D.C. Parashar

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 .

Kinetics of growth of thin anodic oxides of silicon at constant voltages

Abstract Constant voltage anodization of silicon was carried out to grow thin silicon oxide layers on silicon. Four different forming solutions, i.e. ethylene glycol + 0.04(N) HNO 3 , KNO 3 , NH 4 NO 3 and Ba(NO 3 ) 2 were used. Oxidation proceeds at the rate of 6 A V − . The current decay consisted of one sharply and another slowly decaying exponential. Initially, growth is linear with time when the rate of growth of the oxide is maximum. This is followed by drastic deviation from linearity towards saturation. The ionic current efficiency is highest for the forming solution containing NH 4 NO 3 and the best value for this solution is 0.88% at 80 V. The refractive index of these oxides was found to be 1.46. The oxygen evolution at the anode during oxidation and the current caused by this evolution were studied using gas chromatography. The electronic properties, viz. mobile charge, fixed charge and interface states density of these oxides were measured by capacitance-voltage techniques and the best values were obtained for the solution containing 0.04(N) NH 4 NO 3 .

Estimate of methane uptake potential by Indian soils

Abstract The annual sink strengths of soils under rabi and kharif crops, forests, pastures and long fallow areas have been estimated to be 0.11, 0.34, 0.01 and 0.05 Tg yr−1, respectively for the atmospheric methane. The total annual sink provided by Indian soils is 0.51 Tg yr−1 and is about 4% of the total annual methane emission attributed to anthropogenic sources in India.

Evaluation of oxygen nonstoichiometry in high-Tc superconductors

A sensitive method has been developed for the determination of oxygen nonstoichiometry in YBa2Cu3O6.5+x superconductors to critically examine the orthorhombic phase containing low-Tc or high-Tc superconducting material. Oxygen is evolved on reacting a few mg of powdered sample with dilute nitric acid in helium atmosphere in a closed circuit in a specially designed glass sampler and analyzed by gas chromatographic techniques using a thermal conductivity detector. In the samples analyzed, the x value varies from 0.47 to 0 indicating the change from the high-Tc to the low-Tc orthorhombic phase. The accuracy of the measurement is better than 3%.

Methane Emission Studies and Estimate from Indian Paddy Fields

Methane emission has been measured during 1991 wet season over all the major paddy growing areas in India. Measurements have been carried out at 24 different sites covering diverse agro-climatic regions. Methane emission studies over the entire cropping period was done at only 10 sites located in West Bengal, Bihar, Assam, Uttar Pradesh, Orissa, Tamil Nadu, Kerala and Delhi. Integrated methane emission over the entire cropping period gave different values in the range 8 to 44 g m−2 for waterlogged (flooded) fields located in different regions and in the range 0.1 to 2.1 g m−2 for intermittently flooded irrigated fields. Occasionally negative methane flux was also observed in intermittently flooded irrigated fields. Methane budget for all paddy cultivation on the basis of data obtained for wet season is estimated to be 4.0 Tg yr−1. Consideration of lower methane emission at lower soil temperatures during other cropping seasons may lead to lower estimate of methane budget from Indian paddy fields.