Richest Man Under 40 Is Going All-In on Green at a Perilous Time

Nothing about the curly-haired young man standing in a vegetable patch in a “Don’t Farm Naked” T-shirt suggests the staggering wealth and influence he commands. Nor the tragedy he’s lived through. Nor his maverick role in the world’s richest dynasty.

His forehead damp with sweat, the 38-year-old extols a future that “we could be proud to share with our children.” His shirt is a cheeky nod to covering soil with crops between harvests, a tenet of sustainable farming.

This is Lukas Walton, grandson of Walmart Inc. founder Sam and son of John, an avid pilot who died ...