One thing is becoming clear about dealing with all the sources of nitrogen that find their way into the Bay: You have to think BIG.

Recent evidence has shown that large amounts of the nitrogen damaging the Chesapeake's water quality stem from air pollution that originates far outside the Bay's watershed.

And now, a Penn State researcher says that policy-makers who are adjusting their thoughts to dealing with a 350,000 square mile "airshed" -- which covers an area 5.5 times larger than the watershed -- may not be thinking big enough.

Rather, they should be thinking of a "corn shed" or "soybean shed," said Les Lanyon, an associate professor of soil fertility. Those "sheds" might encompass half the country -- including anyplace that ships grains for animal operations in the Chesapeake basin.

In a paper recently published in the Journal of Production Agriculture, Lanyon said that technological improvements, policy provisions and economic efficiencies in crop and animal production have led to lower food costs, but have also massively increased nutrient imports to many areas of the country that produce animals, including the Chesapeake watershed.

The imports are so great, Lanyon said, nitrogen no longer "cycles" in the classic sense. Historically, many crop nutrients were in scarce supply and it was necessary to cycle nutrients within a region. In agriculture, this was primarily done by feeding crops to animals on the farm, then returning the manure to the same crop fields.

The advent of chemical fertilizers, Lanyon said, has lead to a process by which crops are often grown in one region, then exported to another. For example, he said, much of the grain fed to animals in the Bay watershed is imported from many places outside the watershed, including the Midwest.

But it is not economical to ship the animal wastes back to Midwest fields-- it's cheaper to use more manufactured fertilizers.

Many of the incentives that exist in the Midwest to use commercial fertilizer instead of manure also exist here. Manure is more expensive to transport and more difficult to apply than chemical fertilizers, and the use of "smelly" animal wastes can draw public objections.

"Instead of a cycle, there is actually the potential for nutrient accumulation on the animal farm," Lanyon said. "So the nitrogen cycle actually looks like a nitrogen path, or a one-way nitrogen transfer."

When the amount of fertilizer available exceeds crop needs, problems such as groundwater contamination and the pollution of surface waters, such as the Bay, can result.

Nitrogen -- along with phosphorus -- is the target of a 40 percent nutrient reduction goal that the Bay states are trying to achieve by the turn of the century. When excessive amounts of nutrients enter the Bay, they stimulate algae blooms that cloud the water and block sunlight for the underwater grasses that provide important food and shelter for ducks, blue crabs and other species. When the algae dies, it sinks to the bottom and depletes the water of oxygen other species need to survive.

To limit runoff, farmers across the watershed are adopting practices to minimize potential runoff.

But fundamentally, Lanyon said, the incentives may not be in place to stem the one-way flow of nutrients coming into the watershed.

The issue has been attracting the attention of policy-makers. In Pennsylvania, part of a nutrient management law that recently went into effect established a special committee to find innovative ways to reduce the amount of manure produced and to get rid of it.

"We keep accumulating more; the idea is to get rid of some of this stuff. Ó said Vic Funk, of the state Department of Environmental Protection's Bureau of Land and Water Conservation. "You just can't assimilate it all into the system here at an endless pace. The soil has become saturated, so to speak, with more and more buildup of nutrients that's not utilized fast enough by plants. So down the road, we're looking at bigger problems unless we figure out a way to get more of it somewhere else, out of the area."

The committee will explore ways that excess manure may be marketed to other areas. It will also explore ways to reduce the nutrient content of manure by managing animal feed.

The root of the problem dates to the late 1800s and early 1900s. At that time, major world powers developed techniques to "fix" nitrogen from the atmosphere where it is the most common element, but is in a form not available to plants. Certain forms of nitrogen are critical to the manufacture of explosives -- as seen in the Oklahoma City bombing last year -- and countries needed to assure themselves that they had a nitrogen source that could not be cut off during wartimes.

After World War II, the U.S. government privatized its nitrogen-fixing plants, giving rise to the commercial production of nitrogen fertilizer. The increased availability of nitrogen fertilizer increased the corn yield. That, combined with the modern transportation system, changed the "scale" of agriculture, Lanyon said. Crop and animal agriculture no longer needed to be integrated; whole regions could become focused on a single type of agriculture.

"Technology, policy and economics are driving the production of corn and soybeans where they are best adapted," Lanyon said, "and then we have the transportation to move them away from those locations."

On a crop farm, the nitrogen applied goes mainly to produce a crop which is harvested and removed, Lanyon said. But on a farm specializing in animal production, only about 25 percent of the incoming nutrients are ultimately "exported" in the form of a product, such as milk. About 75 percent stays behind in the waste, in the form of manure.

"Biologically, when you import fertilizer for crops, you get more of the nutrients leaving a farm as cash crops than when you import feed for animals," Lanyon said. "Transfer of nutrients from fertilizer to crops is more efficient than transfer of nutrients from feeds into animals and their products."

The environment is generally not considered in this process. It can become a "loser" when parts of a region are saturated with excess nutrients, Lanyon said, while consumers are "winners" because they benefit from products produced with the lowest, short-term costs.

If the system is changed to be more environmentally sensitive, there will be -- at least in the short term Ñ different winners and losers, Lanyon said. Those could include farmers, feed suppliers, consumers or even crop growers.

Several years ago at Lake Okeechobee in Florida, a program was developed to buy out dairy cows from farms near the lake to control phosphorus, which was polluting the water. But as a result of fewer dairy cows in the area, three of the eight local feed mills, as well as a slaughterhouse, went out of business. Even the Lions Club sale of flags for the Fourth of July suffered.

"They predicted an overall loss of about 500 jobs that had grown dependent on the dairy industry on the shores of Lake Okeechobee," Lanyon said. "It can decrease the phosphorus loading to the lake, but that kind of drastic measure also has effects on businesses and communities."

The same principles of nutrient cycling would apply to humans. City dwellers eat a diet of food brought in from the country that would be discharged to the waterways if it were not for the sewage treatment plant where large amounts of nutrients can be removed by chemical or biological means.

"To finance a sewage treatment plant, you have easily recognized customers to share the costs," Lanyon said. "If you look at the nutrients accumulating on a farm where the animal products come from, how does the farmer spread the costs around?"

Lanyon said the "take home message" from his paper is that people should understand just how big the issue really is -- and how everyone, including consumers, have benefited. "It's not just the farmer who happens to be closest to the manure pile," he said.

Technology, policy and economics have created a process that provides low- cost food in terms of dollars, but breaks down the basic biological cycles of agriculture. Changing that, Lanyon said, means that somebody will pay more. The question is, who.