Ashis Chakraborty

Pesticide residue level in tea ecosystems of Hill and Dooars regions of West Bengal, India

In the present study we quantified the residues of organophosphorus (e.g. ethion and chlorpyrifos), organochlorine (e.g. heptachlor, dicofol, α-endosulfan, β-endosulfan, endosulfan sulfate) and synthetic pyrethroid (e.g. cypermethrin and deltamethrin) pesticides in made tea, fresh tea leaves, soils and water bodies from selected tea gardens in the Dooars and Hill regions of West Bengal, India during April and November, 2006. The organophosphorus (OP) pesticide residues were detected in 100% substrate samples of made tea, fresh tea leaves and soil in the Dooars region. In the Hill region, 20% to 40% of the substrate samples contained residues of organophosphorus (OP) pesticides. The organochlorine (OC) pesticide residues were detected in 33% to 100% of the substrate samples, excluding the water bodies in the Dooars region and 0% to 40% in the Hill region. The estimated mean totals of studied pesticides were higher in fresh tea leaves than in made tea and soils. The synthetic pyrethroid (SP) pesticide residues could not be detected in the soils of both the regions and in the water bodies of the Dooars. Sixteen percent and 20% of the made tea samples exceeded the MRL level of chlorpyrifos in Dooars and Hill regions respectively. The residues of heptachlor exceeded the MRL in 33% (April) and 100% (November) in the Dooars and 40% (April) and 20% (November) in the Hill region. Based on the study it was revealed that the residues of banned items like heptachlor and chlorpyrifos in made tea may pose health hazards to the consumers.

Characterization and crop production efficiency of diazotrophic bacterial isolates from coastal saline soils

Use of eco-friendly area specific salt tolerant bioinoculants is better alternatives to chemical fertilizer for sustainable agriculture in coastal saline soils. We isolated diverse groups of diazotrophic bacteria from coastal saline soils of different forest and agricultural lands in the Sundarbans, West Bengal, India, to study their effect on crop productivity in saline soils. Phenotypic, biochemical and molecular identifications of the isolates were performed. The isolates produced indole acetic acid, phosphatase, and solubilized insoluble phosphates. Sequence analysis of 16S rDNA identified the SUND_BDU1 strain as Agrobacterium and the strains SUND_LM2, Can4 and Can6 belonging to the genus Bacillus. The ARA activity, dinitrogen fixation and presence of nifH genes indicated they were diazotrophs. Field trials with these strains as bioinoculants were carried out during 2007-2009, with rice during August-December followed by Ladys finger during April-June. Microplots, amended with FYM inoculated with four bioinoculants individually were compared against sole FYM (5 t ha(-1)) and a sole chemical fertilizer (60:30:30 kg ha(-1) NPK) treated plot. The strain Can6 was by far the best performer in respect of yield attributes and productivity of studied crops.

Relationship between acidity and microbiological properties in some tea soils

The present study was conducted to investigate the effects of different forms of soil acidities on microbial biomass C, ergosterol content, microbial metabolic quotient, microbial respiration quotient, and fluorescein diacetate-hydrolyzing activity of some tea-growing soils of India. Total potential and exchangeable acidity and extractable and exchangeable aluminum were higher in Tripura followed by Jalpaiguri and Kharagpur soil. Different forms of acidity were significantly and positively correlated with each other. All the microbiological properties investigated were significantly and positively correlated with soil organic C content. The ratio of organic C with microbial parameters was significantly and negatively correlated with different forms of acidity. Principal component analysis indicated that the microbial activities were not directly affected by the extractable aluminum and total potential acidity. Although the tea soils had higher microbial biomass and activities because of higher organic matter content than other soils, the ratios of microbial parameters/organic carbon indicated that inhibition of microbial growth and activities had occurred because of acidity stress.

Review of Some Factors Influencing Jute Fiber Quality

Different factors that influence the production of quality jute fibers are presented. These include the soil, retting, and jute genotype. Several soil quality parameters influence fiber quality. Different aspects of retting, right from quality and quantity of retting water, microorganisms with balanced pectinolytic and xylanase activities with minimal or low cellulase activities, largely determine fiber quality. Efficient pectinolytic bacteria as well as fungi could be used in retting process. Future research needed in this respect has been expressed.

Effect of pencycuron on microbial parameters of waterlogged soil

A laboratory study was conducted to monitor the effect of pencycuron [1-(4-chlorobenzyl)-1-cyclopentyl-3-phenylurea] on microbial parameters of alluvial (AL) soil (Typic udifluvent) and coastal saline (CS) soil (Typic endoaquept) under waterlogged condition. Pencycuron at field rate (FR), 2FR and 10FR affected the microbial biomass C (MBC), soil ergosterol content and fluorescein diacetate hydrolyzing activity (FDHA) differentially. The DCM amendment did not seem to have any counteractive effect on the toxicity of pencycuron on the microbial variables. The change in microbial metabolic quotient (qCO2) and microbial respiration quotient (QR), indicated pencycuron induced disturbance at 10FR. Present study revealed that the metabolically activated microbial population was more suppressed compared to the dormant population.

Factors affecting cross protection of fusarium wilt of pigeon pea by soilborne nonpathogenic fungi

Preinoculation of pigeon pea (Cajanus cajan (L.) Millsp.) seedlings with soilborne fungi nonpathogenic to pigeon pea, namely,Fusarium oxysporum f.sp.niveum; F. oxysporum f.sp.ciceris; F. solani f.sp.pisi; andCephalosporium sacchari, before challenge inoculation with the pathogenFusarium udum, or simultaneous inoculation of the seedlings with nonpathogen and pathogen was effective in controlling wilt of pigeon pea to a great extent. Inoculation with the nonpathogens before the challenge inoculation was more effective than simultaneous inoculation and gave up to 81.6% protection. The higher the spore concentration of the nonpathogenic fungi, the better was the degree of protection. The shorter the period was (in the range of 2–7 days) between nonpathogen inoculation and challenge inoculation, the greater was the degree of protection. Injury to the roots resulted in a decrease of the effect. Maximum disease reduction was obtained when the seedlings were kept at 20-30°C before inoculation; at 5°C and also at 40°C, protection was much less.