Recently, there has been a resurgence of interest in bioorganic fertilizers as part of sustainable agricultural practices to alleviate drawbacks of intensive farming practices. N-2-fixing and P-solubilizing bacteria are important in plant nutrition increasing N and P uptake by the plants, and playing a significant role as plant growth-promoting rhizobacteria in the biofertilization of crops. A study was conducted in order to investigate the effects of two N2-fixing (OSU-140 and OSU-142) and a strain of P-solubilizing bacteria (M-13) in single, dual and three strains combinations on sugar beet and barley yields under field conditions in 2001 and 2002. The treatments included: (1) Control (no inoculation and fertilizer), (2) Bacillus OSU-140, (3) Bacillus OSU-142, (4) Bacillus M-13, (5) OSU-140 + OSU-142, (6) OSU-140 + M-13, (7) OSU-142 + M-13, (8) OSU-140 + OSU-142 + M-13, (9) N, (10) NR N and NP plots were fertilized with 120 kg N ha(-1) and 120 kg N ha(-1) + 90 kg P ha(-1) for sugar beet and 80 kg N ha(-1) and 80 kg N ha(-1) + 60 kg P ha(-1) for barley. The experiments were conducted in a randomized block design with five replicates. All inoculations and fertilizer applications significantly increased leaf, root and sugar yield of sugar beet and grain and biomass yields of barley over the control. Single inoculations with N2-fixing bacteria increased sugar beet root and barley yields by 5.6-11.0% depending on the species while P-solubilizing bacteria alone gave yield increases by 5.5-7.5% compared to control. Dual inoculation and mixture of three bacteria gave increases by 7.7-12.7% over control as compared with 20.7-25.9% yield increases by NP application. Mixture of all three strains, dual inoculation of N-2-fixing OSU-142 and P-solubilizing M-13, and/or dual inoculation N-2-fixing bacteria significantly increased root and sugar yields of sugar beet, compared with single inoculations with OSU-140 or M-13. Dual inoculation of N-2-fixing Bacillus OSU-140 and OSU-142, and/or mixed inoculations with three bacteria significantly increased grain yield of barley compared with single inoculations of OSU-142 and M-13. In contrast with other combinations, dual inoculation of N-2-fixing OSU-140 and P-solubilizing M-13 did not always significantly increase leaf, root and sugar yield of sugar beet, grain and biomass yield of barley compared to single applications both with N-2-fixing bacteria. The beneficial effects of the bacteria on plant growth varied significantly depending on environmental conditions, bacterial strains, and plant and soil conditions.