Changes in Diazotrophic Population in Paddy Soil on N-Fertilisation Alone or in Integration With Certain Growth Promoting Rhizobacteria

Changes in Diazotrophic Population in Paddy Soil on N-Fertilisation Alone or in Integration With Certain Growth Promoting Rhizobacteria

Certain plant growth-promoting rhizobacteria (Azospirillum brasilense and Azotobacter chroococcum) were inoculated on rice cultivar of cv. IR-64 of Oryza sativa L in integration with different levels of urea-nitrogen. The experiments were conducted in earthenware pots containing unsterilised paddy soil in West Tripura in rainy autumn (aman) season in 2008. The result showed that, the viable counts, i.e., colony forming units (CFU) in paddy soil increased due to inoculation of both the rhizobacteria, viz., A.brasilense and A.chroococcum, however, in overall, the cells were less in the treatments where urea-nitrogen was nil and increased in the treatments, where ureanitrogen was 50 percent of recommended dose. But, further increase of urea-nitrogen to 75 percent and 100 per cent of recommended dose minimized the CFU to greater extend, thereby suggesting non-linear response by these rhizobacteria to urea-nitrogen.Again, A.chroococcum appears to be more sensitive to excess urea-nitrogen in comparison to A.brasilense..