Table 6 reports the direct field emissions that were calculated.
Emissions to air proved relatively homogeneous across all three
systems, with the notable exception of methane emissions. Rw
systems emit a median amount of 76 g CH4 per kg of paddy rice,
compared with 158 g and 176 g for Iw and Id systems, respectively.
Lower CH4 emissions in rain-fed conditions relate first to the water
regime in the pre-season before the cultivation period (non-flooded
conditions for more than 180 days) and second to the management
of organic residues (incorporated more than 30 days
before cultivation). CH4 emission figures broadly concur with those
of the IPCC (2006), which reports that approximately 120 g of CH4
are released into the atmosphere for each kg of rice produced;
however, our results reveal significant local differences based on
cropping systems and water management practices. With regards
to emissions towater, Id systems systematically emit more nitrates,
phosphates, and agro-chemicals per both functional units, on account
of the overall lower productivity of chemical inputs.