* Winter wheat contracts slip from 3- to 4-month peaks
* Recent run-up fuelled by investor short covering
* Improved weather in Argentina weighs on corn, soy (Adds closing prices, adds corn export sales)
CHICAGO, Jan 31 (Reuters) - U.S. winter wheat futures turned lower on Wednesday in a profit-taking setback from multi-month highs after five straight sessions of gains fuelled by concerns over poor crop conditions in the United States.
Soybeans were also lower as traders banked profits from a recent grain market rally and a slightly improved crop weather forecast for Argentina, where drought has reduced yield potential for crops. Corn ended unchanged on better Argentine weather and improving U.S. export demand.
"Today's lower trade is a day down in an overall two-week rally. I wouldn't say this is the end of the rally, certainly not for wheat," said Rich Nelson, chief strategist with consultancy Allendale Inc.
Chicago Board of Trade March soft red winter wheat fell 5-1/2 cents to $4.51-3/4 a bushel in the steepest drop in 2-1/2 weeks. The contract hit a three-month high the previous day.
March K.C. hard red winter wheat touched a fresh four-month high early in the session but ended 2-1/2 cents lower at $4.67-1/4 a bushel. The contract posted its strongest rally in seven months on Tuesday on record-large trading volume.
Condition ratings for winter wheat declined in January in several southern U.S. Plains states that have been hit by drought, including top producer Kansas, the U.S. Department of Agriculture said on Monday.
Dry weather is expected to continue for the central Plains wheat belt, sapping needed soil moisture from the HRW crop, forecasters said.
Corn and soybean traders are monitoring weather in Argentina as drought has reduced plantings and hurt yield potential for both crops. A slightly cooler and wetter forecast for the world's No. 3 corn and soybean exporter and top supplier of soymeal and soyoil weighed on corn and soy futures on Wednesday.
"Whenever you throw in some cooler temps, you're going to take some weather premium out," said Ted Seifried, analyst with Zaner Ag Hedge.
U.S. corn export sales have accelerated as the cereal is the currently cheapest feed grain in the world. The USDA on Wednesday confirmed 145,000 tonnes in old-crop sales to unknown destinations, the agency's sixth large daily sales announcement in seven days.
CBOT March corn held steady at $3.61-1/2 a bushel after reaching a 2-1/2-month high the previous day. CBOT March soybeans were 4-1/2 cents lower at $9.95-3/4 a bushel, pulling back from Tuesday's near two-month high. (Additional reporting by Naveen Thukral in Singapore and Nigel Hunt in London; editing by Susan Thomas and Sandra Maler)