most acute hazards of climate change. She has found two such genes so far. They can be used to breed new hybrid varieties.

“I am convinced,” she said, “that decades from now, farmers are going to need very different kinds of seeds.”

Dr. Lorence is among an army of rice breeders developing new varieties for a hotter planet. Multinational seed companies are heavily invested. RiceTec, from which most rice growers in the southeastern United States buy seeds, backs Dr. Lorence’s research.

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The new frontier of rice research involves Crispr, a gene-editing technology that U.S. scientists are using to create a seed that produces virtually no methane.

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In Bangladesh, researchers have produced new varieties for the climate pressures that farmers are dealing with already. Some can grow when they’re submerged in floodwaters for a few days.

Others can grow in soils that have turned salty. In the future, researchers say, the country will need new rice varieties that can grow with less fertilizer, which is now heavily subsidized by the state. Or that must tolerate even higher salinity levels.