High spatio-temporal variation in CH4 emissions among cascade positions
was found in both rice cascades. Bottom fields showed the
highest rate and cumulative CH4 emissions in both rice cascades. The
spatial variability in CH4 emissions among the toposequence positions
in this experimentwas related to the different sediment deposition patterns
across the cascade, which influenced physical and chemical properties
of soil along the toposequence rice fields. The CH4 flux of summer
ricewas higher than spring rice in all toposequence positions suggesting
that fresh crop residue should not be incorporated into the soil during
land preparation before transplanting of summer rice. Across various
cascade positions, the application of mineral fertilizers mitigated CH4
emission from paddy rice as compared to non-fertilized parts in this
study. Recommended type of fertilizer management practice such as
ammonium based fertilizers is an effective way to reduce CH4 emission
from toposequence rice fields but different management practices
should be done for different toposequence positions to mitigate CH4
emission in this watershed area.
Acknowledgment