Prabhat K. Gupta

Methane emission from flooded rice fields under irrigated conditions

In a study on CH4 emission from flooded rice fields under irrigated conditions, fields planted with rice emitted more methane than unplanted fields. The CH4 efflux in planted plots varied with the rice variety and growth stage and ranged from 4 to 26 mg h-1m-2. During the reproductive stage of the rice plants, CH4 emission was high and the oxidation power of rice roots, in terms of α-naphthylamine oxidation, was very low. The CH4 emission reached a maximum at midday and declined to minimum levels at midnight, irrespective of the rice variety. The peak CH4 emission at midday was associated with higher solar radiation and higher soil/water temperature.

Effect of soil temperature on methane emission from paddy fields

Abstract Methane emission measurements using the closed chamber method from Indian paddy fields, specially prepared to study the effect of soil temperature, indicate a definite increase in methane emissions with soil temperature up to 34.5 ± 0.5°C and a decrease in the rate of emission above this temperature.

Methane budget from paddy fields in India

Abstract Results of national methane campaign launched in 1991 to assess methane budget from Indian paddy fields are reported. The campaign involved a number of scientific institutions and universities with National Physical Laboratory at Delhi operating as a nodal agency and covered most of the major rice growing regions of India. Methane emission rates ranged between −0.64 and 84.1 mg −2 h −1 . The methane budget from Indian paddies has been estimated to be around 4.0 TgY −1 with a range between 2.7 to 5.4 TgY −1 .

Methane production in rice soil is inhibited by cyanobacteria

The present study was aimed at understanding the role of cyanobacteria and Azolla in methane production and oxidation in laboratory simulation experiments using soil samples from rice fields. All the seven cyanobacterial strains tested effected a significant decrease in the headspace concentration of methane in flooded soil, incubated under light. Synechocystis sp. was the most effective in retarding methane concentration by 10-20 fold over that in controls without cyanobacteria. The decrease in the headspace concentration of methane was negligible in nonsterile soil samples, inoculated with Synechocystis sp. and then incubated under dark. Moist soil cores (0-5 cm depth), collected from rice fields that had been treated with urea in combination with a cyanobacterial mixture, Azolla microphylla, or cyanobacterial mixture plus A. microphylla, effected distinctly more rapid decrease in the headspace concentration of methane added at 200 microl(-1) than did the soil cores from plots treated with urea alone (30, 60, 90 and 120 kg N ha(-1)), irrespective of the rate of chemical nitrogen applied to rice fields. Besides, soil cores from plots treated with urea alone at 60, 90 and 120 kg N ha(-1) oxidised methane more rapidly than did the core samples from plots treated with urea alone at 30kg N ha(-1). Cyanobacteria and A. microphylla, applied to flood water, appear to play a major role in mitigation of methane emission from rice fields-through enhanced methane oxidation.

Biomass burning and related trace gas emissions from tropical dry deciduous forests of India: A study using DMSP-OLS data and ground-based measurements

Biomass burning is one of the major sources of trace gas emissions in the atmosphere. In India the major sources of biomass burning include deforestation, shifting cultivation, accidental fires, controlled burning, fire wood burning, burning from agricultural residues and burning due to fire lines. Studies on biomass burning practices gain importance due to increasing anthropogenic activities and increasing rates of deforestation. Satellite data have been widely used over the globe to monitor the rates of deforestation and also with respect to biomass burning studies. But, much of the polar orbiting satellites, due to their repetitive cycle, have limitations in observing such events and in the tropics, due to cloud cover, getting a cloud-free image during the daytime is difficult. In this study we used Defence Meteorological Satellite Program Operational Line Scanner (DMSP-OLS) night-time data to study the biomass burning events over a period of 10 years from 1987 to 1998 for the Eastern Ghats region, covering the northern part of Andhra Pradesh, India. Two ground-based experiments were carried out to quantify the emissions from biomass burning practices. The results of the study with respect to trace gases suggested emission ratios for CO, CH4, NOx and N20 during the burning to be about 12.3%, 1.29%, 0.29% and 0.07% at the first site and 12.5%, 1.59%, 0.29% and 0.05% at the second site, suggesting low inter-fire variability between the sites. The variation has been attributed to the fuel load, vegetation characteristics, site conditions and local meteorological parameters affecting the relative amounts of combustion. Using the DMSP OLS derived areal estimates of active fires, the trace gas emissions released from the biomass burning were quantified. The results suggested the emissions of 8.2 2 10 10 g CO 2, 1.8 2 10 8 g CO, 6.0 2 10 6 g N 2 O, 3.0 2 10 6 g NO x and 1.2 2 10 8 8 g CH 4 during March 1987. The emissions increased to 1.0 2 10 11 g CO 2, 2.3 2 10 g CO, 7.8 2 10 6 g N 2 O, 3.9 2 10 7 g NO x and 1.6 2 10 8 g CH 4, over a period of 10 years. The results of the analysis suggest the possible use of monitoring biomass burning events from DMSP-OLS night-time data.

Effects of agriculture crop residue burning on children and young on PFTs in North West India.

Variations in pulmonary function tests (PFTs) due to agriculture crop residue burning (ACRB) on children between the age group of 10 to 13 years and the young between 20 to 35 years are studied. The effects of exposure to smoke due to rice-wheat crop residue burning on pulmonary functions like Force Vital Capacity (FVC), Force Expiratory Volume in one second (FEV(1)), Peak Expiratory Flow (PEF) and Force Expiratory Flow in 25 to 75% of FVC (FEF(25-75%)) on 40 healthy subjects of rural/agricultural area of Sidhuwal village of Patiala City were investigated for a period from August 2008 to July 2009. Measurements were taken by spirometry according to the American Thoracic Society standards. High volume sampler (HVS) and Anderson Impactor were used to measure the concentration levels of SPM, PM(10) and PM(2.5) in ambient air of the Sidhuwal village. A significant increase in the concentration levels of SPM, PM(10) and PM(2.5) was observed due to which PFTs of the subjects showed a significant decrease in their values, more prominently in the case of children. PFTs of young subjects recovered up to some extent after the completion of burning period but the PFT values of children remained significantly lower (p<0.001) even after the completion of burning episodes. Small size particulate matter (PM(2.5) and PM(10)) affected the PFTs to a large extent in comparison to the large size particulate matter (SPM). The study indicates that ACRB is a serious environmental health hazard and children are more sensitive to air pollution, as ACRB poses some unrecoverable influence on their PFTs.

Studies on aerosol optical depth in biomass burning areas using satellite and ground-based observations

Biomass burning in the tropics is a source of trace gas fluxes and particulate matter. During the last decade, the shifting cultivation practices have been increased in the tropical forest of Eastern Ghats, Andhra Pradesh, India. In order to quantify the fluxes emitted from the biomass burning due to shifting cultivation practices, a field experiment has been conducted on February 16-25, 1999. The present study provides the variation of aerosol optical depth over the shifting cultivation areas of Rampa Revenue Division, Eastern Ghats using a sunphotometer in synchronism with satellite data. Optical depth values increased up to 2.0 during the burning phase and then returned to normal values (0.2-0.5). The atmospheric correction of the satellite data using the optical depth values suggested improvement in the overall contrast of the image and increase in the dynamic range of the normalized difference vegetation index (NDVI) values of various features in the image.

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 saliva 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.

CH4 emissions from biomass burning of shifting cultivation areas of tropical deciduous forests – experimental results from ground-based measurements

Abstract Context Abstract : Tropical deciduous fires from shifting cultivation process in India are characterized by the highly differential nature of fire behavior due to fragmented burning patterns. Our study from ground-based experiments from biomass burning of tropical deciduous forest fires suggests smoldering combustion as the dominating process during biomass burning which leads to evolution of more incompletely oxidized products such as Methane when compared to other ecosystems such as Savannas. In the study, we report emission ratios and emission factors for methane from biomass burning of tropical deciduous forests. As tropical deciduous forests in India cover more than 50% of overall forests, the emission factors obtained in the present study can be used widely for methane emission estimation from forest biomass burning studies in other parts of India and in modeling studies of Methane from forest biomass burning in India. Main Abstract : Biomass burning is an important source of trace gas emissions to the atmosphere. Methane emitted from the biomass burning contributes to the atmospheric greenhouse effect and is sufficiently long-lived to enter the stratosphere and take part in the stratospheric ozone cycles. In India, though CH 4 emissions from the different sources such as rice paddy fields and domestic animals have been well studied, there are relatively no field-based studies with respect to CH 4 emissions from biomass burning. In the present study, we report for the first time, the CH 4 emissions from biomass burning of tropical deciduous forests cleared for shifting cultivation purposes. Trace gas emissions from the biomass burning plumes have been collected through grab sampling in canisters as well as from online measurements through instruments. Site characteristics with respect to species composition, amount of biomass burnt and relative amounts of combustion, viz., flaming, mixed and smoldering have been determined. Modified combustion efficiency has been used to differentiate relative amounts of combustion. Emission ratios were calculated with respect to CO 2 and emission factors based on the amount of biomass consumed. Results of the study with respect to biomass estimations prior to burning suggested values of 12–14 t ha −1 at the first site and 13.5–15.3 t ha −1 at the second site. The mean modified combustion efficiencies during flaming, mixed and smoldering combustion phases for the first site were found to be 95.7%, 91.1% and 74.4% and 95.31%, 90.63% and 72.89%, respectively, for the second site. The average biomass consumed during the fire ranged from 4.7 t ha −1 (site 1) to 3.4 t ha −1 (site 2), indicating low amount of biomass burnt during the first phase of burning in shifting cultivation areas. Results suggested the CH 4 emission ratios of 1.29% at the first site and 1.59% at the second site. The CH 4 emission ratios obtained in the present study are closer to the most accepted estimates of 1.2±0.5% obtained for tropical forests elsewhere. Using the emission ratios obtained in the study and estimating the amount of methane emissions from biomass burning suggests that nearly 0.99 Tg of methane is emitted annually from shifting cultivation process in India. Also, in the study, a detailed comparison of emission ratios and emission factors of CH 4 has been made.

Scientific basis for establishing country greenhouse gas estimates for rice-based agriculture: An Indian case study

A comprehensive scientific assessment of CH4 budget estimation for Indian rice paddies, based on a decade of measurements in India, is presented. Indian paddy cultivation areas contain soils that have low to medium levels of soil organic carbon. The average seasonally integrated CH4 flux (Esif) values calculated from these measurements were 15.3 ± 2.6 g m−2 for continuously flooded (CF), 6.9 ± 4.3 g m−2 for intermittently flooded (IF) single aeration (SA) and 2.2 ± 1.5 g m−2 for IF multiple aeration (MA) rice ecosystems. For CF and IF (MA) rice ecosystems having high soil organic carbon, without organic amendments, the CH4 flux (Esif) may be increased by 1.7 times relative to low soil organic carbon, whereas it may enhance by 5.3 for CF if amended organically. Organic amendment and high soil organic carbon paddy areas do not alter the methane budget estimates for India (3.6±1.4 TgY−1) much, due to their small paddy harvested area. Methane estimated using average emission factors (Esif) for all paddy water regimes, which include harvested areas having soils with high organic carbon and organic amendments, may give a budget of 5 TgY−1 for India.