Joe Biden set out on a frozen, windswept eight-day bus tour of rural Iowa last weekend to shore up support for his presidential campaign following a September swoon.

His main talking point: something so seemingly obscure as regenerative agriculture.

Riding shotgun in the Bidenmobile: former governor and US agriculture secretary Tom Vilsack and his wife Christie.

They were primed to talk in 18 farm counties, through freezing rains and prairie blizzards, about how a refashioned agriculture can help save the planet and restore fading, often forgotten, towns that voted for Donald Trump out of sheer pent-up frustration.

“You’re going to be the new carbon sink for the world, like the Amazon,” Biden told me as the bus rolled past the shuttered storefronts on the backstreets of Sac City, whose population has shrunk by a third since the 1970s. That was when agriculture secretary Earl Butz exhorted farmers to plant fencerow to fencerow to feed the world by using more chemicals and designer seeds just coming on board. We would all be rich and the Chinese would be well-fed on American produce. Except, it didn’t work. We have half as many farmers today, and we are in a trade war with the Chinese seemingly without end.

Former vice-president Joe Biden arrives on his bus to speak to local residents during a tour stop in Mason City, Iowa. Photograph: Charlie Neibergall/Associated Press

Biden, 77, has been rolling past the fields of corn and soy stubble since 1988 en route to the White House, a familiar and comforting figure to over half the Democrats leery of radical change. He is coming off a post-summer poll dip that has seen a field of four top candidates emerge – Biden, Pete Buttigieg, Bernie Sanders and Elizabeth Warren – with the first-in-the-nation caucuses fast approaching on 3 February. All of them are leading large with a refigured agriculture to point our way out of climate crisis by capturing carbon and preventing further water pollution.

“This is really big. It’s everything we’ve been talking about for years,” said Vilsack, who still commands wide respect back home. It is no small thing to see the Vilsacks stand by the Bidens at this late stage.

Vilsack is among the leaders of an unorganized cadre of politicians, farmers, scientists and journalists pushing for a different approach from 50 years of rural decline. They’re getting across the idea to all presidential candidates of paying farmers for environmental services – something that the Iowa Farmers Union and the Iowa Farm Bureau have preached from opposite pulpits for close to 30 years. The contenders have had the crash course on regenerative agriculture, which plants grass or rye in rotation with corn and soybeans, and sees cattle grazing on the landscape again. It builds soil health, promotes resilience against extreme weather (now the norm, when you can’t plant or harvest for the gulley-washers), controls weeds and pests, and improves yields while reducing or eliminating chemical use. These practices suck carbon out of the atmosphere and plant it in the soil, and prevent nitrogen from adding to greenhouse gases.

All the campaigns call for beefing up funding for conservation, which the Republican-controlled Congress slashed in half during the last farm bill. Biden proposes tripling the size of the Conservation Stewardship Program, which pays farmers for planting cover crops like rye or buffer strips of grass on working lands. The program was authored by former senator Tom Harkin, a Democrat from Iowa, like Vilsack, a hero among Tall Corn state Democrats. Ten years ago, Harkin saw the CSP emerging as the main alternative to the system of crop subsidies, disaster payments and insurance in place since the Great Depression – which unintentionally props up corporate agriculture.

Warren has the boldest plans of all, proposing $15bn for the CSP and breaking up the huge agriculture chemical companies like Bayer and Dow. Buttigieg, the mayor of South Bend, Indiana, was among the first to support using agriculture as the tip of the spear in the climate crisis battle. Climate is at the center of Bernie Sanders’ campaign as well.

“Global warming can be turned into a gigantic opportunity,” Biden said as Vilsack nodded. “We are on the verge of providing significant job opportunities in rural America.”

Joe Biden speaks during a stop on his ‘No Malarkey!’ campaign in Algona, Iowa. Photograph: Brian Snyder/Reuters

Nobody was talking about net zero emissions in 2016, and there were mere murmurs in 2018. But this year, climate is center stage in Iowa as thousands of acres were washed away by spring floods and incessant rains delayed the harvest and added to costs. Farmers are the ones leading the way.

“It hasn’t been any fun this year,” said Kevin Cone, a farmer in Storm Lake, Iowa, noting that most of his peers have lost money for seven years running. Younger farmers are convincing older ones like Cone to give winter cover crops a try, to reduce costs and prevent runoff to surface water, which is suffocating the Gulf of Mexico.

Cone is a little defensive when farmers take the sole rap for surface water pollution. “Really, nobody cares more about water quality than the American farmer. No-till has never been higher. All farmers are always looking for ways to improve,” he said.

He put in 40 acres of virgin prairie to help protect Little Storm Lake from runoff. He supports conservation and wishes there were more of it. He just planted a couple acres for monarch butterflies.

Cone is keenly aware of the changing climate. It just keeps getting wetter in the upper midwest, interrupted by scary dry spells. Absolute humidity has been rising 5% per decade, according to Iowa State University, which leads to all these torrential rains and, counterintuitively, episodes of drought.

“My cousin is a geologist in Alaska. She studies the ice melt up there, and she told me to get used to it. It’s only gonna get worse.”

When Vilsack talks, farmers do listen.

“People like him. We know Joe Biden. You cannot redefine him,” Vilsack said. “Being president is a lot more than making a good speech.”

‘People like him. We know Joe Biden,’ said Tom Vilsack, the former US agriculture secretary. Photograph: Brian Snyder/Reuters

A good speech about a month ago launched Buttigieg into the forefront of the Iowa field.

Biden and Vilsack cooked up a speech that in large part was about re-investing in rural places with solar arrays, wind turbines, small food processors and local farm markets to provide jobs paying double the current rural work rate of $12-16 per hour.

Ultimately, rural is where Iowa is claimed: can you peel off enough support from these red counties to pull through? Vilsack is navigating the places that he won, by listening for Biden. The former governor rejects the idea that small towns are doomed as so many of us believe, with good evidence – two-thirds of Iowa’s counties lose population every year, and county seats like Sac City are emptying out while huge confinements housing thousands of sows owned by the Chinese move in.

Vilsack shook his head when asked if rural decline and more consolidation around chemicals are simple destiny, and if all this talk is just that given all the decades of neglect.

Biden, the talker, chimed in.

“We can do anything if we put our mind to it,” Biden said. He then jaunted into a dissertation on the Obama-era green energy programs that Trump dumped by the roadside.

Climate crisis is front of Biden’s mind. It’s on the minds of constitutionally conservative people who continue to press every campaign about a different course from the past half-century.

“This is a battle for the soul of the nation and the future of the planet,” Biden said. “The future of the country lies in rejuvenating these places. You’re 20% of the population with half the answers. I will focus heavily on rural America.

“And I keep my promises.”

Vilsack nodded his head yes. Democrats in north-west Iowa noticed.