The cumulative CH4 emissions over the whole rice season were
significantly affected by the rate of N fertilization (Table 2 and
Fig. 4a–c). Based on the measurements from 2005 to 2007, the seasonal
CH4 emissions ranged from 127.3 to 190.1 kg C ha−1 in the N0
treatment, from 98.7 to 124.6 kg C ha−1 in the N150 treatment and
from 72.3 to 75.5 kg C ha−1 in the N250 treatment. Obviously, the
seasonal CH4 emissions decreased consistently in the plots receiving
urea-based fertilizers in the three rice seasons investigated.
Overall, the decreases in the seasonal CH4 emissions were approximately
21–34% and 42–60% for the N150 and N250 treatments,
respectively, as compared to the N0 treatment, although there was
no significant difference between the N150 and N0 treatment. In
comparison with the treatment with a low rate of N application,
i.e., the N150 treatment, applying N fertilizers at the common rate
of 250 kg N ha−1 generally produced a further decreased in the CH4
emissions (Fig. 4a–c).