The figure was larger than earlier reports of 3 million acres of flooded farmland and amounts to 1.1 percent of land usually planted in the two dozen principal US field crops.

Arkansas is the hardest-hit with 1 million acres flooded, including 300,000 acres of rice and 120,000 acres of wheat, said the American Farm Bureau Federation, based on a survey of its state affiliates.

AFBF listed flood totals as 650,000 acres in Tennessee, 600,000 acres in Mississippi, 570,000 in Missouri, 500,000 acres in Illinois and 280,000 acres in Louisiana.

Bob Young, AFBF chief economist, said the economic impact of the flood will be massive but some growers still may be able to plant a crop this year.

"There is no doubt about it, the effect of the flooding on farmers and ranchers is being felt deeply across the south," Young said in a statement. "One is reminded of the '93 or '95 floods in terms of scale of affected area."

Analysts say flooding and a rainy, cold spring may disrupt farmers' plans to expand US corn plantings by 5 percent this year, to 92.2 million acres and rebuild lean stockpiles. Last week, the Linn Group estimated corn plantings will total 89.5 million acres and soybean planting would reach 75.1 million acres, compared to the 76.6 million acres estimated by USDA based on a survey of growers in March.

Doubts about the size of the US corn crop are driving up futures prices, said agricultural economist Darrel Good at the University of Illinois on Monday. Speculation about corn plantings will continue until June 30, when the Agriculture Department reports on its farmer survey of crop plantings.

Copyright Reuters, 2011