State officials have tried unsuccessfully over the past few decades to identify and set aside high-quality farmland that can be protected from urbanization.

Now city planning officials are asking the public to weigh in on what should be included in a new map of the island’s important agricultural acreage.

Owners of the properties on the final map would have a much harder time taking them out of farming and replacing them with residential, commercial or other urban uses. They also would be eligible for incentives to keep their land in agricultural use.

More than 56,000 acres is under consideration for Important Agricultural Lands (IAL) designation on a draft map that’s being circulated by the city Department of Planning and Permitting.

"The objective here is to identify good farmland, whether (genetically modified organisms) are growing on it or local crops or something else," city DPP Director George Atta told Hono­lulu Star-Advertiser editors and reporters Wednesday. "And once you’ve identified them, at the county level you can put more stringent regulations on them," he said.

Scott Ezer, a principal with HFF Planners, which is helping the city develop its IAL map, said the project seeks to draw the proverbial line in the sand. "These are what we consider to be inviolate agricultural lands," he said.

Once the IAL properties are formally mapped, they will also be eligible for incentives designed to keep them in active farm use, including tax breaks, grant assistance and less rigid building code and water regulations, Atta said.

The map made available by DPP shows the roughly 56,000 acres of private agricultural land on Oahu that meets one or more of the three qualities deemed most essential to meet the definition of IAL designation: land currently in agricultural production, land with prime soil qualities and growing conditions, and land with sufficient availability of water to sustain agricultural development.

The two largest swaths under consideration are in the Wahiawa-North Shore region and Kunia, while others are scattered throughout more rural parts of Oahu including the Wai­anae Coast, Mili­lani Mauka, Wai­mea-Sunset Beach, Kahuku-Laie, Hauula-Puna­luu, Kaa­awa and Wai­ma­nalo.

Three public meetings are scheduled on consecutive Wednesday evenings in April in Kapo­lei, Mili­lani and Kane­ohe. DPP, which is developing the plan, will give an overview of the plan’s objectives before yielding to public comments and recommendations.

DPP officials are hoping to send a completed proposal to the Hono­lulu City Council for its approval by the end of the year. The plan would then be submitted to the state Land Use Commission, which would have the final say over Oahu’s and the other counties’ maps.

Atta said the call to identify and set aside the state’s most agriculturally significant land was spawned during the 1978 Hawaii Constitutional Convention. Part of the reason to sift out IAL properties is to distinguish them from land that has been designated as "agriculture," even when it’s not conducive to agriculture, simply because it did not qualify as urban or conservation use.

"Anything they didn’t know what to do with, they threw in the ag district," Atta said. "So what happened is in the ag district you have good ag land and you have junk ag land."

About 123,000 acres on Oahu, or about 32 percent, is currently designated for agriculture, so less than half is being considered for IAL designation.

For years, state planners have tried to come up with a plan on how best to identify IAL land that was agreeable to government planners, landowners, farmers and other stakeholders. The lack of computer-driven data needed to properly identify the properties also hindered the process.

In the early 2000s the state Legislature tasked the four counties with creating the IAL maps but provided no funding for it, Atta said.

The process for determining the properties now under consideration for IAL designation began with approval of the city’s Oahu General Plan in the late 1970s, which consciously shifted urban growth into the Ewa Plain and the southeastern section of Central Oahu, Atta said.

Then, regional development plans and urban growth boundaries were created in the 1980s and the 1990s, respectively,

The state law says land already designated for residential and commercial use or other types of urban uses cannot be designated as IAL, Atta said. As a result, the Central Oahu land where Castle & Cooke is developing Koa Ridge — which received zoning from the Council last year — and the Ewa-Kapo­lei land where D.R. Horton-Schuler Division is seeking rezoning for its 11,750-home Hoo­pili project were both not eligible for IAL designation, he said.

On the other hand, the agricultural land in Malaekahana, between Laie and Kahuku, being proposed for Hawaii Reserves Inc.’s Envision Laie project is eligible for IAL designation and could play a role in any possible future growth there, city officials confirmed after meeting with Star-Advertiser staff.

Ezer stressed that the criteria used to develop its potential IAL areas did not consider who owned what properties.

"We’re not looking at property lines," he said.

Another key IAL rule is that the city can require no landowner to have more than 50 percent of its Oahu properties designated as important agricultural land, a provision that gives landowners incentive to come in on their ownand choose what land is offered for IAL designation.

City officials noted that Kame­ha­meha Schools, the state’s largest private landowner, petitioned the LUC successfully earlier this month to give IAL designation for nearly 10,000 acres it owns along the North Shore and Koo­lau Loa.

Kamehameha Schools also has promised $17 million for processing facilities and other farm-related infrastructure on that land at Kawai­aloa and Puna­luu.

Castle & Cooke also succeeded in getting a portion of its Central Oahu land designated for IAL.

IAL designation does not necessarily mean land will be kept in agricultural use forever. But it will take a supermajority of two-thirds of the LUC or Council to OK urban uses, instead of the simple majority required for most rezonings and reclassifications, Atta said.

Nalo Farms owner Dean Oki­moto, among those on a city advisory committee who helped DPP get to this point, said he’s pleased with the cooperation that’s taken place among representatives from the city, farmers and landowner interests. "It’s far from perfect, but it is something that I think is workable, and at least it’s gotten this far," he said.

One of the farmers who pushed for IAL designation to become reality, Oki­moto said that setting aside agricultural land is only part of the equation for a sustainable farming industry.

Ensuring there are enough farmers to make use of the land, as well as the availability of water, are also important, he said.

The project website will be available from Wednesday at mapoahuagland.com. Meanwhile, background information can be found at bitly.com/HnlDPPIAL.