* Wheat curbed by steady U.S. crop rating

* Chances for improved field weather also cap grain prices

* Russian grain estimates above expectations

* Investors adjust positions before crop, economic data

CHICAGO, April 9 (Reuters) -

Chicago Board of Trade (CBOT) wheat, soy and corn futures fell for a second straight day on Tuesday, weighed down by sustained competition abroad and improving U.S. planting weather on the horizon, analysts said.

Traders adjusted their positions ahead of Wednesday's U.S. inflation data and Thursday's release of U.S. Department of Agriculture's monthly supply and demand report and Brazilian agency Conab's monthly national crop forecasts.

Most-active CBOT May wheat futures settled down 8 cents at $5.57-3/4 a bushel. CBOT soybeans closed 7 cents lower at $11.74-1/2 a bushel, while corn settled down 4-1/4 cents at $4.31-1/4 a bushel.

Forecasts for more rain in the U.S. Plains next week and drier conditions in the southern Delta area eased fears about weather-related stress to wheat crops and delays to corn planting, traders said.

Meanwhile, U.S. Department of Agriculture (USDA) crop progress figures released on Monday showed a good/excellent rating for U.S. winter wheat of 56%, despite worries over the impact of past dry weather in the wheat-growing Plains.

That lack of bearish weather news caught the market by surprise and weighed on wheat futures, said Austin Schroeder, a senior commodity analyst at Brugler Marketing.

Commodity analysis firm Argus raising its estimates for Russian wheat production also dragged down wheat futures, analysts said.

"Russia has been flooding the market with cheap wheat so it's been hard for the U.S. to compete," said Schroeder.

Going into Wednesday's session, traders will be watching for signs of fund managers shifting their investments either into - or out of - commodities markets, depending on the

hotly anticipated

Consumer Price Index report, said Darin Fessler of Lakefront Futures. (Reporting by Renee Hickman in Chicago; Additional reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore; Editing by Sherry Jacob-Phillips, Shweta Agarwal and Richard Chang)