GRAINS-Wheat futures tumble on increasing global supply estimates

* U.S. crop ratings, increased Russian forecast curb wheat

* Corn ticks down after rising on U.S. planting delays

* Soybeans also subdued, investors await U.S.-China news (Updates with U.S. trading, changes byline/dateline)

CHICAGO, April 16 (Reuters) - U.S. grain and soybean futures slumped on Tuesday with strong crop ratings and increased forecasts for global harvests pushing Chicago Board of Trade wheat to a one-month low.

Wheat prices came under pressure after the U.S. Department of Agriculture, in a weekly report on Monday, rated 60 percent of the U.S. winter wheat crop in good to excellent condition. That was unchanged from the previous week and in line with trade expectations, but up from 31 percent a year ago.

The ratings helped fuel projections for plentiful global inventories, traders said, after Germany's association of farm cooperatives said the country's wheat harvest will jump 20.6 percent in 2019.

Agriculture consultancy SovEcon on Monday raised its forecast for Russia's 2019 wheat crop to 83.4 million tonnes from 80 million tonnes, signaling bigger supplies in the world's top exporter.

"Wheat is the loss-leader today," said Karl Setzer, operations manager for Citizens LLC, a U.S. grain elevator company.

The most active wheat contract on the CBOT was down 15-1/4 cents at $4.44-1/4 a bushel by 12:52 p.m CDT (1752 GMT). K.C. hard red winter wheat and MGEX spring wheat set contract lows.

CBOT corn was down 4-3/4 cents at $3.58 a bushel. Soybeans sank 11-1/2 cents to $8.87-1/4 a bushel.

The USDA, in its Monday report, said 3 percent of the corn crop has been planted, behind the five-year average of 5 percent. Wet weather has slowed planting in parts of the Delta region and Midwest, and more rain is expected later this week, according to forecasters.

However, traders said they were not overly worried about planting delays yet because there is still time to put the crop in the ground without reducing yields. Also, farmers can use large planting machines to plant crops quickly.

"Planting delays don't mean anything right now," said Jim Gerlach, president of U.S. broker A/C Trading.

In the soybean market, heavily reliant on Chinese imports, hopes for a positive outcome from U.S.-China trade talks have underpinned prices. But massive disruptions to China's pig sector due to the hog disease African swine fever could cut demand for soymeal feed even in the event of a trade agreement with Washington.

Also, the details and timing of a trade agreement remain uncertain, Gerlach said.

"If you're a bull in the market, everything you can hang your hat on right now is an 'if' or a 'maybe,"' he said. "The bears are trading the here and now." (Reporting by Tom Polansek in Chicago. Additional reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore; Editing by Jan Harvey and Bill Trott)