GRAINS-Soybeans retreat from over 2-year high ahead of USDA report

* Soybeans snap winning streak despite Chinese demand

* USDA reports spate of Chinese orders

* Wheat firms on concerns over Black Sea production

SYDNEY, Sept 10 (Reuters) - U.S. soybean futures on Thursday edged lower for the first time in 13 sessions, as traders locked in profit after the oilseed climbed to its highest in more than two years following strong demand from China - the world’s largest importer.

Grain markets are turning their attention to the monthly supply-and-demand forecasts by the U.S. Department of Agriculture (USDA), scheduled for Sept. 11 to gauge the impact of dry weather and storm damage on U.S. corn and soybean harvest prospects.

Analysts expect the government to lower its forecasts of U.S. 2020/21 corn production and ending stocks, although stockpiles should remain relatively plentiful.

Corn firmed on Thursday, while wheat rose for the first time in six sessions.

The most active soybean futures on the Chicago Board Of Trade were down 0.2% at $9.76-1/2 a bushel by 0342 GMT, after having firmed 0.6% on Wednesday, when prices hit a June 2018 high of $9.81-3/4 a bushel.

Despite U.S. soybeans edging lower, analysts said losses were limited by strong demand from top consumer China.

“The, seemingly daily, stream of USDA notices flagging chunky sales of U.S. soybeans to China is hard to ignore,” said Tobin Gorey, director of agricultural strategy, Commonwealth Bank of Australia.

The USDA confirmed soybean sales to China for a fourth straight business day, announcing sales of 238,000 tonnes to the Asian country and another 132,000 tonnes to unknown destinations.

The most active corn futures were up 0.1% at $3.60-1/2 a bushel, having closed 0.4% lower in the previous session.

The most active wheat futures were up 0.4% at $5.46 a bushel, having closed down 0.1% on Wednesday.

The gains in wheat came amid concerns over production in the Black Sea.

Dry weather in Ukraine has delayed the sowing of winter grains for the 2021 crop in one of the top Black Sea grain exporters, while neighbour Russia also needs rain, although sowing there is running ahead of the last year’s pace, analysts said. (Reporting by Colin Packham, Editing by Sherry Jacob-Phillips)