(Adds closing prices, market details)
By Mark Weinraub
CHICAGO, Jan 4 (Reuters) - U.S. soybean futures fell on Thursday, with traders locking in profits from three straight days of gains after forecasts boosted the prospects for rain in Argentina.
Wheat futures also dropped on profit-taking, but ongoing concerns about crop damage in key growing areas of the United States kept losses in check. Corn futures eased on technical pressure.
All three commodities closed above session lows with bargain buyers limiting the declines.
The weather outlook for Argentina tempered recent concerns about dryness in the world's No. 3 soybean exporter.
"Lack of new threatening forecasts for Argentina ... caused some traders to run for cover," Farm Futures analyst Bryce Knorr said in a note. "While temperatures could top 100 degrees (Fahrenheit) today in the key central growing region, cooler temperatures and better chances for rain emerge after that, with the second week of the forecast looking wetter."
Chicago Board of Trade March soybean futures SH8 ended 1 cent lower at $9.67-3/4 a bushel.
A sharp drop in palm oil futures, which had hit a one-month high on Wednesday, also reduced support for soybeans. POI/
CBOT March soft red winter wheat WH8 was 2 cents lower at $4.34 a bushel. K.C. hard red winter wheat KWH8 , which had risen to a six-week peak while leading the gains in grains earlier this week, was off 1-1/4 cents at $4.39-3/4 a bushel.
The wheat market has drawn support from sub-zero temperatures across the U.S. Plains and as forecasts for continued dryness raised the prospect of a reduced harvest. extreme cold snap in the U.S. also has the agricultural markets firmly in its grip," Commerzbank (DE:CBKG) analysts said in a note.
However, traders said wheat might struggle to rally further without clearer evidence of crop losses, given that a record Russian harvest has swollen ample global supplies. Cold damage is difficult to quantify until crops emerge from their winter dormancy, keeping some bulls on the sidelines.
CBOT March corn CH8 was 2 cents lower at $3.51 a bushel.