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A modified McIntyre and Phillip approach to measure top‐soil gas diffusivity in‐situ
Author(s) -
SchackKirchner Helmer,
Gaertig Thorsten,
v. Wilpert Klaus,
Hildebrand Ernst E.
Publication year - 2001
Publication title -
journal of plant nutrition and soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.644
H-Index - 87
eISSN - 1522-2624
pISSN - 1436-8730
DOI - 10.1002/1522-2624(200106)164:3<253::aid-jpln253>3.0.co;2-g
Subject(s) - dilution , exponential function , monte carlo method , thermal diffusivity , linear regression , diffusion , soil science , tracer , soil gas , function (biology) , sampling (signal processing) , chemistry , mathematics , analytical chemistry (journal) , statistics , environmental science , soil water , thermodynamics , physics , optics , chromatography , mathematical analysis , nuclear physics , evolutionary biology , detector , biology
The McIntyre and Phillip method yields the product of a gas‐diffusion coefficient (D S ) and the gas‐filled proportion of soil volume ε. Until now, ε had to be measured independently from soil cores in order to obtain D S . To avoid soil sampling, we broke up chamber measurement results by means of an empirical relationship D S = f(ε). In contrast to an exclusive use of such an empirical relationship, this approach is advantageous in that the site‐specific information concerning pore continuity is integrated into the result. Another modification involves the use of a non‐linear regression technique, which fits the unknown parameters of the mechanistic dilution function of the tracer gas to the measured values. In this way, the independent measurement of chamber clearance with a ruler could be replaced with an estimation based on the dilution function. We could then show, by means of a Monte Carlo simulation, that the exponential parameter of the dilution function contributes to the highest error of the diffusion coefficient estimation from the 6 input parameters. We then compared the results of the following methods at 6 sites. The methods included: (a) the approach described above, (b) the laboratory measurement on soil cores, and (c) the original McIntyre and Philip method. This method is a combination of in‐situ chamber measurement and laboratory measurement of the air‐filled soil fraction. We did not detect any significant differences in the means of our method (a) in any of the aforementioned cases, as well as in the laboratory measurement (b). Deviations between individual measurements could be attributed to differences in spatial integration. These deviations are a result of scale‐dependent spatial heterogeneity and thereby provide site‐specific information on soil structure.