Response of onion (Allium cepa L.) to combined application of biological and chemical nitrogenous fertilizers

A field experiment was conducted during the summer season of 2000-2001 at the Vegetable Research Farm of Indian Agricultural Research Institute (I.A.R.I.), New Delhi (India) to test the efficacy of three Azotobacter strains as a potential supplement to nitrogenous fertilizer in improving growth and yield of onion cv. Pusa Madhvi. The treatments consisted of factorial combination of four levels of nitrogen (0, 25, 50 and 75 kg N ha -1 ) and three Azotobacter strains (CBD-15, AS-4 and M-4) with two uninoculated controls one with full dose of N (100 kg ha -1 ) and the other without NPK. Application of 75 kg N ha -1 along with inoculation of CBD-15 was found to have significantly increased most of the growth and yield parameters, soil available nitrogen, and nitrogen content in the bulb followed by M-4 inoculation as compared to application of full dose of nitrogen without the inoculation. Days to bulb initiation were significantly reduced due to inoculation with CBD-15 or M-4 along with 50 kg N ha -1 whereas days to bulb maturity were significantly reduced due to inoculation with any of the strains along with the same N rate (50 kg ha -1 ) as compared to application of full dose of nitrogen without the inoculation. The finding demonstrated a saving of 50 kg N ha -1 without significantly affecting yield and an average increase of 13.5% marketable yield due to Azotobacter inoculation in the presence of 75 kg N ha -1