Donald Trump's trade war is on track to cost Iowa's farmers millions of dollars, but many are still backing him — for now.

When the US slapped $34 billion worth of tariffs on goods from China a week ago, Beijing immediately retaliated with 25 per cent tariffs targeting US agriculture.

It's no coincidence that China's tariffs hit America's rural farming communities — they are the ones who voted Donald Trump into the White House.

"We're concerned," fifth-generation Iowa farmer Rick Kimberley told the ABC.

The Kimberley corn and soybean farm in Maxwell in central Iowa sprawls 4,000 acres (1,618 hectares).

Rick Kimberley's corn and soybean farm was famously visited by Xi Jinping in 2012. ( Stephanie March )

One third of his soybean crop is destined for export. The soybean price had already been falling when China imposed its 25 per cent import tax — this week it hit a 10-year low.

"In short, it is going to impact my income and it's going to impact every farmer's income," Mr Kimberley said.

Mr Kimberley voted for Donald Trump. While he does not always like the way the President goes about governing, when it comes to the trade imbalance with China he believes something must be done.

"I'd say we're a very loyal and patriotic people out here in the Midwest and so yes I think we want to see this resolved but I think there are issues that need to be addressed and taken care of so that's what he's doing," Mr Kimberley says.

The Kimberleys have a unique connection with China — now President, Xi Jinping, visited the Kimberley farm in 2012. A photo of Mr Kimberley showing Mr Xi how to drive a John Deere tractor made the front pages of newspapers in both nations.

A working model of the Kimberley's farm is being built in Luanping County in the hope of transforming farming in the Asian nation.

Mr Kimberley knows as well as any politician what is at stake — for both sides.

"If this is long-term tariffs, it could be significant. We're hoping that cooler heads will work together and trade tariffs are not good for anyone — not the United States, not the farmers — but also not China and Chinese people," he says.

"It's going to cost them more to purchase soybeans and so their food costs are going to go higher."

Last week Donald Trump's Treasury Secretary, Steven Mnuchin, said trade talks with China had "broken down", which is not a good sign for Iowan farmers gearing up for a September harvest.

Dave Young says smaller growers may be forced to sell off due to increased competition. ( Stephanie March )

If the tariffs are still in place then, and prices are still low, it could be a big problem.

"I think it could affect some of my smaller growers," says Dave Young, who owns a grain elevator in Aurora and deals with corn and soybean farmers from across the region.

"They might be forced to sell off — you know it's kind of a really competitive market."

Mr Young did not vote for Mr Trump — but he believes something has to be done to sort out America's trade deficit with China.

"Something needs to change, you know? You'd hope it doesn't affect you, but I think it's going to affect everyone actually."

It is not just grain farmers who have been hit — Iowa is America's biggest pork producer.

In the last month, pig farmers have been hit with a 20 per cent tariff from Mexico and a 25 per cent tariff from China.

In Winthrop, just north of Cedar Rapids, Aaron and Trish Cook market about 30,000 pigs per year — one in four is exported. Their break-even price per head is $US140. The fourth-quarter price is now $US110.

Mr Cook says since the trade war began the price per head dropped by $US20 ($26.94).

"The tariffs have definitely scared the markets and the traders," Mr Cook told the ABC.

"Hopefully they're overreacting, but it's definitely pretty scary for this fall."

Aaron Cook says the US-China trade war could dog Donald Trump's presidency. ( Stephanie March )

Time is of the essence for Donald Trump to resolve this trade dispute — farmers will start to feel the pinch in September or October, and in November voters will head to the polls for the mid-term elections.

A Trump supporter, Mr Cook is backing the President's trade tactics, but there may come a time when his faith is tested.

"I think President Trump could really come out of this looking like a hero or it could be something that really dogs him in the future too," Mr Cook says.

"If all this was for nothing, it could be something that he has to deal with in a couple years when he goes for re-election."