Azotobacter is a nitrogen-fixing bacterium, found in soils world-wide, with many features relevant to energy consumption and carbon sequestration, For assessment the effects of agricultural practices and land use on the occurrence and distribution of Azotobacter, the present investigation was made in the pastures, deciduous and coniferous woodlands, and dry and irrigated (with sewage and river waters) farmlands of Hamedan in northwester of Iran, Sampling was carried out at depth of 0-30 cm with maximum of plant cover diversity in may, 2003. According to heterogeneity of lands, sampling plan was completely randomized with unequal numbers of repetitions. Some soil physical, chemical and biological properties were investigated. Data statistically analyzed for standard deviation (s), and F-test to assess the land use effect on each soil property. Means were calculated and Duncans new multiple range test was made to assess the soil management systems. The highest population of Azotobacter was found in soil sampled from sewage water irrigated farmland. Among soils, dry farmlands and coniferous woodland soils had the lowest fertility. The lowest population of Azotobacter was found in soil sampled from coniferous woodland. The occurrence of Azotobacer correlated positively with soil organic matter (SOM), electrical conductivity, total nitrogen, available phosphorous, available potassium, C/N ratio, and substrate-induced respiration (SIR) and negatively with soil carbonates.
