Methane production potential, soil health and rice yields under inorganic and organic management in the Brahmaputra Valley of Assam, India

Methane (CH 4 ), a powerful greenhouse gas emitted from flooded rice soils is a major contributor to climate change. Its production is significantly influenced by on-farm nutrient management practices. The present study compared the effects of long-term inorganic and organic management practices on methane production potentials, selected soil health indicators, and grain yields in farmers’ rice fields of Assam. We hypothesized that long-term organic nutrient management increases soil CH 4 production potential due to enhanced carbon availability, but simultaneously improves soil health and rice productivity compared to inorganic fertilization. Considering both the years of study, CH 4 production potential ranged between ~133 and ~236 CH 4 g -1 day -1 , organic carbon between 0.38 and 0.70%, microbial biomass carbon between 400 and 547 µg g -1 , and grain yield between ~2809 and ~5684 kg ha -1 in the inorganic fields. Similarly, in the organic fields, CH 4 production potential, organic carbon, microbial biomass carbon and grain yield ranged between ~167 and 344 CH 4 g -1 day -1 ; 0.50 and 0.91%; 300 and 890 µg g -1 ; ~5267 and ~7731 kg ha -1 respectively. Comparatively higher CH 4 production rates in organic fields may be due to enrichment of the soil organic carbon pool via decomposition of applied organic amendments, leading to enhanced microbial biomass and activity. CH 4 production under organic management showed good association with soil pH, organic carbon, and microbial biomass carbon. However, higher CH 4 production in organic fields was partly compensated by improved soil properties and rice yields than inorganic fields. Higher grain carbohydrate in organic fields indicate efficient carbohydrate partitioning to the grains and better nutrient utilization by the crop. Vermicompost and vermiwash applied fields recorded lower CH 4 production among the organic treatments and higher yield among all the studied treatments. Cow manure and Azolla application also significantly reduced CH 4 production but improved yield to a comparatively lesser extent. Our findings suggest that appropriate organic management practices could reduce CH 4 production rates in rice soils while enhancing soil health and crop yield.