Agriculture Reference
In-Depth Information
Table 8.2
Estimates of global CH
4
emissions from ricefields in chronological order
Method
Source strength
(
Tg year
−
1
)
1 Methane production in incubated samples of rice soils
multiplied by estimated amounts of soil (Koyama,
1963)
190
2
Uniform emission factor based on flux measurements
multiplied by harvest area of rice (Cicerone and
Shetter, 1981; Holzapfel-Pschorn and Seiler, 1986;
Schutz
et al
., 1989a, respectively)
59, 70-170, 50-150
•
Excluding upland rice area
−
12%
•
Allowing for average temperature during growing
season (IPCC, 1997)
60-105
3a Methane emission proportional to net primary
production, e.g. 3-7% (Aselman and Crutzen, 1989),
5%(Taylor
et al
., 1991)
60-140
•
Allowing for soil CH
4
emission potential (Bachelet
and Neue, 1993)
47
3b Methane emission proportional to carbon returned to the
soil: 30% of the carbon retuned emitted as CH
4
(Neue
et al
., 1990)
63
•
Allowing for soil CH
4
emission potential (Bachelet
and Neue, 1993)
52
4
Specific emission factors for specific ecosystems,
regions or management, or all (IPCC, 1997)
•
Rice ecosystem-specific emission factors (Neue and
Sass, 1998)
30-50
•
Country-specific emission factors (Neue and Sass,
1998)
32
•
Regional rice statistics (Yao
et al
., 1996)
15 (China only)
5
Empirical models using data from national statistics
linked to GIS (Kern
et al
., 1997)
10
±
3 (China only)
6 Mechanistic models using weather, soil, agronomic and
other data linked to GIS
Cao
et al
. (1996)
53
Huang
et al
. (1998)
7.2-13.6 (China only)
Matthews
et al
. (2000a)
6.5-17.4 (70% of area)
Source
: adapted from van der Gon
et al
. (2000). Reproduced with kind permission of Kluwer Academic Publishers.
the anaerobic decomposition of organic matter, mostly after inorganic terminal
electron acceptors have been exhausted (Section 5.3). Transport occurs by ebul-
lition (Section 2.3), by diffusion through the soil to root surfaces and then via
the plant aerenchyma to the atmosphere (Section 6.2), and to a lesser extent by
diffusion directly to the floodwater and atmosphere. Oxidation is also microbially
mediated, mainly by obligate aerobes in the oxic floodwater-soil and root-soil
interfaces. The sensitivity of these processes to many variables suggests the pos-
sibility of interventions to decrease emissions. It also complicates the prediction
of emissions from readily measurable parameters.
