ROSCOE, S.D. — Robert Malsam nearly went broke in the 1980s when corn was cheap. So now that prices are high and he can finally make a profit, he's not about to apologize for ripping up prairieland to plant corn. Across the Dakotas and Nebraska, more than 1 million acres of the Great Plains are giving way to corn fields as farmers transform the wild expanse that once served as the backdrop for American pioneers.