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Source: Minamikawa and Sakai (2006b).

With (+S) and without (—S) rice straw incorporation (51DW ha-1).

Source: Minamikawa and Sakai (2006b).

With (+S) and without (—S) rice straw incorporation (51DW ha-1).

Annual variations in weather conditions usually affect the CH4 emission. The field experiment was conducted in 2003 with the relatively cool summer and in 2004 with normal temperature summer. The effects of weather conditions were observed in the total CH4 emission with continuous flooding and also rice yield level (Table 14.4). However, with Eh control, the total CH4 emissions in both years were similarly low. Consequently, Eh control can always minimize CH4 emission with regard to weather conditions and other field management.

14.4.3.3 Modification of Eh Limits

Is it possible to shift the Eh limit to more oxidative one both for further decreasing CH4 emission and increasing rice yield? The experiment was carried out to examine the modifying effects of the upper limit (+100 or +300 mV) and the lower limit (-150 or -100 mV) in the Andosol field.

Table 14.5 shows the total CH4 emission and rice yield with four combinations of the Eh limits. Rice yields with all Eh ranges were similar to or more than the conventional level, but the effects of the Eh limit were not significant because of the spatial variation within the field. Modification of lower limit (from -150 to — 100mV) had positive effects on decreasing CH4 flux during flooded period, but the total CH4 emission was predominated by a large amount of CH4 flux during drainage, especially in the later period. While the lowest CH4 emission was, as expected, observed in the Highest range (-100, +300 mV), the emissions from other ranges were fluctuated by the following reasons.

Table 14.5 Effects of shifting the Eh limit on the total CH4 emission and rice yield

CH4 emission

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Narrowest Widest Highest Lowest

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