Chicago crops put in another weak start, as talk of an imminent US frost failed to bite, while news from China and Australia gave investors reason to sell.
While some investors talked of the prospect of a freeze early next week, which would threaten forecasts of bumper yields, it appeared a minority view.
Meteorlogix forecast "generally favourable conditions for pod setting and filling soybeans through the Midwest although more rainfall would benefit in some areas. Warmer weather benefits crop development."
While some analysts continued to talk of colder temperatures on the horizon, they may not arrive for two weeks.
External markets, by the way, were stable, with the dollar making small headway and oil marginally lower.
Staying on supply, Australia raised its wheat forecast by 3.4% to 22.72m tonnes, after rains boosted prospects for harvests in Western Australia, the biggest producing state, and southern parts of the country.
There was weak news for demand too, with China saying that soybean imports may drop below 2m tonnes next month, the lowest for two years, albeit before a recovery in November and December,
The country, responsible for more than half global soybean imports, bought record amounts of soybeans in the first half of the year.
November soybeans, in their first day as the near-term contract following the expiry of September on Monday, stood 4.75 cents lower at $9.04 ¼ a bushel at 06:15 GMT.
December wheat was 1.5 cents lower at $4.52 ½ a bushel, while corn dipped 0.5 cents to $3.17 ¼ a bushel.
In Kuala Lumpur, palm oil put in a better performance, but only after closing down 3.5% on Monday at an eight-week low.
Traders said that data from cargo surveyor Intertek Testing Services showing a 20% slump, to 530,000 tonnes, in Malaysian palm exports in the first 15 days of September had been reflected in Monday's fall.
Some investors were also reported as unwilling to maintain positions with holidays for the Muslim festival of Eid al-Fitr festival approaching.
Benchmark November palm oil closed the morning session on the Bursa Malaysia Derivative Exchange up 37 ringgit at 2,107 ringgit a tonne.