Farmers in California's agricultural heartland say record-high gas and diesel prices are putting pressure on their bottom lines, but economists say it's unlikely that will translate into significantly higher food prices across the U.S.

Keith Nilmeier, a fourth-generation farmer in Fresno County, has cut down on using his farm equipment to compensate for climbing fuel costs.

Among other changes, Nilmeier—who grows fruit on 300 acres near Sanger—makes only one pass, instead of three, through the orchards and vineyards with his disking machine linked to a furrower. And he keeps farm supervisors driving smaller, fuel-efficient cars around his fields.

When it comes to rising fuel costs, farmers get hit with a double whammy: They're spending more to refuel farm equipment such as harvesters and tractors, and they're having to pay fuel surcharges to people mechanically harvesting or transporting their produce. Yet they are loath to impose surcharges on anyone, because they're afraid of being less competitive when they sell their products.

For more, see: High gas, diesel prices hurt Calif. farm industry