The case has been closely watched by environmentalists and agribusiness. A federal judge in San Francisco barred the planting of genetically engineered alfalfa nationwide until the government could adequately study the crop's potential impact on organic and conventional varieties.

St. Louis-based Monsanto is arguing that the ban was too broad and was based on the assumption that their products were harmful. Opponents of the use of genetically engineered seeds say they can contaminate conventional crops, but Monsanto says such cross-pollination is unlikely.

Organic groups and farmers exporting to Europe, where genetically modified crops are unpopular, have staunchly opposed the development of such seeds.