ALBERT

Description: Java citronella (Cymbopogon winterianus Jowitt) is an important perennial aromatic grass cultivated in different parts of India. The steam-volatile essential oil from the citronella herb is widely used in perfumery, in manufacture of deodorants and mosquito repellent creams and in flavouring beverages. Systematic cultivation of this crop is being taken up and application of large quantities of N fertilizers was found to increase yield (Narayana et al. 1975; Bommegowda, 1978; Singh, Pathak & Bodoloi, 1980; Prakasa Rao et al. 1983). However, the efficiency of N utilization by this crop was found to be quite poor (Prakasa Rao et al. 1983). No systematic data are available in India on the effect of harvest season and N fertilizers on the principal constituents of citronella oil. Therefore the present experiment was made with two objectives: (i) to determine the effect of harvest season and N fertilizers on the essential oil concentration and the principal constituents of the oil which determine the oil quality, and (ii) to determine the effect of neem cake, an indigenous cheap material which is reported to have nitrification inhibitory properties, on the herb and essential oil yields of citronella.

Description: SummaryA field experiment was conducted for 2 years during the crop seasons of 1980–2 to study the effect of diverse plant spacings and rates of nitrogen application on the yields of herb and essential oil of palmarosa (Cymbopogon martini Stapf. var. motia). The results indicated that at closer plant spacings of 30 × 30 cm (110 000 plants/ha) and 45 × 30 cm (74000 plants/ha), palmarosa responded to higher amounts of N fertilizer (240 kg N/ha/year). It was suggested that a plant spacing of 30 × 30 and 45 × 30 cm and application of 240 kg N/ha/year result in high essential oil yield of palmarosa.

Description: SUMMARYThe influence of addition of sulphate on acetylene reduction in three paddy soils differing in their properties under two water regimes was investigated in a laboratory experiment. Nitrogenase activity was high in a P-deficient alkaline soil and addition of sulphate further enhanced the activity under two water regimes, with a pronounced stimulation under non-flooded conditions. Sulphate application to submerged alluvial soil enhanced nitrogenase activity with no apparent effect under non-flooded conditions. In acid sulphate saline Pokkali soil sulphate addition had little effect on the nitrogenase activity. Sulphate addition did not result in significant changes in the soil pH and redox potential. No relationship seemed to exist between the sulphate disappearance and stimulation of nitrogenase in these soils. A differential stimulation of N2-fixing microorganisms was noticed as a result of sulphate application. Results suggest that sulphate-induced stimulation of nitrogenase activity occurs in non-flooded soils.

Description: Brown planthopper, Nilaparvata lugens (Stal), is one of the most serious insect pests of rice (Oryza sativa L.) throughout Asia. Introduction of resistant varieties could be an effective means of minimizing losses from the pest. Several hundred rice cultivars resistant to the pest have been identified and the genetics of resistance has been analysed. Studies have shown that the genes for resistance to brown planthopper, bph-4, and to green leafhopper, Glh-3, are linked (Sidhu & Khush, 1979). Ideka & Kaneda (1983) reported that bph-2 for brown planthopper resistance was linked with the gene d2 for dwarfness. The present study sought to ascertain relationships between resistance to brown planthopper and tungro virus and grain characteristics.

Description: The nonlinear problem of the steady-state interaction of a closed fluid-filled cylindrical elastic membrane with a slow viscous shear flow has been solved by a series-expansion technique. The problems of successive orders were both formulated and solved by a symbolic manipulation program, and the calculations were carried to sixth order in a dimensionless parameter related to the applied shear rate. Moderately large deformations (aspect ratios approaching 3) fall within the range of this analysis, which yields the dependences of the following global variables on the system parameters: membrane deformation, orientation, and strain, as well as tank-treading frequency, and mean internal pressure. The solution for the flow field around an isolated capsule is also used to calculate the apparent viscosity of a dilute suspension of flexible cylindrical particles, which yields the paradoxical result that the apparent viscosity decreases as the internal viscosity increases. © 1994, Cambridge University Press

Description: A simple two-equation model is derived which has the properties that the total contaminant exposure, the mean time of arrival, the temporal spread, and the skewness, are asymptotically correct at large distances downstream of a discharge. The role of changes in the breadth of a river upon the dispersion process is investigated by a means of an illustrative example. This reveals cubic dependence upon the breadth, and hence the great importance of wide reaches of rivers as regards contaminant dispersion. © 1987, Cambridge University Press. All rights reserved.

Description: A continuum model based on the critical-state theory of soil mechanics is used to generate stress, density, and velocity profiles, and to compute discharge rates for the flow of granular material in a mass flow bunker. The bin-hopper transition region is idealized as a shock across which all the variables change discontinuously. Comparison with the work of Michalowski (1987) shows that his experimentally determined rupture layer lies between his prediction and that of the present theory. However, it resembles the former more closely. The conventional condition involving a traction-free surface at the hopper exit is abandoned in favour of an exit shock below which the material falls vertically with zero frictional stress. The basic equations, which are not classifiable under any of the standard types, require excessive computational time. This problem is alleviated by the introduction of the Mohr-Coulomb approximation (MCA). The stress, density, and velocity profiles obtained by integration of the MCA converge to asymptotic fields on moving down the hopper. Expressions for these fields are derived by a perturbation method. Computational difficulties are encountered for bunkers with wall angles these are overcome by altering the initial conditions. Predicted discharge rates lie significantly below the measured values of Nguyen et al, (1980), ranging from 38% at 15° to 59% at 32°. The poor prediction appears to be largely due to the exit condition used here. Paradoxically, incompressible discharge rates lie closer to the measured values. An approximate semi-analytical expression for the discharge rate is obtained, which predicts values within 9% of the exact (numerical) ones in the compressible case, and 11% in the incompressible case. The approximate analysis also suggests that inclusion of density variation decreases the discharge rate. This is borne out by the exact (numerical) results - for the parameter values investigated, the compressible discharge rate is about 10% lower than the incompressible value. A preliminary comparison of the predicted density profiles with the measurements of Fickie et al, (1989) shows that the material within the hopper dilates more strongly than predicted. Surprisingly, just below the exit slot, there is good agreement between theory and experiment. © 1991, Cambridge University Press. All rights reserved.

Description: Petroleum refineries are major sources of air pollution, giving off particulate matter, volatile hydrocarbons, and oxides of sulphur and nitrogen. The field-study here reported was conducted in the vicinity of Barauni Petroleum Refinery, in the Begusarai district of Bihar, India, with the objects of measuring the level of pollution through phytomonitoring and assessing the overall impact of the Refinery's emissions on vegetation.

Description: SummaryIn a laboratory incubation study, the effect of natural and artificial soil salinity on the soil N2 fixation, nitrogenase (C2H2 reduction) and N2-fixing populations was evaluated in rice soils under two water regimes. N2 fixation was less pronounced in two saline soils and in a normal non-saline soil amended with salt mixture (salinity level of 4 and 30 dS/m) than in a non-saline soil under flooded and nonflooded conditions. Flooded soils amended with rice straw showed higher N2-fixing activity than the non-flooded soils at all salinity levels used in the study. Leaching the saline soil improved N2 fixation. An increase in the soil salinity led to a decrease in the populations of at least three groups of N2-fixing micro-organisms. The population density of anaerobic N2 fixers and Azospirillum in a saline soil increased considerably after leaching or after addition of rice straw. Azotobacter populations were little affected by the salinity levels used in this study. Results indicate that soil amelioration for salinity with leaching and organic matter addition would improve the implicated microbial populations and N2 fixation in salt-affected rice soils.