When it opens this fall in Brooklyn, a new urban farm will grow a new crop: farmers. The Square Roots campus, co-founded by entrepreneurs Kimbal Musk and Tobias Peggs, will train new vertical farmers in a year-long accelerator program. “Young people contact me all the time to articulate issues with the industrial food system but they are frustrated by their perceived inability to do anything about it,” says Musk. “It’s relatively easy to set up…