This study was conducted with sugar beet in greenhouse and field at two soil type with different organic matter (containing 2.4 and 15.9% OM, referred as the low- and high-OM soil) conditions in order to investigate seed inoculation of sugar beet, with five N-2-fixing and two phosphate solubilizing bacteria in comparison to control and mineral fertilizers (N and P) application. Three bacterial strains dissolved P; all bacterial strains fixed N-2 and significantly increased growth of sugar beet. In the greenhouse, inoculations with PGPR increased sugar beet root weight by 2.8-46.7% depending on the species. Leaf, root and sugar yield were increased by the bacterial inoculation by 15.5-20.8, 12.3-16.1, and 9.8-14.7%, respectively, in the experiment of low- and high-OM soil. Plant growth responses were variable and dependent on the inoculants strain, soil organic matter content, growing stage, harvest date and growth parameter evaluated. The effect of PGPR was greater at early growth stages than at the later. Effective Bacillus species, such as OSU-142, RC07 and M-13, Paenibacillus polymyxa RC05, Pseudomonas putida RC06 and Rhodobacter capsulatus RC04 may be used in organic and sustainable agriculture. (c) 2005 Elsevier Ltd. All rights reserved.