Abstract

Salinization of soil is a serious problem and is increasing steadily in many parts of the world. Recently, soil biotechnology application can improve the potential of saline soils land use in agriculture. The aim of this research was determining the salinity effect on free-living diazotroph and total bacterial populations in two saline soils. Soil samples with salinity of 35 and 70 dS/m selected. The heterotrophic and free-living diazotrophic bacterial populations were counted on nutrient agar and free-nitrogen medium. The salinity effect on population of each soil was determined on same media supplemented with 0.44 and 1.02 M NaCl (equal with EC 35 and 70 dS/m of each soil). The results showed that, the free-living diazotrophic and total heterotrophic bacterial populations in soil sample 1 was significantly (P < 0.05) more than soil sample 2. Also the heterotrophic and diazotrophic bacterial population in each soil sample were significantly less in the presence of salt. Soil salinity is a stress factor relating to microbial selection process and can reduce bacterial diversity and control microbial abundance, composition and functions. Use of soil halotolerant or halophyl bacterial strains which can either fix atmospheric nitrogen will be environmentally begin approach for nutrient management and ecosystem function for saline soils.

Key words: Salinity, bacterial population, diazotrophic, heterotrophic