BackgroundClimate change alters modern drought episode patterns by making them longer, more frequent and more severe, in particular in arid and semi-arid agroecosystems. Amending soil properties and enhancing its fertility is a needed sustainable strategy for mitigating drought's damaging effects on crop production and food security. Here, we planned to investigate the potential benefits of biochar-compost mixture (BxC) as a biochar-based fertilizer (BCF) in enhancing the drought tolerance of rice plants cultivated in low-fertile sandy soil.ResultsUnder drought stress, rice plants cultivated in unamended soil (no BxC) exhibited severely wilted, rolled and discolored shoots. Furthermore, the shoot dry biomass reduction ratio was 73.3% compared to 44.2 and 27.6% for plants treated with 5 and 15% BxC, respectively. Root anatomical and architectural traits were significantly less impaired in BxC plants and reflected better performance under drought compared to no BxC plants. During the induced drought episode, soil moisture content was enhanced by 2.5-fold through adding BxC, compared to unamended soil, thereby reducing the negative impact of drought stress. Moreover, the less drought-stressed rice plants (BxC-treated) rapidly recovered after rewatering and displayed the unwinding of previously rolled leaves and reproduced panicles. On the other hand, no BxC plants failed to recover and eventually perished completely. The expression profiles of several drought responsive genes suggest that leaves of more stressed rice plants (no BxC) significantly accumulated more cytosolic free calcium (OsCML3) and apoplastic H2O2 (OsOXO4) which eventually may trigger fast and prolonged stomatal closure (OsSRO1c). In addition, more drought-stressed plants (no BxC) may over-produce the reactive oxygen species (ROS) superoxide anion molecules (OsRbohB), the negative situation that has been further complicated by a possible reduction in the activity of the antioxidative enzyme SOD (OsSOD), and thus more lipid peroxidation (3.5-fold increase MDA) in drought-stressed (no BxC) plant shoots compared to BxC plants.ConclusionIt is suggested that soil amendment BxC (biochar-compost mixture) could promote drought stress tolerance in rice plants by retaining more soil moisture content, thereby mitigating the negative effects of drought stress, such as the over-production of ROS in leaves, and thus eventually facilitating recovery after rewatering.