Traders also bought soybeans and sold corn after active unwinding of those spreads over the previous two sessions as the oilseed battles to recapture US planted acres this spring.

Corn was flat, held back by profit-taking a day after its steepest rally in three months as the US Department of Agriculture confirmed a large corn export sale to an unknown buyer widely believed to be China.

Wheat drifted lower, following corn.

"Two days of getting out of those bean-corn spreads was plenty," said ABN Amro analyst Charlie Sernatinger.

Soybean futures have mostly outpaced gains in corn since early February as US farmers were expected to bolster corn acreage this spring, some of it at the expense of soybeans.

Old-crop contracts have also steadily climbed in that time as lower supplies from Brazil and Argentina following a drought in the crucial growing phase in January and February bolstered demand for US supplies.

The USDA said in a report on Friday that drought had reduced the soybean crop in Brazil, the world's No. 1 exporter, by 9 percent, and Argentina's crop by 11 percent, over the past three months.

Export prospects for US soybeans were improving despite rising prices as many global buyers had expected more South American supplies to be available, analysts with Oil World said on Tuesday.

Gains in old-crop soybeans exceeded gains in new-crop months amid spreading linked to tight supplies from last autumn's harvest.

"I think beans are buying acres from corn and also there should be a couple of weeks of big soybean export sales," said Rich Nelson, research director for Allendale Inc.

Benchmark Chicago Board of Trade May soybeans rose 1.2 percent to $13.51 per bushel by 10:33 a.m. CDT (1533 GMT) while new-crop November gained 0.9 percent to $13.11.

Corn futures climbed modestly despite USDA confirmation of a 240,000-tonne sale of US corn to an unknown buyer on Tuesday.

Futures were up nearly 4 percent over the previous two sessions amid widespread rumors that China had bought US old-crop corn.

"There's some buy-the-rumor, sell-the-fact selling in the corn," said ABN Amro analyst Charlie Sernatinger. "It's highly likely that it's China, a private purchase."

CBOT corn for May delivery rose 0.3 percent to $6.61-1/2 a bushel, while new-crop December corn eased 0.3 percent to $5.66-3/4 a bushel.

Wheat drifted lower after two days of gains, with May dipping 0.4 percent to $6.49 a bushel.