Methane emission from rice paddy soils, aerotolerance of methanogens and global thermal warming

In vitro methane emissions from different rice paddy soils and algal mats were studied under anoxic and atmospheric conditions. Methane production from rice paddy soils cultivating different strains of rice was found to be appreciable under anoxic conditions, but considerably reduced under atmospheric conditions, and dependent on rice cultivars (strains). A contradictory result was obtained with a Gobindabhog cultivated rice field (a strain of rice with aroma), where methane yield under anoxic was greater than that under atmospheric conditions. The results indicated aerotolerance of methanogens or the possible existence of microaerophilic methanogens. The results from algal mats corroborated these findings. Methane has been considered to be an important greenhouse gas contributing significantly to global thermal warming (GTW). Flooded rice paddy fields have been considered to be a most prominent source of abiogenic methane emission, though considerable uncertainty exists regarding the true estimates of methane emission. Factors affecting methane emission and its abatement have been examined. In spite of increasing methane emission, rice cultivation leads to enormous utilization of the ‘green house gas’ carbon dioxide and release of oxygen to the atmosphere. Thus, the contribution of methane to GTW (from rice paddy cultivation) is more than compensated by carbon dioxide absorption. Appropriate steps have been suggested for the reduction of methane emissions, the most important of which is the restoration of methane sinks.