Dhruba Jyoti Nath

Effect of 10 years of biofertiliser use on soil quality and rice yield on an Inceptisol in Assam, India

In the present study, field experiments were performed over 10 consecutive years (2006–15) to assess the effects of biofertiliser and enriched biocompost on soil quality, total organic carbon (TOC) and rice yields in an Inceptisol. Experiments were conducted in a randomised block design with four replicates and five treatments: unfertilised control (T1); recommended doses of inorganic fertiliser (T2); biofertiliser with reduced (50%) inorganic N and P fertilisers (T3); reduced (50%) inorganic N and P fertilisers with 1 t ha–1 enriched biocompost (T4); and reduced (75%) inorganic N and P fertilisers with 2 t ha–1 enriched biocompost (T5). T3 improved soil chemical and biological properties with enhanced soil quality index (40%), total P (23%), total K (42%) and fungal (38%) and bacterial (44%) colony counts. T5 significantly improved the carbon pool index (29%) and available nutrients (N, P and K at rates of 37%, 22% and 10% respectively) and increased soil pH (11%), resulting in a higher sustainable yield index (39%) of rice. Fraction 2 (labile carbon) of TOC, total P, available K, microbial biomass carbon and phosphate-solubilising bacteria were key indicators to assess the suitability of these fertilisers in rice cultivation in north-east India.

Temporal responses of soil biological characteristics to organic inputs and mineral fertilizers under wheat cultivation in inceptisol

ABSTRACT A 2-year field experiment was conducted in wheat ecosystem to assess the key soil biological characteristics in inceptisols of northeastern region of India. Nine treatments using organic inputs (farmyard manure and vermicompost) and mineral fertilizers were applied by modulating the doses of organics and mineral N fertilizer. Soil enzymes (urease, phosphatase, dehydrogenase, fluorescein diacetate (FDA) and arylsulphatase), microbial biomass carbon (MBC), bacteria and fungi populations were measured before seed sowing (GS1), at flowering stage (GS2) and after harvest (GS3) of wheat, whereas total organic carbon (TOC) was studied at GS3. GS2 recorded significantly higher soil enzyme activities, except FDA, which increased considerably at GS3. Enzyme activities, available N and TOC significantly (p ≤ 0.05) enhanced with application of organic inputs even with reduced (50%) mineral N. Except urease and phosphatase, other enzymes did not respond significantly to mineral fertilization. Vermicompost application increased mean enzyme activities, MBC, microbial growth and TOC fractions (particulate organic carbon, humic acid and fulvic acid carbon) than farmyard manure. Significant (p ≤ 0.05) positive correlations (r = 0.61–0.87) were obtained between TOC and its fractions with studied soil enzymes. Thus, in conclusion, 5 t ha–1 organics incorporation (especially vermicompost) in wheat fertility programme can uphold soil biological health, reduce (50%) N application and would be a sustainable option for wheat grown in inceptisols of northeastern region of India.

Molecular characterization and PCR-based screening of cry genes from Bacillus thuringiensis strains

Novel cry genes are potential candidates for resistance management strategies, due to their different structures and modes of action. Therefore, it is desirable to clone and express novel cry genes from several new isolates of Bacillus thuringiensis (Bt). In the present study, 28 Bt strains were characterized at morphological and molecular level. All these strains are Gram positive, endospore forming and had shown different crystal morphologies when viewed under the microscope. The ARDRA (16S rDNA PCR-RFLP technique) with AluI, HaeIII, HinfI and TaqI produced unique and distinguishable restriction patterns used for the molecular characterization of these isolates. Based on UPGMA clustering analysis, Bt strains showed significant molecular diversity and the dendrogram obtained differentiated 28 Bt strains into 1 major cluster at a similarity coefficient 0.56. PCR analysis demonstrated that the Bt strains showed diverse cry gene profiles with several genes per strain. The Bt strain G3C1 showed the presence of maximum cry-type genes by PCR. The toxicological characterization of these cry genes will have huge importance in transgenic technology and will be useful in transgenesis of crop plants for better resistance management.