Corn skidded by nearly 8 percent, down 53 cents to $6.4225 per bushel. That also pulled down wheat, which fell more than 3 percent, and soybeans, down 1 percent.
On Thursday, the most recent trading day, the Agriculture Department said that corn supplies were higher than analysts and traders previously expected. The USDA also said that farmers intend to plant more corn than they did last year. Those two developments combined to push corn prices down 5 percent on Thursday.
Todd Hultman, a grain analyst at DTN/The Progressive Farmer in Omaha, Neb., said the reasons for the surprising report are still a matter of debate. Some analysts think it's because demand for corn has been muted so far this year. Others think the crop estimates were too low in the first place.
"Either way," Hultman said, "it looks like we have more corn than expected."
That's a different atmosphere than last summer, when prices for wheat, corn and soybeans shot higher because a crippling drought slashed crop supplies. Still, Hultman said that some traders are concerned about the drought's lingering effects: A lot of crop-producing states still have soil that is too dry. That could impact harvests this year,(equals) and eventually push prices higher.
On Monday wheat fell 23.75 cents to $6.64 per bushel. Soybeans lost 14 cents to $13.9075 per bushel.
Oil fell after an industry group, the Institute for Supply Management, said growth in U.S. manufacturing activity slowed in March.
Benchmark oil for May delivery fell 16 cents to $97.07 per barrel in New York. It was the first decline since March 21.
In other energy trading, wholesale gasoline fell 1 cent to $3.10 a gallon. Natural gas fell 1 cent to $4.02 per 1,000 cubic feet. Heating oil was the outlier, rising 2 cents to $3.07 a gallon.
Metals were mixed. June gold edged up $5.20 to $1,600.90 per ounce. May silver fell more than 1 percent, down 37.9 cents to $27.944 per ounce.
May copper fell 2.75 cents to $3.3745 per pound. June palladium jumped 2 percent, up $15.70 to $783.95 per ounce. July platinum rose 1.5 percent, up $24.20 to $1,598.80 per ounce.