The third chapter in a story about turfgrass nitrate leaching

Nitrate concentrations of groundwater are increasing in residential areas. One probable cause is input of nitrogen fertilizers to maintain healthy turfgrass. This study was conducted to evaluate differences in nitrate concentrations in soil water between sites fertilized with chemical or organic fertilizer. To obtain nitrate concentrations leaching below turfgrass and evaluate the impact to groundwater in Suffolk County, NY we installed suction lysimeters at one meter and collected monthly samples of soil water from January 2003 to January 2006 beneath two sites treated with chemical fertilizer, five sites treated with organic fertilizer, one site not treated with fertilizer and one forest site (2005 only). We also installed lysimeters at variable depths at four of these sites and collected monthly samples. Yearly average concentrations under fertilizer turfgrass reach values much higher than those under forest cover (0.08 ppm) and higher, on average, than unfertilized turfgrass (0.90 ppm) but remain below the drinking water standard of 10 ppm nitrogen as nitrate. The use of organic fertilizer alone does not guarantee lower nitrate concentrations in the pore water. Some of the highest concentrations were found beneath sites fertilized by organic fertilizers, however, the likelihood of concentrations of soil water to exceed this standard are 20% for sites treated with organic fertilizer and 32% for sites treated with chemical fertilizer. It is unlikely that turfgrass fertilization alone would raise groundwater concentrations above the drinking water standard. There is evidence from the variable depth profiles that nitrate concentrations are not conservative with depth but decrease with depth. A better understanding of this process will aid in evaluating turfgrass fertilization impact on groundwater quality. Introduction Concentrations above the current Environmental Protection Agency drinking water standard of 10 ppm nitrogen as nitrate (NO3-N) is know to cause blue baby syndrome in infants. It is important to prevent drinking water from reaching these levels not only for health concerns but due to high remediation cost. All potable water on Long Island, NY is derived from groundwater heightening the need to minimize contamination. Nitrate is being detected more often and at higher concentrations in Suffolk County groundwater within the past decade. Other researches have noted that fertilizer is a major source of nitrate in Long Island (Flipse and Bonner, 1985; Flipse et al., 1984; Kreitler et al., 1978; Porter, 1980). A major land use in Suffolk County, 25% as mapped in the late 1970’s, is turfgrass. Nitrogen is an important nutrient needed for healthy, green turfgrass. The soils on Long Island have low pH and lack nutrients needed to support turfgrass and so the need for fertilizer application. Lime is also added to maintain a proper pH and provide Ca and Mg. Irrigation is required during the summer since the rainfall on Long Island is not enough to maintain most turfgrass species. We measured NO3-N concentrations of soil water collected monthly from January 2003 to January 2006 at one meter beneath turfgrass and forest sites in addition to samplers from depth profiles beneath four turfgrass sites. We present these data in the framework of our evolving hypotheses and assumptions as they changed over the course of our three year study. Overview 2003 and 2004 Initial Questions How does turfgrass maintenance influence nitrate concentrations in groundwater? What is the difference between nitrate concentrations in soil water collected at one meter between organically fertilized, chemical fertilized and not fertilized turfgrass sites? Assumptions Nitrate concentrations at one meter are below the depth of turfgrass influence. Nitrate concentrations are conservative, i.e. remain unchanged, from one meter to the groundwater table. Organic fertilizer should have a reduced affect compared with chemical fertilizers. Methods (Munster, 2003) Installed soil water samplers, suction lysimeters, at one meter below turfgrass at (1) two sites treated with chemical fertilizer (2) five sites maintained by an organic landscaper and (3) one site not fertilized. Installed multiple suction lysimeters at different depths for two sites treated with chemical fertilizer and two sties treated with organic fertilizer. Sampled monthly for soil water. Measured nitrate concentrations at the Marine Science Research Center, Stony Brook University using the nutrient analyzer, a colorimetric method. Major findings Fertilizer practices between sites are not easily compared due to differences in site characteristics. The use of organic fertilizer alone does not guarantee lower nitrate concentrations. Nitrate is not conservative from 60 cm to 150 cm depth. Of the four sites, one has increasing nitrate concentration from 100 cm to depth, two have decreasing nitrate concentrations from 100 cm to depth and for one site remains unchanged. 2005 New Questions What controls nitrate concentrations at one meter? What controls changes in nitrate concentrations with depth in the unsaturated zone? How can we distinguish which fertilizer practice minimized nitrate concentrations in the groundwater? New Assumption Decreases in nitrate concentrations with depth are likely from denitrification. New Methods At three sites we split treatment so that half the site was fertilized with chemical fertilizer and the other half with organic fertilizer and installed new lysimeters at one meter in the new treatment areas. In this way the affects of site properties should be minimized. Installed rain gauges at each site. Installed one lysimeter beneath the forest floor at one meter. Major findings Patterns in nitrate leaching varied between years. Average nitrate concentrations under fertilized turfgrass reach values much higher than the forest and slightly higher than the non fertilized turfgrass site. Most average values are below the drinking water standard. Results from split sites suggest that soil properties play a vital role in controlling nitrate concentrations of soil water. Results and Discussion