Suitability of amended vermiculite as a carrier for bacterial inoculants.

摘要

Vermiculite, the hydrated micaceous mineral consisting of magnesium and ferro-magnesium aluminium silicates, was evaluated as a carrier material for the preparation of bacterial inoculants. Different grades of raw and exfoliated vermiculite were initially analysed for their physical, chemical and biological characteristics and based on the results obtained, exfoliated grade V vermiculite was selected to be used as the carrier material. The material was amended with charcoal and humic acid at 5 and 10% levels, and with lignite at 10 and 20% levels based on their organic carbon content. Evaluation of the shelf life of bacterial inoculants was conducted with two nitrogen fixing strains viz., Rhizobium COG 15 and Azospirillum lipoferum AZ 204 and a phosphobacterium strain PB 1 (Bacillus megaterium var. phosphaticum). All the three inoculants recorded more than 107 cells/g dry weight upto 245 days after inoculation (DAI). Maximum population of phosphobacterium PB 1 was observed in 10% humic acid amended vermiculite carrier on 210 DAI (20.66x1014 cfu/g dry weight) followed by 20% lignite amended vermiculite inoculant (41.09x1012 cfu/g dry weight). Population of Rhizobium COG 15 was maximum on 175 DAI in 5% humic acid amended vermiculite (28.98x1013 cfu/g dry weight) followed by 20% lignite amended vermiculite carrier (27.21x1013 cfu/g dry weight). In case of Azospirillum AZ 204, lignite amended treatment recorded the maximum population at both 10 and 20% levels (1.33x1010 cfu and 7.67x109 cfu/g dry weight, respectively) at 245 DAI. pH of the carrier did not vary significantly, whereas there was considerable moisture loss during the storage period. The results clearly indicated longer shelf life of bacterial inoculants in vermiculite for about eight months (>108 viable cells/g dry weight) and even better survival, when added with suitable amendments, indicating the more suitability of vermiculite as a carrier for bacterial inoculant production.