An annual U.S. crop tour estimated Wednesday that Illinois will join states across the Midwest in producing a lower corn yield than last year, due to damaging heat and dryness.

The Pro Farmer Midwest Crop Tour projected Illinois' corn yield at 156 bushels an acre based on surveys of fields. That was down from the tour's 2010 estimate of 166.5 bushels an acre and the three-year average of 166.9 bushels an acre.

The tour also surveyed soybean fields, projecting Illinois will have an average of 1,196 soybean pods per three-foot-by-three-foot square. Last year's tour estimate was 1,308.3 soybean pods, and the three-year average is 1,236.9 pods. "The pod counts were a little more encouraging than the corn," said Brian Grete, senior market analyst for Pro Farmer.

Grain users and traders are paying close attention to the forecasts because supplies of corn and soybeans are estimated to be historically low. Strong global demand for the crops, particularly from China, has drained inventories and pushed prices to lofty levels.

Intense heat and dryness in July hurt the crops across the Midwest. The weather was especially harmful for the corn crop, as it was in a key period of development during the stressful conditions.

The tour earlier this week confirmed crops in Indiana, Ohio, South Dakota and Nebraska suffered damage. It estimated Indiana's corn yield at 143.1 bushels an acre, down sharply from 167.1 bushels an acre last year and the three-year average of 162.7 bushels.

The tour on Monday estimated Ohio's corn yield at 156.3 bushels an acre, down from its 2010 estimate of 165.6 bushels an acre for the state. The tour projected South Dakota's corn yield at 141.1 bushels an acre, down from its estimate of 143.6 bushels last year.

The scouts in Illinois were on the eastern portion of the four-day tour. Several groups departed from Bloomington, Ill., on Wednesday morning to survey different routes and met up in Iowa City on Wednesday night to compare their results.

There is a western portion of the tour that departed Wednesday from Nebraska City, Neb., and met up in Spencer, Iowa on Wednesday night.

Scouts from the eastern and western groups will come together in Austin, Minn. on Thursday.

Pro Farmer, an agricultural advisory firm, is slated to issue corn and soybean crop estimates Friday based partly on results from the tours.