Denitrification potential of a salt marsh soil: Effect of temperature,pH and substrate concentration

Denitrification was studied using samples of salt marsh soils collected from the New Jersey coast. The pH, organic matter content, NO₃^? and NO₂^? concentrations were determined on samples from marshes with and without grasses. Denitrification was measured in laboratory studies over a temperature range from 4° to 60°C and a pH range from 5.0 to 9.0 by monitoring NO₃^? reduction, NO₂^? reduction and N₂ evolution. Optimum conditions were controlled by a temperature-pH interaction which caused shifts in the pH optima relative to the change in temperature. No₃^? and NO₂^? were reduced over a broad range of No₃^? concentration; whereas, 0.2 mg NO₂^?-N ml^?1 completely inhibited denitrification. The presence of NO₃^? reverses this inhibition. N₂O was produced only at low pH values and low NO₃^? concentrations. It was concluded that the NO₂^? reducing system was the most easily disrupted of the three main processes of denitrification.     

Evaluation of water management systems in a tubewell irrigated farm

Land development, improved systems of irrigation and drainage, and proper irrigation scheduling are becoming more and more important for the success of command area development of the various major and minor irrigation schemes. For realistic planning and execution of such programmes or for improving existing ones, a systematic evaluation of the various components of the existing systems would be necessary but is invariably lacking. This paper presents an attempt made in this direction at C.S.S.R.I. farm, Karnal (India) to evaluate the integrated effect of water management technology on the efficiency of the irrigation system. The parameters selected for evaluation were the efficiencies of pumping, conveyance and field application. Besides these three parameters, water use efficiency, an index of crop production per unit of water applied, was also evaluated.Investigations revealed that pumping efficiency for electrically driven centrifugal pumps was about 52% and the corresponding value for diesel engine run pumps sets was 30%. The conveyance efficiency in the study area was as high as 93% because the seepage loss in the field channels laid in the alkali soils of the study area was only 7%. The field layout for water application in the study area consisted of long, narrow borders. The water application efficiency for this system was 58% for a wheat crop and 42% for rice. The overall system efficiency for wheat crops was observed to be 54% as against a value of 39% for rice.The observed average total water requirements and water use efficiencies for wheat were 46 cm and 70 kg/ha cm^?1 and for rice 150 cm and 46 kg/ha cm^?1, respectively. At these efficiencies, it was also noted that a cavity tubewell would command an area of 4.5 ha, with rice and wheat as the principal crop rotation.From this study, it can be inferred that reasonably high irrigation system efficiencies (54% as against the national average of about 30%) are possible with good water management at farm level.     

Delineation of chemically polluted groundwater regions in Visakhapatnam Basin,India

Water quality investigations were carried out in the Visakhapatnam basin to delineate groundwater pollution. It was observed that the groundwater in some localities of the basin is contaminated due to natural geological formation sources, industrial effluents, irrigation, and urbanization. The ring average method used in geophysical interpretation to separate regional and residual anomalies was modified and applied to the water quality data in the basin to locate chemically polluted groundwater regions. It is observed that the method can be applied successfully to delineate regions of groundwater pollution and it may also be helpful in identifying the sources.     

Characterization of a begomovirus causing horsegram yellow mosaic disease in India

The virus causing horsegram (Macrotyloma uniflorum) yellow mosaic disease has been shown to be a typical Old World bipartite begomovirus. The viral origin of the disease has been established through agroinoculation of horsegram using partial tandem repeat clones of both DNA-A and DNA-B. The DNA-A genome shows less than 89% identity with the corresponding sequences of all the begomoviruses in the databases earlier to this sequence submission (AJ627904). Therefore Horsegram yellow mosaic virus (HgYMV-[IN:Coi]) can be considered to be a new species of the genus Begomovirus (family Geminiviridae). Phylogenetic analysis shows that this virus is part of the cluster of mungbean yellow mosaic viruses of legumes from South and South East Asia.     

Alterations in the activity of certain enzymes in the gills of a carp <Emphasis Type="Italic">Labeo rohita</Emphasis> exposed to an azo dye,Eriochrome black T: a biochemical investigation

In Labeo rohita exposed to sub-lethal concentrations of an azo dye, Eriochrome black T for 4 days, gills show considerable alterations in the activity of certain metabolic enzymes—alkaline phosphatase, acid phosphatase, carboxylesterase, lactate dehydrogenase, and succinate dehydrogenase; and antioxidant enzymes—catalase and peroxidase. The activities of alkaline phosphatase, acid phosphatase, carboxylesterase, succinate dehydrogenase, catalase, and peroxidase decline significantly. This has been associated with impaired metabolic function of the gills due to azo dye toxicity. The activity of lactate dehydrogenase, in contrast, shows a gradual increase, reflecting a shift from aerobic to anaerobic metabolism. In the fish kept for recovery for 8 days, after exposing the fish to the dye for 4 days, activity of succinate dehydrogenase, alkaline phosphatase, and lactate dehydrogenase gradually become similar to control. Nevertheless, activity of acid phosphatase, catalase, peroxidase, and carboxylesterase, although recover gradually, remained significantly low as compared to that of control. This study signifies that the dye is highly toxic to Labeo rohita and suggests that the activity of metabolic and antioxidant enzymes can be used as biomarker for fish toxicity.     

Lipoxygenase Metabolites of α-linolenic Acid in the Development of Resistance in Pigeonpea, Cajanus cajan (L.) Millsp, Seedlings Against Fusarium udum Infection

Lipoxygenase (LOX) activity was measured in germinating pigeonpea Cajanus cajan seedlings, resistant (ICP-8863) and susceptible (ICP-2376) to wilt fungus, before and after infection with Fusarium udum. LOX activity was significantly higher in the resistant than in the susceptible cultivars of pigeonpea and was enhanced further in response to infection with Fusarium udum. This increase in LOX activity in the resistant cultivars of pigeonpea appears to be due to the induction of lipoxygenase isozymes in response to infection. Analysis of the endogenous LOX metabolites in pigeonpea seedlings revealed the predominant formation of 13-hydroperoxyoctadecadienoic acid (13-HPODE) in healthy seedlings and 13-hydroperoxyoctadecatrienoic acid (13-HPOTrE) in infected seedlings. Further studies on the effects of LOX metabolites on the growth and multiplication of Fusarium udum showed that HPOTrEs, LOX metabolites of -linolenic acid, are more anti-fungal compared to HPODEs, LOX metabolites of linoleic acid.     

Penetration and metabolism of 2-isopropoxyphenyl N-methyl-N-(2-methyl-4-tert-butylphenylsulfenyl) carbamate in the house fly and honeybee

The penetration and metabolism of 2 - isopropoxyphenyl N-methyl-N-(2-methyl-4-tert - butylphenylsulfenyl)carbamate or sulfenyl-propoxur was examined in the house fly and honeybee. Reduced penetration was found to be a factor contributing to the lower toxicity of sulfenyl-propoxur to the honeybee. Honeybees and house flies metabolized sulfenyl-propoxur qualitatively in a similar manner. Quantitatively, larger amounts of propoxur were found in the house fly than in the honeybee soon after treatment with sulfenyl-propoxur. The slower rate of conversion of sulfenyl-propoxur to propoxur was considered as another factor responsible for the lower toxicity of the sulfenylated derivative to bees. The high susceptibility of bees to propoxur was related to high internal amounts of unchanged propoxur found soon after treatment.