Nitrogen rate, irrigation and rainfall impacts on groundwater nitrate levels in sandy coastal golf courses

There have been concerns over fertilizer nitrogen (N) applied to turfgrass areas affecting groundwater quality in sandy coastal areas since the 1970s . Extensive amount of small-scale research studies has determined the major factors that contribute to excessive nitrate-N leaching from turfgrass ecosystems. There are limited data on large-scale groundwater monitoring of turfgrass sites, such as golf courses, which are related to management inputs. There are land-use regulations limiting the amount of fertilized turfgrass in coastal area in the United States which assume a linear relationship between the amounts of N applied and leached. The purpose of this study is to evaluate the long-term impact of yearly variations in N application rate, irrigation amounts, and seasonal precipitation on groundwater quality on golf courses in critical groundwater recharge areas. Two golf courses, The Bridge and Sebonack Golf Club, in this study are in eastern Long Island, NY with systematic groundwater monitoring for NO₃–N. Each golf course follows best management practices (BMP) including limitations on amount, rate, source and timing of N applications as well as controlled irrigation based on on-site evapotranspiration measurements. The results of this study clearly show that on golf courses in sandy critical groundwater recharge areas that follow BMP, the amount of N applied is not related to NO₃–N levels in groundwater. Rainfall amounts more closely followed NO₃–N levels in groundwater, thus abnormally high rainfall can result in higher NO₃–N levels. Implementing fertilizer BMP can be very effective in protecting groundwater quality.