Evaluating the influence of novel cyanobacterial biofilmed biofertilizers on soil fertility and plant nutrition in wheat

Microbial inoculants suffer from the major problem of poor survival in rhizospheric soil and their plant growth-promoting abilities are dependent upon their competence in this niche. An interesting observation regarding the biofilms, which urged us to evaluate them with crop, was the increased nitrogen-fixing potential or ARA (Acetylene Reduction Activity), even after 10 and 24 weeks of incubation under laboratory conditions. Our present investigation was therefore aimed toward evaluating novel biofilmed preparations developed using cyanobacterium Anabaena torulosa as a matrix for agriculturally useful bacteria (Azotobacter, Mesorhizobium, Serratia and Pseudomonas) in wheat crop. The performance of such phototroph-heterotroph biofilmed preparations was evaluated using individual cyanobacterium, available bacterial inoculants and dual cultures of the partners. Comparison of biofilms was undertaken using RP (Rock phosphate) for phosphate solubilizers - Serratia, Pseudomonas and their combinations only. Nitrogen-fixers - Azotobacter, Mesorhizobium and their combinations, including biofilmed preparations were compared using SSP (single super phosphate) as phosphate source. An enhancement in ARA in the range of 40-50% was recorded in the treatments inoculated with biofilms even after 14 weeks of inoculation, as compared to 4 weeks old samples. The performance of Anabaena-Serratia biofilm and dual culture inoculant, in the presence of RP was most promising, as they exhibited highest ARA even at harvest stage. Anabaena-Pseudomonas biofilm showed highest P uptake, illustrating the interrelationships of nitrogen fixation with increased P uptake by plant. The observations highlighted the synergism among the partners, which emphasizes the need for evaluation at field level for their promise as a green technology for agriculture. (C) 2013 Elsevier Masson SAS. All rights reserved.