Cape Cod Lawn Fertilizer Compromise

My neighbor Phil smiles when Thurman, his miniature dachshund, rolls on the dense green turf surrounding his Cape Cod home. His next-door neighbor Kate shuns Phil’s lawn. She claims that Phil’s lawn fertilizer pollutes the artisan well that provides drinking water to her family. Phil’s lawn care program and Kate’s fertilizer aversion summarize a prominent Cape Cod environmental issue.

Residential lawns like Phil’s require food, air, water and sunshine. Green plants manufacture food through photosynthesis, the conversion of carbon dioxide, water and light into carbohydrates and oxygen. Green plants also convert soil based nutrients into food through cation exchange. In this chemical process, positively charged cations or negatively charged anions uptake plant food through absorption

Soil borne nutrients include seventeen macro and micro-elements. Macro-elements include nitrogen, phosphorus, potassium, calcium, magnesium and sulfur. Micro-elements include iron, zinc and others used in small amounts. Like a magnet held over iron filings, negatively charged organic humus and clay compounds attract positively charged elements to plant root systems.

Nitrogen is the primary green plant element. Plants consume nitrogen in large amounts. They acquire nitrogen from rainfall, organic decomposition or fertilizer applications. Rainfall and organic decomposition from clippings or fallen leaves cannot sustain the deep green color desired by homeowners like Phil, so they apply fertilizer.

Plants consume nitrogen in the nitrate form. They cannot use the stable nitrogen form found in the air we breathe. They convert ammonium from fertilizer into nitrites then into nitrates. Some chemical fertilizers bypass this process by adding readily usable nitrate compounds.

Plants ingest nitrate and other element forms through roots. They cannot access every nitrate molecule in the soil and this creates a problem. Nitrate has a negative charge, just like the clay particles found in soils, and we know what happens when two negatively charged magnets touch; they repel each other. This makes nitrate very mobile and prone to leaching through permeable sand into groundwater.

Fertilizer compounds

Many Cape Cod residents apply granular lawn fertilizer sold in many home and garden stores. A majority know little about chemical fertilizer compounds. More importantly, they don’t understand how different fertilizer types impact groundwater purity. They often make their purchasing decision on marketing rhetoric that includes background images of manicured golf course turf.

Plant fertilizer comes in two types. Water soluble nitrogen (WSN) fertilizers dissolve quickly and release nutrition speedily to the plant. Water insoluble nitrogen (WIN) fertilizers deliver nitrogen slowly, sometimes over months or years.  When Phil and Thurman returned from a trip to the hardware store I noticed three bags of  WSN fertilizer in his trunk.

Chemical lawn fertilizers usually contain the macro-elements nitrogen, phosphorus and potassium. Fertilizer manufacturers clearly identify element percentages on the bag. For example, the fertilizer rate 22-10-15 has 22% nitrogen, 10% phosphorus, and 15% potassium. The remaining percentage consists of inert carrier compounds needed to keep the components stable and in granular form. Premium fertilizers also contain micro-elements.

In the early fall, I watched Phil spread fertilizer on his lawn with a clunky wheeled spreader that requires calibration to apply desired fertilizer rates. Spreader calibration requires advanced mathematical skills.  One must calculate the lawn area, dispersal efficiency of the spreader, and active element percentage. If improperly calibrated, over fertilization will occur.

Spreader manufacturers simplify calibration with a dial that disburses fertilizer based on a selected letter. Phil selected the letter J to spread the recommended cool-season grass fertilization rate of one pound of nitrogen per 1000 square feet of turf area.

After Phil poured fertilizer granules into his barrel-shaped hopper, a spinning device on the bottom whirled the fertilizer onto the lawn as he walked. This process can also create excessive fertilization. For example, when he stopped to wave Thurman from his intended fertilizer route, the spreader leaked fertilizer.

A week after his latest fertilizer application, Phil savored his green lawn. His WSN fertilizer dissolved quickly after a rainy day, and the readily available food source created well-fed grass plants. Thurman played on the turf with my dog Ruby while next door, Kate gazed toward Phil and muttered: “Nice guy but he’s endangering my grandchildren.”

 

Nitrate Groundwater Pollution and Soil Structure

To better understand the issues behind our neighborhood fertilizer spat, Phil and I got down on our knees the next day and examined his lawn with a magnifying glass. Like a steel furnace loaded with hot coke, Phil’s fertilizer applications had accelerated photosynthesis allowing millions of individual bluegrass, ryegrass and fescue grass plants to produce the deep greenness of well-fed turf.

I used a pointed shovel to extract a small sod clump then I isolated a single bluegrass plant. The dark green leaves could be used in a lawn care commercial. We next removed a three foot circle of sod. Like a cold-cut sandwich, a lawn has layers. I dug down two feet and after shooing an inquisitive Thurman from the excavation we examined Phil’s soil profile.

Phil’s lawn has six inches of black topsoil on top, then six inches of an orange clay/sand mix followed by yellowish sand. Pictures taken when he installed a new septic system confirmed that the sand continued for another ten feet.

I filled a two-liter plastic bottle with sand from the excavation then I punched holes in the bottom. Next, I poured water into the bottle and in a few seconds all the water drained through the sand onto the ground. It was like pouring water through a cheese grate.

I told Phil that Kate was correct; his sandy soil profile and fertilizer type promotes nitrate leaching into groundwater. I explained that scientists claim that elevated nitrate levels in groundwater adversely impact human health. Phil agreed to my offer to change his lawn care program.

 

Nitrate leaching on Cape Cod

The long sandy sweep of Cape Cod has one interconnected underground water source, or aquifer, that provides drinking water to residents. Cape Cod doesn’t have expansive above ground drinking water storage like Boston’s Quabbin Reservoir so residents consider groundwater purity an important issue.

Nitrate leaching became a serious public health issue after a 1945 study by H.H.Conly identified a correlation between increased nitrate levels in groundwater and methemoglobinemia, an infant blood disorder also known as “blue baby syndrome.” Conly’s research fueled public concern about groundwater nitrate pollution by farmers who liberally applied fertilizer to their crops.

Driven by growing environmental awareness created by the 1970 Earth Day protests, groundwater pollution became a national concern. In response, Congress created the Environmental Protection Agency (EPA) and assigned it powerful regulatory responsibilities. Immediately, the EPA intensively reviewed groundwater contamination.

According to the website epa.gov, after identifying the uniqueness of the Cape Cod aquifer and the predominantly sandy Cape Cod soil profile, the EPA designated the Cape Cod groundwater supply a Sole Source Aquifer in 1974.  The same year, the EPA identified safe water consumption standards by releasing the National Primary Drinking Water Regulations.  In 1976, the EPA released a list of primary groundwater pollutants that categorized nitrates with powerful carcinogens like cadmium and radium.

Nitrate is also a naturally occurring groundwater compound. The EPA couldn’t assign a “zero tolerance” level, so they set a maximum groundwater containment level (MCL) of 10 parts of nitrate-nitrogen (NO₃-N) per million parts of drinking water. They approved this number after a comprehensive health study concluded that it was acceptable..

Cape Codders Take Action

After the EPA classified nitrate a primary groundwater pollutant, regional governments funded studies that further examined groundwater pollution. In 1978, the Long Island Comprehensive Waste Management Plan tracked groundwater pollution from waste water, domestic animals, and fertilizer applications. In 1979, the Cape Cod Planning and Economic Development Commission released the results of a similar study.

In 1990, the Massachusetts Legislature, driven by resident desires to preserve the fragile Cape Cod ecosystem, created the Cape Cod Commission (CCC), a regional regulatory authority. Armed with expansive environmental enforcement powers, the CCC made nitrate groundwater pollution a major concern. They targeted golf courses and cranberry bogs as probable nitrate polluters because of their substantial fertilizer use.

The CCC required that several new Cape Cod golf courses install monitoring wells on their property. The Cohen et al study confirmed that typical golf course fertilizer applications rates produce MCL readings below the EPA standards. This study also confirmed that fertilizer generated nitrates are very mobile in sandy Cape Cod soils.

Knowing that groundwater well monitoring would continue, the Cape Cod golf course industry reviewed application rates and available fertilizer products to identify ways to reduce nitrate loading. Golf course managers learned that WSN fertilizers contributed to the problem by releasing nitrogen at a rate higher than the plants could use. They began to use safer alternatives such as:

• Urea formaldehyde (UF)
• Isobutylidine diurea (IBDU)
• Sulfur coated urea (SCU)
• Organic sources such as compost, seaweed, or activated sewage sludge.

A University of Rhode Island lawn care fact sheet explains that slow release fertilizers UF, IBDU, and SCU contain harder granule surfaces or integrated formulations that release nitrogen slowly. Organic sources provide naturally occurring nitrogen forms that take months or years to convert into available nitrate.

Community groundwater regulations

On Cape Cod, several local organizations provide environmental guidelines to conservation commissions and local residents. Phil’s lawn is within the Buzzards Bay National Estuary Program scope, and they recommend a yearly nitrate leaching rate of 1.08 lbs of nitrogen per 5000 square feet lawn, or .36 lbs per 1000. This leaching rate is the amount of nitrate that travels through the soil profile into groundwater.

A few calculations confirmed that Phil had to purchase another fertilizer to comply with the guidelines. A recent Grounds Maintenance magazine article explained that WSN fertilizer has a leaching rate of 25%, and IBDU has a reduced leaching rate of 8%. Leaching rate is the percentage of active ingredient that leaches into groundwater. Phil spends freely on lawn care and his dog so he readily accepted my advice to convert to an IBDU fertilizer.

He now applies four yearly applications of 25-6-12 IBDU at the rate of 1 pound per 1000 square feet. In one year, he will apply a total of four pounds of fertilizer with 25%, or one pound, as active nitrogen. IBDU fertilizer will leach 8% of this nitrogen into the groundwater, creating a theoretical nitrate loading rate of .08 lbs per year, well under the BBNEP guidelines.

Last summer, Kate and Phil chatted amiably on Phil’s lawn during our neighborhood block party.  In the early spring, I discussed the information contained in this article with them. That summer, Phil used IBDU at the recommended rate, Kate served bottled water to her newborn granddaughter, and many afternoons Thurman snoozed on Phil’s dense green grass.

 

 

 

 

 

 

 

 

Sources

 

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Comly, H. H. (1987). Cyanosis in Infants Caused by Nitrates in Well Water. JAMA: The Journal of the American Medical Association, 257(20), 2788-2792. doi:10.1001/jama.1987.03390200128027

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