* Soybean market wants concrete evidence of Chinese buying
* Wheat drops on U.S. export concerns (Rewrites throughout with U.S. market open, adds quote, updates prices, changes byline, changes dateline from HAMBURG)
CHICAGO, Dec 4 (Reuters) - U.S. soybean futures edged higher on Tuesday on hopes that a U.S.-China trade war truce over the weekend would result in fresh Chinese demand for U.S. soybeans, although no deals have been struck yet.
Corn also firmed slightly, following soybeans, while wheat eased on dull demand.
At Saturday's Group of 20 meeting in Argentina, U.S. President Donald Trump agreed to postpone new tariffs during the 90-day truce, while his Chinese counterpart pledged to purchase more agricultural products from U.S. farmers immediately.
However, China will need to lift tariffs it imposed on U.S. farm products, including soybeans, before it can realistically buy substantial volumes of U.S. goods.
"The market's taking a wait-and-see approach with China," said Jim Gerlach, president of A/C Trading.
Chicago Board of Trade January soybeans were up 3-3/4 cents at $9.09-1/2 a bushel at 11:46 a.m. CST (1746 GMT), well off of a four-month high notched on Monday in response to the truce.
Trump on Tuesday held out the possibility of extending the truce but warned he would revert to tariffs if the two sides could not resolve their differences.
Soybean futures also remain anchored by ample U.S. supplies and a massive Brazilian harvest due in early 2019 that would make it more difficult for U.S. shipments to compete in the export market.
CBOT March corn futures were up 1-3/4 cents at $3.73 a bushel, while CBOT March wheat was flat at $5.21-1/4 a bushel.
Wheat has been supported recently by hopes that Russian export supplies will sell out after big sales this year and that export demand will be transferred to the United States. But Russian grain continues to undercut U.S. prices.
Russian wheat was the cheapest in a Bangladesh tender on Tuesday. (Additional reporting by Michael Hogan in Hamburg and Naveen Thukral in Singapore Editing by David Goodman and Richard Chang)