Biochar-based Bradyrhizobium inoculum improves growth of lupin (Lupinus angustifolius L.) under drought stress

•The potential use of biochar as a carrier for Bradyrhizobium sp. inoculants as provided for lupin (Lupinus angustifolius L.), under drought conditions were evaluated.•The survival of BR populations was higher in hydrochar HTC) carrier material than it was in pyrolysis biochar from maize and pyrolysis biochar from wood.•A hydrochar-based Bradyrhizobium sp. inoculant significantly enhanced plant growth, N and P uptake, and lupin nodulation under drought conditions.•Hydrochar-based formulation of Bradyrhizobium sp. is an effective inoculum carrier providing a promising and practical approach for improving growth and symbiotic performance of lupin under drought conditions.

Drought stress has a major abiotic impact on the symbiotic performance of legumes, inhibiting plant growth and nodulation. We evaluated the potential use of biochar as a carrier for Bradyrhizobium sp. inoculants as provided for lupin (Lupinus angustifolius L.), and to determine the response of lupin to the biochar-based inocula of Bradyrhizobium sp. (BR) in pot experiments, under irrigated and drought conditions. The survival of BR populations was higher in HTC-char carrier material than it was in pyrolysis biochar from maize (MBC) and pyrolysis biochar from wood (WBC). An HTC-based Bradyrhizobium sp. inoculant (HTC-BR) significantly enhanced plant growth, N and P uptake, and lupin nodulation under drought conditions in comparison with BR strain inoculation. BR was more likely to survive under drought stress conditions when introduced as HTC-based inocula in comparison with direct inoculation. Overall, this experiment indicates that a HTC-based formulation of Bradyrhizobium sp. is an effective inoculum carrier providing a promising and practical approach for improving growth and symbiotic performance of lupin under stress conditions.