Soybeans opened Wednesday's trade lower on profit-taking and corn-soybean spreading, sources say.

March corn opened Wednesday's session 1 3/4 cents higher at $6.35 per bushel, while March wheat was 1 cent higher at $6.45 3/4, according to Barchart.com. January soybeans -- which saw monster gains in Tuesday's session -- fell 6 cents at the open to $11.93 3/4 per bushel.

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The South American crop-stressing weather situation remains the primary driver of the grains Wednesday, notably in the absence of the Eurozone debt crisis as a market factor. But, that influence manifested itself differently in the Tuesday/Wednesday overnight trade and earlier Wednesday morning.

"We're seeing some profit-taking, especially in beans. Maybe some spreading, too, with buying corn and selling soybeans," says AgTraderTalk.com market analyst and trader Kevin Penner. "Thin holiday volume can really magnify these market moves."

Another main feature of the prices so far Wednesday comes from the specifics of the South American weather situation; there are a lot of soybean acres yet to be planted on account of the dry conditions, but the corn is in the middle of pollination, arguably the most critical development time for the crop. That could aim more upward momentum toward the corn pits.

"It's the realization that corn is hurting a lot worse in South America right now than soybeans," Penner says. Corn is pollinating and there's still really another month before heat will jack up the beans."