China's leader-in-waiting Xi Jinping reached out to heartland America Thursday with billions of dollars in farm deals, as Republican Mitt Romney slammed the "prosperous tyranny" of Beijing.

China's vice president, who is expected to lead the rising Asian power for a decade starting next year, hopped onto a tractor on an icy soybean and corn farm in Iowa and declared his love for the "very homey environment."

"This is away from the sound and the fury of the cities, and the air here is very fresh," Xi told fifth-generation farmers Rick and Martha Kimberley, smiling as their 36-year-old son Grant welcomed him in Chinese.

Xi, who a day earlier reminisced with Iowans he recalled fondly from his first visit to the United States in 1985, is on a camera-friendly week-long US tour seen as an attempt to show a gentler side of fast-emerging China.

Xi dined on local pork and cupcakes during a gala dinner Wednesday in the State Capitol building of Iowa, whose exports to China shot up by nearly 1,300 percent between 2000-2010 as the Asian power's growing middle class eats more imported meat and soybeans, used to make tofu.

A Chinese business delegation accompanying Xi signed deals including commitments to buy 317 million bushels of soybeans from major US companies, in a deal estimated to be worth $4.3 billion.

Xi, in a speech in Iowa's capital Des Moines before visiting the farm in Maxwell, said that developing a stable agricultural sector was critical for "strong, sustainable and balanced growth" at a time of global economic uncertainty.

US Agriculture Secretary Tom Vilsack, receiving Xi at the headquarters of the World Food Prize named after anti-hunger leader Norman Borlaug, called for the two countries to work together to boost food production in poorer nations.

"We have a responsibility and opportunity to work together to address the causes of global hunger that affect more than 925 million people," Vilsack said.

The tone was characteristic for Xi's visit, with both sides looking to start off on the right foot under the next Chinese leader and putting on the backburner issues that have sharply divided the world's two largest economies.

President Barack Obama welcomed Xi to the White House on Tuesday and the Pentagon offered him an honor ceremony with cannons.

Xi flew out of Iowa later Thursday for Los Angeles, where he was expected to take in a Lakers basketball game.

He started his 36-hour West Coast visit with a tour of the Port of Los Angeles, the biggest US port in terms of container throughput and a major gateway for Chinese goods arriving from across the Pacific.

On Friday he will attend an economic forum in downtown LA, announce a deal with the film giant DreamWorks Animation to build and operate a studio in Shanghai, and watch the NBA game before leaving for Ireland.

While the White House has called the trip an investment in the future, Mitt Romney -- one of the Republican candidates vying to replace Obama in November elections -- called Xi's visit "empty pomp and ceremony."

Romney vowed that he would designate China a currency manipulator -- which would pave the way for US retaliatory measures -- for allegedly undervaluing its yuan to boost exports.

He called the US military commitment to Asia "vastly under-resourced" and vowed to speak out against China's "barbaric" policy of barring most couples from having more than one child.

"The sum total of my approach will ensure that this is an American, not a Chinese century," Romney, the former governor of Massachusetts, wrote in The Wall Street Journal.

"We have much to gain from close relations with a China that is prosperous and free. But we should not fail to recognize that a China that is a prosperous tyranny will increasingly pose problems for us, for its neighbors and for the entire world," Romney wrote.

The Obama administration has declined to declare China a currency manipulator, preferring quiet diplomacy. Beijing has let its yuan appreciate since 2010, although most experts say the chief reason is to control inflation rather than to address foreign concerns.

Xi has been trailed throughout his trip by protesters, with flag-waving Tibetans marching through Des Moines to denounce what residents say is a clampdown in Tibetan areas where at least 20 people have set themselves on fire to protest Beijing's rule.