Arun Kumar Rath

Effect of continuous and alternate water regimes on methane efflux from rice under greenhouse conditions

Abstract In a greenhouse study, the effect of moisture regimes (continuously flooded, continuously nonflooded, alternately flooded) on methane efflux from an alluvial soil planted to rice was studied using the closed chamber method. Methane efflux was almost 10 times more pronounced under continuously flooded conditions than under continuously nonflooded conditions. Intermittently flooded regimes (alternately flooded and nonflooded cycles of 40 or 20 days each) emitted distinctly less methane than the continuously flooded system. A significant negative correlation was found between methane emission under different water regimes and rhizosphere redox potential. Extractable Fe2+, readily mineralizable carbon (RMC) and root biomass presented a significant positive correlation with cumulative methane emission. The correlation of methane emission with other plant parameters and microbial biomass was not significant. Our results further suggest the possibility of reduced methane emissions through appropriate water management in a rainfed rice ecosystem.

Diurnal variation in methane efflux at different growth stages of tropical rice

Diurnal variation in CH4 efflux from continuously flooded fields planted to rice (Oryza sativa L. cv. IR-36) was examined at different crop growth stages using a closed chamber method during the wet season. CH4 emission showed a distinct diurnal pattern especially at tillering, panicle initiation and maturity stages of a field-grown rice crop, with maximum emission in the early afternoon (12.00 to 15.00) followed by a decline to a minimum around midnight. Among several variables (ambient temperature, flood water temperature, redox potential, soil pH, and root oxidase activity), a significant negative correlation existed between oxidase activity of the root base and diurnal fluctuations in CH4 efflux at tillering stage. Evidence also suggested that redox status in the rhizosphere region and atmospheric, soil, and water temperatures influenced CH4 emission from rice fields probably by their contrasting effects on CH4 production and oxidation.

Wetland rice soils as sources and sinks of methane: a review and prospects for research.

Abstract Rice paddies are an important human-made ecosystem for the global CH4 budget. CH4, which is produced in the predominantly anaerobic bulk soil layers, is oxidized significantly before it reaches the atmosphere. Roots of rice, in addition to supporting the consumption of CH4, contribute to the total CH4 production in the soil. The various controls of CH4 emission from this ecosystem depend on the structure of plant and microbial communities and their interactions. Availability of organic substrates, electron acceptors and other soil- and plant-related factors influence the activities of microbial communities. Agronomic practices including fertilization and application of pesticides have effects on CH4 emission. Recent studies using molecular retrieval approaches with small subunit rRNA-encoding gene (rDNA) sequences and functional genes, showed the richness of diversity of the microbial community in rice paddy soils, which includes members of the Archaea and methanotrophs. There is need for further research to know the consequences, at the ecosystem level, of changes in microbial diversity and microbial communities in paddy soils. This will aid in understanding the mechanisms involved in the mitigating effects of certain agricultural practices.

Methane production in unamended and rice-straw-amended soil at different moisture levels

Abstract CH4 production in an alluvial soil, unamended or amended with rice straw (1% w/w), was examined under nonflooded [–1.5 MPa, –0.01 MPa and 0 MPa (saturated) and flooded (1 : 1.25 soil to water ratio)] conditions during a 40-day incubation in closed Vacutainer tubes. CH4 production was negligible at –1.5 MPa, but increased with an increase in the moisture level. Addition of rice straw distinctly increased CH4 production in the soil at all moisture levels including –1.5 MPa. Evidence, in terms of the drop in redox potential and Fe2+ accumulated, suggested that the addition of rice straw hastened the reduction of the soil, even under nonflooded conditions; thus its addition stimulated even the nonflooded soil to produce CH4 in substantial amounts. Our results indicate that many currently unidentified sources of CH4, possibly including organic-amended nonflooded soils, may make a significant contribution to the global CH4 budget.

Effect of pesticides on microbial biomass of flooded soil

Abstract Application of 2,4–13 and its analog 2,4,5-T at 0.75 μg g −1 soil led to a distinct increase in microbial biomass carbon content over that of untreated soil samples both under flooded and nonflooded conditions. 2,4-D was inhibitory to microorganisms at 7.5 and 15.0 μg g −1 soil. Repeated applications of a commercial formulation (an isomeric mixture) of hexachlorocyclohexane (HCH) to flooded soil caused a marked increase in microbial biomass content. Technical grade γ-HCH was also stimulatory to microbial biomass content. Suspensions of soil treated even once with commercial HCH formulation effected rapid aerobic degradation of α- and γ-HCH, but not β- and δ-HCH in a mineral salts medium supplemented individually with these isomers as a single carbon source.

Influence of the insecticide carbofuran on the production and oxidation of methane in a flooded rice soil

Abstract Applications of a commercial formulation of carbofuran, a carbamate insecticide, at rates of 2kg and 12kg active ingredient ha–1 to flooded fields planted to rice led to significant inhibition of methane emission. Likewise, laboratory incubation studies showed that carbofuran applied at low rates (5 and 10μgg–1soil) inhibited the net methane production relative to that of the control, but stimulated it when applied at a rate of 100μgg–1soil. Interestingly, carbofuran increased the oxidation of methane when applied at low rates and inhibited it when applied at a rate of 100μgg–1soil.