Nitrate and Ammonium Leaching in Cool-Season Turfgrass as Affected by Temperature and Potential Evapotranspiration

Nitrogen (N) fertilizer is often added to turfgrass during times of low temperature when soil N mineralization cannot meet plant needs. However, the spring and fall in humid temperate regions often receive more precipitation than evapotranspiration (ET). Excess soluble N in the soil has the potential to be leached into groundwater, especially when groundwater is being recharged. Temperature and ET are hypothesized to influence N uptake independently; however, their individual contributions have not been characterized in turfgrass systems. Therefore, the objective of this study was to evaluate ammonium (NH₄–N) and nitrate (NO₃–N) leaching of applied fertilizer from different cool-season grasses under a wide range of temperature and potential ET conditions observed in the cooler periods of the year in temperate climates. Kentucky bluegrass (Poa pratensis L.) and a mixture of tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] and fine fescue (Festuca longifolia Tracey) were established in 36-cm-deep containers on a sandy loam soil. The treatments were combinations of six temperatures (0, 2, 4, 6, 8, and 10°C) and three potential ET rates (1.0, 2.5, and 5.1 mm d^-1). Approximately 10 d after a 49-kg ha^-1 application of soluble N, leaching was induced. As temperature and ET decreased (independently), more NO₃–N was recovered in leachate. Ammonium leaching was low and not affected by any factor. ET had a larger influence on NO₃–N leaching at higher temperatures than at lower temperatures. These results suggest that both forecasted temperature and ET could be useful for developing NO₃–N leaching risk assessment models.