A federal judge extended his nationwide ban on the planting of genetically engineered alfalfa Thursday and faulted federal officials for approving an herbicide-resistant strain of the crop without studying the dangers of contaminating other farmers’ alfalfa or breeding tougher weeds. [...] ”The contamination cannot be undone,” he said. ”It will destroy the crops of those farmers who do not sell genetically engineered alfalfa. ... It is not in the public interest to take action that has the potential of eliminating the availability of a non-genetically engineered crop without adequate investigation into the long-term impact of such action.” [...] ”This crop represents a very real threat to their crops and their livelihood,” Kimbrell said. ”This ruling is a turning point in the regulation of biotech crops in this country.”