Soybeans extended their advantage over the grains in Chicago on Monday, helped by hopes for Chinese imports and lower plantings estimate from Argentina.
Not even a weaker dollar could help corn and wheat out of the doldrums. The greenback slid from four-week highs, after Ben Bernanke, the chairman of the US Federal Reserve, trimmed expectations of a US interest rate rise.
A weaker dollar, which slipped back to $1.49 against the euro at one point, should help US exports such as crops by making them more competitive.
But wheat closed down 1.9% at $5.26 ½ a bushel for December delivery in late trade, and off 1.8% at $5.48 a bushel for March.
Corn was 1.3% lower at $3.68 ¾ a bushel for December and down 1.2% at $3.83 ½ a bushel for March.
As US Commodities, the Iowa broker, pointed out, it will take a big shift in the dollar to make American grain exports competitive, even of corn, where the market fundamentals are tighter.
"Argentina continues to sell corn below the US values by $7-$8 a tonne. Argentina has about 1.5m tonnes of corn to sell," the broker said.
The day was left to soybeans, which built on gains in China's Dalian market, where soybeans hit new highs.
This news is especially sensitive coming from the country which is the world's biggest buyer of foreign soybeans, whose attractions will only be improved by strong domestic prices.
"This month, China could potentially import more soybeans than in June that has been the record month to date," Commerzbank said, noting an estimate from the China National Grain and Oils Information Centre of imports of at least 4.6m tonnes – albeit with much representing shipments already purchased.
Meanwhile, competition from South America may not be quite as intense next year as had been expected, with Argentina's government cutting its plantings estimate by 500,000 hectares to 18m hectares.
Soybeans for January ended up 1.0% at $10.53 ½ a bushel.