CHICAGO, May 9 (Reuters) - Chicago Board of Trade corn and soybean futures dropped on Tuesday, under pressure from a fast pace of planting across key production areas of the U.S. Midwest and an outlook for good growing weather once seeding is finished, traders said.

Soft red winter wheat futures also weakened, with the benchmark CBOT soft red winter wheat futures contract dropping 1.6% due to good field conditions in the eastern U.S. Midwest where much of that crop is grown.

"Given the weather conditions in the United States largely being favorable, you are just not going to have buying interest," said Scott Harms, ag risk specialist at Archer Financial Services. "The corn market, the soybean market and the wheat market just does not have a friend right now."

K.C. hard red winter wheat contracts were firm due to dry soil limiting harvest potential in the U.S. Plains. MGEX spring wheat contracts also posted gains, with the market underpinned by planting delays in North Dakota.

CBOT July corn futures settled down 11-3/4 cents at $5.84-3/4 a bushel.

Concerns about weakening export demand pushed corn futures below their overnight lows after the U.S. Agriculture Department announced that private exporters reported the cancellation of sales totalling 272,000 tonnes of corn headed to China.

CBOT July soybean futures closed 19-1/2 cents lower at $14.14-1/4 a bushel.

The USDA said on Monday farmers had planted 35% of their intended soybean acreage as of May 7, the second fastest pace on record.

CBOT July soft red winter wheat was off 10-1/2 cents at $6.43-1/2 a bushel.

Grain markets eased from two-week highs hit on Monday when doubts about the continuation of the Black Sea corridor deal had supported prices.

The United Nations said inspections resumed of outbound vessels on Tuesday under a deal allowing the safe Black Sea export of Ukraine grain, which Moscow has threatened to quit on May 18 over obstacles to its own grain and fertilizer exports. (Additional reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore; Editing by Sherry Jacob-Phillips, Sonia Cheema, Chizu Nomiyama, Paul Simao and Richard Chang)