US soyabean futures slumped on Wednesday on rising supplies from the ongoing US harvest and concerns about a delay in finalizing a "phase one" trade deal with China that could speed imports by the world's top buyer.
Corn also weakened on harvest pressure and dull demand for US supplies, while wheat firmed on technical buying and short-covering as adverse weather has reduced wheat production prospects in the southern hemisphere.
The market's focus has been on Friday's monthly supply and demand report from the US Department of Agriculture (USDA) for a fresh indication on this year's rain-disrupted US corn and soyabean crops as well as drought-hit southern hemisphere wheat production.
But news that a meeting between US President Donald Trump and Chinese President Xi Jinping to sign a long-awaited interim trade deal could be delayed until December triggered selling at midmorning, pushing soyabeans to session lows.
"Any delay is obviously not a good thing," said Jim Gerlach, president of A/C Trading.
Chicago Board of Trade (CBOT) January soyabean futures were down 5 cents at $9.29-1/4 a bushel at 11:33 a.m. CST (1733 GMT), while December corn was down 1/2 cent at $3.81-1/4 a bushel.
CBOT December wheat rose 3-1/4 cents to $5.18-1/2 a bushel, a 1-1/2 week high, after holding technical chart support at its 20-day moving average.
Wheat prices were supported by concerns about crop output in Argentina and Australia as a tighter grain supply could boost export prospects for US shipments.
Commodity brokerage INTL FCStone said a poll of its clients estimated Australia's 2019/20 wheat crop at 15.54 million tonnes, 19.1% lower than Australia's official estimate of 19.2 million tonnes.