C. Kammann et al., A new sampling technique to monitor concentrations of CH4, N2O and CO2 in air at well-defined depths in soils with varied water potential, EUR J SO SC, 52(2), 2001, pp. 297-303
A new sampling technique for measuring the concentrations of trace gases (C
H4, CO2 and N2O) in the soil atmosphere from well-defined depths is describ
ed. Probes are constructed from silicone tubing closed with silicone septa
on both ends, thereby dividing an inner air space from the outer soil atmos
phere without a direct contact. The gas exchanges between the inner and out
er atmosphere only by diffusion through the walls of the silicone tube. Tes
ts revealed that the gases N2O, CO2 and CH4 in the enclosed space reached 9
5% equilibrium with the surrounding atmosphere at 20 degreesC within 7 h or
faster. The probe measurements are reproducible: the standard deviation of
samples taken from 26 probes stored in the laboratory atmosphere equalled
that of a standard gas. The probes can easily be constructed and installed
at specified depths in the soil.
The method has the following advantages compared with other methods that us
e spaces with holes in them for gas exchange: (i) the silicone probe enable
s trace gases to be sampled in wet soils, including ones that are waterlogg
ed or temporarily saturated; (ii) the sampling itself does not create low p
ressure and hence does not create mass flow in the soil matrix from undefin
ed depths; and (iii) the probe can be made to take samples of gas of any re
quired size. The silicone probes did not show ageing effects during 18 mont
hs of use in the field in a mineral soil under grass. The probes yielded co
mparable results: three probes inserted at 5 cm depth in a uniformly treate
d 100-m(2) plot provided nearly identical average trace gas concentrations
within the measurement period.