For almost a half-century, California has given tax incentives to farmers in an effort to protect their land from urban sprawl.

Now, the state's budget crisis has placed that program's future in jeopardy, and local governments in farming regions like the San Joaquin Valley are fighting to save it.

But are the tax breaks even working? Not really, according to several studies of the Williamson Act, a 45-year-old law that assesses farmland at rates based on its agricultural use instead of its potential development value.

More than half of California's farmland is enrolled in Williamson Act contracts. In Fresno County, more than 1.5 million acres are covered under the Williamson Act or a related provision, Farmland Security Zones. But only a tiny fraction -- about 3.5% -- lies in areas that regional planners say are threatened by urban sprawl over the next 40 years.

"People like to talk about the Williamson Act as a way to slow sprawl, but when you actually look at it, you find out that it's not being used in that way," said Robert W. Wassmer, chairman of the Department of Public Policy and Administration at California State University, Sacramento.

In reality, the program gives tax breaks to farmers even if their land is miles from any potential source of development pressure. In fact, farmers whose land adjoins existing cities are the least likely to use the program.

As a result, a map of Williamson Act and Farmland Security Zone contracts shows what Wassmer calls a "ring" of unprotected land encircling most Central Valley cities.

Rather than curbing growth of cities, the contracts provide at most a short-term tax break to farmers waiting for development to reach them. That's almost never enough to drown out the siren song of a builder bearing a big check.

Take, for example, Paul Betancourt. He farms more than 700 acres in western Fresno County, including 27 acres next to his home on land abutting Kerman's sphere of influence -- the city's reserve for growth.

Seven years ago, Betancourt said, land across Highway 180 from him sold for $43,500 an acre. That prompted him to consider selling out.

"The farmland value, even with almonds on it, is only $10,000 an acre," he said. "It's kind of hard to turn that [$43,500] down."

When the housing market crashed a few years later, Betancourt back-burnered the idea. But when the cycle turns up again and builders begin offering more money for developable land, the pressure to sell will return, said Ryan Jacobsen, executive director of the Fresno County Farm Bureau.

"No matter what the tax break is, you're not going to be able to offset the lure of development" on land adjacent to cities, Jacobsen said.

Selma grower Todd Hirasuna said that for high-value crops such as fruits and vegetables the Williamson Act benefit is typically too small to be a factor in any such decisions.

"Don't get me wrong -- every little bit helps," he said. "But whether or not a piece of land is currently enrolled in the Williamson Act is a secondary concern when it comes to land development."

Changing course

Farmers on the urban fringe often withdraw their land from the Williamson Act -- a process called "non-renewal" -- when development draws near.

A decade ago, Pat Ricchiuti, a fruit grower on the northern fringe of Clovis, notified Fresno County that he wanted to terminate Williamson Act contracts on more than 500 acres near the northeast corner of Willow and Shepherd avenues. That started a 10-year phase-out period, now ending, after which the land will be eligible for development.