Selection of rice genotypes for lower methane emission

Methane emission from paddy fields can vary with rice cultivars, growth stages of the rice plants ( Oryza sativa L.) and environmental conditions. Efforts are being made to study methane emission from rice paddies in different ways. In particular, selection of rice cultivars that emit less methane is practical because it does not change farmer practices. Assam state is a rice-growing state of the northeastern part of India. Assam state is very rich in the rice genepool. Here, we screened rice cultivars popularly grown during the monsoon season of Assam. Five traditional cultivars and five high-yield modern cultivars were grown in the field. Methane emission was measured for the whole crop-growing season. Crop growth parameters including plant height, tiller number, leaf number, plant biomass, leaf area index and grain yield were recorded. Soil parameters such as soil temperature, soil pH and soil organic carbon were also recorded. Our results show that the methane emission of rice cultivars ranged from 8.83 g m(-2) to 18.63 g m(-2) over three and a half months. Variety IR 36 was found to emit the least methane amongst all the cultivars. Five cultivars were identified as high methane-emitting cultivars (> 15 g m(-2)). Methane flux values of the crop-growing season exhibited a positive correlation with leaf number, tiller number and leaf area index. Traditional rice cultivars with profuse vegetative growth recorded higher methane flux values compared with high-yielding varieties. This study clearly suggests the possibility of reducing methane emission from the wetland rice ecosystem through appropriate selection of rice cultivars to achieve an economically feasible and technically sound mitigation option of methane emission from farmers' fields.