INTERACTION OF 2,4-DICHLOROPHENOXYACETIC ACID (2,4-D) WITH NITROGEN-FIXING BACTERIAL-POPULATIONS AND NITROGEN-FIXATION ASSOCIATED WITH RICE

In a greenhouse study the effects of 2,4-dichlorophenoxy acetic acid ( 2,4-D) on the populations of nitrogen-fixing bacteria, soil and root a ssociated nitrogenase activity were evaluated under flooded and nonflo oded conditions in unplanted and planted series. Results indicate a si gnificant stimulation of root associated and soil nitrogenase activity upon the application of 2,4-D at 5 and 10 ppm levels under both flood ed and nonflooded conditions. This stimulation of nitrogenase was more pronounced in the rhizosphere samples. Microbial analysis indicate a significant increase in the populations of Azospirillum sp. following the application of 2,4-D under flooded conditions, while the populatio ns of Azotobacter and anaerobic nitrogen fixers were rather inhibited. These results indicate the possibility of manipulation of nitrogen fi xation associated with crop plants through herbicide and water regimes .