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