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CBOT December corn settled down 1/4 cent at $3.47-3/4 per bushel.
Analysts polled by Reuters expect the USDA to raise its US corn yield estimate in a monthly crop supply and demand report on Thursday.
The USDA late Monday said the US corn crop was 70 percent harvested, in line with trade expectations but behind the five-year average of 83 percent.
Futures fell despite another export sales announcement on Tuesday. The USDA confirmed private sales of 130,000 tonnes of US corn to unknown destinations for delivery in the 2017/18 marketing year in the second such sale in as many days.