* Rains boost some crops in northern Brazil
* Argentina to seek higher export tax on meal, oil
* Wheat drops on dim US export outlook
CHICAGO, Dec 18 (Reuters) - U.S. corn futures fell on Monday and soybean futures were mixed as traders assessed crop-boosting rains in dry areas of South America amid improved demand for U.S. shipments.
Higher soymeal and soyoil markets helped to lift soybeans at times after top soy product supplier Argentina said it would seek to raise export taxes on meal and oil.
Wheat was lower in a technical-selling and profit-taking setback as U.S. exports continue to struggle in the global market with cheap Russian grain readily available.
Trading was choppy as market participation was beginning to dwindle ahead of the year-end holidays.
Investors monitored weather forecasts for South America, where rains have aided recently planted crops in northern Brazil following a hot, dry start to the season. But parts of the region were missed by rains and may remain dry again through this month, forecasters said.
"We have made gains in stabilizing the crops in Brazil, and we think we have a better crop in Argentina ... but we're not out of the woods yet," said Mike Zuzolo, president of Global Commodity Analytics.
Good export demand also underpinned soybeans following a series of large sales announced last week and talk of continued buying interest from China.
The U.S. Department of Agriculture (USDA) on Monday also reported corn and soybean export inspections last week near the high end of a range of trade estimates.
Chicago Board of Trade January soybeans were up 4 cents at $13.19-3/4 a bushel by 12:06 p.m. CST (1806 GMT), while March corn was down 7-1/4 cents at $4.75-3/4 a bushel.
CBOT March wheat fell 8 cents to $6.21-1/4 a bushel.
Plentiful world wheat supplies, particularly from Russia, weighed on prices, with Russia expected to supply a substantial part of a hefty 1.35 million tons bought by Saudi Arabia on Monday along with EU suppliers. (Additional reporting by Michael Hogan in Hamburg, Naveen Thukral in Singapore and Peter Peter Hobson in Canberra; Editing by Sonia Cheema, Chizu Nomiyama and Grant McCool)
