Abundance of Azotobacter in Great Soil Groups of North-West Himalayas

Out of 66 soils studied, 51 showed presence of Azotobacter. The soils of Paleudalfs and Dystrochrepts were devoid of Azotobacter. Its population varied widely, constituting less than 1 per cent of total bacteria. Haplustalfs and Hapludalfs had higher counts than other soil groups. Despite a lot of variation in nitrogen fixing capacity of various Azotobacter isolates, higher content was observed in isolates grown in Jenson's culture solution than that in Burks. Of the various soil properties positively correlated with Azotobacter population, significant correlation was seen only with pH, available P and exchangeable Mg²⁺. Regression analysis was also worked out. Three species viz. Azotobacter chroococcum, A. beijerinckii and A. vinelandi were identified. Seed inoculation of maize with Azotobacter numerically increased the plant biomass and grain yield.