The Fate of Nitrogenous Fertilizer 
Applied to Differing Turfgrass Systems

A Research Report by Peter F. Schucman 

I.                   Introduction


The American suburban landscape with lush green lawns is part of our national culture and identity.  Over the past year, Americans have spent more on their lawns than they have at the movies, an astonishing 17.4 billion dollars (PLCAA, 2001).  The maintenance of the suburban lawn often requires the use of artificial or organic fertilizers.  These fertilizers contain ample amounts of nitrogen, which is an essential element for healthy turf growth, as well as other nutrients.  In addition, they can often be mixed with pesticides and herbicides.  Nitrogenous fertilizer applied to ornamental turf could pose a threat to groundwater quality (Petrovic, 1990).  The fate of fertilizer nitrogen is a concern in highly populated suburban regions that rely upon groundwater as their sole source of municipal water.  Management of fertilizer nitrogen must consider plant uptake, atmospheric loss, soil storage, and runoff in order to lessen the amount of nitrate that leaches into groundwater.

Maintaining high quality surface and groundwater supplies is a concern at the national and local level.  Groundwater accounts for 86% of the total water resources in the USA and provides 24 to 95% of the drinking water supply for urban and rural areas respectively (Petrovic, 1990; Scott, 1985).  On Long Island, NY, groundwater is the sole source of drinking water for the two counties of Nassau and Suffolk (Hughes and Porter, 1983).  The development of these counties with their growing populations has had an effect on groundwater quality over the past century.  During this time, much of the landscape has changed from rural agriculture to suburban development.  These development patterns are particularly noticeable in Nassau and Western Suffolk Counties where the largest single crop cultivated is ornamental turf.  (Porter, 1980)   Nitrate concentrations in the region’s groundwater have increased markedly during this period of development, and a significant amount of this increase is attributed to lawn and garden fertilizer as well as cesspool and septic-tank discharges. (Flipse et al., 1984)  Of the nitrogen species, nitrate poses the greatest threat to groundwater quality due to its mobility and health threat.  

The management of nitrogen is essential to protect the region’s drinking water supplies and the ecological balance of marine bays and harbors.  This study aims to monitor the fate of nitrogen applied to ornamental turf and measure for nitrate nitrogen leaching from the study sites.  The monitoring will implement tension ceramic cup lysimeters to collect and analyze soil waters.  The project has two study sites: one is located by the Earth and Space Sciences Building at State University of New York (SUNY) at Stony Brook, NY; the other is located at the Suffolk County Water Authority (SCWA) Administration Building in Oakdale, NY.  The two sites differ in the age and nature of their plots.  The SUNY site will be used to examine the fate of fertilizer applied to newly planted sod and the SCWA site will be used as a control site, with a turf system that has been established for many years.  Soil waters will be collected by the lysimeter system at various depths, to assess the leaching of nitrogen through the turf root zone and subsequently into the groundwater supplies.


II.                Background


Nitrate and the Nitrogen Cycle on Long Island


            Nitrogen is plentiful: in the atmosphere it is nearly 80 percent by total volume, on average 15 percent of living matter.  Some crops require 200 lbs/acre/year for survival (L.I. Planning Board, 1978).  It exists in multiple forms as part of a complex cycle.  Nitrogen found in soil and water originates from atmospheric deposition, application of fertilizer, manure, waste material, and dead plant and animal tissues (West, 2001).  Nitrate (NO3-) is one of the chemical forms of nitrogen.  Other forms of nitrogen commonly found in soil or water may be nitrite (NO2-), ammonium (NH4+) and organic nitrogen. 

            Exposure to nitrate in concentrations over 10 mg/l has been associated with a condition called methemoglobenemia or “blue-baby” syndrome in infants six months of age or younger (USEPA, 1990).  The nitrate fed to the baby, via baby formula or breast milk, is converted into nitrite in the baby’s stomach.  Nitrite changes the infant’s hemoglobin (the oxygen carrying part of blood) to methemoglobin, which is unable to bind with oxygen, thus depriving the cells of oxygen (West, 2001).  Although it is a serious medical condition, no cases of nitrate-induced methemoglobinemia have been reported between 1990 and 1995 according to an EPA publication (National Research Council, 1995).  West speculated that this might be because there is no requirement to report cases of methemoglobinemia.  Because of its multiple sources, it is difficult to show concise relationships between nitrate contamination and other health problems.  Recent studies have however implicated nitrate exposure as a possible risk factor associated with non-Hodgkin’s lymphoma, gastric cancer, hypertension, thyroid disorder and birth defects (Gilli et al., 1984, Rademacher, 1992).  The USEPA (1976) also linked the possible development of cancer from nitrosamines, resulting from the ingestion of water containing high concentrations of nitrate or nitrite (Safe Drinking Water Committee, 1977). 

Long Island has historically had problems with contamination of groundwater by nitrate.  The early history of the region was agricultural, helping to feed the growing metropolis.  Over the last century, development has led to the altering of land use from agrarian to suburban.  This combination of past agriculture and 20th century suburban waste began to have a noticeable effect on the Island’s groundwater. In 1949, the detection of nitrate contamination in shallow public supply wells in the Levittown area produced an awareness that eventually led to the abandonment of the Upper Glacial aquifer in the County (Nassau Dept. of Health, 1971; LI Regional Planning Board, 1978).  Nitrate levels increased and eventually led to sewering of household wastewater in most of Nassau County and some housing areas in Suffolk County.

Due to the concerns over nitrate contamination, numerous studies have been implemented to determine the sources to the region.  In a study during the eighties, Porter found that the two principal sources of nitrogen on Long Island are human waste and fertilized turf (Porter, 1980).  This report further stated that the sewering in regions of the county did not necessarily have the desired effect in reducing nitrate levels due to loading from other sources such as fertilized turf, domestic animals, precipitation, and past land use.  In a study using nitrogen and oxygen isotope ratios, Bleifuss found that nitrates in the Northport (NY) public supply wells originated from both residential households and past cultivation practices (Bleifuss, 1998).


Fate of Turf Nitrogen


Leaching of nitrogen from turf systems is of concern for environmental and economic reasons.  Examining turf systems poses interesting questions, for there are multiple variables that must be taken into account.  Leaching of fertilized nitrogen applied to turfgrass has been shown to be highly influenced by soil texture, source, rate and timing, irrigation/rainfall and the age of the turf system (Petrovic, 2000 and Porter, 1980). 

Leaching is most noticeable during periods when temperature is low and precipitation (minus potential evapotranspiration) is high.  These conditions reduce the loss of nitrogen from the turf system by limiting denitrification, ammonia volatilization, microbial immobilization and plant uptake.  In northern climates these conditions are found in October through April, which is also a time period when fertilizers are applied to turf.  During very dry months with minimal precipitation, leaching of nitrogen should be insignificant, and other avenues of nitrogen loss may dominate.  When the soil is dry, the ammonium, which absorbs readily onto negatively-charged soil surfaces, will be reduced to nitrate or nitrite.  If the area were then to undergo a deep watering, the potential for leaching the mobile nitrate would be significant.

The age of the lawn may also contribute to leaching.  Lawns greater than 10 years in age have been shown to accumulate nitrogen under turf until equilibrium is reached.  Subsequently, the possibility of over fertilizing and leaching of nitrogen would be much greater for such lawns (Porter, 1980).  Leaching may also be a threat to newly established sod turf systems, since fertilizers may be applied at a rate greater than the uptake by the vegetation in order to establish the turf. 

Studies on Long Island have indicated that lawn fertilizers are an important source of nitrate into the region’s aquifer system.  In 1984, Flipse, et al. published a report looking at the sources of nitrate in a sewered housing development in central Long Island; the Twelve Pines Study.  This study found that fertilizers contributed the largest load of nitrogen into the study area, with 25 kg of nitrogen leaching into the groundwater per acre per year.  Being a sewered area, the wastewater, and its nitrogen load, is removed from the area, leaving fertilizers as the major source.  Isotopic data supported the argument that the fertilization of residential lawns is the principal source of nitrate nitrogen in this study and in regions with similar wastewater management and hydrology.

The soils of Long Island generally limit losses of nitrogen other than losses due to plant uptake and leaching.  This is due to the physical properties of the soil and the relatively acidic precipitation.  Long Island soils are dominantly quartz sediment based with a relatively high permeability.  These soils are light and well aerated with a low pH, therefore the conditions do not favor gaseous loss of nitrogen by the volatilization of ammonia or through denitrification (Porter, 1980).  Petrovic (2000) found that up to 47% of the nitrogen, applied as urea, was lost to leaching.  The results are different for other regions, with data ranging from none to half of the applied nitrogen leaching from turf.  Overall, it has been assumed that nitrate leaching from turf is a major source for the aquifer system.  The Cornell Cooperative Extension Service has estimated that the total nitrogen load in fertilizer applied to all types of turf on Long Island is about 9,300 tons per year, of which 5,600 tons per year may leach to groundwater (L.I. Regional Planning Board, 1978).  These figures assume that 55 % of the applied nitrogen will leach from the turf systems.