Evaluation of minimum water-filled pore space (WFPS) to ensure detectable N2 fluxes for Central Experiments in DASIM

Methods Incubation of DASIM soils in Thünen microcosm system under the following conditions: N2-depleted atmosphere(2% N2 in pure He or in 20%O2/78%He) (Lewicka-Szczebak et al., 2017) Target flow rate: 20 mL/min Core diameter: 14,4 cm Core heights:10 cm Bulk density: according to DASIM protocol: Fuhrberg, arable (sand) = 1.5; Rottalmünster, arable (silt loam) = 1.3; Gießen, grassland = clay loam (1.2) 15N-labeling: addition of K15NO3 (60 at% 15N), target content of 50 mg N/kg Litter: all treatments without litter WFPS levels: 60 /65/70/75 % Incubation sequence: 1 week aerobic (20%O2), one week anaerobic Temperature: 20°C Gas sampling for IRMS: twice a week GC analysis online about 3 times a day IRMS analysis: see Lewicka-Szczebak et al. 2013) Calculation of ap and fs: see Spott et al. (2006) and Buchen et al. (2016) Determination of limit of detection (LOD): Monte-Carlo modelling using SD of 29R and 30R of IRMS analysis soils were sieved to 10 mm, preincubates at 50% WHCmax and 20°C for two weeks, fertilized, packed to target height and BD and wetted to target WFPS. Final WFPS and NO3--N was not measured.