None of the justices in arguments at the high court seemed ready to endorse farmer Vernon Hugh Bowman’s argument that cheap soybeans he bought from a grain elevator are not covered by the Monsanto patents, even though most of them also were genetically modified to resist the company’s Roundup herbicide.

Chief Justice John Roberts wondered “why in the world would anybody” invest time and money on seeds if it was so easy to evade patent protection.

To protect its investment in their development, Monsanto has a policy that prohibits farmers from saving or reusing the seeds once the crop is grown. Farmers must buy new seeds every year.

The case is being closely watched by researchers and businesses holding patents on DNA molecules, nanotechnologies and other self-replicating technologies.

The issue for the court is how far the patents held by the world’s largest seed company extend. More than 90 percent of American soybean farms use Monsanto’s “Roundup Ready” seeds, which first came on the market in 1996.

The 75-year-old Bowman bought the expensive seeds for his main crop of soybeans, but decided to look for something cheaper for a risky, late-season soybean planting.

He went to a grain elevator that held soybeans it typically sells for feed, milling and other uses, but not as seed.

Bowman reasoned that most of those soybeans also would be resistant to weed killers, as they initially came from herbicide-resistant seeds too. He was right, and he repeated the practice over eight years. In 2007, Monsanto sued and won an $84,456 judgment.

Across the court’s conservative-liberal divide, justices expressed little sympathy for Bowman’s actions.

Justice Stephen Breyer said Bowman could make many uses of the soybeans he bought from the grain elevator. “Feed it to the animals. Feed it your family or make tofu turkey,” Breyer said.

But patent law makes it illegal for Bowman to plant them. “What it prohibits here is making a copy of the patented invention and that is what he did,” Breyer said.

Mark Walters, Bowman’s Seattle-based lawyer, tried to focus the court on the claim that Monsanto has used patent law to bully farmers.

“What they are asking for is for the farmer to assume all the risk of farming, but yet they can sit back and control how that product is used,” Walters said.

Monsanto lawyer Seth Waxman said the company put 13 years and hundreds of millions of dollars into developing herbicide-resistant seeds.

“Without the ability to limit the reproduction of soybeans containing this patented trait, Monsanto could not have commercialized its invention and never would have produced what is now the most popular patented technology” in farming, Waxman said.

The Obama administration also is backing the company.

Consumer groups and organic food producers have fought Monsanto over genetically engineered farm and food issues in several settings. They lost a campaign in California last year to require labels on most genetically engineered processed foods and produce. Monsanto and other food and chemical companies spent more than $40 million to defeat the ballot measure.

A decision is expected by June.

The case is Bowman v. Monsanto Co., 11-796.