Fig. 14.11 Typical patterns of the changes in soil Eh causing higher CH4 emission. (a) Narrow range keeps the semi-reductive conditions, (b) Wide range has the long-term reductive conditions. Dotted line is the Eh limit
Figure 14.11 shows typical changing patterns of soil Eh that cause a large amount of CH4 emission. The Narrowest range (-100, +100mV) had frequent routines, and did not dry the soil enough (Fig. 14.11a). The soil with the continuous semi-reductive conditions is ready to produce CH4. Once the flooded period is kept longer, then CH4 emission occurs. On the other hand, the widest range (-150, +300 mV) took a long time to lower soil Eh to — 150mV, and thus kept the reductive conditions, causing CH4 emission (Fig. 14.11b). Therefore, under the conditions of this experiment, the combination of —100 and +300 mV (the Highest range) would be the best range that dries the soil enough and also has several times of short-term flooding. It will be possible to determine the ideal Eh range according to the soil type and other management practices.
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