Soybeans led a slide in crop prices after a surprise move by China to raise short-term interest rates, leading to fears that Beijing would squeeze the demand which has been central to commodities' rally.
Matters were made worse by the impact of China's move, delivered through a rate rise at a three-month bill auction, on the dollar, to which investors rushed in a quest for security.
The greenback pressed the euro back below $1.43 at one point, gaining more than 1 cent on the day, making US exports such as crops more expensive to European buyers.
They were more dear for Japanese buyers too, after Japan's new finance minister, Naoto Kan, stoked the dollar's rise by saying he wanted a cheaper yen, which fell to a three-month low.
A broad range of commodities lost ground, with copper closing 1.9% lower in New York, and oil down 0.7% at $82.64 a barrel at 08:00 GMT.
Among crops, vegetable oils, of which China is a huge importer, were the big losers.
March palm oil tumbled 2.7% from seven-month highs to 2,630 ringgit a tonne in Kuala Lumpur, while in Paris, February rapeseed ended down E2.50 at E291.50 a tonne.
In Chicago, March soybeans ended down 3.1% at $10.26 a bushel. The soon-to-expire January lot closed down 3.1% at $10.17 ¾ a bushel.
"China is by far the largest customer for US bean exports so any slowdown in Chinese bean import demand would have a big negative impact on this market," Vic Lespinasse, the GrainAnalyst.com analyst, said.
Indeed, the news was serious enough to demote hopes for fund rebalancing, forecast to start in earnest on Friday, and supposed to favour 2009's commodity laggards, including grains.
"The bears' fear of large scale index fund buying starting late tomorrow has been replaced, at least for now, with the bulls' fear of a slowdown in Chinese soybean import demand," Mr Lespinasse said.
Investors were slightly more sparing with the grains, given they are less dependent on Chinese demand.
Nonetheless, poor weekly export sales data, of 365,000 tonnes for corn and just 93,000 tonnes for wheat, hinted that few other countries wanted them either.
"Disappointing export sales do not inspire much confidence in a rebound for the grains," US broker Benson Quinn Commodities said.
And, indeed, they didn't. Corn closed down 4.25 cents at $4.17 ½ a bushel for March.
March wheat ended down 9.5 cents at $5.57 ¾ a bushel despite some thoughts it may gain support from US data next week expected to show soft autumn plantings data for the 2010 harvest, with those that were sown potentially damaged by the cold winter weather.
"Wheat continues to be supported by the concern about cold temperatures and the expectation of lower winter wheat acres in next week's report," Darrell Holaday at Country Futures said.
"The problem is that increases in price cause a lot of problems in a world market where US wheat is currently priced about $30 per ton above the Black Sea price for wheat."
And Paris wheat made an effort to keep up competitiveness by ending down E2.25 at E128.00 a tonne for January and E0.25 at E134.00 a tonne for March, factoring out some of the impact of a rising euro.
London wheat was cushioned somewhat by sterling, which managed to lose ground even against a falling dollar, amid a fragile political situation following (yet another) coup attempt on Prime Minister Gordon Brown.
January wheat ended up $0.40 at £108.00 a tonne, although the March contract lost £0.65 to £109.45 a tonne.