Throughout the four-part series, “America Revealed” explores the structures and processes of four sectors that keep America humming: food, transportation, manufacturing and energy. In many respects, tonight’s episode marvels at the wonders of modern agriculture and the productivity of a system where, for the first time in human history, less than 2% of the population can feed the other 98%. As host Yul Kwon crisscrosses the country to see how this machine feeds nearly 300 million Americans on a daily basis, he stops in Kansas to tour Stone Acres, a large family farm that grows corn, and witness Grace in action. That machine doesn't just feed Americans, it feeds the world. U.S. farm exports were a record $136.3 billion in calendar year 2011.

“In the last 60 years, America’s farmers, on average, have tripled their yield, dwarfing the productivity of every previous generation,” Kwon narrates. And yet, “It’s getting harder and harder for farmers … just to keep up with the food machine’s relentless demand.”

Grace appears 33 minutes into the episode, right after viewers learn about the European corn borer and the devastating effect it can have on corn. As a crop consultant explains, “This is a constant battle producers have to face year in and year out all the way through the Midwest. If you don’t treat, you could lose significant yield.”

Enter Robert Grace, who Kwon describes as “an expert in the aerial deployment of bug-killing chemicals” and one of the 3,500 ag pilots in the U.S. In the three-minute portion on agricultural aviation and crop protection products, Grace explains why ag flying is so different from any other form of flying and reflects on how much things have changed for Grace Flying Service in a generation. “When my father started, they had a handful of chemicals, one or two or three. Now, it’s not unusual for us to have 40 or 50 products available because without that the yields would suffer,” he said.

Kwon also visits an urban farmer in Detroit who exemplifies the locally grown, organic food movement. While acknowledging the cache this grassroots farming method holds for many consumers, Kwon opines, “How far it can ultimately go, however, is open to question. After all, how many small-scale farmers … would it take to supply every one of [America’s] food outlets even if America found cravability in local greens and grass-fed meats? In spite of its problems, our food machine meets this challenge and feeds 300 million Americans every day.”

Near the episode’s conclusion, 50 minutes in, Grace reappears as he gives Kwon a majestic aerial tour in his Boeing Stearman. “When you have an increasing population, automatic, you have to have larger and larger yields every year, forever,” Grace said.

There are several ways to view “America Revealed’s” episode on agriculture. You can check your local listings to find out when tonight’s episode will air in your market. A search mechanism on PBS’s website can also help you determine the airtime in your area. For anytime access, the episode is already available in its entirety on the PBS iPhone and iPad apps and will be available for viewing on PBS’s website beginning tomorrow.