BACKGROUND
Limited information is available about the effectiveness of biochar with plant growth‐promoting rhizobacteria (PGPR) and compost. A greenhouse study was conducted to evaluate the effect of biochar in combination with compost and PGPR (Pseudomonas fluorescens) for alleviating water deficit stress. Both inoculated and un‐inoculated cucumber seeds were sown in soil treated with biochar, compost and biochar + compost. Three water levels – field capacity (D0), 75% field capacity (D1) and 50% field capacity (D2) – were maintained.

RESULTS
The results showed that water deficit stress significantly suppressed the growth of cucumber; however, synergistic use of biochar, compost and PGPR mitigated the negative impact of stress. At D2, the synergistic use of biochar, compost and PGPR caused significant increases in shoot length, shoot biomass, root length and root biomass, which were respectively 88, 77, 89 and 74% more than in the un‐inoculated control. Significant improvements in chlorophyll and relative water contents as well as reduction in leaf electrolyte leakage demonstrated the effectiveness of this approach. Moreover, the highest population of P. fluorescens was observed where biochar and compost were applied together.

CONCLUSION
These results suggest that application of biochar with PGPR and/or compost could be an effective strategy for enhancing plant growth under stress. © 2017 Society of Chemical Industry