Not much progress has been made in using soil classifi-
cations and soil maps to identify extrapolation domains
for regional and global estimates of methane emission.
Most criteria used for soil classification do not directly
affect methane production. All soil types show a
wide range of methane production potential. No general
simple correlation between any stable soil property
and methane production is evident. Relationships to
dynamic soil properties are well established. Signifi-
cant methane production requires a soil redox potential
lower than -150 mV, for molecular fatty acids derived
from easily degradable organic matter, a pH between
6 and 8, low sulfate concentrations, and temperatures
above 10
C (Wang et al., 1992, 1993). Sandy soils
produce more methane than clay soils with similar carbon
contents. In calcareous and alkaline soils, methane
production may occur within hours after flooding an
air-dried soil, whereas in acid soils it may take weeks
before methane is formed.In highly acid soils, methane
may not be formed at any time. Higher soil temperature
speeds up methane formation but total amounts may
not differ when comparing weeks or month rather than
Not much progress has been made in using soil classifi-cations and soil maps to identify extrapolation domainsfor regional and global estimates of methane emission.Most criteria used for soil classification do not directlyaffect methane production. All soil types show awide range of methane production potential. No generalsimple correlation between any stable soil propertyand methane production is evident. Relationships todynamic soil properties are well established. Signifi-cant methane production requires a soil redox potentiallower than -150 mV, for molecular fatty acids derivedfrom easily degradable organic matter, a pH between6 and 8, low sulfate concentrations, and temperaturesabove 10 C (Wang et al., 1992, 1993). Sandy soilsproduce more methane than clay soils with similar carboncontents. In calcareous and alkaline soils, methaneproduction may occur within hours after flooding anair-dried soil, whereas in acid soils it may take weeksbefore methane is formed.In highly acid soils, methanemay not be formed at any time. Higher soil temperaturespeeds up methane formation but total amounts maynot differ when comparing weeks or month rather than
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