K. Bharati

Methane emission from rice fields at Cuttack, India

Methane (CH4) emission from rice fields at Cuttack (State of Orissa, eastern India) has been recorded using an automatic measurement system (closed chamber method) from 1995–1998. Experiments were laid out to test the impact of water regime, organic amendment, inorganic amendment and rice cultivars. Organic amendments in conjunction with chemical N (urea) effected higher CH4 flux over that of chemical N alone. Application of Sesbania, Azolla and compost resulted in 132, 65 and 68 kg CH4 ha−1 in the wet season of 1996 when pure urea application resulted in 42 kg CH4 ha−1. Intermittent irrigation reduced emissions by 15% as compared to continuous flooding in the dry season of 1996. In the wet season of 1995, four cultivars were tested under rainfed conditions resulting in a range of emissions from 20 to 44 kg CH4 ha−1. Application of nitrification inhibitor dicyandiamide (DCD) inhibited while Nimin stimulated CH4 flux from flooded rice compared to that of urea N alone. Wide variation in CH4 production and oxidation potentials was observed in rice soils tested. Methane oxidation decreased with soil depth, fertilizer-N and nitrification inhibitors while organic amendment stimulated it. The results indicate that CH4 emission from the representative rainfed ecosystem at the experimental site averaged to 32 kg CH4 ha−1 yr−1.

Influence of salinity on methanogenesis and associated microflora in tropical rice soils.

In a laboratory incubation study, methane (CH4) production in two saline soils and a nonsaline soil sample was investigated under flooded conditions. Mean CH4 production was remarkable (630.86 ng CH4/g) in nonsaline alluvial soil, but low (12.97 ng CH4/g) in acid sulfate saline (Pokkali) soil which was attributed to the high sulfate content of the later. CH4 production was also low in the coastal saline (Canning) soil (142.36 ng CH4/g) but increased upon leaching the soil of its salt content. Addition of salts to the nonsaline alluvial soil at 4, 8, 16 and 20 dS/m progressively decreased CH4 production. The inhibition of CH4 production was related to low microbial activities as reflected by decreased microbial biomass C and low soil microbial population including that of methanogens.

Influence of six nitrification inhibitors on methane production in a flooded alluvial soil

The influence of six nitrification inhibitors (NI) on CH4 production in an alluvial soil under flooded condition was studied in a laboratory incubation experiment. The inhibition of CH4 production followed the order of sodium azide > dicyandiamide (DCD) > pyridine > aminopurine > ammonium thiosulfate > thiourea. Inhibition of CH4 production in DCD-amended soils was related to a high redox potential, low pH, low Fe2+ and lower readily mineralizable carbon content as well as lower population of methanogenic bacteria and their activity. In the presence of higher levels of urea N (40 μg), the inhibitory effect of DCD was only partially alleviated. Results indicate that several NIs can differentially regulate CH4 production in a flooded alluvial soil.

Effect of the herbicide butachlor on methane emission and ebullition flux from a direct-seeded flooded rice field

Abstract Application of a commercial formulation of the herbicide butachlor (N-butoxymethyl-2-chloro-2′,6′-diethyl acetanilide) at 1 kg a.i. ha–1 to an alluvial soil planted with direct-seeded flooded rice (cv. Annada), significantly inhibited both crop-mediated emission and ebullition fluxes of methane (CH4). Over a cropping period of 110 days, the crop-mediated cumulative emission flux of CH4 was lowered by ∼20% in butachlor-treated field plots compared with that of an untreated control. Concurrently, ebollition flux of CH4 was also retarded in butachlor-treated field plots by about 81% compared with that of control plots. Significant relationships existed between CH4 emission and redox potential (Eh) and Fe2+ content of the flooded soil. Application of butachlor retarded a drop in soil redox potential as well as accumulation of Fe2+ in treated field plots. Methanogenic bacterial population, counted at the maturity stage of the crop, was also low in butachlor-treated plots, indicating both direct and indirect inhibitory effects of butachlor on methanogenic bacterial populations and their activity. Results indicate that butachlor, even at field-application level, can effectively abate CH4 emission and ebollition from flooded soils planted to rice whilst maintaining grain yield.

Influence of a commercial formulation of tridemorph on methane production and oxidation in a tropical rice soil

In a laboratory incubation study, application of a commercial formulation of tridemorph to a tropical rice soil under flooded condition significantly stimulated CH 4 production at low levels (5, 10 and 20 μg.g -1 ) but inhibited the process at higher levels of 50 and 100 μg.g -1 . Oxidation of CH 4 , however, was progressively inhibited with increasing concentrations of the fungicide. Increase in CH 4 production in tridemorph-amended soil was attributed to a hastening in the soil reduction, increase in the K 2 SO 4 -extractable C content and an increase in the population of methanogenic bacteria. Inhibitory effect of the fungicide on the oxidation of CH 4 , on the other hand, was related to the inhibition in the population of methanotrophic bacteria.

Influence of flooded and non-flooded conditions on methane efflux from two soils planted to rice

Abstract In a greenhouse study, CH4 flux from alluvial and laterite soils planted to rice (cv. CR 749-20-2) was monitored under non-flooded and flooded conditions. CH4 flux from continuously non-flooded pots was always lower than from pots maintained under flooded conditions. The cumulative CH4 flux was 150 and 880 mg pot−1 in laterite and 105 and 405 mg pot−1 in alluvial soils under non-flooded and flooded conditions, respectively. While non-flooded conditions exhibited a single CH4 peak at vegetative stage, flooded conditions showed additional peak at reproductive stage. CH4 flux maxima was more intense under flooded conditions and persisted for a longer period during the reproductive stage than at the vegetative stage. Soil contents of Fe2+, readily mineralizable carbon (RMC) and ninhydrin reactive nitrogen (NRN) exhibited significant positive relationship with CH4 flux. Among the plant characters, a significant negative relationship existed between CH4 flux and α-naphthylamine oxidase activity of the root base under flooded condition and root tip under non-flooded conditions.