GRAINS-Wheat gains for sixth day on rising demand; soybeans slide

* Feed, export demand boost wheat after recent lows

* Weekly U.S. wheat export sales at two-year high

* Corn up for fifth time in six days

* Soybeans slide for third day on South America harvest

(Recasts, adds quotes, updates prices; changes byline, dateline, previous PARIS/SYDNEY) CHICAGO, March 14 (Reuters) - U.S. wheat futures rose for a sixth straight session on Thursday on robust demand from domestic livestock feeders and exporters, which booked their biggest weekly sales in two years last week. Corn prices climbed for the fifth time in six sessions, supported by concerns about tight old-crop supplies. Soybeans fell for a third straight session on South American harvest pressure and concerns about slowing import demand from top buyer China. "The demand for wheat has picked back up. We had good, solid wheat export numbers this morning. Corn and wheat are roughly on par in value so we're seeing more wheat feeding and we're seeing some wheat trickle into the ethanol market in the eastern corn belt," said Karl Setzer, an analyst with MaxYield Cooperative. "There's a little bit of the risk premium coming out of the soybeans. There's not as much concern today as there was three months ago over depleting soy inventories," he said. Chicago Board of Trade May-delivery wheat rose 12 cents to $7.22 per bushel by 10:47 a.m. CDT (1547 GMT), a 1.7 percent gain and the highest in 1-1/2 weeks. May corn added 4-1/4 cents, or 0.6 percent, at $7.14-1/2 a bushel, while May soybeans fell 12-1/2 cents, or 0.9 percent, to $14.34-1/2 per bushel. Weekly U.S. Department of Agriculture data showed a net 888,500 tonnes of wheat export sales for the current marketing year and 198,500 tonnes for the next marketing year. Combined sales were the largest for a single week since February 2011.

"With U.S. wheat competitive all over the world and a tight U.S. corn market, we don't see prices currently having much potential to fall," French grains consultant Offre & Demande Agricole said. The rally in wheat has taken it away from its lowest level in nearly nine months, struck last week when prices were hurt by weak demand and improved conditions in the drought-hit U.S. grain belt. Demand for feed-grade wheat has firmed since then, following corn's rise above wheat after the USDA pegged corn end-of-season stocks for the 2012/13 year at a 17-year low. Demand for feed wheat also increased after BNSF Railway last week cut its rate to ship U.S. soft red winter wheat from Chicago to the U.S. cattle hubs of west Texas and western Kansas. U.S. soybean futures have come under pressure from a rapidly advancing South American harvest. Traders said Brazilian beans were now being offered at prices competitive enough to appeal to traders, despite a backlog of shipments. Concern about slowing Chinese demand for soybean imports further weighed on the market.

Prices at 10:53 a.m. CDT (1553 GMT)

LAST NET PCT YTD CHG CHG CHG CBOT corn 715.25 5.00 0.7% 10.6% CBOT soy 1434.25 -12.75 -0.9% 19.7% CBOT meal 424.70 -4.20 -1.0% 37.3% CBOT soyoil 49.24 -0.28 -0.6% -5.5% CBOT wheat 723.25 13.25 1.9% 10.8% CBOT rice 1463.50 -14.50 -1.0% 0.2% EU wheat 235.00 2.00 0.9% 16.0%US crude 92.77 0.25 0.3% -6.1% Dow Jones 14,515 60 0.4% 18.8% Gold 1587.26 -.03 0.0% 1.5% Euro/dollar 1.2972 0.0012 0.1% 0.2% Dollar Index 82.7910 -0.0980 -0.1% 3.3% Baltic Freight 880 5 0.6% -49.4%

(Additional reporting by Colin Packham in Sydney, Gus Trompiz in Paris; Editing by Dale Hudson and David Goodman)