Monsanto bought 155 acres, including the southwest corner of Sanders and Twin Peaks roads, in Avra Valley last week.

Monsanto Corp. bought 155 acres in the Avra Valley northwest of Tucson last week, solidifying its efforts to build a greenhouse there to grow corn and soybeans for research.

The St. Louis-based company paid $3.74 million Wednesday to a company owned by the Kai farming family of Marana for the land, county records show.

The acreage of the purchase raises questions about what if any operations or projects Monsanto plans for the site besides the seven-acre greenhouse. The timing raises questions about why the company bought the site before a proposed tax incentive deal with Pima County is brought to the Board of Supervisors for approval.

A Monsanto spokeswoman didn’t return a phone call or an email seeking comment on the purchase. Pima County Administrator Chuck Huckelberry said in an email that he hasn’t heard anything from Monsanto about the purchase, so he can’t answer questions about it.

The purchase came nearly two months after Monsanto said it plans to build a greenhouse on seven acres in the Tucson area. The company has said it will hire 40 to 60 employees and its representatives have said it will invest $100 million.

It came a few days after the Star reported that Pima County and Monsanto are negotiating a possible incentive deal that would reduce the company’s property tax burden on the site by two-thirds. That proposal probably will go to the Board of Supervisors in November or December, Huckelberry has said. The company has said it plans to start construction on the greenhouse by the end of 2016.

The incentive being considered would expand the county’s foreign trade zone to include the Monsanto site. Inclusion in the zone reduces import duties and would offer Monsanto other benefits besides property tax abatements.

Monsanto’s proposal is opposed by two of the five county supervisors. They are Democrat Richard Elías, an outspoken liberal and environmental advocate, and Republican Ally Miller, a fierce critic, in general, of Huckelberry’s economic development efforts involving incentives.

Monsanto is popular among many farmers who say its seed research and other operations have increased crop production and crop resistance to herbicides. It’s unpopular with other farmers who believe it has too much power, particularly after its recent takeover by Bayer, another seed giant and pharmaceutical manufacturer. The company is also opposed by some environmentalists who don’t like its use of genetically modified seed crops and its production of the Roundup weedkiller, although Monsanto has said it doesn’t intend to plant many, if any, GMO crops in the Avra Valley greenhouse.

Republican Supervisor Ray Carroll, another outspoken environmentalist, said he’s still neutral on the proposal, adding he’s been sympathetic to most county economic development efforts. Supervisors Sharon Bronson and Ramon Valadez, who are Democrats, haven’t commented on it yet.

On Friday, Carroll said the large land purchase shows that “maybe Monsanto has ideas for other uses. They’re buying a lot more than they need for a greenhouse. I can only assume they’re doing it to make sure they have plenty of room to expand into any other ancillary outgrowth of the arid land greenhouse operation.”

As for the purchase’s timing, Carroll said the company seems to be “putting the cart before the horse.”

“These people have shown their hand, they’re making a gung-ho move here. Usually, they wait, to see how your foreign trade zone went down and your tax incentives are approved,” he said.

At the same time, Carroll said he’s supported several recent job-creation incentive packages including those for WorldView and Caterpillar. He made it a point to say that Monsanto hasn’t announced plans for any activities here that have been controversial elsewhere, such as GMOs.

Miller took Huckelberry and the Monsanto incentive package to task on Facebook last week.

“Just read the Monsanto article in the paper,” Miller posted on Tuesday. “Well now, another back room deal being negotiated?? People are outraged? It is about time.

“These deals need to be thoroughly researched and vetted. Let’s see how many days notice we get on this deal before it is served up for a rubber stamp! Disgusting that I am hearing about this in the media as a county administrator does the deal in the dark of night. Disgusting! Pima County taxpayers deserve better!” Miller said.

A Huckelberry spokesman has said that in general, the county administrator believes disclosing details of negotiations can hurt economic development efforts.

Contact reporter Tony Davis at tdavis@tucson.com or 806-7746. On Twitter: tonydavis987.