NEW YORK, Jan 21 (Reuters) - U.S. commodity markets were mixed on Tuesday, as soybeans tumbled on forecasts of rain in key exporter Argentina, gold slid, and natural gas futures rallied as cold weather threatened the eastern half of the United States.
The Thomson Reuters/Core Commodity Index, a benchmark for global commodities markets, eased slightly as eight of the index's 19 components fell.
U.S. soybean futures led the day's losses, tumbling 2.7 percent as forecasts for rain in Argentina eased worries over soybean yields in the major exporter.
Wheat prices also fell, while corn edged higher.
Gold fell nearly 1 percent in its biggest drop so far in 2014 on widespread speculation that the U.S. Federal Reserve may announce a further cut in its bond-buying program at a meeting next week.
Spot gold hit a one-week low of $1,235.68. Silver sank 2.2 percent.
Elsewhere in metals, copper and nickel posted gains.
Energy markets were largely up. Natural gas futures for next-day delivery rallied on cold weather.
U.S. crude futures gained as traders covered positions ahead of the expiration of the February contract. A forecast of strong demand supported Brent oil.
Coffee and cocoa fell, while sugar was flat.
Cotton rallied on bullish chart signals and concern over supplies in the United States, the world's top exporter.
Prices at 4:30 p.m. EST (2130 GMT)
LAST/ NET PCT
CLOSE CHG CHG
US crude 94.88 0.62 0.7% Brent crude 106.84 0.49 0.5% Natural gas 4.431 0.105 2.4% US gold 1241.80 -10.10 -0.8% Gold 1241.55 -11.64 -0.9% US Copper 3.35 0.01 0.2% LME Copper 7339.00 25.00 0.3% Dollar 81.078 -0.147 -0.2% CRB 278.399 -0.011 0.0% US corn 425.00 1.00 0.2% US soybeans 1280.50 -36.00 -2.7% US wheat 562.25 -1.25 -0.2% US Coffee 116.20 -0.95 -0.8% US Cocoa 2679.00 -21.00 -0.8% US Sugar 15.22 0.00 0.0% US platinum 1452.00 -0.60 0.0% US palladium 748.05 -0.50 -0.1%
(Reporting by Chris Prentice; Editing by Nick Zieminski)