The organic carbon in flooded soils is replenished by
exudation and decay of roots and by incorporation of straw
and other organicmatter. Addition of rice straw or compost
is common practice in rice agriculture and results in a
strong stimulation of CH4 production (20–22). The halflife
of rice straw in flooded soils is about two years (23).
Organic matter is also provided by the plant roots
through exudation of part of the photoassimilated carbon,
sloughed off cells, and decaying roots (24). Pulse-labeling studies showed that about 5% of the photoassimilated
14CO2 was converted to CH4 within a few days and
reemitted into the atmosphere (25).
