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Shortcomings in the Commercialized Barometric Process Separation Measuring System

^a Univ. of Hohenheim, Institute of Soil Science and Land Evaluation, Biogeophysics Section, D-70593 Stuttgart, Germany
^b UFZ, Helmholtz Centre for Environmental, Research Dep. of Soil Physics, Theodor-Lieser-Strasse 4, D-06120 Halle/Saale, Germany
^c China Agricultural Univ., College of Agricultural Resources and Environmental Sciences, Beijing, 10009, P.R. China

View larger version (11K): [in this window] [in a new window]   Fig. 1. Sum of carbonate species as implemented in the Umweltanalytische Mess-Systeme (UMS) barometric process separation (BaPS) system and the corrected calculation as a function of pH (see Eq. [8]). The calculations were performed assuming a CO2 partial pressure of 30 Pa and a temperature of 10°C (dissociation constants used were log KH = –6.298 mol L–1 Pa–1, log KH2CO3 = –6.35 mol L–1, and log KHCO3= –10.33 mol L–1).

View larger version (21K): [in this window] [in a new window]   Fig. 2. Nomogram for the error in the calculation of the O2 nitrification rate caused by a pH unit error in calculating the carbonate equilibrium in the Umweltanalytische Mess-Systeme barometric process separation (BaPS) data evaluation algorithm. The calculation (see Eq. [9]) was performed for 10°C and assuming that the incubation chamber was loaded with seven 100-cm3 soil cores with a volumetric water content of 25% (water volume = 0.175 L). The dissociation constants used were log KH = –6.298 mol L–1 Pa–1, log KH2CO3 = –6.35 mol L–1, and log KHCO3 = –10.33 mol L–1.

View larger version (13K): [in this window] [in a new window]   Fig. 3. Nomogram for the error in the calculation of O2 nitrification rate caused by the error in the Umweltanalytische Mess-Systeme barometric process separation (BaPS) data evaluation algorithm when the respiration quotient 1. The ratio, i.e., the molar ratio between O2 consumption and CO2 assimilation during autotrophic nitrification, was set to the default value of 7.3. The nomogram was computed using Eq. [11].

View larger version (25K): [in this window] [in a new window]   Fig. 4. Comparison of measured gross nitrification rates using the 15N pool dilution technique, the Umweltanalytische Mess-Systeme (UMS) barometric process separation (BaPS) system, and corrected BaPS calculations. Soil was taken from a slightly alkaline topsoil at the Dongbeiwang Agricultural Experimental Station of the China Agricultural University, Beijing. Soil pH was 7.6 in 0.01 mol L–1 CaCl2 and 8.0 in water. In the corrected BaPS calculation, a negative NxOy value, which was on average –5.9 µmol h–1, was handled by using the "distributed error adjustment" or the "unknown process" procedure. Bars with the same index are not significantly different ( = 0.05). The error bars give the standard deviation (n = 3).

View larger version (19K): [in this window] [in a new window]   Fig. 5. Comparison of measured gross nitrification rates using the 15N pool dilution technique, the Umweltanalytische Mess-Systeme (UMS) barometric process separation (BaPS) system, and corrected BaPS calculations. Soil was taken from a slightly alkaline topsoil at the Julius-Kühn-Feld experimental station in Halle (Saale), Germany. Soil pH in 0.01 mol L–1 CaCl2 was 7.4 and in water 7.8. With one of the three replicates, the NxOy value was negative (–1.0 µmol h–1). In this case, the data were adjusted using the "unknown process" procedure. Bars with the same index are not significantly different ( = 0.05). The error bars give the standard deviation (n = 3).