CHICAGO, Jan 17 (Reuters) - Chicago Board of Trade soybean futures tumbled near a two-year low on Wednesday as Brazilian crops benefited from improved weather and challenged U.S. exports on the global market, analysts said.

Corn futures set a three-year low, while wheat ended nearly unchanged after touching a seven-week low on Tuesday.

Traders monitored production potential and exports from Brazil, the world's top soy supplier, as rains recently improved conditions for South America's soybean and corn crops.

Analysts have slashed forecasts for Brazil's harvests due to earlier drought damage.

However, February and March shipments of soybeans to China, the world's biggest importer of the oilseed, are cheaper from Brazil than from the U.S. Gulf, said Arlan Suderman, chief commodities economist for broker StoneX.

"That tells me that Brazil is not concerned about the size of their crop," Suderman said. "The world can get it a lot cheaper from Brazil right now."

The CBOT's most actively traded soybean futures ended down 21-1/2 cents at $12.05-3/4 a bushel. They finished close to the session low of $12.05 and near Friday's two-year low of $12.03.

Corn futures slipped 1-1/4 cents to close at $4.42-1/4 per bushel after falling earlier to $4.40, the lowest level since December 2020.

"Expectations of big crops in South America have got everyone running for the hills," said Ole Houe at IKON Commodities in Sydney.

Corn also remained under pressure after the U.S. government on Friday raised its U.S. yield estimate to a record high and said domestic stocks in December were up 13% from a year earlier.

Gains in the dollar and a risk-off trading mentality also loomed over agricultural markets, said Matt Wiegand, commodity broker for FuturesOne. The dollar index hit a one-month high, making U.S. farm products look less attractive to importers.

"You've had a massive dollar spike to start the week," Wiegand said. "That's certainly not helping."

Most-active CBOT wheat settled up 1/2 cent at $5.82-1/2 per bushel, while deferred wheat contracts weakened. (Reporting by Tom Polansek in Chicago. Additional reporting by Gus Trompiz in Paris and Peter Hobson in Canberra; Editing by Marguerita Choy, Tasim Zahid and Lisa Shumaker)