Central Sericultural Research and Training Institute, Berhampore - 742 101, India.
* Corresponding author.
** Department of Soil Science, Palli Siksha Bhavana (Institute of Agriculture), Visva Bharati, Sriniketan- 731236, India.
Three fungicides and three insecticides were tested against three nitrogen fixing bacteria namely Azotobacter chroococcum, Azospirillum brasilense and Beijerinckia indica isolated from mulberry rhizosphere. There were variable effects of pesticides on the growth of three nitrogen fixing bacteria. In vivo study showed that amongst fungicides, Carbendazim reduced the bacterial population at all concentrations but Mancozeb and Wettable sulphur stimulated the same at 1g/1 and reduced it at higher concentration. Amongst insecticides, Methylparathion followed by Dimethoate were comparatively more toxic than Endosulfan and they completely killed the nitrogen fixing bacteria at 2 and 4 mill concentrations respectively. In vivo studies indicated stimulatory effect of 0.1% carbendazim and Dimethoate on their pollution both in rhizosphere and on phylloplane. The other pestioides reduced the population of nitrogen fixing bacteria. There was a trend of regaining equilibrium of nitrogen fixing bacteria particularly in rhizosphere after a gap of 3 weeks.
