The Agriculture Department is trying to block the planting and distribution of a long-grain rice seed because it may contain traces of genetically engineered rice, officials said Monday.

The seed, known as Clearfield CL131, is trademarked by BASF AG, a German company that is the world's largest chemical maker, and licensed for marketing by Horizon Ag of Memphis, Tenn. Farmers also are being notified, the department said.

Clearfield CL131 was not developed as a genetically modified rice, the department said. Even so, BASF and Horizon Ag reported to the department last week that test results had shown possible traces of unapproved genetic material.