Nitrate-nitrogen and dissolved reactive phosphorus in subsurface drainage from managed turfgrass

ABSTRACT:

Recent evidence suggests that turfgrass nutrients in runoff and subsurface flow pose potential risks to surface water quality. Research on water quality associated with turfgrass has generally focused on surface runoff, not subsurface flows. Quantifying the delivery of nutrients, nitrate nitrogen (NO₃-N) and dissolved reactive phosphorus, to streams from subsurface drainage features on managed turf sites, and relating the transport to fertility management and season is important for many urban managers, especially those under regulatory scrutiny. NO₃-N and dissolved reactive P concentrations from two French drains located on the Morris Williams' Municipal Golf Course in Austin, Texas, were measured over a four-year period (March, 1999 to March, 2003). Time series statistics were used to analyze and relate NO₃-N and dissolved reactive P concentrations to weather and management. A weak statistical relationship (r² = 0.55) was detected between discharge and NO₃-N concentration at one of the two drains. The relationship between discharge and dissolved reactive P concentration was not significant. Median NO₃-N concentrations from the two drains were 1.27 mg L⁻¹ and 0.32 mg L^−1. NO₃-N loading from the drains was 2.7 kg ha⁻¹ (2.4 lb ac⁻¹). The NO₃-N concentrations and load from the turf area were approximately 10 percent of those values reported for typical row crop agriculture. Median dissolved reactive P concentrations were 0.11 mg L⁻¹ and 0.09 mg L⁻¹ while dissolved reactive P loading was 0.46 kg ha⁻¹. Significant (α = 0.05) seasonal tendencies were found with respect to NO₃-N and dissolved reactive P. A strong correlation was evident between the timing of peak NO₃-N losses and nitrogen application; and between the timing of peak NO₃-N losses and air temperature. There was a similar correlation between the timing of peak dissolved reactive P losses and phosphorus application. Our results suggest NO₃-N transport in subsurface drainage from this golf course is not a water quality issue. However, our findings suggest significant dissolved reactive P transport through the drains and a need for an integrated (turf, nutrients, and water) management plan that includes consideration of subsurface drainage fluxes.