Corn prices on the Chicago Board of Trade dropped significantly this morning after a report (pdf) from USDA predicted that this year’s crop will be much larger than investors and analysts expected:

Corn planted area for all purposes in 2009 is estimated at 87.0 million acres, up 1 percent from last year but 7 percent below 2007. This is the second largest planted acreage since 1946, behind 2007. Planting proceeded behind the normal pace, similar to last year, as frequent spring precipitation and cold temperatures slowed early season fieldwork and planting activities in the central and eastern Corn Belt, Ohio Valley, and northern Great Plains. On May 10, corn planting was 48 percent complete, down 23 points from 5-year average. In late May, however, dryer conditions allowed farmers to make rapid progress. Farmers reported that 97 percent of the intended corn acreage had been planted at the time of the survey interview compared with the 10-year average of 98 percent.

Corn prices plummeted 30 cents per bushel — the maximum allowed in one day — on the news.

The Des Moines Register reports that investors expected that about four million fewer acres had been planted this year. This morning’s price drop would cut the value of the corn crop in Iowa alone by about $700 million.