US corn futures hit a two-month low on Monday and soyabean futures touched their lowest in seven weeks on forecasts for improving crop weather in South America and uncertainty about prospects for a US-China trade deal, analysts said.
Wheat futures rose as worries about tightening global supplies sparked a round of short-covering.
As of 12:43 p.m. CST (1843 GMT), Chicago Board of Trade December corn futures were down 3 cents at $3.68-1/4 per bushel after dipping to $3.68, the contract's lowest since Sept. 18. CBOT January soyabeans were down 7-1/4 cents at $9.11 a bushel after hitting $9.10, their lowest since Sept. 30.
Forecasts called for beneficial rains in portions of Brazil and Argentina, the world's No. 1 and No. 3 soyabean producers.
The trade's attention is shifting to South American crop prospects as the US harvest winds down. Ahead of the US Agriculture Department's weekly crop progress report, analysts surveyed by Reuters on average expected the government to report that US farmers harvested 77% of the corn crop and 91% of the soyabean crop by Sunday.
Corn and soya futures were also pressured, along with Wall Street equity markets, after CNBC reported that the mood in Beijing about a trade deal was pessimistic due to President Donald Trump's reluctance to roll back tariffs.
Earlier, Chinese state media had said Washington and Beijing held "constructive talks" on trade in a high-level phone call on Saturday that included Vice Premier Liu He, US trade representative Robert Lighthizer and Treasury Secretary Steven Mnuchin.
The soyabean market is particularly sensitive to developments in the trade negotiations as the oilseed was the most valuable US agricultural export to China prior to the dispute that has seen Beijing impose retaliatory tariffs on US farm goods.
Wheat futures firmed, bucking the weak trend in corn and soyabeans. CBOT December wheat was up 4 cents at $5.06-3/4 a bushel, rallying after recording a one-month low at $4.98-1/2.
Commodity funds hold a net short position in CBOT wheat futures, leaving the market vulnerable to bouts of short-covering.