Soil amendment with biochar could increase soil microbial activity and biomass. This study contributes to an understanding of the synergistic effects of biochar and phosphate solubilizing microorganisms on safflower yield and soil microbial activity enhancement. In the split plot experiments that repeated in two years, the main factor was biochar types included cow manure, wheat straw, wood biochar and control. The sub factors were phosphate solubilizing microorganisms included the mycorrhizal fungi (Glomus etunicatum and G. mosseae), Bacillus lentus, Pseudomonas fluorescence and control. The highest levels of dehydrogenase, urease activity and microbial biomass carbon were obtained from the cow manure biochar. The maximum activity of acid phosphatase was in the plots inoculated by P. fluorescence in all treatments, whether using or not using biochar. The grain yield of plants inoculated with B. lentus and P. fluorescence was in the same statistical group. The highest grain yield equal to 1527 kg/ha was obtained when using cow manure biochar. According to the results, the application of cow manure biochar and phosphate solubilizing microorganisms, especially mycorrhiza species, can be recommended for improving soil biological traits and safflower yield traits.
