CHICAGO: US corn futures declined on Tuesday on expectations of rapid harvest progress this week, analysts said.

Wheat futures also sagged while soyabean futures were choppy, paring losses as traders squared positions ahead of quarterly stocks data due on Wednesday from the US Department of Agriculture.

As of 1:09 p.m. CDT (1809 GMT), Chicago Board of Trade December corn was down 2-1/4 cents at $3.64-1/2 per bushel. December wheat was down 1-1/2 cents at $5.48-3/4 a bushel and November soyabeans were down 2 cents at $9.94-1/4 a bushel.

Weather forecasts called for mostly dry conditions over the next week in the US Corn Belt, which should favour field work.

"We could be seeing rapid harvest progress pretty much across the Corn Belt. We look for a big jump in harvesting numbers next week," said Terry Reilly, senior analyst with Futures International in Chicago.

The USDA late Monday said the US corn crop was 15% harvested, behind the five-year average of 16%, while soyabeans were 20% harvested, ahead of the five-year average of 15%.

Traders also noted a slowdown in export demand from China, a big buyer of US soyabeans and corn over the last month.

"US export developments are a little quieter this week, so that is another reason for the downward pressure," Reilly said.

The USDA on Wednesday is scheduled to report on the amount of US grain and soya stored on and off farms as of Sept. 1, a quarterly report that has a history of jolting CBOT futures markets.

Ahead of the report, analysts surveyed by Reuters on average expected the USDA to report Sept. 1 corn stocks at 2.250 billion bushels, which would be the largest Sept. 1 figure since 2017.

For soyabeans, the average estimate of 576 million bushels would be the second-largest Sept. 1 soya figure on record, but down from a peak of 909 million bushels a year earlier.

The USDA on Wednesday will also update its estimates of US 2020 wheat production.