CHICAGO (REUTERS) - US farmers said they would push ahead with plantings planned before US-China trade tensions eased. And now that the two countries have resumed talks, they will take a wait-and-see approach to President Donald Trump's promises for more sales to China.

Over the weekend, the world's two largest economies pledged to keep talking about how China could import more energy and agricultural commodities from the United States to narrow a US$335 billion (S$449 billion) annual US goods and services trade deficit with Beijing.

The agreement came after Mr Trump threatened to impose up to US$150 billion in punitive tariffs to lower the trade deficit and combat what he calls Beijing's misappropriation of US technology.

China threatened equal retaliation, including tariffs on some of its largest US imports, including soybeans and other agricultural commodities.

The reluctance of some farmers to adjust their planting plans in the light of the latest negotiations shows they are uncertain about the outcome. For many, it is also simply too late to change their minds after buying seed, fertiliser and farm chemicals.

"We're so far along in our planting season that we can't change anything," said Mr John Brink, who grows corn, soy and wheat in Richview, Illinois.

As of Sunday (May 20), farmers had planted 81 per cent of the US corn crop, 56 per cent of the nation's soybeans and 36 per cent of sorghum, a grain used for livestock feed, according to US Department of Agriculture data issued on Monday.

"Until we see some hard evidence that some major concessions have been made or whatnot, we're kind of taking a wait-and-see approach," Mr Brink said. "We just kind of understand this is politics in play."

The United States appeared to have won promises of more imports by China, although there were few specifics on Monday.

Farmers said they wanted more details.

"The news is encouraging, but a lot of us on the farm would like to hear some contracted sales that have been placed," said Mr Monte Peterson, a soybean farmer in Valley City, North Dakota.

Mr Kirby Hettver, who was wrapping up soybean planting on his farm in DeGraff, Minnesota, said he wanted to see a long-term deal in place before he makes any changes on his farm in response to trade policies.

"I view it as part of the process," Mr Hettver, president of the Minnesota Corn Growers Association, said of the latest stage of the US-China talks.

"Our plan for this year was already in place. We had seed bought, fertiliser bought."

The US Grains Council, which promotes US exports, would like China to speed up import approvals of US biotech crops such as corn and reduce tariffs on shipments of US ethanol and an ethanol byproduct known as distillers' dried grains, chief executive Tom Sleight said.

Last Friday, China dropped an anti-dumping investigation into US sorghum that had raised costs for buyers of the grain.

As a result, the Grains Council may dial back plans made during China's investigation to find more buyers in other countries for US sorghum, Mr Sleight said.

"We may be not quite so aggressive now because China could come back as a huge buyer," he said. "You don't want to build a big market and then not have something to deliver."

The United States shipped 4.76 million tonnes of sorghum to China in 2017, worth around US$1.1 billion and making up the bulk of China's roughly 5 million tonnes of imports of the grain, according to Chinese customs data.

Some US farmers scrapped plans to plant sorghum this spring, opting for corn instead, after China's probe halted US sorghum imports.

But Mr Kent Winter, who farms outside Wichita, Kansas, and is president of the Kansas Grain Sorghum Producers Association, was planning to double his sorghum plantings when the latest trade talks were announced. He will plant the crop across about 400 acres in about three weeks, hoping that China resumes US imports soon after ending its anti-dumping probe.

"It gives us more confidence going forward that we can get this foreign market opened back up," Mr Winter said.