There's a new Connecticut law that's confounding to anyone with a lawn or anyone who works with them-that is, if they're bothering to follow it.

Public Act No 12-155, passed last May, seeks to reduce the overuse of phosphorus - that's the "P" in the N-P-K listing required on bags of fertilizer - on residential lawns. The law, which took effect on January 1, is well-intended, probably not enforceable and some fear it could do more harm than good.

I promise you won't need a chemistry class to read this column and I understand if your eyes glaze over. My husband's regularly do when we have our annual lawn argument. I, Ms. Green, want to save the environment, he, Mr. Mower, just wants a good-looking lawn that will pass the muster of our male neighbors.

"Many people don't realize that phosphorus pollution is the principle cause of declining water quality in Connecticut's lakes and ponds," Dawn Pettinelli, manager of the University of Connecticut's Soil Nutrition Analysis Laboratory, explained on my CT Outdoors radio show last week. "It's what causes the green algae bloom in fresh water, which leads to oxygen depletion, fish kills and weedy lakes."

While nitrogen, the "N" of the 3-letter equation, degrades the water quality in Long Island Sound and can cause nitrate buildup in groundwater, phosphorus is the inland culprit. Too much of either element can have human health effects.

There's very little phosphorus in our natural soils, she says, which is one reason our lakes are naturally so clear. But it doesn't take much of it to upset the balance, and most established lawns don't need an extra shot of it every year.

The P law requires a recent soil test (within the past two years) to show that phosphorus needs to be applied to an established lawn. It doesn't apply to new or reseeded lawns, because the element is used to encourage root growth. Agricultural lands and golf courses are exempt.

"The bottom line is you should know what your phosphorus levels are, have your soil tested," Pettinelli says. "If your phosphorus is below optimum, you can use a regular lawn maintenance fertilizer with phosphorus and apply it as directed."

For $8 per sample, UConn's lab test includes a standard nutrient analysis (NPK, trace elements and lead), soil pH, a quick hand texture test that gives a ballpark estimate or organic matter and recommends how much fertilizers and lime (to change soil pH) are needed, if any.

The organic lawn and land care community is up in arms over how the law puts organic fertilizers and compost in the same bag as synthetic compounds, which means these could trigger the P threshold. While synthetic fertilizer manufacturers can adjust their mixes of chemicals to leave out the P, it can't be stripped from organic materials. They fear this could dissuade the use of these natural products, which usually contain less nitrogen and improve the health of the soil as they decompose.

Since the law doesn't address nitrogen, which greens up the lawn, they say it tempts lawn crews to jack up the nitrogen and perform multiple applications throughout the year to keep crews and equipment productive. That leads to continual runoff of nutrients, especially after heavy rains. A similar law in New Jersey treats organic fertilizers differently and caps nitrogen levels.

Of course, enforcement of this new law is questionable: although there are provisions for a $500 per incident fine, do we really expect the state budget to support "P-patrols" any time soon?

For readers who enjoy chemistry and discussion of this topic, or want to order a soil test, see www.soiltest.uconn.edu.

And speaking of UConn, don't miss the university's annual Home Gardener Conference, Friday, March 22, from 8 a.m. to 4:30 p.m. on the Storrs campus Hear Connecticut and national gardening experts talk about invasive and new pests in Connecticut gardens; shade gardens and entry gardens; and how to design attractive vegetable gardens. Featured speaker Jeff Gillman, horticultural professor at the University of Minnesota, will present "The Truth about Garden Remedies." Walk-in registration is $90 and includes lunch. See www.2013garden.uconn.edu for details.

To hear more of Suzanne's discussion with Dawn Pettinelli, see her March 12 "CT Outdoors" show in the On Demand archives at www.wliswmrd.net.