When the rains are paltry, rice farmers don't even plant a third rice crop, as they had before, or they switch to shrimp, which is costly and can degrade the land further. It has depleted aquifers, driven up fertilizer use, reduced the diversity of rice breeds that are planted, and polluted the air with the smoke of burning rice stubble.

On top of that, there's climate change: It has upended the rhythm of sunshine and rain that rice depends on.

So in dry years, farmers now rush to sow rice 10 to 30 days earlier than usual, researchers have found. Wlsewhere, farmers will have to shift their calendars for rice and other staple grains, researchers concluded in a recent paper.

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

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.

Floods inundate a rice farm in Humnoke, Ark. Rice is central to the story of the United States.

There's the problem created by the very success of so much intensive rice farming: Groundwater is running dangerously low. Mark Isbell, a second-generation rice farmer, signed up.

His experiment, carried out over seven years, concluded that by not flooding the fields continuously, farmers can reduce rice methane emissions by more than 60 percent.

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