On a recent sunny morning, Isidro Fuentes spent several hours thinning out two-week-old rows of romaine lettuce.

In years past, that job would have been done by 30 people. But today Fuentes, 56, sits alone atop a tractor with a specialized mechanical attachment that handles the entire operation.

“This is the future,” he says.

The future, in fact, has many farmers nervous. The company Fuentes works for provides labor to Ocean Mist Farms, which has begun turning to automation because farm workers are both in short supply and increasingly costly.

“There’s nothing better than a hand-picked crop,” says Jeff Percy, vice president of southern production for Castroville-based Ocean Mist, the country’s largest grower of fresh artichokes.

“But there’s the minimum wage, the cost,” he says. “The bottom line is, we have to compete.”

California farmers, anchors of a $50 billion industry that represents 13 percent of the nation’s agricultural value and a critical source of its produce and milk, are facing an unprecedented squeeze on their livelihoods that could have repercussions in households from coast to coast.