* Brazil raises grain crop f'cast on bumper corn, soybean output
* Heat, drought to spur early corn harvest in U.S. grain belt
* China Aug soybean imports at 9.35 mln T on large Brazilian supplies
SINGAPORE, Sept 7 (Reuters) - Chicago corn futures eased on Thursday, trading close to three-year lows as record production in top exporter Brazil and supplies from an early U.S. harvest weighed on the market.
Soybean and wheat prices also fell, giving back some gains made on Wednesday.
"Large immediate supply of corn is likely to weigh on the market," said Ole Houe, director of advisory services at Australian agricultural brokerage IKON Commodities.
"There excess supply of feed wheat in the market.
The most-active corn contract on the Chicago Board of Trade (CBOT) lost 0.1% at $4.85-1/4 a bushel, as of 0435 GMT, not far from $4.73-1/2 a bushel, the lowest since December 2020, reached last month.
Prices have dropped nearly 30% so far this year.
Soybeans fell 0.3% to $13.71-3/4 a bushel and wheat slipped 0.3% to $6.07-1/4 a bushel.
Corn harvesting in parts of the western U.S. Midwest is starting sooner than normal after hot, dry weather sped the crop to maturity, analysts and agronomists said.
The rapid finish is likely to provide the market early supplies but may lower crop quality or reduce grain yields.
Commodity brokerage StoneX lowered its estimate of the average U.S. 2023 corn yield by 2 bushels an acre to 175 bushels an acre and downgraded its harvest estimate to 15.102 billion bushels.
A farmer survey by brokerage Allendale forecast a lower U.S. 2023 corn yield of 171.51 bushels per acre.
However, Brazil should produce a record 131.8 million metric tons of corn due to an abundant second crop that farmers have nearly finished harvesting, Brazil's food supply agency Conab said.
Conab forecast 50 million tons of corn exports and almost 97 million tons of soy exports for Brazil in the 2022/23 cycle, forecasting soybean production at a record 154.6 million tons.
Brazil is set to surpass the United States as the biggest corn exporter this year.
In the soybean market, large purchases by top importer China are likely to support prices.
China imported 9.35 million metric tons of soybeans in August, Reuters calculations based on customs data showed on Thursday, as large purchases of cheap Brazilian beans continued to encourage purchases.
Ukraine also has a bumper corn crop, with the 2023 harvest set to rise by 5.8% this year to 29.3 million metric tons, French consultancy Agritel said.
In wheat markets, Russia's Agriculture Minister Dmitry Patrushev said fuel shortages threatened to disrupt autumn harvesting and sowing.
That could hinder the flow of cheap grain from Russia, the world's biggest wheat exporter, which has suppressed prices.
Russia also said Turkey had agreed in principle to handle 1 million metric tons of grain that Moscow plans to send to Africa at a discounted price with financial support from Qatar.
Reuters on Thursday released polls of analysts' expectations for U.S. grain production, U.S. grain stocks and global grain stocks ahead of a U.S. Department of Agriculture September crop supply/demand report.
Commodity funds on Wednesday were net sellers of CBOT corn but net buyers of wheat and soybeans, traders said. (Reporting by Naveen Thukral; Editing by Rashmi Aich)
