GRAINS-Soybeans drop after hitting seven-week high above $10 a bushel

* Corn and wheat slip after multi-week highs Wednesday

* Traders keep eyes on dry weather in Argentina

* Global grain supplies remain ample (Adds U.S. trading, changes byline/dateline from SINGAPORE)

CHICAGO, Jan 25 (Reuters) - U.S. soybean futures turned lower after topping $10 a bushel for the first time in seven weeks on Thursday, retreating from gains fuelled by concerns about dry weather in rival exporter Argentina and a weaker U.S. dollar.

The market pulled back after rising for the previous eight sessions. If prices had closed higher again, it would have been the longest string of consecutive advances in nearly six years.

Corn and wheat futures also slipped after rising on Wednesday.

Traders were closely watching weather conditions in Argentina because it is the world's third-largest soybean producer and largest exporter of soymeal and soyoil. Dryness there could reduce harvests and tighten large global inventories.

However, the United States has ample supplies of crops from years of bumper harvests, while Brazil, the world's biggest soy exporter, is on track for a record crop.

"There is not a shortage," said Jason Roose, vice president of Iowa-based broker U.S. Commodities.

The most actively traded soybean contract on the Chicago Board Of Trade dipped 2-3/4 cents to $9.89-1/2 a bushel by 11:30 a.m. Central. Prices traded as high as $10.02, the highest since Dec. 7.

CBOT wheat and corn each reached their highest prices since Dec. 4 before falling. Wheat was down 1/4 cent at $4.32-3/4, while corn was down 1-1/2 cents at $3.55 a bushel.

Earlier gains in the markets had prompted farmers to sell corn and soybeans they had been keeping storage from previous harvests due to low prices, agricultural merchants said.

"The massive amount of old grain out in the country is limiting any upside," Roose said.

Farmers and traders were keeping an eye on movements in the U.S. dollar as declines make greenback-priced commodities cheaper to global buyers. The dollar hit its lowest since December 2014 against a basket of other currencies.

On Wednesday, traders buying back previously sold, or short, positions had helped push prices to multi-week highs.

"To see a setback following the volume of short covering corn has enjoyed this week is not surprising," said Karl Setzer, risk management team leader for MaxYield Cooperative in Iowa.

"The question in the market now is if funds have covered all they wish to at this point or if we will see more buying surface." (Additional reporting by Naveen Thukral in Singapore; Editing by Amrutha Gayathri and Alistair Bell)