Last summer, U.S. Department of Agriculture officials floated a nationwide standard to limit the amount of phosphorus farmers could apply to fields. But by December, they had pulled it back in the face of stiff opposition from a group of agriculture scientists.

Their decision disappointed many of the scientists and advocates working on Chesapeake Bay restoration. The short-lived proposal and the hot debate it generated also illuminates the complexity of establishing an agriculture pollution-control policy to protect the nation's waters.

The proposal to have a single, national guideline for phosphorus application was part of an overhaul of the USDA's National Resource Conservation Service's nutrient management guidelines. The overhaul aimed to find a long-term, sustainable approach to guide the application of manure and synthetic fertilizer for both maximum crop growth and water protection.

It would have phased in an upper limit for the amount of phosphorus in soil. Once a soil test showed the phosphorus had reached that amount, farmers would have been discouraged from applying more. The proposed upper limit was 200 parts per million, a number believed to represent a point at or beyond which phosphorus begins to leave the field by dissolving in rain runoff or leaching into groundwater.

NRCS chief Dave White said the proposed national standard was a draft, going through its normal paces and not ready for the public comment process when some of the agency's technical people "got ahead of themselves" putting the word out and met the strong opposition of an influential group of soil scientists and the livestock industry.

The opponents argued that one limit did not fit all fields, and that an approach that considered both the likelihood that phosphorus would leave the land and the amount of phosphorus in the soil was better for guiding manure and fertilizer applications.

Most states use this multifactored approach, which is called a phosphorus index. Although the indexes and their phosphorus thresholds vary from state to state, all take into account factors such as how close a field is to water, how fast water drains from the field, how much phosphorus is in the soil, how sloped is the terrain, and how and when fertilizer and manure is applied.

The indexes include a soil test, but they also give farmers credit for conservation practices such as grass buffers and using no-till. So, if a particular field tests high for phosphorus but conservation practices are in place, and it's not close to waterways, a farmer may decide to go ahead and put more phosphorus on that field. The index, in other words, allows farmers to make decisions on what's best for them economically while taking water quality into consideration.

The new standard wouldn't have been mandatory, but it would have been significant. It would have set the same upper limit of phosphorus in soil for all states. Farmers would have incorporated the limits into their nutrient management plans, which they are supposed to use to guide their fertilizer applications and curb pollution.

A nationwide standard would also level the playing field for livestock producers. Concentrated animal agriculture, such as dairies, poultry and hog farms, generates massive amounts of manure. Typically, the manure is spread on fields as fertilizer. While the crops are thirsty for the nitrogen in the manure, they rarely need all of the phosphorus, so it builds up in soil. That's especially true when poultry or hog manure is used, as it has disproportionately high phosphorus concentrations relative to crop needs.

Livestock producers in states without strict phosphorus limits on fields have an advantage over those in states that do, because it's easier for them to dispose of their manure. A national limit would take away that advantage.

Many scientists and regulators interviewed for this article said a national standard would reduce the amount of phosphorus entering waterways. Several have pointed to Ohio, where a strict standard has been in place for more than a decade, as an example of an approach that works.

Russ Brinsfield, the director of the University of Maryland's Center for Agro-Ecology, said he thought the national standard would have gone a long way toward reducing phosphorus on fields. He's hoping that more dialogue with the NRCS will at least lead to a Baywide standard.

"When it got pulled, I was very discouraged," Brinsfield said of the standard. "It's still unclear to me as to why they decided to pull back."

The agency is now looking to the scientists who opposed the nationwide standard, members of a research consortium known as SERA-17, to refine the index approach to help reduce phosphorus. The group takes its name from the Southern Extension Research Activity, part of the USDA, and it was the 17th such group to form under the regional branch of the extension service.

Andrew Sharpley, the University of Arkansas soil scientist who is leading the effort, says he expects that work will take about a year.

The standard "just went too far," says Douglas Beegle, an agronomy professor at Penn State University, and a member of the group.

"It would have been a very bad situation for the farmers," adds Josh McGrath, a soil fertility and nutrient management specialist at the University of Maryland. "Is it right to tell people they can't apply phosphorus, if they have this manure they have to dispose of?"

Peter Kleinman, a soil scientist with the USDA's Agriculture Research Service, argued that because of its limitations, the standard likely wouldn't help the Bay. A soil test tells only part of the story — the nutrients in a certain place at a certain time. An index approach takes into account not only the amount of phosphorus as determined by the soil test, but also how likely its nutrients will get into waterways. The index prioritizes areas that need the most protection because they have the greatest affect on water quality.

"There are soils that are low in phosphorus (but likely to allow the phosphorus to reach a waterway), and if you went blindly with a soil-based approach, you would apply manure to these types of soils, so you would end up with more of a problem," Kleinman says. "It really, really will harm things in the Chesapeake Bay."

And yet, even those who tout the index approach acknowledge its use in the Bay region for the past two decades has not gotten the Bay watershed to its water-quality goals. The SERA-17 scientists say that is because, while the science behind the index is sound, it's not scientists who set the limits — it's policy-makers. If the index included tighter limits, they argue, it would bring greater reductions.

"There is quite a bit of argument on how detailed it should be," says Beegle, who said the index is too lenient in some places. "It's still more of a political or social decision on how much risk (of water pollution) we're willing to accept."

But environmentalists, regulators and some water-quality scientists say the index simply isn't working. There are too many variables to consider, and the indexes too often allow more manure to be placed on fields that in some cases are so loaded in phosphorus that they don't need any more for 40 or 50 years.

A national standard, they say, would have been simple, easy to enforce and fair across the country. Plus, they said, the goal of environmental protection should be to safeguard water quality, not necessarily to help farmers solve their manure problems.

"If you want your phosphorus to stop going up, you've got to stop putting it on," says John L. McCoy, who directs the ecosystem restoration center at the Maryland Department of Natural Resources and who spent nearly a decade studying the effect of manure on water quality in the Pocomoke River. "One might question how we're going to accomplish reducing the phosphorus to the Bay from nonpoint (runoff) sources if the land mass continues to increase in soil phosphorus levels."

The debate over how to tackle phosphorus in the watershed is almost as old as the Bay cleanup effort itself. In the 1980s, shortly after the first Bay agreement was signed, several states enacted phosphate bans on laundry detergent that significantly reduced the amount entering waters.

In those days, phosphorus on agricultural land often wasn't perceived as a big problem: It was thought to bind to the soil, and therefore not run off. If farmers could control erosion through best management practices, such as grass buffers and terraces to trap sediment, the conventional wisdom went that they could control phosphorus. Nitrogen, the Bay's other main pollutant, was thought to be more of a problem and therefore got more attention.

By the early 1990s, research showed that phosphorus did run off, particularly after storms. The problem was particularly associated with manure, which was often overapplied simply as a means of disposal.

During the same two decades, concentrated animal feeding operations, particularly the poultry industry, grew rapidly in the Chesapeake watershed, generating still more manure. Meanwhile, the amount of cropland decreased as suburbs grew and agriculture practices changed, meaning there was even less land on which to safely apply manure. The imbalance between animal numbers and available land is most acute on the Delmarva Peninsula, the Shenandoah Valley and Lancaster County, Pa.

So, nearly 20 years ago, NRCS began talking about three options to control the phosphorus problem. One would be a national standard; a second would be an approach that required farmers to use only as much manure as their crops need, and dispose of the rest by transporting it to other farmers who needed it; and a third would be a phosphorus index.

Most states settled on an index, although scientists outside SERA-17 questioned the approach even then.

"You're sort of minimizing the impact of doing something that is taking you in the wrong direction," said the Center for Agro-Ecology's Ken Staver, who published several papers in the 1990s about the need for better phosphorus management.

Those who wonder how a regionwide or statewide phosphorus standard might work need only to look west a few hundred miles to Ohio.

The Buckeye State has had a phosphorus standard in place since 1987, according to Kevin Elder, the executive director of the Ohio Department of Agriculture's livestock permitting program. Since that time, the standard has been tweaked and some laws have been changed, and now Ohio has one of the strictest phosphorus limits in the nation.

Under Ohio's law, all concentrated animal feeding operations require a permit. And all permits require a soil test. If a soil test shows phosphorus levels higher than 100 parts per million, the farmer can only apply a limited amount of manure annually, and not on steep slopes. If the test shows more than 150 parts per million, the farmer can't apply any at all. The rule requires one sample for 25 acres.

Elder says the department vigorously enforces those laws; every CAFO must file a nutrient management plan and follow it.

"It's very difficult and time-consuming to be real tight on the enforcement, but we need to make sure everyone understands that they should not be overapplying nutrients," Elder says.

All new and expanding facilities use the 150 ppm threshold. Ohio does have a phosphorus index, and it uses that tool to help older farms that have legacy phosphorus issues balance their nutrient levels. If a farm has too much phosphorus, Elder says the department works with its managers to ship the excess manure to a farm where it is needed.

The state has a certified livestock manager training program to help farmers manage and transfer their manure. So far, Elder says, 600 people have been trained.

Ohio has come a long way since the 1980s, when, as Elder says, the EPA was primarily worried about nitrogen and didn't keep a staff of agronomists to warn about the dangers of too much phosphorus.

To address phosphorus problems in Lake Erie, the U.S. and Canadian governments set an annual target load of 11,000 metric tons for the lake in 1981. It has been met in nearly every year since, according to the EPA. That's particularly significant in the Maumee River, the lake's largest tributary, where the majority of the phosphorus comes from agriculture. Phosphorus levels in the Maumee peaked in 1991, and dropped to their second lowest levels in 30 years in 2001.

Elder is not sure the same approach would have such an affect in the Chesapeake region. Eastern Shore soils are far sandier, and the Shore has more animal manure in a much smaller area. Maryland would likely have to ship its manure out of state. And, Elder says, many places would be glad to have it. Commercial fertilizer requires intense energy to produce and is expensive, whereas the only cost for manure is transportation.