Ashok Choudhury

In-Situ Differentiation of Acidic and Non-Acidic Tundra via Portable X-ray Fluorescence （PXRF） Spectrometry

Abstract Frozen soils or those with permafrost cover large areas of the earths surface and support unique vegetative ecosystems. Plants growing in such harsh conditions have adapted to small niches, which allow them to survive. In northern Alaska, USA, both moist acidic and non-acidic tundra occur, yet determination of frozen soil pHs currently requires thawing of the soil so that electrometric pH methods can be utilized. Contrariwise, a portable X-ray fluorescence (PXRF) spectrometer was used in this study to assess elemental abundances and relate those characteristics to soil pH through predictive multiple linear regressions. Two operational modes, Soil Mode and Geochem Mode, were utilized to scan frozen soils in-situ and under laboratory conditions, respectively, after soil samples were dried and ground. Results showed that lab scanning produced optimal results with adjusted coefficient of determination (R2) of 0.88 and 0.33 and root mean squared errors (RMSEs) of 0.87 and 0.34 between elemental data and lab-determined pH for Soil Mode and Geochem Mode, respectively. Even though the presence of ice attenuated fluoresced radiation under field conditions, adjusted R2 and RMSEs between the datasets still provided reasonable model generalization (e.g., 0.73 and 0.49 for field Geochem Mode). Principal component analysis qualitatively separated multiple sampling sites based on elemental data provided by PXRF, reflecting differences in the chemical composition of the soils studied. Summarily, PXRF can be used for in-situ determination of soil pH in arctic environments without the need for sample modification and thawing. Furthermore, use of PXRF for determination of soil pH may provide higher sample throughput than traditional eletrometric-based methods, while generating elemental data useful for the prediction of multiple soil parameters.

Screening of phosphorus solubilizing bacteria from tea rhizosphere soil based on growth performances under different stress conditions

Rhizospheric soil from tea [Camellia sinensis L.] was screened for the presence of phosphate solubilizing bacterial populationin-vitro where eighteen isolates were initially selected based on their growth characteristics. These isolates were further screened based on their growth performances under different stress conditions like growth temperature (15, 20, 25, 30 and 35°C), pH of growth medium (4 and 5.4), six Al concentrations using AlCl3 (2.5, 5, 7.7, 10, 25 and 50 mM) and desiccations with five concentrations of polyethylene glycol 6000 (0, 20, 30, 40 and 50%). A score sheet was developed for screening the efficient PSB strains which can tolerate stress by giving equal weightage to their growth performance under different stress conditions. A total of 11 PSB isolates were finally selected and further study is warranted for inoculating these isolates for increasing P nutrition for tea crop.

Evaluation of chemical and biological indices for carbon and nitrogen mineralization of various organic matters used in tea garden

The objective of this study was to evaluate the performance of chemical and biological indices to predict carbon and net nitrogen mineralization from a range of organic amendments that differed in their total carbon and nitrogen and the carbon quality. Three decomposed materials i.e. vermi compost (VC), farm yard manure (FYM), poultry manure (PM) and four un-decomposed materials i.e. raw cow dung (RCD), fish meal (FM), tannery waste (TW) and mustard cake (MC) were used for the experiment. Carbon mineralization was determined using alkali traps. Aerobic nitrogen mineralization was estimated using incubation and leaching method, whereas, anaerobic N-mineralization was done under waterlogged condition at 40oC. It was observed that water soluble organic carbon (WSOC) had significant correlation with C-mineralization (r=0.885**) and net aerobic N-mineralization (r=0.805*). Linear regression analysis also exhibited that WSOC had a very high linear relation with C-mineralization (r2=0.7835) and net N-mineralization (r2=0.649). Biological parameter i.e. 7 days anaerobic N-mineralization (ANI7) at high temperature exhibited significant correlation with C-mineralization (r=0.960**) and net aerobic nitrogen mineralization (r=0.855*). Net N-mineralization (aerobic) when regressed against anaerobic nitrogen index i.e. ANI-7, ANI-14 and ANI-21, R2 value of 0.733, 0.945 and 0.960 were found, respectively, indicating that anaerobic nitrogen mineralization index can be a useful tool for predicting nitrogen mineralizing capacity of various organic matters.

Studies on In situ Net N Mineralization in Soils from Mathura Tea Garden and Cultivated Land of North Bengal

Organic matter is one of the sources of nitrogen in the soil. Nitrogen mineralization depends on application method, kind of organic matter, microbial activity, aeration and moisture. Soil samples were taken from Mathura tea garden and Uttar Banga Krishi Viswavidyalaya cultivated field, West Bengal. Nitrogen mineralization was studied on tea soil and cultivated soil. Seven organic matters were collected for this study. Vermicompost (VC), farm yard manure (FYM), poultry manure (PM) were decomposed, whereas, raw cow dung (RCD), fish meal (FM), tannery waste (TW) and mustard cake (MC) were undecomposed. The mean maximum and minimum soil temperature for the entire in situ incubation period were respectively 26.33°C and 16.03°C. Net mineralization data (mg N/kg soil) showed that over the period of 84 days it varied from 26.43 to 62.19 for VC, , 7.77 to 31.09 for FYM, 36.86 to 72.62 for PM, 32.65 to 76.19 for RCD, 59.08 to 106.51 for FM, 76.96 to 119.72 for TW and 29.54 to 108.06 for MC. The average of the weekly mineralized nitrogen from organic matter was in the decreasing order of TW >FM>MC >PM>RCD>VC>FYM.

Solubilization of Tricalcium Phosphate and Production of IAA by Phosphate Solubilizing Bacteria Isolated from Tea Rhizosphere Soil

Rhizospheric soil from tea [Camellia sinensis L.] was screened for the presence of phosphate solubilizing bacterial populationin-vitro where eight isolates were able to solubilize tri calcium phosphate in Pikovskayas agar. These isolates were also screened for phosphate solubilization in liquid medium. Phosphate solubilizing activities of these strains were associated with a drop in the pH of the medium. Furthermore, these 8 isolated strains were inoculated in specific media containing tryptophan to produce growth regulating substances indole acetic acid (IAA) under in-vitro conditions. Amount of phosphate solubilized ranged from 11.07±0.91–82.77±0.96mg/l and IAA production ranged from 11.23–28.78 mg/l. These bacterial strains may be further characterized and field tested for their use as effective growth promoters for hill crops.