ASSOCIATION OF NITROGEN-FIXING, PLANT-GROWTH-PROMOTING RHIZOBACTERIA (PGPR) WITH KALLAR GRASS AND RICE

Leptochloa fusca (L.) Kunth (kallar grass) has previously been found t o exhibit high rates of nitrogen fixation. A series of experiments to determine the level of biological nitrogen fixation using N-15 isotopi c dilution were carried out in nutrient solution and saline soil. Thes e studies indicated an agronomically significant amount of nitrogen be ing fixed in soil. Kallar grass has a similar growth habitat to rice. Therefore similar studies were carried out with rice after isolating v arious diazotrophs from the roots which were also screened for their a bility to produce auxin (IAA). Five such strains namely Azospirillum l ipoferum N-4, Azospirillum brasilense Wb-3, Azoarcus K-1, Pseudomonas 96-51, Zoogloea Ky-1 were selected for inoculating two rice varieties i.e. NIAB-6 and BAS-370 under aseptic laboratory conditions. The nitro gen fixed was quantified using the N-15 isotopic dilution method. Vari ety BAS-370 had nearly 70% nitrogen derived from atmosphere (Ndfa) whe n inoculated with Azospirillum N-4. Similar studies with the mixed ino culum using N-15 fertilizer in the micro plots indicated that nearly 2 9% of plant nitrogen was derived from the atmosphere.