Rice Cultivation to Mitigate Greenhouse Gas Emissions in Degraded Peatlands.

Rewetting drained peatlands creates favorable reduced conditions for denitrification, but, the potential of restored peatlands to act as N₂O sink is poorly characterized.  We monitored N₂O emissions in rewetted peatlands converted to rice paddies with a range of soil organic carbon (SOC) (6%, 11%, and 23%) during the growing season.  Negative N₂O emissions were repeatedly observed in all sites, which were not affected by nitrogen fertilization at 80 kg N ha^-1.  The highest consumption rates amounted to 8.2 tones CO₂ eq ha^-1 yr^-1, 32% of the average CO₂ emissions from drained peat soils.  Porewater N₂O concentrations were frequently less than the calculated in situ N₂O equilibrium concentrations, suggesting diffusional constraints on atmospheric N₂O into pore water.  Redox potentials were correlated to N₂O emission rates (r² = 0.40, p < 0.01).  However, relatively higher frequencies and magnitudes of negative N₂O emissions were mostly observed during the period of water draw down for rice harvest activities, especially in the field with the highest SOC.  It is likely that drainage by reducing water depth removed the diffusional barrier for atmospheric N₂O into the soil.  In all, the capacity of rewetted peatlands to act as atmospheric N₂O sinks can be significant and seemingly can be managed through manipulating water depths.