Four turfgrass systems in or near the Pinehurst Resort and Country Club, Sandhills region, North Carolina, USA was sampled. Twenty intact soil cores (5 cm diameter x 10 cm length) were collected from each turfgrass system in January and August 2016, respectively. For each turfgrass system, a total of 12 intact soil cores were used to measure N effluxes during three-week incubation, representing three replicates and four treatments: (1) no N input and 23 °C, (2) low N input (i.e., addition of 5.9 mg N as NH4NO3, equivalent to 30 kg N ha-1) and 23 °C, (3) high N input (i.e., addition of 11.8 mg N as NH4NO3, equivalent to 60 kg N ha-1) and 23 °C, and (4) high N input and 13 °C for winter samples (or 33 °C for summer samples). On day 0, water and NH4NO3 solution were added to the respective soil cores to bring soil moisture to 60% water filled pore space (WFPS). Here, we estimated soil bulk density and moisture content from the other eight intact soil cores and then calculated soil porosity assuming that soil particle density was 2.65 g cm-3. These soil cores were also used for soil pH measurement. Soil N2O and CO2 effluxes were measured almost daily via soil cores closed for 2 h and then 30-ml gas samples withdrawn from headspaces using gas-tight push button syringes with one-way luer stopcocks. On day 4, 11, and 18, roughly 80 ml leachate was collected from each soil core after 80 ml distilled water poured slowly to soil surface, drained up to 2 h, and then vacuum pumped out. Nitrous oxide was measured using a dual quantum cascade laser (QCL) N2O measurement system (Model CWQCL-200-D, Aerodyne, Billerica, MA, USA) (Chen et al., 2016). The efflux rate of N2O (µg m-2 h-1) was calculated as: ((Csample-Cair) × M × V) / (r × m × t), where Csample and Cair are the N2O concentrations in the headspace of intact soil core and ambient air (ppbv), respectively; V is the volume of intact soil core headspace (L); M is the molar mass of N2O (g mol-1); r is the molar volume at 1 atm (23.47 L mol-1 at 13 oC, 24.29 L mol-1 at 23 oC, and 25.11 L mol-1 at 33 oC), m is soil core surface area (m2), and t is the incubation time (h). The QCL system also provided the mixing ratio of natural abundance of 15N in the center and edge position of N2O, i.e., 15Nα and 15Nβ, respectively. After normalized to total N2O-N concentration, these ratios were used to calculate the natural abundance of 15Nα and 15Nβ of N2O. Then, 15N site preference was estimated by δ15Nα - δ15Nβ and used to help probe the biological source of N2O efflux.

This dataset is associated with the following publication: Chen, H., T. Yang, Q. Xia, D. Bowman, D. Williams, J. Walker, and W. Shi. The extent and pathways of nitrogen loss in turfgrass systems: Age impacts. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, NETHERLANDS, 637638: 746-757, (2018).