Effect of herbicides on nitrogen fixation (C2H2 reduction) associated with rice rhizosphere.

In a field study nitrogenase activity associated with rice rhizosphere was differently influenced by the applied herbicides. Pretilachlor at two application levels had no effect on nitrogenase activity while butachlor and benthiocarb exerted marginal stimulation. Cinmethylin consistently stimulated nitrogenase activity throughout the plant growth period. Anilofos when applied singly had no substantial effect on nitrogenase activity but in combination with 2,4-D the activity was enhanced. Populations of anaerobic nitrogen-fixing bacteria and Azospirillum sp. and Azotobacter sp. were stimulated in such a combination.