The first rule of the Phosphorus Symposium: There will be no discussion of the PMT.

The PMT. That stands for phosphorus management tool, the science-based calculation and proposed regulation that was developed to guide the application of phosphorus on farm fields. The tool would have banned the application of phosphorus to soils already saturated with the nutrient. It would be a major departure from the current tool, the phosphorus index, which recommends no application of phosphorus in certain situations, but doesn’t forbid it.

The tool, and its tougher requirements, would have meant that about half of the farms on the Eastern Shore would not be able to spread poultry manure on their fields. Poultry manure is high in phosphorus. On the Shore, it is also overabundant and inexpensive. The proposed PMT was extremely unpopular there. On his inauguration day, Gov. Larry Hogan pulled the regulation just before it was published. Farmers were ecstatic, environmentalists were livid and government officials were perplexed about how the state would meet its targeted phosphorus reductions required by the Chesapeake Bay Total Maximum Daily Load.

For the first annual Phosphorus Symposium, which was organized to give farmers and regulators a better understanding of the current phosphorus science, it created a strange situation. The world’s experts on phosphorus in soil were all in a room on the Eastern Shore, and the very issue they had come to explain was off the table.

The organizers of the conference, which included the Maryland Grain Producers Utilization Board, the Chesapeake Bay Foundation and the University of Maryland Extension, made it clear several times that the symposium was not about the tool, the policy surrounding it or its future. It was about the science of phosphorus, how it moves, where we need it, and where we don’t. Even with the ample advance warnings over e-mail in the days before the conference, 358 people attended — and several were on a wait list.

Despite the warnings not to discuss the regulations, the subject cropped up in various ways — notably when the scientists talked about efforts elsewhere to limit or stop entirely the spreading of manure on farmland.

Andrew Sharpley, a prominent soil scientist at the University of Arkansas, told of litigation in the Illinois River watershed, where he works, that forced a large chicken-producing area to stop spreading manure. The state of Oklahoma sued Arkansas over water pollution that stemmed from the growth of two billion chickens a year in Arkansas. Because of that litigation, 33 percent of the Arkansas poultry litter’s manure had to be exported. Today, that number is up to 45 percent.

“We did adapt,” Sharpley said. “It did work. It does work. It can work.”

As a result of those reductions, the concentration of phosphorus in the waterways dropped. But, Sharpley added, scientists spent a lot of time with farmers, explaining the water pollution problems associated with too much phosphorus, and worked closely with farmers to find ways to export the manure.

Walter Boynton, who has studied eutrophication in the Chesapeake Bay for nearly 40 years, explained that once phosphorus-saturated sediments enter waterways, the excess phosphorus degrades the benthic organisms. Algae blooms begin an “amazing feedback loop,” Boynton explained, where the algae block light, take up oxygen, sink to the bottom, and then complete the cycle again. With low-dissolved oxygen, filter feeders don’t have a chance — not just oysters, but clams, worms and small shrimp.

“The phosphorus just pours out of sediments when there’s low-dissolved oxygen,” Boynton said. “The evidence is so compelling. If you don’t get the dissolved oxygen under control, you have a vicious cycle.”

In some cases, the solutions that scientists have long touted don’t solve the problem.

Peter Kleinman, a soil scientist with the U.S. Department of Agriculture’s Agricultural Research Survey, cautioned that no-till farming, where the farmer doesn’t turn over the earth, resulted in a 95 percent reduction in erosion. But no-till farms can actually be higher in dissolved phosphorus. Cover crops, too, can be a source of “green manure,” because dissolved phosphorus may travel in subsurface pathways under the farm. And drainage is a vector for phosphorus to move off the land.

The Shore has a high water table and poor drainage in many locations. More extreme weather events are likely to make the problem worse.

On the Shore, even as the phosphorus management tool is being debated and no solution is at hand for the excess manure, construction workers are building ever-larger chicken farms near rivers that are among the most polluted in the watershed.

Many in the audience came to hear Josh McGrath, who was the architect of the phosphorus management tool. McGrath worked at the University of Maryland for several years but left for Kentucky last year as the controversy heated up. He said he was just following a great job offer, but noted that in Kentucky, the soils aren’t saturated with phosphorus.

McGrath was characteristically frank when his time came to talk. Best management practices to mitigate pollution, he argued, aren’t a solution — the better tactic is to tackle the systemic problems that encourage farmers to put the manure there in the first place.

“We do know a lot. And we do need to stop kicking the can down the road,” he said. “What are we going to do in the next four years for water quality? Whatever we do is going to cost us money, cost us time, and cost us our sanity, maybe. But these are not things that make you money. They do not help you produce more corn.”