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SOIL BIOLOGY & BIOCHEMISTRY

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

^* Corresponding author (jingwer{at}uni-hohenheim.de).

In a growing number of studies, the barometric process separation (BaPS) method has been applied for measuring gross nitrification rates in soil. In 2000, the company Umweltanalytische Mess-Systeme (UMS) GmbH (Munich, Germany) presented the first and only commercially available automatic BaPS measuring system. In an ongoing project, we have used the UMS BaPS system to measure gross nitrification rates in two alkaline agricultural soils. During data evaluation, we came across certain shortcomings in the UMS data evaluation routine. We identified three problems: (i) a unit error in the calculation of the carbonate equilibrium, (ii) an erroneous calculation when the respiration quotient is unequal to unity, and (iii) an inappropriate procedure for handling a negative rate of N gases produced by denitrification (N_xO_y). Particularly the error in calculating the carbonate equilibrium caused a significant overestimation of the gross nitrification rate at pH values >6. A literature review showed that the BaPS method works well in acidic to weakly acidic soils. For soils with higher pH values, its performance remains unclear. More research is needed to test the applicability of the BaPS method in neutral and alkaline soils.

Abbreviations: BaPS, barometric process separation • UMS, Umweltanalytische Mess-Systeme GmbH