Joe Waldman is saying goodbye to corn after yet another hot and dry summer convinced him that rainfall won't be there when he needs it anymore.

"I finally just said uncle," said Waldman, 52, surveying his stunted crop about 100 miles north of Dodge City, Kansas. Instead, he will expand sorghum, which requires less rain; let some fields remain fallow; and restrict corn to irrigated fields.

While farmers nationwide planted the most corn this year since 1937, growers in Kansas sowed the fewest acres in three years, instead turning to less-thirsty crops such as wheat, sorghum and even triticale, a wheat-rye mix popular in Poland. Meanwhile, corn acreage in Manitoba, a Canadian province about 700 miles north of Kansas, has nearly doubled over the past decade due to weather changes and higher prices.

Shifts such as these reflect a view among food producers that this summer's drought in the United States — the worst in half a century — isn't a random disaster. It's a glimpse of a future altered by climate change that will affect worldwide production.

"These changes are happening faster than plants can adapt, so we will see substantial impacts on global growing patterns," said Axel Schmidt, a former senior scientist for the International Center for Tropical Agriculture now with Catholic Relief Services.

While there is still debate about how human activity is altering the climate, agriculture is already adapting to shifting weather patterns.

Agribusiness giant Cargill is investing in northern U.S. facilities, anticipating increased grain production in that part of the country, said Greg Page, the chief executive officer of the Minneapolis-based company.

"The number of rail cars, the number of silos, the amount of loading capacity" all change, Page said in an interview in New York. "You can see capital go to where there is ability to produce more tons per acre."

Losses in some areas will mean gains in others, Page said. A native of Bottineau, a small town on North Dakota's border with Canada, Page said that when he was in high school in the 1960s, "you could grow wheat, or wheat. That was it," he said.

"You go to that very same place today — they can grow soybeans, they can grow canola, they can grow corn, they can grow field peas and export them to India," he said. "A lot of that has been to do with the fact that they have six, eight days more of frost-free weather."

This year's US drought was the most severe since 1954, according to the Palmer Drought Index, which has measured such weather phenomena since 1895. The hot, dry conditions pushed estimates for the country's corn harvest to the lowest level in six years and the projected average cash price to an all-time high.

September was the 331th consecutive month in which temperatures worldwide topped the 20th-century average, the U.S. National Climatic Data Center said Monday. Corn futures in Chicago, which reached a record $8.49 a bushel in August, have since declined 13 percent, closing Monday at $7.325.

The Department of Agriculture this year updated its plant hardiness map for the first time since 1990, shifting many regions into zones that are 5 degrees Fahrenheit warmer than in the late 20th century.

The data show a climate in transition, with agriculture needing to adapt, said Wolfram Schlenker, an environmental economist at Columbia University in New York. Even small changes in average temperature may shift climate patterns, affecting rainfall, evaporation rates and the ability of plants to thrive in certain environments, he said.

"We'll see a real mix of crop signals and climate signals," he said in an interview. For farmers in poorer countries, adaptation to new weather patterns "can be a matter of life and death," he said.

Crop insurance paid out to farmers experiencing lost yields may top $25 billion this year, with the biggest losses concentrated in Midwest states, according to Kansas State University. Corn yields may average 122 bushels an acre this year, the lowest since 1995, the USDA said last week.

Western Kansas is in its second year of severe drought. Last year was the third-driest in Dodge City since record- keeping began in 1900; this year, the town's temperatures were above-average every month through July.

Weather has always been harsh in the region where Dust Bowl storms first blew, requiring farmers to rely on low-water crops like wheat to survive. The harnessing of the Ogalalla Aquifer, a massive underground lake that runs from South Dakota to west Texas provides about 30 percent of U.S. irrigation groundwater, has allowed corn to flower where rainfall can't support it. New varieties of hybrid plants and genetically modified seed have also helped.

That expansion may be ebbing with the drought, and the Ogalalla.

Ty Rumford, who manages High Choice Feeders south of Scott City, Kansas, is planting less corn and more triticale to feed the 37,000 animals in his company's two feed yards. A hardier crop is necessary as water availability falls, he said.

"When the wells were put down here in the '40s, they went 30 foot down into a 180-foot-deep aquifer,'' he said. ''Those wells were pumping 1,500, 2,000 gallons a minute in the '50s. Now we're at 135 feet deep, and they're pumping 200, 250 a minute. We've got to make sure we have enough water."

Triticale works for feedlots because it's used on-site in cattle rations, lowering costs, Rumford said. Its appeal is less for farmers who grow crops for the marketplace, he said.

"We're consuming everything we grow, so it's not important to have an outside market" for triticale, he said.

Corn, meanwhile, is too embedded in American life to lose its position as the country's most valuable crop, Rumford said. The grain was worth $76.5 billion last year, more than twice the value of soybeans and five times that of wheat.

Most U.S. ethanol comes from corn. Cattle eat corn. High- fructose corn syrup is a common sugar substitute. Shippers such as Cargill and Archer Daniels Midland, based in Decatur, Ill., are set up to trade and process corn. Farmers buying insurance against losses have a wealth of data for the grain. Policies for triticale, canola, or edible beans, for example, are less common in Kansas because of a lack of actuarial data.

For the most part, the country's mid-section, with its infrastructure, its soil and its usually beneficial weather, will remain the nation's Corn Belt, said Jerry Rowe, manager of the Heritage Grain Cooperative in Dalton City, Ill., traditionally the second-biggest corn-producing state.

"I don't have a place to store pinto beans, OK?" said Rowe, who has managed his community's grain elevator for 25 years. "This is corn and soybean ground. The reason someone else is more diverse is because there's more money in being diverse. It's all economics."

Still, the hotter, dryer weather pattern may change crop rotations even in the heart of the Corn Belt. "Wheat acres will be very high" next year, said Tabitha Craig, who sells crop insurance for Young Enterprises, an agricultural services and input dealer in New Hartford, Mo.

Climate change will probably push corn-growing regions north while making alternatives to the grain more important elsewhere, said John Soper, the vice president of crop genetics research and development for Pioneer, the seed division of DuPont. The company's researchers anticipate more corn in Saskatchewan and Manitoba, traditional Canadian wheat-growing areas, while sorghum and sunflowers may experience a revival in Kansas as rainfall declines and irrigation becomes less practical, he said.

The company is developing new varieties of corn, both in traditional hybrid and genetically modified seeds, while boosting research in sorghum and other crops that don't need irrigation in areas where they're expected to make a comeback, he said.

Still, fighting drought with better seeds and new trade sources only mitigates the effects of climate change, said Roger Beachy, the first head of the U.S. Department of Agriculture's National Institute for Food and Agriculture and now a plant biology professor at Washington University in St. Louis. New crops — and new markets for those crops — will be needed to ease what will be a wrenching transition for some farmers and consumers, he said.

"We need to use biodiversity and crop varieties to our advantage," said Beachy, whose work with Monsanto in the 1980s and 1990s led to the first genetically modified food crop.