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* Investors were squaring positions ahead of the US Agriculture Department's closely watched monthly supply and demand report on Wednesday.
* Analysts were expecting the USDA to trim its forecasts for US corn production and yield.
* USDA said on Tuesday that good-to-excellent ratings for the corn crop rose 1 percentage point to 58 percent in the latest week.
* The corn market had firmed but turned lower after the benchmark CBOT December corn futures hit technical resistance as it neared the 50-day moving average.