CANBERRA, Sept 7 (Reuters) - Chicago corn prices fell on Thursday, slipping back towards three-year lows as concerns over the condition of U.S. crops scorched by hot and dry weather were offset by a record-breaking harvest in top exporter Brazil.

Soybean and wheat prices also fell, giving back some gains made on Wednesday.

FUNDAMENTALS:

* Most-active Chicago Board of Trade (CBOT) corn futures were down 0.3% at $4.84-1/4 a bushel at 0054 GMT after last month touching $4.74, the lowest since Dec. 31, 2020. Prices have dropped nearly 30% so far this year.

* Chicago soybean futures fell 0.2% to $13.74 a bushel and wheat slipped 0.4% to $6.06-1/2 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 may lower crop quality or reduce grain yields and farmers with lower quality corn may have to sell it at a discount, they said.

* 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.

* 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.

* Commodity funds on Wednesday were net sellers of CBOT corn but net buyers of wheat and soybeans, traders said.

* 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.

MARKETS NEWS

World stock indexes fell on Wednesday while the benchmark U.S. Treasury yield rose and the U.S. dollar hit its highest in six months after stronger-than-expected U.S. services sector data suggested that U.S. inflation pressures remain.

(Reporting by Peter Hobson; Editing by Sherry Jacob-Phillips)