OrganicCarbon

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).