An expected large Russian order for American wheat failed to materialize this week.
But without reserves, American wheat and corn prices react quickly to the outlook for the current harvest.
But the losses were limited by news that China was interested in buying American wheat.
As more American wheat is sold abroad, overseas prices fall.
Soft red is the second-largest class of American wheat after the hard red winter variety.
The development means less competition for American wheat on the world market.
Trade between the countries in 1987, the last year for which figures are available, was nearly $2 billion, most of it American wheat.
China has been the leading buyer of American wheat this year, taking 6.4 million tons since June 1.
The British in particular depended on American wheat during the 1860s for a fourth of their food supply.
Analysts said the problems in China might make new orders for American wheat unlikely.