U.S. corn futures surged Wednesday as poor weather delaying planting fueled fears inventories could run short before the fall harvest.

Corn for July delivery, the most-actively traded contract, rose its one-day limit of 30 cents before trimming gains. The contract ended up 29 1/2 cents, or 4.1%, at a 2.5-week high of $7.49 3/4 a bushel at the Chicago Board of Trade. Wheat and soybean futures also soared.

Leading prices higher were concerns that the corn harvest will not come soon enough to replenish low supplies and ease pressure on grain users. Excessive rains have slowed planting, which indicates the harvest will likely start later than usual.

Grain users are on edge about the delays as inventories are expected to reach a 15-year low by Aug. 31, the end of the crop's marketing year. The supply situation for corn is "getting more serious" as planting drags on, said Rich Feltes, vice president of research for R.J. O'Brien.

The Linn Group predicted Wednesday that plantings would fall short of the U.S. Department of Agriculture's latest estimate because of poor weather. The firm pegged plantings at 89.5 million acres, down nearly 3% from the government's March estimate.

Farmers need to plant and harvest a big crop to rebuild inventories needed to meet strong demand from foreign buyers and domestic livestock and ethanol producers. Corn futures reached record highs last month as demand stayed strong in the face of high prices and are down about 4% from that level.

Corn supplies are under increased pressure since foreign demand increased after prices dropped to six-week lows last week as part of a broader selloff of commodities. South Korea bought 125,000 metric tons of corn for delivery before Aug. 31 Monday, suggesting a "heightened sense of alarm" about the shrinking U.S. corn supply, Feltes said.

In other news, wheat futures surged as a French drought and excessive rains in the U.S. northern Plains and Canada threatened output. Soft red winter wheat for July delivery ended up 53 cents, or 6.9%, at $8.17 a bushel.

Soybean futures felt spillover support from rallies in the grains and in crude oil, according to traders. Broad buying of commodities boosted all the markets, they noted. Soybeans for July delivery advanced 38 1/2 cents, or 2.9%, to $13.79 1/2 a bushel.

Other Markets

Rice futures rose their one-day limit of 50 cents, with the July contract gaining 3.5% to $14.89 per hundredweight. July oats jumped 2.8% to $3.67 a bushel, while July ethanol rose 2.4% to $2.649 per gallon. July soymeal climbed 3% to $361 per short ton, and July soyoil added 2.2% to $57.30 cents per pound.

At the Kansas City Board of Trade, hard red winter wheat for July delivery soared 4.9% to $9.38 a bushel. Hard red spring wheat for July delivery surged the one-day limit of 60 cents, or 6.4%, to $9.96 1/4 a bushel at the MGEX in Minneapolis.