* The US dollar index rose nearly 1 percent, pressuring dollar-backed commodities including grains and soy, on worries over euro zone sovereign funding and signs of weakness in the region's banks. * The Buenos Aires Grains exchange kept its estimate for Argentina's 2011/12 commercial corn area unchanged at 3.74 million hectares, predicting ample rains in the days ahead. * But the US Climate Prediction Center warned that La Nina, the weather phenomenon widely blamed for drought in the southern United States and South America, may persist longer than expected, into the Northern Hemisphere spring. * Drought in Brazil's southernmost state, Rio Grande do Sul, will cut corn output by a quarter and soy output by 4 percent, the state's technical assistance agriculture body Emater said. * Cargill said it would close a crushing plant in Des Moines, Iowa, next month, citing a difficult industry environment for soymeal. * Cash basis values for soymeal were flat in the US Midwest as a sharp drop in soymeal futures failed to spur new demand.