Floods delay Argentine soy planting-exchange

* Heavy Southern Hemisphere spring rains cause flooding

* Only 2 pct of soy area planted, lagging last season

* Farmers hope sunshine next week can jumpstart sowing

* Grains exchange sees 19.7 mln hectares sown with soy

BUENOS AIRES, Oct 25 (Reuters) - Floods have severely delayed Argentine soy planting at a time when consumer nations are counting on the country to help control soaring grains prices by replenishing supplies, a key grains exchange said on Thursday. Food prices have surged this year due to the worst U.S. drought in decades combined with dry crop weather in Russia and Australia. Poor yields from these countries have put the supply onus on South American breadbaskets Argentina and Brazil. ``Soy planting has begun, although with severe and continuous interruptions,'' the Buenos Aires Grains Exchange said in its weekly crop report. Only 2 percent of Argentina's projected soy area had been planted as of Thursday, lagging last year's tempo by 4.2 percentage points, the exchange said. The weather forecast is unstable for the three days ahead with more rains possible. But, starting on Monday, farmers hope that the forecasted string of sunny days will help prepare their soppy soils for planting. Argentina, the world's No. 3 soybean exporter, has been pelted by unusually strong rains since August, slowing first corn and now soy planting as farmers stand by as their seeding machines sink in the Pampas mud. Unlike last season, when a lack of rain was the main problem in Argentina, growers have been praying for the sunshine needed to firm up topsoils so that planting can resume. Soy is Argentina main agricultural export. The country is also the top world supplier of derivatives such as soymeal cattle feed and soyoil, used in cooking and to make biofuels. The exchange estimates 2012/13 soy area at 19.7 million hectares (48.7 million acres), up 4.5 percent from a 2011/12 season hobbled by a December-January dry spell that parched soy and corn plants. Problems posed by too much rain are less debilitating than those posed by drought as excess moisture allows for wider planting area, helping to offset losses caused by flooding. This season's soy plantings have started in key farm areas such as north-central Santa Fe province, north-central Cordoba and east-central Entre Rios.

``Continuous rains since the start of the month ... have saturated wide areas in the eastern part of the farm belt, generating more and more prolonged delays,'' the report said. Consumers are anxious to secure more grains supply since the dry U.S., Russian and Australian weather has pumped Chicago soy futures 30.5 percent higher since January. Chicago corn is meanwhile up 16 percent and wheat a whopping 35 percent. The U.S. Department of Agriculture forecasts Argentine soy production in the upcoming season at 55 million tonnes, well above the 41 million tonnes collected in 2011/12. The Argentine government says 2012/13 soy output could smash previous records and hit 58 million tonnes.

CORN, WHEAT As of Thursday, Argentine farmers had sown 37 percent of the 3.4 million hectares expected to be dedicated to commercial-use corn this year, according to the exchange. Corn planting advanced 5 percentage points over the previous week, but it trails last season's rhythm by 18 percentage points. The USDA sees 28 million tonnes of Argentine 2012/13 corn production and 11.5 million tonnes of wheat. The exchange said that 4 percent of Argentina's 2012/13 wheat crop has been harvested. ``Prevailing wet conditions caused by continuous rainfall during the (Southern Hemisphere) spring have contributed to the spread of diseases affecting wheat crops,'' the report said. ``And last weekend's overflow of rivers, streams and canals in the farm belt caused the loss of some wheat fields.'' But the exchange said it kept its wheat crop estimate unchanged at 10.1 million tonnes, thanks to good growing conditions in southeast and southwest Buenos Aires province, the country's biggest wheat-growing region.

(Reporting by Hugh Bronstein; Editing by Marguerita Choy)