Impact of Water Management on Methane and Nitrous Oxide Emission Dynamics in Asian Paddy Ecosystems

With increasing demand for rice productivity linked with intense pressure on water availability in Asia, novel strategies are sought to optimise water management in paddy cultivation without compromising the yield. The conventional submerged paddy ecosystems not only consume water excessively but also constitute a major source of methane (CH4) and nitrous oxide (N2O), two highly potent greenhouse gases (GHG). The main objective of this study is to investigate the alternate wetting and draining (AWD) method as an emerging water-saving strategy for Asian countries, which could potentially minimise GHG emissions while maintaining crop productivity. Seasonal CH4 and N2O emissions from Sri Lankan and Indian experimental sites under the AWD method were compared with emissions from the conventional completely flooded (CF) method, while Japanese experimental sites were used to examine CH4 ebullition under CF conditions. Emission measurements were conducted in both wet and dry seasons with no alterations to country-specific applications of fertiliser and soil amendments. Overall results revealed that AWD could potentially suppress CH4 emissions by 32 to 43% without a significant statistical contrast (p > 0.05) in the crop yield. Measurements in Japan revealed that ebullition accounted for 60% of the total methane emissions at the heading stage under CF conditions. Results further emphasise the use of agricultural amendments with caution in paddy cultivation as they may lead to enhanced methane emissions.