Nitrate, Ammonium, and Urea Leaching in Hybrid Bermudagrass as Affected by Nitrogen Source

Nitrate leaching in turfgrass has been widely studied and found to increase when N was over-applied, soluble N sources were used, N was applied to sandy soils, or excessive irrigation was applied. The objective of this study was to evaluate N leaching as nitrate, ammonium, and urea from hybrid bermudagrass on three soils (Sumter clay [fine-silty, carbonatic, thermic Rendollic Eutrudept], Marvyn loamy sand [fine-loamy, kaolinitic, thermic Typic Kanhapludult], and sand) with three N sources (urea, polymer-coated urea, urea plus nitrification/urease inhibitor) and a control. Field lysimeters were fertilized at 7.3 g N m(-2) in July, and leachate collected for 10 to 12 wk each year for 2 yr. Leachate was analyzed for nitrate-N, ammonium-N, and urea-N. In the first year, significant nitrate-N was collected, regardless of N source. In that year nitrate-N in leachate from the clay soil frequently exceeded 10 mg N L-1, even in the unfertilized treatment. High organic matter in the clay soil and N mineralization following construction contributed to nitrate leaching. In the second year, nitrate-N in leachate never exceeded 10 mg N L-1, regardless of N source or soil type. Differences in total nitrate-N and ammonium-N leached due to N source were found in the loamy sand and sand soils, typically in the order: urea >= urea + inhibitor >= polymer-coated urea = unfertilized control. Small quantities of urea-N leached throughout the experiments. If applied at a recommended rate to established turfgrass, leaching of N did not present an environmental hazard. Use of a slow-release N source sometimes further reduced N losses in leachate.