LUBBOCK, Texas -- Crop circles in this part of the country have begun to take a peculiar shape: On some farms, they're cut in half.

Agriculture has been the mainstay here for more than a century, made possible by the seemingly inexhaustible Ogallala Aquifer, which underlies the plains of West Texas and seven other states. Farming and ranching accounts for 95 percent of water use in the region.

But after decades of groundwater pumping, aquifer levels are dropping in many areas. Some farmers here have seen their wells yield less water, forcing them to scale back their crops. And for the first time, the local water district here is beginning to limit how much water farmers can pump from their wells.

The new regulations have provoked discontent among some growers, and a few have founded a group to fight the new rules. They also likely will lead to a court battle here when a moratorium on enforcing the regulations expires in 2014. The Texas Supreme Court has already been grappling with the issue in a similar case elsewhere in the state.

With less water available, some farmers are returning to dryland farming -- watering their crops with whatever moisture the skies provide. But in the long run, some water experts quietly wonder whether farming will survive here, as droughts become more frequent in a changing climate, or what could replace it on these vast, riverless flatlands.

Texas has about 100 water districts, but the High Plains Underground Water Conservation District is one of the first to regulate groundwater pumping.

The district, which oversees groundwater in 16 West Texas counties, adopted rules last January that restrict how much water farmers can pump from their wells. They also require that new wells have meters so that groundwater use can be measured. The move followed the worst drought in Texas' history.

The High Plains district regulations are designed to ensure that 50 percent of the water in the aquifer in 2010 will be available through 2060. That target is part of a larger, statewide effort to better manage groundwater under legislation passed in recent years by the state Legislature.

Jim Conkwright, general manager of the High Plains district, said the new rules are necessary to prolong the life of the aquifer and ensure that there is enough water to go around in the coming decades. The thickness of the aquifer varies and that determines how much groundwater is available from one farm to the next, but on average the Ogallala has been declining by at least three-quarters of a foot per year in the area, he said.

"We have large areas of the aquifer that are in rapid decline," he said during a tour of agricultural lands in West Texas organized by the Society of Environmental Journalists as part of its annual conference in Lubbock from Oct. 17 to Sunday. "We believe the best way to manage it is to have strong regulations from local conservation districts. As much as people see the decline in the aquifer, they don't want to stop using it."

But some farmers vehemently oppose any government-imposed limits on their water use, which until now has been unrestricted. J.O. Dawdy, who grows cotton on his 160-acre farm northeast of Lubbock, believes the new rules are onerous, are unnecessary and could put some farmers out of business.

"They're gonna severely damage our ability to make a living out here," Dawdy said in a phone interview. He and three other farmers formed the Protect Our Water Rights Coalition to fight the rules.

If the regulations had been enforced this year -- the district postponed issuing violations until 2014 -- he would have reached his irrigation limit in late July, Dawdy said.

"At that time, I would have had to cease irrigation or expose myself to tremendous fines" of about $3,000, he said. "And if I had cut my water off, I would have lost my crop."

Dawdy argues that the economics of water use would sort out the problem much more effectively than regulations could. With aquifer levels dropping in some places, some farmers have had to reduce their crops anyway because their wells are no longer able to pump as much water as they previously did.

"Economics will take care of it, as it has for 100 years," he said. "People adapt to whatever resources they have. As their water supplies drop in certain areas, they'll do things like they'll go to a half circle or a rotation -- plant a winter crop like wheat and a summer crop like cotton. They'll adapt on their own. Better than the government stepping in and imposing fines."

Court battles

Next month, two members of the High Plains district board are up for re-election. If they are voted out and the new board members are more sympathetic to opponents of the rules, the reconfigured board may opt to reverse the board's earlier decision.

But if the district begins enforcing the new regulations in 2014 as planned, farmers who oppose the rules are expected to file suit. Dawdy is likely to be among the first.

"The bottom line is that we feel this is a property rights issue, we feel like we've had no due process, we feel this is an unconstitutional taking, under both the state and federal constitution," he said. "We don't intend to just sit here and take it."

In fact, Dawdy's group prepared a lawsuit when the water district first adopted the rules but held off filing it after a Texas Supreme Court ruling earlier this year in another case involving groundwater pumping by two ranchers in South Texas.

The ruling, issued in February, affirmed that the ranchers, Burrell Day and Joel McDaniel, do own the groundwater beneath their lands. But it also upheld the right of the Edwards Aquifer Authority, which manages groundwater in that area, to regulate pumping. The court also found that the Edwards Aquifer Authority could compensate the ranchers for the limits on their use of groundwater. The aquifer authority had argued that granting compensation could open it up to a deluge of litigation from other landowners as well.

But at what point such regulations result in a "taking" of a landowner's private property right that requires compensation remains unanswered. The court sent the case back to the district court to address the matter.

Dawdy's coalition feels that the state Supreme Court ruling invalidates the High Plains district's rules. But the district believes the decision does not apply to it, because the case involved the Edwards Aquifer, which recharges much more quickly than the Ogallala Aquifer.

If the new rules do stand, Dawdy said, farmers should be compensated for the loss of their water, because it is their property under state law. Compensation funds could come from the Texas Water Development Board, which received bond money for water projects last year, he said.

Does farming have a future?

On average, the Ogallala Aquifer declined 10 feet over the 15-year period between 1990 and 2004 in West Texas, according to Kevin Mulligan, an associate professor of geography at Texas Tech University in Lubbock who studies groundwater use in the state. Mulligan and his colleagues used well data from the Water Development Board, which monitors groundwater use.

"The aquifer is being mined just like an oil field, and it's going to be depleted, largely," he told reporters at Texas Tech's Center for Geospatial Technology in Lubbock on Saturday during the SEJ conference.

When the saturated thickness of the aquifer drops to about 30 feet, "it becomes difficult to maintain central pivot irrigation," he said. Central pivot irrigation involves using a long, rotating irrigation arm that waters fields in a circular motion from a center anchor.

Other parts of the Ogallala Aquifer, however, are in good shape, Mulligan added. While southwestern Kansas and eastern Colorado are also seeing groundwater levels drop, in areas where the aquifer is much thicker, such as the Sandhills in Nebraska, the aquifer is "not being depleted at all," he said.

About 12.5 percent of the cropland on the Great Plains is irrigated; the rest is farmed using rainfall in what is known as dryland farming, he added. And while 180 counties overlie the Ogallala Aquifer, 36 are seeing problems, he said.

Those 36 counties, though, are "some of the most productive counties on the Great Plains," Mulligan noted.

Regardless of whether limits on groundwater pumping hold up in court, some question how long farmers will be able to continue to rely on the aquifer. Hydrologists expect less groundwater to be available in many areas in the years to come, as climate change brings more frequent droughts and pumping increases to make up for the lack of rainfall.

Since less water means smaller crops and less profit, some farmers may be forced to find alternative ways to make a living. One way farmers could diversify their income and help ease the economic pain of new water restrictions would be to get in on the wind power boom in the state. Already, massive alabaster turbines jut skyward from the West Texas plains in a few areas.

But wind power could bring its own set of challenges, Mulligan said.

"I start wondering what the landscape will look like with 10,000 turbines," which is what studies say the area could support if new power lines are put in, he said. "I don't think the people of Lubbock realize what's coming."

Reese writes from Santa Fe, N.M.