Former Florida govenror Jeb Bush waves to the crowd before speaking at the Iowa Agriculture Summit on Saturday. (Charlie Neibergall/AP)

A day-long forum on agriculture here, where likely Republican presidential candidates courted Iowa’s farming industry, revealed sharp policy differences among the contenders, from immigration to energy subsidies.

The nine White House aspirants used their turns on stage Saturday at the Iowa State Fairgrounds to blast President Obama and his administration as being heavy-handed and indecisive, arguing that a change in leadership is necessary to stimulate agricultural growth.

Calling the Environmental Protection Agency “a pig in slop,” Jeb Bush said, “We have to begin to rein in this top-down driven regulatory system.” Asked how to achieve that, the former Florida governor said, “The first thing you do is you change presidents.”

The industry-sponsored summit — in which each hopeful answered questions on energy, the environment, immigration and food safety in solo sessions with agriculture businessman Bruce Rastetter — highlighted the demands that Iowans place on candidates to pay attention to the state that hosts the first presidential caucuses.

Saturday’s forum was one of a series of events on Iowa’s political calendar this spring and summer designed to draw the candidates to the state and take positions on its pet issues. Iowa has long pushed for federal support for its ethanol industry, and many people have argued that without the high-profile caucuses, the subsidies would have been harder to sustain.

Fuel subsidies became a point of contention as Rastetter tried to draw support from a new generation of presidential hopefuls. While many of the prospective candidates said they backed the subsidies, the event was notable for the number of dissenters, with Sen. Ted Cruz (Tex.) being the most explicit, saying the Renewable Fuel Standard should be repealed.

“The answer you’d like me to give is, ‘I’m for the RFS, darnit,’ ” Cruz said. “But I’ll tell you, people are pretty fed up, I think, with politicians who run around telling one group one thing, another group another thing, and then go to Washington and they don’t do anything they said they’d do.”

Bush said that whether it is ethanol or any other fuel, “the markets are going to have to decide this.”

But New Jersey Gov. Chris Christie said he supports the subsidies and blamed the Obama administration for not being forceful enough in establishing a standard. “Certainly anybody who’s a competent president would get that done in their administration,” he said.

Wisconsin Gov. Scott Walker said he would continue the subsidies for now but phase them out once ethanol producers are assured access to markets. “I think eventually you can get to that,” he said. “But you can’t get to that unless you deal with market access.”

Differences also emerged between the likely candidates on immigration. Making his first trip to Iowa this year, Bush defended his support for comprehensive immigration reform, which has drawn stinging criticism from many conservative activists.

“If we want to be young and dynamic and growing again, where the debate isn’t about who’s taking from whom rather than having an expanding pie, where opportunities exist for all of us, I think we need to fix this broken immigration system,” Bush said. “Immigrants that are here need to have a path to legalized status.”

Bush called for bringing immigrants who are in the country illegally “out from the shadows” by making them pay fines, learn English, hold jobs with provisional work permits and “earn legalized status over the long haul,” without receiving government assistance.

Sen. Lindsey O. Graham (S.C.) called for Republicans to compromise with Democrats to enact comprehensive immigration reform, saying the issue is damaging the GOP brand. “I’ve got one solution to this problem,” he said. “Be practical. Get it behind us.”

Other contenders used hotter rhetoric to sound the alarm on amnesty. Former Arkansas governor Mike Huckabee asked, “What do we do to stem the tide of people who are rushing over because they’ve heard that there’s a bowl of food just across the border?”

If the Republicans disagreed on immigration and energy subsidies, they were unanimous in their criticism of Obama’s diplomatic overtures to Cuba. Former Texas governor Rick Perry said the negotiation to release U.S. government contractor Alan Gross was “a bad deal.” He added, “We traded Mr. Gross for three Cuban spies and, in my opinion, we got the way short end of that deal.”

Unlike previous GOP candidate forums, Saturday’s summit drew no mention of Hillary Rodham Clinton, the former secretary of state and likely front-runner for the Democratic presidential nomination.

At Saturday’s forum, the contenders displayed different styles and motivations. Unlike other so-called cattle calls, likely presidential candidates did not give speeches here and instead each answered questions posed by Rastetter for about 20 minutes.

While Bush tried to showcase his intellectual firepower by answering questions directly, as if he were sitting for an interview with an agricultural policy journal, Graham used humor as a way to stir the crowd and make sharp points about foreign policy and the need for comprehensive immigration reform.

Despite the day’s focus on agriculture policy, Huckabee wove into his answers an economic populist pitch.

“People are working harder this year than they were before, lifting heavy things, sweating through their clothes every day, and they have less to show for it,” Huckabee said. He added that the United States must “get serious and honest and tough” with China. “We need to start making it so that Americans can prosper, and not just so the Chinese can buy Louis Vuitton and Gucci bags,” he said.

Former senator Rick Santorum (Pa.) used his answers to highlight his emphasis on economic policies aimed at working families. He lamented that with the decline of manufacturing, “the middle of America [is] hollowing out.”

Christie tried to make his case for strong executive leadership by repeatedly leveling broadsides at Obama and his administration, including first-term EPA administrator Lisa Jackson. When a heckler interrupted him, Christie quipped, “I’m glad to see that New Jersey has come to Iowa. . . . My people follow me everywhere!”

Saturday’s forum also was an opportunity for likely contenders to display knowledge of rural issues and connect with Iowa’s farmers. Walker waxed nostalgic about growing up as the son of a Baptist preacher in the small Iowa town of Plainfield, where he said he learned that “farming isn’t just a business, it’s a way of life.”

Perry talked about growing up in remote Paint Creek, in a home with no running water and 16 miles from the nearest post office. As a young man on his family farm, Perry recalled, “I watched my wheat go to hell in a handbasket.” Former New York governor George Pataki also talked about being born and raised on a family farm.

Christie joked that despite grappling with more-urban concerns back home, “New Jersey is the Garden State. It’s not like I come out here not knowing any of this.”

Ed O’Keefe contributed to this report.