Agriculture Secretary Thomas Vilsack met with Warren Buffett last week to urge the billionaire investor to make sure his BNSF railroad is ready for an expected record corn and soy harvest this year. Vilsack said on Tuesday that Buffett, who heads the sprawling conglomerate Berkshire Hathaway, recognized the challenge and indicated his company was taking steps. Speaking at a conference sponsored by Growth Energy, a biofuel trade group, Vilsack said BNSF was making “significant” investments. BNSF is a unit of Berkshire Hathaway.